Category: Energy storage

Renewable energy requires various technologies for energy storage, e.g. Batteries, pumped storage, capacitors, power-to-gas, flywheels, etc.

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Life cycle analysis of natural graphite

Natürliches Graphitgranulat aus einer österreichischen Mine

DOI: 10.13140/RG.2.2.19123.59682

In the production of lithium-ion batteries, not only lithium is a crucial raw material, but also graphite. The widespread use of graphite is attributed to its low price, natural availability, high energy and power density, and long lifespan. This makes graphite a very advantageous choice for anodes in lithium-ion batteries.

As alternatives to lithium-graphite anodes, silicon anodes have been explored in recent years due to their high theoretical capacity, availability, and low cost. However, issues such as volumetric expansion and reliability reduce the chances of successful commercialization, especially in electric vehicles.

Battery-grade anode active material is derived from naturally mined or synthetic graphite. Graphite from natural ores generally has lower production costs but also lower purity and quality. Its anisotropic crystal structure can impair performance in lithium-ion batteries, even though it often allows for higher capacities. However, this advantage typically comes with a reduced lifespan.

In contrast, synthetic graphite is more expensive to produce but offers significantly higher purity and consistency. Synthetic graphite is obtained from carbon precursors such as petroleum coke or coal tar. Due to its higher purity, it accounted for a higher market share of 60% of global revenue in 2025. The higher revenue share is also attributed to higher prices.

Due to its isotropic crystal orientation, synthetic graphite possesses better thermal stability, lower thermal expansion, and faster lithiation kinetics. As a result, it provides overall stronger battery performance and a longer lifespan, although it typically has lower capacities.

As the global battery market grows, its supply chain must also be robust and sustainable. Canada has rich resources of natural graphite, which is mined and processed in the province of Quebec. To better understand the environmental impacts of this new supply chain, a sustainability analysis was conducted for one graphite mine and one graphite processing facility in Quebec by researchers at Concordia University in Montreal. The results were recently published in the journal MDPI Batteries.

The study integrated site-specific data on mining and processing (2022–2025) with Ecoinvent in OpenLCA and mainly focuses on the potential for greenhouse gas (CO₂ equivalents) reduction and water usage.

The researchers showed that the production of one ton of anode-capable graphite in Quebec generates approximately 1.44 tons of CO₂ equivalents. This is significantly less than the 9.6 tons of CO₂ generated per ton of Chinese graphite. Therefore, the sustainability analysis in Quebec indicates a significant reduction in carbon intensity.

The modeled chain included open-pit mining through drilling, blasting, and hauling, as well as processing through crushing, grinding, flotation, and dewatering. Finally, the final processing of anode-capable graphite through micronization and spheronization, acid leaching purification, and carbon coating, followed by finishing and packaging, was also investigated. Spheronization converts the concentrate into spherical graphite granules to enhance bulk density and packing efficiency in the anode. Significant by-products are generated, e.g., as fine particles.

Within the processing facility in Quebec, micronization and spheronization, as well as purification and coating, are the most energy-intensive steps. Acid leaching purification also represents the largest single contributor to CO₂ and water scarcity impacts. However, the very low carbon intensity of the grid (hydropower) significantly mitigates the footprint of these electrical loads. In contrast, natural gas used for high-temperature purification and coating remains the largest direct source of CO₂.

The CO₂ emissions from mining are mainly caused by diesel in trucks and heavy equipment. Detailed equipment data showed that hauling dominates fuel consumption. Water impacts at the concentrator are elevated due to flotation and waste treatment. However, a closed water system and dedicated wastewater treatment reduced fresh water intake and stress from waste effluent.

The researchers also interpreted the results of their sustainability analysis to assess impacts, identify sustainability focal points, and determine the phases with the highest resource intensity and the highest emissions profiles. This analysis facilitated the representation of environmentally burdensome intermediate steps. Natural gas used for purification and coating in the processing facility was the largest source of CO₂, followed by diesel and electricity consumption.

In addition to graphite, the extraction of lithium and trace elements also plays a significant role in the sustainability of batteries. However, these were not the focus of the study. Nevertheless, graphite dominates the market for anode materials, accounting for up to 98% of the market share, while Li4Ti5O12 makes up only about 2%.

The study concluded with an integrated synthesis of the results and provided targeted recommendations for process optimization, emission reduction, and improving sustainability throughout the entire supply chain. This systematic and transparent methodology ensured a robust assessment of the environmental impact of the production of anode-grade graphite.

Despite the significant reduction in CO₂ emissions compared to graphite extraction and processing in China, the research highlights further opportunities for improvement. In particular, electrification of mining equipment to reduce diesel consumption and minimizing or substituting natural gas consumption during cleaning and coating at the facility could further decrease CO₂ emissions.

At Frontis Energy, we are closely monitoring the decarbonization and diversification of supply chains and provide products from various sources

Vegh, et al., 2026, Toward sustainable anode materials: LCA of natural graphite processing in Québec, MDPI Batteries, 12, 68. DOI: 10.3390/batteries1202006

Image: Natural graphite from an Austrian mine

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Ammonia electrosynthesis in a palladium membrane flow cell

Fertilizer granules

Ammonia (NH₃) is a crucial raw material for fertilizer production and a potential renewable, carbon-free energy storage solution. It is produced in the Haber-Bosch process using natural gas (CH4). During this process, natural gas is converted into hydrogen (H₂) and CO₂ by steam reforming. The Haber-Bosch process accounts for approximately 1-3% of global CO₂ emissions. This method requires stable energy supply and CAPEX intensive facilities, leading to highly centralized ammonia production. In contrast, alternative electrochemical pathways for ammonia production represent sustainable and decentralized solutions.

Electrochemical ammonia production is not a new process and is based on hydrogen electrolysis. In a subsequent step, hydrogen is used for catalytic nitrogen reduction. Experimentally, lithium and calcium have been used as electrocatalysts. Ammonia has been produced in continuous flow cells with efficiencies of up to 76%, as well as in other electrochemical cells. However, stable ammonia production in flow cells requires dry and purified hydrogen.

The primary issue with moist hydrogen is the excessive formation of lithium hydroxide (LiOH):

2 Li + 2 H₂O → 2 LiOH + H₂

However, water electrolysis could be completely eliminated if the protons (H+) generated from water oxidation were directly supplied to the lithium-coated cathode. This would further simplify systems and lower investment costs.

