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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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Energy storage in the European Union

Grid integration of renewables

In our previous post of this blog series on Electrical Energy Storage in the EU we briefly introduced you to different technologies and their use cases. Here, we give you a short overview over the EU energy grid.  Supplying approximately 2,500 TWh annually to 450 million customers across 24 countries, the synchronous interconnected system of Continental Europe (“the Grid”) is the largest interconnected power network in the world. The Grid is made up of transmission system operators (TSOs) from 24 countries stretching from Greece to the Iberic Peninsula in the south, Denmark and Poland in the north, and up to the black sea in the east. The European Network of Transmission System Operators (ENTSO-E) serves as the central agency tasked with promoting cooperation between the TSOs from the member countries in the Grid. The ENTSO-E, in essence, acts as the central TSO for Europe. With over 140 GW of installed wind and solar PV capacity, the EU trails behind only China in installed capacity. A breakdown of the individual contributions of EU member states is shown below in the figure above.

Energy Storage in the EU

For this study a number of European countries were selected for more detailed investigation into energy storage needs. These countries were selected based on a combination of existing market size, intentions for growth in non-dispatchable renewable energy and/or energy storage, and markets with a track record of innovation in the energy sector.

On a total capacity basis (installed and planned MW) the top three energy storage markets within the EU are: Italy, the UK, and Germany. These countries were selected on the basis of these existing market sizes.

Spain and Denmark were selected based on their large amounts of existing renewable energy capacity and − in the case of Denmark − the forecasted growth in renewable energy and energy storage capacity.

While still lagging behind the rest of the EU in terms of decarbonization efforts and having a small portion of their energy from renewable sources, the Netherlands were also selected for further investigation.

Each of the selected countries (Germany, UK, Italy, Spain, Denmark, Netherlands) are discussed in the proceeding sections, providing a more detailed overview outlining their current electricity portfolios and decarbonization efforts, current energy storage statistics, and a brief discussion on market outlook.

Pumped Hydro Storage

With over 183 GW of installed capacity worldwide, pumped hydro storage is the most widely implemented and most established form of energy storage in the world. Due its extensive market penetration, technology maturity, and the fact that this blog is aimed at emerging new storage technologies, the data presented in the following posts excludes this technology.

Find more details about the energy storage market of selected European countries in our next postings.

(Jon Martin, 2019)

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Electrical energy storage

Electrical Energy Storage (EES) is the process of converting electrical energy from a power network into a form that can be stored for converting back to electricity when needed. EES enables electricity to be produced during times of either low demand, low generation cost, or during periods of peak renewable energy generation. This allows producers and transmission system operators (TSOs) the ability to leverage and balance the variance in supply/demand and generation costs by using stored electricity at times of high demand, high generation cost, and/or low generation capacity.
EES has many applications including renewables integration, ancillary services, and electrical grid support. This blog series aims to provide the reader with four aspects of EES:

  1. An overview of the function and applications of EES technologies,
  2. State-of-the-art breakdown of key EES markets in the European Union,
  3. A discussion on the future of these EES markets, and
  4. Applications (Service Uses) of EES.

Table: Some common service uses of EES technologies

Storage Category

Storage Technology

Pumped Hydro

Open Loop

Closed Loop



Flow Batteries


Thermal Storage


Molten Salts



Chilled Water


Compressed Air Energy Storage (CAES)


Gravitational Storage

Hydrogen Storage


Fuel Cells

H2 Storage


Unlike any other commodities market, electricity-generating industries typically have little or no storage capabilities. Electricity must be used precisely when it is produced, with grid operators constantly balancing electrical supply and demand. With an ever-increasing market share of intermittent renewable energy sources the balancing act is becoming increasingly complex.

While EES is most often touted for its ability to help minimize supply fluctuations by storing electricity produced during periods of peak renewable energy generation, there are many other applications. EES is vital to the safe, reliable operation of the electricity grid by supporting key ancillary services and electrical grid reliability functions. This is often overlooked for the ability to help facilitate renewable energy integration. EES is applicable in all of the major areas of the electricity grid (generation, transmission & distribution, and end user services). A few of the most prevalent service uses are outlined in the Table above. Further explanation on service use/cases will be provide later in this blog, including comprehensive list of EES applications.


Service Use / Case

Discharge Duration in h

Capacity in MW



Bulk Storage

4 – 6

1 – 500

Pumped hydro, CAES, Batteries


1 – 2

1 – 500

Pumped hydro, CAES, Batteries

Black Start




Renewables Firming

2 – 4

1 – 500

Pumped hydro, CAES, Batteries

Transmission & Distribution

Frequency & Voltage Support

0.25 – 1

1 – 10

Flywheels, Capacitors

Transmission Support

2 – 5 sec

10 – 100

Flywheels, Capacitors

On-site Power

8 – 16

1.5 kW – 5 kW


Asset Deferral

3 – 6

0.25– 5


End User Services

Energy Management

4