Researchers at Imperial College London followed exactly that approach. They coupled continuous water oxidation directly to lithium-mediated nitrogen reduction under non-aqueous conditions in a two-chamber flow cell. They recently published their results in the journal ACS Energy Letters.

The coupling was achieved through an electrically isolated, hydrogen-permeable palladium membrane between the chambers. On the anodic side (aqueous), water was oxidized at an iridium oxide-coated titanium anode to produce protons, meaning adsorbed H. This form of hydrogen permeated the palladium membrane. It then entered the dry, non-aqueous cathodic chamber, where N₂ was reduced on lithium.

Schematic palladium membrane ammonia synthesis

The palladium membrane was not integrated into the external circuit during nitrogen reduction. It simultaneously served as both a proton source and sink, made possible by its electrical conductivity and hydrogen permeability.

The scientists first validated proton transport through the palladium membrane while preventing water crossover through symmetric cell tests and ¹H-NMR isotopic exchange using water (H₂O) and deuterium oxide (D₂O, heavy water).

Real-time mass spectrometry of D₂O at the anode confirmed that deuterons supplied through the palladium membrane were incorporated into ammonia (ND₂H). This demonstrates that the protons in NH₃ originated from water oxidation and not solely from the ethanol used as well. It was evidence for linear charge transfer while maintaining negligible water transport.

As a control, an experiment was conducted using a Nafion™ membrane to demonstrate that membranes allowing water crossover prevented lithium-mediated ammonia synthesis. Nafion™ permits proton transfer while being permeable to water.

The researchers showed that the electrical conductivity of the palladium membrane enabled it to operate simultaneously as both an anode and a cathode. This allowed for continuous conversion of nitrogen and water into ammonia without producing molecular hydrogen as an intermediate. The Nafion™ control proved that the transport of protons while preventing water crossover allowed for lithium-mediated ammonia synthesis.

The necessity for pre-hydration of the membrane and the gradual increase in membrane potential during pulsed operation indicated that the kinetics of hydrogen transfer and membrane stability were key factors for performance. This was because the system was optimized for the neutral aqueous electrolyte with isotopic labeling. The researchers proposed ways to improve efficiency in their article, including the exploration of alternative hydrogen-permeable metals and alloys.

The presented membrane could find applications beyond ammonia synthesis, in other electrochemical transformations where anhydrous conditions and controlled proton release are required. These include CO₂ reduction and non-aqueous redox flow batteries.

For further research, the authors suggested:

  • Increase proton flow and reduce membrane transition resistance,
  • Test alternative hydrogen-permeable metals or alloys to reduce costs, and
  • Conduct pulse and idle protocols to monitor lithium loss.

At Frontis Energy, we are eager to see how individual monolithic palladium membranes will enter in the market. Continuous ammonia electrosynthesis represents a conceptual advancement towards simpler, more robust green fertilizer production and energy storage.

Ye et al. 2026, Continuous ammonia electrosynthesis from nitrogen and water in a monolithic Pd membrane-based flow cell, ACS Energy Letters, DOI: 10.1021/acsenergylett.5c03617

Image: Pixabay

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Stability of anion exchange membranes for electrolysis

Electrolyzer in China

DOI: 10.13140/RG.2.2.18396.65927

Energy security and climate change are among the greatest challenges of our time. To reduce dependence on fossil fuels, renewable energy sources are emerging as key solutions for sustainable energy production. To this end, scalable solutions are essential for storing and transporting renewable energy. Hydrogen produced in water electrolyzers and reconverted into electricity in fuel cells can help balance the seasonal variability of renewable energy.

Fuel cells have the potential to significantly contribute to the decarbonization of the transport sector. Transport of people and goods accounts for almost one‑third of global greenhouse gas emissions. Despite this potential, the widespread adoption of modern fuel cells and electrolyzers remains limited due to high investment costs. This is mainly due to expensive noble‑metal catalysts and perfluorinated proton exchange membranes.

This challenge has sparked growing interest in anion exchange membranes. Under alkaline conditions, they offer several advantages:

  • Use of non‑noble metal catalysts thanks to non‑corrosive conditions
  • More sustainable membrane materials

However, there are hurdles to their introduction, particularly their short lifetime under alkaline conditions and oxidative stress. The formation of hydrogen peroxide and hydroxyl radicals under alkaline conditions is responsible for the accelerated degradation of polymer membranes. Investigation radical‑induced degradation of anion exchange membranes is therefore of central importance.

Hence, efficient radical generation in the laboratory is required. Current methods such as thermal decomposition or UV activation of hydrogen peroxide are inefficient and prone to side reactions, limiting their relevance to real operating conditions. Immersion in oxygen‑saturated alkaline solutions has provided useful insights, but cannot distinguish between natural membrane degradation and radical‑accelerated breakdown.

Radioactivity and electromagnetic pulse radiation allow precise control of radical formation but require expensive, specialized infrastructure. Affordable and practical solutions are needed to study radicals under realistic laboratory conditions.

Researchers from SINTEF in Norway and ETH Zurich have addressed this challenge. They introduced adapted photochemical methods to generate radicals and study their influence on the stability of anion exchange membranes independently of other degradation processes. The results were recently published in Membranes.

By irradiating aqueous potassium nitrite solutions or titanium oxide suspensions with UV light at 365 nm, hydroxyl radicals or a combination of hydroxyl and superoxide radicals were successfully generated. Tests on three commercial anion exchange membranes – PiperION®‑40 (PiperION), FM‑FAA‑3‑PK‑75 (Fumasep), and PNB‑R45 (Polynorbornene) – showed clear differences in durability. As expected, thinner, non‑reinforced membranes degraded faster than thicker, reinforced ones, likely due to the limited penetration depth of highly reactive radicals.

Both methods proved to be practical, affordable, and accessible tools for evaluating the stability of anion exchange membranes against radical attack. Photochemical radical generation was thus a viable way to study radical‑induced degradation under controlled conditions. The nitrite‑based approach selectively generated hydroxyl radicals, while titanium oxide suspensions produced both hydroxyl and superoxide radicals. Longer irradiation intensified membrane damage, clearly demonstrating the critical role of radicals in membrane decomposition. Experiments at pH 10 enabled differentiation between natural and radical‑driven causes.

Beyond laboratory use, both methods are also of industrial relevance. Combined with low‑cost laboratory equipment, they provide widely applicable and reproducible tools for evaluating commercial and prototype anion exchange membranes. By reducing costs and extending durability tests under realistic conditions, the development of robust anion exchange membranes for fuel cells and electrolyzers can be accelerated.

Frontis Energy is part of the mission to provide cost‑effective solutions for the development of efficient energy conversion technologies. In doing so, we strengthen the global transition to clean, resilient, and sustainable energy systems.

Solyom, et al., 2025, Photochemical methods to study the radical-induced degradation of anion-exchange membranes. Membranes, 15, 305. DOI: 10.3390/membranes15100305

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Unlocking the potential of conducting polymers for sustainable water treatment and energy solutions

DOI: 10.13140/RG.2.2.13132.07045

Carbon based materials have a broad range of applications such as energy storage and conversion, electronics, nanotechnology, water purification, and catalysis. They are made of an element which is available everywhere.

In recent times, the electrochemical features of carbon-based electrodes are being enhanced by using conducting polymers. Carbon cloth, woven from carbon microfibers, serves as a promising carbon-based electrode, which acts as a durable and cost-effective medium for facilitating electrochemical reactions that degrade pollutants and improve water quality. These electrodes, notable for their mechanical flexibility, strength, and cost-effectiveness, are employed in processes such as electrochemical oxidation, microbial fuel cells, and other advanced wastewater treatment technologies.

Due to a few limitations of pristine carbon cloth electrodes such as low specific capacitance and limited wettability associated with its inherent hydrophobicity, scientists conduct research to improve the modern electrodes. For instance, since wettability is crucial for for immersing the electrode surface in liquid and ensuring interaction with contaminants, enhancing it is always beneficial for the process. Improving the performance of carbon cloth electrodes could lead to more efficient treatment, faster reaction times, and better overall performance.

A research group at San Diego State University undertook the task of addressing these limitations by making conformal conducting polymer films on carbon fibers via oxidative chemical vapor deposition (oCVD) method. They recently published their results in the Advanced Material Interface Journal. With antimony pentachloride (SbCl5) as the oxidant, they developed a highly uniform coating of poly(3,4-ethylenedioxythiophene) (PEDOT) on three-dimensional porous fibers. The oCVD technique ensures uniform coatings while preserving the geometric and functional properties of the carbon cloth, making it a promising approach for enhancing electrochemical performance.

The PEDOT-coated carbon cloth electrodes achieved a remarkable improvement in specific capacitance and pseudocapacitance compared to pristine carbon cloth. Depending on the deposition temperature, the oCVD PEDOT-coated electrodes showed a 1.5- to 2.3-fold enhancement in specific capacitance. Notably, the electrode fabricated at a deposition temperature of 80 °C exhibited the highest specific capacitance and superior electrochemical performance. Adjusting the deposition temperature to optimize performance can help tailor carbon cloth electrodes for specific wastewater treatment needs.

The investigation underscores the effectiveness of the oCVD method in addressing the limitations of carbon cloth electrodes and expanding their potential applications in wastewater treatment and electrochemical energy storage devices. Furthermore, the researchers showed that PEDOT-coated carbon cloth can be applied as supercapacitors, where flexibility and high capacitance are critical. It should be noted that the study not only showcases significant advancements in material design but also open new avenues for optimizing electrode performance for diverse applications.

Overall, the findings emphasize the growing potential of advanced electrode technologies in addressing industrial challenges. By improving the functionality of carbon-based electrodes through novel material coatings, industries can achieve more efficient and tailored solutions for both wastewater treatment and energy storage. The ability to fine-tune electrode properties to meet specific requirements offers a pathway toward the development of highly efective and cost-efficient technologies, which could be a game-changer for sectors focused on sustainability and resource management. As these innovations continue to evolve, they have the potential to significantly improve operational efficiency and environmental impact across various industries. For example, in wastewater treatment, electrochemical processes such as electrocoagulation, electrooxidation, or electroreduction are often used to remove contaminants.

At Frontis Energy, we believe that improvements and customization can aid in designing electrodes tailored to specific contaminants or types of wastewater.

Heydari Gharahcheshmeh and Chowdhury, 2024, Enhancing Capacitance of Carbon Cloth Electrodes via Highly Conformal PEDOT Coating Fabricated by the OCVD Method Utilizing SbCl5 Oxidant, Advanced Materials Interfaces, 11, 2400118. DOI: 10.1002/admi.202400118.

Image: Pixabay

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Producing liquid bio-electrically engineered fuels from CO2

At Frontis Energy we have spent much thought on how to recycle CO2. While high value products such as polymers for medical applications are more profitable, customer demand for such products is too low to recycle CO2 in volumes required to decarbonize our atmosphere to pre-industrial levels. Biofuel, for example from field crops or algae has long been thought to be the solution. Unfortunately, they require too much arable land. On top of their land use, biochemical pathways are too complex to understand by the human brain. Therefore, we propose a different way to quickly reach the target of decarbonizing our planet. The proce­dure begins with a desired target fuel and suggests a mi­crobial consortium to produce this fuel. In a second step, the consortium will be examined in a bio-electrical system (BES).

CO2 can be used for liquid fuel production via multiple pathways. The end product, long-chain alcohols, can be used either directly as fuel or reduced to hydrocarbons. Shown are examples of high level BEEF pathways using CO2 and electricity as input and methane, acetate, or butanol as output. Subsequent processes are 1, aerobic methane oxida­tion, 2, direct use of methane, 3 heterotrophic phototrophs, 4, acetone-butanol fermentation, 5, heterotrophs, 6, butanol di­rect use, 7, further processing by yeasts

Today’s atmospheric CO2 imbalance is a consequence of fossil carbon combus­tion. This real­ity requires quick and pragmatic solutions if further CO2 accu­mulation is to be prevented. Direct air capture of CO2 is moving closer to economic feasibility, avoid­ing the use of arable land to grow fuel crops. Producing combustible fuel from CO2 is the most promis­ing inter­mediate solution because such fuel integrates seamlessly into existing ur­ban in­frastructure. Biofuels have been ex­plored inten­sively in re­cent years, in particular within the emerging field of syn­thetic biol­ogy. How­ever tempt­ing the application of genetically modified or­ganisms (GMOs) ap­pears, non-GMO technology is easier and faster to im­plement as the re­quired microbial strains al­ready exist. Avoiding GMOs, CO2 can be used in BES to produce C1 fu­els like methane and precursors like formic acid or syngas, as well as C1+ com­pounds like ac­etate, 2-oxybut­yrate, bu­tyrate, ethanol, and butanol. At the same time, BES inte­grate well into urban in­frastructure without the need for arable land. However, except for meth­ane, none of these fuels are readily com­bustible in their pure form. While elec­tromethane is a com­mercially avail­able al­ternative to fossil natu­ral gas, its volumetric energy den­sity of 40-80 MJ/m3 is lower than that of gasoline with 35-45 GJ/m3. This, the necessary technical modifications, and the psychological barrier of tanking a gaseous fuel make methane hard to sell to automobilists. To pro­duce liq­uid fuel, carbon chains need to be elongated with al­cohols or better, hy­drocarbons as fi­nal prod­ucts. To this end, syngas (CO + H2) is theoreti­cally a viable option in the Fischer-Tropsch process. In reality, syngas pre­cursors are ei­ther fossil fu­els (e.g. coal, natural gas, methanol) or biomass. While the for­mer is ob­viously not CO2-neu­tral, the latter com­petes for arable land. The di­rect con­version of CO2 and electrolytic H2 to C1+ fuels, in turn, is catalyzed out by elec­troactive microbes in the dark (see title figure), avoid­ing food crop com­petition for sun-lit land. Unfortunately, little re­search has been under­taken beyond proof of con­cept of few electroactive strains. In stark con­trast, a plethora of metabolic studies in non-BES is avail­able. These studies often pro­pose the use of GMOs or complex or­ganic sub­strates as precur­sors. We propose to systemati­cally identify metabolic strategies for liquid bio-electrically engineered fuel (BEEF) production. The fastest approach should start by screening meta­bolic data­bases using es­tablished methods of metabolic modeling, fol­lowed by high throughput hypothesis testing in BES. Since H2 is the intermediate in bio-electrosynthesis, the most efficient strategy is to focus on CO2 and H2 as di­rect pre­cursors with as few in­termediate steps as pos­sible. Scala­bility and energy effi­ciency, eco­nomic feasibil­ity that is, are pivotal elements.

First, an electrotrophic acetogen produces acetate, which then used by heterotrophic algae in a consecutive step.

The biggest obstacle for BEEF production is lacking knowledge about pathways that use CO2 and electrolytic H2. This gap exists despite metabolic data­bases like KEGG and more recently KBase, making metabolic design and adequate BEEF strain selection a guessing game rather than an educated ap­proach. Nonetheless, metabolic tools were used to model fuel pro­duction in single cell yeasts and various prokaryotes. In spite of their shortcomings, metabolic data­bases were also employed to model species interactions, for example in a photo-het­erotroph consor­tium using software like ModelSEED / KBase (http://mod­elseed.org/), RAVEN / KEGG and COBRA. A first sys­tematic at­tempt for BEEF cul­tures produci­ng acetate demonstrated the usability of KBase for BES. This research was a bottom-up study which mapped ex­isting genomes onto existing BEEF consor­tia. The same tool can also be em­ployed in a top-down ap­proach, starting with the desired fuel to find the re­quired or­ganisms. Some possi­ble BEEF organisms are the following.

Possible pathways for BEEF production involving Clostridium, 3, or heterotrophic phototrophs, 7, further processing by yeasts

Yeasts are among the microorganisms with the greatest potential for liquid biofuel production. Baker’s yeast, (Saccha­romyces cerevisiae) is the most promi­nent exam­ple. While known for ethanol fermentat­ion, yeasts also produce fusel oils such as bu­tane, phenyl, and amyl derivate aldehy­des and alco­hols. Unlike ethanol, which is formed via sugar fer­mentation, fusel oil is syn­thesized in branched-off amino acid pathways followed by alde­hyde reduction. Many en­zymes involved in the re­duction of aldehydes have been identified, with al­cohol dehydro­genases be­ing the most commonly ob­served. The corre­sponding reduc­tion reactions require reduced NADH⁠ but it is not known whether H2 pro­duced on cathodes of BES can be in­volved.
Clostridia, for example Clostridium acetobutylicum and C. carboxidivo­rans, can pro­duce alcohols like butanol, isopropanol, hexanol, and ketones like acetone from complex sub­strates (starch, whey, cel­lulose, etc. ) or from syngas. Clostridial me­tabolism has been clarified some time ago and is dif­ferent from yeast. It does not necessar­ily require com­plex precursors for NAD+ reduction and it was shown that H2, CO, and cath­odes can donate elec­trons for alcohol production. CO2 and H2 were used in a GMO clostridium to produce high titers of isobu­tanol. Typi­cal representa­tives for acetate produc­tion from CO2 and H2 are C. ljungdahlii, C. aceticum, and Butyribac­terium methy­lotrophicum. Sporo­musa sphaeroides pro­duces acetate in BES. Clostridia also dominated mixed cul­ture BESs converting CO2 to butyrate. They are therefore prime targets for low cost biofuel production. Alcohols in clostridia are produced from acetyl-CoA. This reaction is re­versible, al­lowing ac­etate to serve as substrate for biofuel production with extra­cellular en­ergy sup­ply. Then, en­ergy con­servation, ATP syn­thesis that is, can be achieved from ethanol electron bifurca­tion or H2 oxida­tion via respi­ration. While pos­sible in anaero­bic clostridia, it is hitherto unknown whether elec­tron bifurca­tion or res­piration are linked to alcohols or ke­tone synthesis.
Phototrophs like Botryococcus produce C1+ biofuels as well. They synthesize a number of different hydro­carbons including high value alkanes and alkenes as well as terpenes. However, high titers were achieved by only means of ge­netic engineering, which is economically not feasible in many countries due to regulatory constrains. Moreover, aldehyde dehy­dration/deformylation to alkanes or alkenes requires molecular oxygen to be present. Also the olefin path­way of Syne­chococcus depends on molecular oxygen with the cytochrome P450 involved in fatty acid de­carboxylation. The presence of molecular oxygen affects BES performance due to immediate product degrada­tion and unwanted cathodic oxygen reduction. In contrast, our own preliminary experi­ments (see title photo) and a corrosion experi­ment show that algae can live in the dark using electrons from a cath­ode. While the en­zymes in­volved in the production of some algal biofuels are known (such as olefin and alde­hyde de­formylation), it is not known whether these pathways are connected to H2 utilization (perhaps via ferredox­ins). Such a con­nection would be a promising indicator for the possibility of growing hydrocar­bon produc­ing cyanobacteria on cathodes of BES and should be examined in future research.
At Frontis Energy we believe that a number of other microorganisms show potential for BEEF production and these deserve further investi­gation. To avoid GMOs, BES compatible co-cultures must be identified via in silico meta­bolic reconstruc­tion from existing databases. Possible inter-species intermediates are unknown but are prerequisite for suc­cessful BES operation. Finally, a techno-economical assessment of BEEF pro­duction, with and with­out car­bon taxes, and compared with chemical methods, will direct future research.

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Transition between double-layer and Faradaic charge storage in porous carbon nano-material

In electrochemical cells, such as fuel cells or electrolyzers, electric double-layer (EDL) formation occurs on their electrode surfaces. These EDL act as both, capacitors and resistors and impact therefore the performance of electrochemical cells. Understanding the structure and dynamics of EDL formation could significantly improve the performance of, electrochemical systems, for example in energy storage and conversion, including supercapacitors, water desalination, sensors and so forth.

On a planar electrode, electrolyte ions and the solvent are adsorbed at the electrode surface. The resulting capacitance depends on charge, solvation state and concentration. Traditionally, the capacitance of electrochemical interfaces can be divided into two types:

  1. Double-layer capacitance: ions are adsorbed based on their charge. Ion adsorption is non-specific.
  2. Faradaic pseudocapacitance: specific ions are adsorbed, for example through chemical interactions the electrode surface. This may involve charge transfer.

The electrode interface in the most energy application-based technology is, however, not planar but porous. Layer materials in such situations have various degrees of electrolyte confinement and thus different capacitive adsorption mechanisms. Understanding electrosorption in such materials requires a refined view of electrochemical capacitance and charge storage.

A team of researchers from the North Carolina State University, the Paul Sabatier University in Toulouse and the Karlsruhe Institute of Technology reported new insights in electrolyte confinement at the non-planar interfaces in the journal Nature Energy.

Electric double-layer at planar electrodes

The degree of ion solvation (the process of reorganizing solvent and solute molecules) at ideal (planar) electrochemical interfaces determines the ions interaction with the electrodes. There are two distinct cases:

  1. Ions are non-specifically adsorbed: this is the case with strong ion solvation. The electrode’s interactions are primarily electrostatic. This type of interactions can be considered as the induction – charge is induced but not transferred.
  2. Ions are specifically adsorbed: in this case, ions are not solvated and can undergo specific adsorption and chemical bonding to the electrode. This process can be described as charge transfer reaction between the electrode and the adsorbed ion. However, the charge transfer reaction depends on the bonding between the ion and the electrode. This correlates with the state of ion solvation.  Thus, it can be expected that the ion solvation is crucial for understanding the ion-electrode interactions in a nano-confined environment such as porous materials.

Carbon based EDL capacitor – the confinement effect

There is a great interest for understanding the relationship between the porosity of carbon nano-materials and their specific capacitance.

When electric double-layer formation occurs in a nano-confined micro-environment, the EDL capacitor in porous carbon materials deviates from the classic EDL model on flat interfaces. The degree of the ion solvation under confinement is determined by the pore size in nano-porous materials and by the inter-layer distance in layered materials that is, 2D-layer materials.

Confinement of ions in sub-nanometer pores results in their desolvation, leading to the capacitance increase and deviation from the typical linear behavior on the surface area. During negative polarization of porous carbon materials with the pore sizes <1 nm, a decrease of capacitance  is observed. This is due to the ion selection limiting ion transport.

These insights are important for effectively tailoring carbon pore structures and for increasing their specific capacitance. Since carbon material is not an ideal conductor, it is important to consider its specific electric structure. For graphite materials, the availability of the charge carriers increases during the polarization which leads to increased conductivity.

Unified model of electrochemical charge storage under confinement

Since the electrochemical interface in the most technological application is non-planar, the researchers proposed a detailed evaluation and different concept of electrochemical capacitance on such non-ideal interfaces. The team evaluated electrosorption on 2D surfaces and 3D porous carbon surfaces with a continuous reduction in pore size in a step-by-step approach of increasing complexity.

The example provided relates to the charge storage characteristics of lithium ions (Li+) in the graphene sheets of organic lithium-containing electrolytes depending on the number of graphene layers. In a single graphene layer, the capacitive response is potential independent due to the absence of specific adsorption. However, with an increase of graphene sheets, redox peaks emerged that are associated with the intercalation of desolvated lithium ions. Lithium intercalation is responsible for battery wear. The team’s hypothesis was that the transition of solvated lithium ion adsorption on a single graphene sheet into subsequent intercalation of desolvated lithium ions occurs with a continuous charge storage behavior. There can be a seamless transition based on the increased charge transfer between an electrolyte ion and host associated with the extent of desolvation and confinement.

In the presented research, a unified approach was proposed that involves the continuous transition between double-layer capacitance and Faradaic intercalation under confinement. This approach excludes the traditional “single” view of electrochemical charge storage in nano-materials regarded as purely electrostatic or purely Faradaic phenomenon.

The increasing degree of ion confinement is followed by decreasing degree of ion solvation thus the increase ion-host intercalation. This results in a continuum from EDL formation through transitioning state to Faradaic intercalation, typical for EDLC nanomaterial.

Image: Pixabay

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Humidity-resistant composite membranes for gas separation

Hydrogen (H2) is a lightweight alternative fuel with a high energy density. However, its environmental impact and life cycle efficiency are determined by how it is produced. Today, the main processes of hydrogen production is either by coal gasification or steam reforming of natural gas where in the last step the produced carbon dioxide (CO2) is produced. Usually, this CO2 is released to the environment. The hydrogen produced by these processes lead is called black/brown or grey hydrogen. To improve its carbon footprint, CO2 capture is necessary. This hydrogen is then call blue hydrogen. However, to obtain zero-emission green hydrogen, electrolysis of water using renewable energy is necessary. During the electrolysis process, hydrogen and oxygen are produced on two electrodes (download our more about hydrogen production and utilization as fuel can be found in our latest DIY FC manual).

Climate-related economic pressure for more efficient gas separation processes

The produced hydrogen is not pure in any of the mentioned instances. For example, using steam methane reforming reaction there are many byproduct gases like carbon monoxide, CO2, water, nitrogen and methane gas.

Typically, the CO2 of hydrogen gas is up to 50% contributing to the greenhouse effect caused by burning fossil fuels. Currently, around 80% of CO2 emissions come from fossil fuels. It has been predicted that the concentration of CO2 in the atmosphere will increase up to 570 ppm in 2,100 which increases the global temperature of about 1.9°C.

The traditional processes of gas separation such as cryogenic distillation and pressure swing adsorption have certain disadvantages, for example high energy consumption. Therefore, developing high-quality and low-cost technologies for gas separation is an important intermediate step to produce cheap hydrogen while reducing CO2 emissions.

Application of 2D material towards gas separation

Finding low cost alternatives like membrane-based separation methods for hydrogen-CO2 separation is a potentially lucrative research and it is therefor not surprising that numerous publications have investigated the matter. The various membrane materials for gas separation range from polymeric membranes, nano-porous materials, metal–organic frameworks and zeolite membranes. The goal is to reach a good balance between selectivity and permeance of gas separation. Both are key parameters for hydrogen purification and CO2 capture processes.

A study published the journal Nature Energy by researchers of the National Institutes of Japan, offered a material platform as advanced solution for the separation of hydrogen  from humid gas mixtures, such as those generated by fossil fuel sources or water electrolysis. The authors showed that the incorporation of positively charged nanodiamonds into graphene oxide (GO/ND+) results in humidity repelling and high performance membranes. The performance of the GO/ND+ laminates excels particularly in hydrogen separation compared with traditional membrane materials.

Strategy and performance of new membrane materials

Graphene oxide laminates are considered as step-change materials for hydrogen-CO2 separation as ultra permeable (triple-digit permeance) and ultra-selective membranes. Still, graphene oxide films lose their attractive separation properties and stability in humid conditions.

After lamination, graphene oxide sheets have an overall negative charge and can be disintegrated due to the electrostatic repulsion if exposed to water. The strategy to overcome this obstacle was based on the charge compensation principle. That is, the authors incorporated positively and negatively charged fillers as stabilizing agents, and tested different loadings as well as graphene oxide flake sizes. So-prepared membranes were tested for stability in dry and humid conditions while separating either hydrogen from CO2 or oxygen.

The GO/ND+ composite membranes retained up to 90% of their hydrogen selectivity against CO2 exposure to several cycles and under aggressive humidity test. A GO30ND+ membrane with 30% positively charged nano-diamond particles exhibited exceptional hydrogen permeance with more than 3,700  gas permeatin units (GPU) and high hydrogen-CO2 selectivity. Interestingly, incorporation of negatively charged nano-diamond particles had no stabilizing effect. The researcher attributed this mostly to the generation of macro scale voids in ND− systems resulting in the loss of selectivity. This phenomenon is commonly observed in polymer-based nano-composite membranes with poor interfacial interactions

The gas separation properties of the composite membranes were also investigated using an equimolar hydrogen-CO2 feed mixture. The hydrogen permeance decreased by 6% and hydrogen-CO2 selectivity of the GO30ND+ membrane by 13%.

The stability test of the membranes exposure to wet and dry feeds of the equimolar hydrogen-CO2 mixture  and hydrogen-oxygen mixture showed that GO/ND+ membranes were reversible membrane properties. On the other hand, graphene oxide-only membranes could not survive a single complete cycle exposure, becoming fully permeable to both gases. The researchers explained that the advantages of GO/ND+ membranes over graphene oxide-only membranes were caused by changes of the pore architecture such as dimensions and tortuosity, which could be improved by optimizing the nano-diamond loading. This results in better permeability without any notable loss of selectivity.

X-ray diffraction analysis showed that the incorporation of nanodiamonds has two major effects on the membrane microstructure: increasing the overall pore volume and reducing the average lateral size. Both make the membrane structure more accessible for molecular transport.

Nevertheless, this relatively new class of humid-resistant membranes still needs more optimization to compete with current industrial separation processes.

Image: Pixabay / seagul

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Remarkable performance of Fe–N–C cathode electrocatalysts in anion-exchange membrane fuel cells (AEMFC)

Catalysts for low-temperature fuel cells are permanently improved to overcome high costs. Only when low-temperature fuel cells are competitive with internal combustion engines will they be an alternative power source for transportation or even portable devices. The US Department of Energy’s (DOE) milestones for the cost of a light-duty vehicle fuel cell system is $30 per kWnet. However current costs of a proton-exchange membrane (PEM) fuel cells ranges between $45 and $51 kWnet.

Challenged to reduce fuel cell production cost, researchers have suggested changing the fuel cell operating environment from acidic pH to alkaline. This will require to replace PEM by anion-exchange membranes (AEM) in fuel cells. The true advantage of AEM over PEM fuel cells is the cost reduction through cheaper membranes. Additionally, a broader spectrum of materials could be used and the oxygen reduction reaction (ORR) kinetics would be improved. Yet, acidic conditions corrode non-precious metals quickly while at the same time the high loading of platinum group metals (PGM) catalysts  need to be reduced as well.

Synthesis of Fe-N-C electrocatalyst and it structure

Researchers from the University of South Carolina, Columbia (USA) together with their partners recently reported in Nature Energy the remarkable performance of inexpensive Fe-N-C cathode catalysts with single-atom Fe-Nx active sites in AEM fuel cell. The Fe-N-C catalyst was constructed in respect to two important aspects: increase the average pore size (ranging from 5-40 nm, 1 µm) as well as the level of graphitization. Both measures reduce the hydrophobicity of the catalyst layer. To optimize their catalyst’s performance, the researchers went through an iterative process using various material characterization techniques. Energy Dispersive Spectroscopy mapping was used to ensure the catalyst composition was homogeneous. Iron atoms in the catalyst were present as single atoms, which was confirmed by Scanning Transmission Electron Microscopy imaging.

Catalyst performance and integration in AEM fuel cells

The electrochemical analyses carried out by the scientists showed that their Fe-N-C catalyst achieved high ORR activity via four-electron O2 reduction. In this reduction reaction, oxygen is directly reduced to water without the intermediate hydrogen peroxide step. The yield of hydrogen peroxide as function of potential over the entire experimental range was less than 1% – a good result for a non-precious metal catalyst. The current density of the reaction was of 7 mA / cm2.

The Fe-N-C catalyst was used on the cathode of a hydrogen-oxygen AEM fuel cell. An high peak power density of 2 W / cm2 was reported. This performance is the highest reported value for polymer membrane fuel cells (AEM and PEM) using a non-precious metal catalyst. Especially the 4x lower loading of Fe-N-C catalyst compared with previous reports makes this type of fuel cell economically interesting. Moreover, the electrocatalyst was stable at voltages of 0.6 V for more than 100 hours.

To evaluate feasibility of Fe-N-C cathode for more practical application, the fuel cell was tested in the air flow as cathode oxidant. The achieved current density was 3.6 mA / cm2 at 0.1 V with a peak power density of over 1 W / cm2. These results again show the highest reported values in the literature up to date compared to other hydrogen-air AEM fuel cell.

Fuel cell test target DOE-criteria

The cell configuration simulating more realistic operation was intended to benchmark against the DOE targets and the DOE2022 milestones. Cathodes with 0.6 mg Pt / cm2 and a 1 mg Fe-N-C per cm2 were compared. The paired cell was operated under conditions similar to the DOE-defined protocol: 0.9 V iR-free, cell temperature 80°C and 100 kPa partial pressure of O2 and H2. A steady-state current density reached at 0.9 V (iR-free) was approx. 100 mA / cm2. This was more than twice the DOE target.

Finally, the next configuration was designed using the DOE2022 milestones protocol postulating that the total precious metal loading should be less than 0.2 mg Pt / cm2. This was achieved by integrating Fe-N-C cathode with low-loading PtRu/C anodes (0.125 mg PtRu per cm2). This cell reached a peak power density of 1.3 W / cm2 under hydrogen-oxygen operation. Recalculating this value to a specific power output of 16 W per mg Pt results in the highest value of any AEM fuel cell ever reported in the literature.

It has been demonstrated that the Fe-N-C electrocatalyst can compete with noble metal-based catalysts for AEM fuel cells. The reported cell configuration provided remarkable performance in terms of activity and durability under fuel cell condition.

Methodology and electrode preparation

  • Rotating ring disc system – RRDE, was used for evaluation of electrochemical performance for ORR of Fe-N-C catalyst.
  • Fe-N-C catalyst was prepared with higher density of Fe-Nx centers since it has been reported that a higher carbon proportion also results in a higher number of positions in the graphene sheets available for insertion of active sites.
  • For the comparison Pt/C electrode was analyzed.
  • In the electrochemical cell the electrodes were: working electrode – catalyst was cast on the GC disk and stabilized with 5% Nafion® ;
  • Platinum mesh was used as counter electrode and Ag/AgCl as reference electrode, 0.1 M KOH was used as electrolyte.
  • For the tests in anion-exchange membrane fuel cell, gas diffusion electrodes were used: Anode was prepared with low-loading PtRu/C material (0.125 mg PtRu per cm2, 0.08 mg Pt per cm2), while for the cathode Fe-N-C catalyst was used – both were prepared by spraying catalyst ink onto a gas diffusion layer.

Image: iStock

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Multifunctional iridium-based catalyst for water electrolysis and fuel cells

Most of the world’s energy needs are currently served by fossil fuels. The International Energy Agency (IEA) annual projection indicates that the global energy demand will increase twice by 2040, mostly in emerging markets and developing economies.

To meet increasing global energy demands and to replace depleting fossil fuels, policy makers believe that alternative clean and renewable energy sources are the best solution. Such renewable energy sources can be electricity for solar, wind or geothermal energy as well as hydroelectric power. The latter, however, has reached a certain degree of saturation in fully industrialized countries.

While solar and wind energy are available in most places of the world at more or less reasonable cost, their biggest disadvantage is that they are intermittent, difficult to store and transport, and difficult to tank in cars, planes and ships. Converting solar and wind energy in hydrogen gas could be an elegant way out of this dilemma as the fuel’s resource can be abundant water. Diversifying the energy mix by adding hydrogen at acceptable cost may prove more efficient with a lower environmental footprint as compared to other fuels. Hence, the interest for  water electrolysis and fuel cells  is constantly growing.

Most of today’s hydrogen is produced through steam reforming of natural gas. However, it can also be made from water electrolysis. Electrolysis is two-electrode reactions: the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode.

Fuel cells reverse the reaction and harvest electricity produced by fusing the hydrogen and oxygen atoms back together to obtain water. While there are different types of fuel cells, those commonly used with hydrogen as fuel are polymer electrolyte membrane fuel cells, or PEMFC. The PEM acronym is also often used for proton exchange membranes, which can be made of polymers, for example Nafion™.  In PEMFC, energy is liberated through the hydrogen oxidation reaction (HOR) at the anode and oxygen reduction reaction (ORR) at the cathode. To become economically feasible, there are still technical challenges of water electrolyzers and fuel cells to overcome. Some technical problems result in serious system degradation.

Water is pumped into a fuel cell where two electrodes split it into hydrogen (H2) and oxygen (O2)

A study published in Nature Communications by researcher of Technical University Berlin and the Korea Institute of Science and Technology, suggests using a novel iridium electrocatalyst with multifunctional properties and remarkable reversibility. While iridium also is precious and one of the platinum group metals, the novel Ir-catalyst was designed for the processes where electrochemical reactions change rapidly, such as the voltage reversal of water electrolysis and PEMFC systems. This would integrate the two energy conversion systems in one and therefore be a great economical benefit over existing solutions.

Challenges

Unexpectedly changing operating conditions such as a sudden shut-down of water electrolysis result in increased hydrogen electrode potentials which lead to degradation hydrogen producing electrodes.

In fuel cells, fuel starvation can occur at the anode, leading to voltage reversal. Ultimately, this causes degradation of fuel cell components such as the catalyst support, gas diffusion layer and flow field plates. It has been proposed to introduce a water oxidation catalyst to the anode of the PEMFcs in order to promote OER since it is the reaction that competes with the carbon corrosion reaction.

Design of a unique iridium-based multifunctional catalyst

For the study, a crystalline multifunctional iridium nanocatalyst has been designed considering the mentioned challenges in water electrolysis and fuel cell operation.

The reason why an iridium-based material has been selected is its remarkable OER activity as well as good HER and HOR catalytic activity. It is a superior material for anodes and cathodes in electrolyzers and for anodes of PEMFC. For comparisons, the researchers synthesized two catalysts  using the modified impregnation method: carbon-supported IrNi alloy nanoparticles with high crystallinity (IrNi/C-HT) and with low crystallinity (IrNi/C-LT).

The findings indicated that the surface of IrNi/C-HT had reversibly converted between a metallic character and an oxidic IrNiOx character. Under OER operation that is, anodic water oxidation, the crystalline nanoparticles form an atomically-thin IrNiOx layer. This oxide layer reversibly transforms into metallic iridium when returning towards more cathodic potentials. The reversal allows the catalyst to return to its high HER and HOR activity.

The experiments also revealed that the performance of IrNi/C-LT sharply decrease after carrying out the OER. The catalyst degradation was due to the irreversible destruction of the amorphous IrNiOx surface.

In situ/operando X-ray absorption near edge structure (XANES) and depth-resolving X-ray photoelectron spectroscopy (XPS) profiles, suggested that the thin layers of IrNiOx possess an increase in the number of d-band holes during OER, due to which catalyst IrNi/C-HT exhibited excellent OER activity. As expected, under HER conditions, the thin IrNiOx layer was reversibly converted to metallic surface. The mechanistic study of the reversible catalytic activity of the IrNiOx layer has been additionally analyzed by electrochemical flow-cell using inductively coupled plasma-mass spectrometry (ICP-MS). The results demonstrate that the reversible IrNiOx layers come from a dissolution and re-deposition mechanism.

In addition, the performance and catalytic reversibility of synthetized electrocatalysts were used to perform HOR and OER in a real electrochemical device and tested under fuel starvation of the PEMFC. Using voltage reversal, the fuel cell was converted into an electrolyzer.

Fuel starvation experiments were conducted in a single PEM fuel cell built using IrNi/C-HT and IrNi/C-LT as the catalytically active components in the anode catalyst layer. The initial fuel cell performance of IrNi/C-LT and -HT was lower than that of the commercial Pt/C catalyst due to the lower HOR and metal composition.

Further results demonstrate that IrNi/C-HT catalyst retained its bifunctional catalytic activity, reversibing between HER and OER in a real device. This approach promoted the reversibility of nanocatalysts, which enable a variety of electrochemical reactions and can be used as catalysts to resist the reverse voltage in fuel cells and water electrolysis systems.

At Frontis Energy, we are looking forward to adding the novel iridium catalyst to our Fuel Cell Shop as soon as it becomes available.

Photo: Iridium / Wikipedia

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Making zinc-air batteries rechargeable using developed cobalt(II) oxide as a catalyst

Zinc-air batteries are a promising alternative to expensive lithium-ion batteries. Compared with lithium-ion technology, zinc-air batteries have a greater energy density, very low production cost, and superior safety. However, their fundamental inability to recharge has lowered their wide-scale adoption.

Zinc-air batteries use charged zinc particles to store large amounts of electricity at a time. When electricity is required, the charged zinc is combined with oxygen from the air (and water), releasing the stored electricity and producing zincate. This process is known as oxygen reduction reaction (ORR).

Theoretically, this zincate can again be broken down into oxygen and zinc ions by passing electricity through it. This process, in turn, is called oxygen evolution reaction (OER). Using these reactions, zinc-air batteries can be made rechargeable, competing with lithium-ion batteries.

The major challenge of the recharging process is the sluggish kinetics of the reactions which lead to poor cycle life. These batteries require a catalyst that could potentially enhance the ORR and the OER reactions, making their kinetics fast. Hence, the development of highly efficient catalysts is of paramount importance for rechargeable zinc-air batteries.

Previous studies have suggested transition-metal oxides as great bifunctional ORR / OER catalysts because of their ability to provide sites for the reversible adsorption of oxygen. But the methods involved in creating well-defined defects for reversible adsorption of oxygen in such oxides are challenging.

To investigate the use of cobalt(II) oxide nanosheets deposited on stainless steel or carbon cloth as a bifunctional catalyst, a group of researchers from different universities of China and Canada collaborated and conducted several experiments. Their research findings were published in the journal Nano Energy .

Research approach

Preparation of catalyst

Different nano-structures were prepared using simple heat treatment and electrodeposition to test them as bifunctional electrocatalysts. The type of nano-structures prepared were:

      • Cobalt hydroxide  nanosheets on steel and carbon cloth
      • Layered cobalt (II) oxide nanosheet on steel and carbon cloth
      • Cobalt (II) oxide on steel
      • Layered cobalt tetroxide nanosheet on steel

Material Characterization

To understand the characteristics of the prepared samples, various analyticaland tests were carried out:

Charging and discharging tests

Later discharge and charge cycling tests of single cells were operated by the battery testing system.

Results

The simple heat treatment strategy created oxygen vacancy sites. According to the authors, layered cobalt-oxide nano-sheets exhibited excellent bifunctional ORR / OER performance. Investigations suggested abundant oxygen vacancies and cobalt sites be the reason for enhanced ORR / OER performance. Later, the developed layered cobalt-oxide nanosheets on steel were used as an electrode in a rechargeable zinc-air flow battery and a record-breaking cycle life of over 1,000 hours with nearly unchanged voltage was observed. Galvanostatic discharging-charging cycles also demonstrated long life and high energy efficiency.

This research carried out provides a new method to design highly efficient bifunctional ORR / OER catalysts that could be used to enhance the cycle life of rechargeable zinc-air flow batteries. At Frontis Energy we are looking forward to industrial applications.

(Photo: Engineersforum)

Reference: https://doi.org/10.1016/j.nanoen.2020.105409 Wu et al., Cobalt (II) oxide nanosheets with rich oxygen vacancies as highly efficient bifunctional catalysts for ultra-stable rechargeable Zn-air flow battery, 2021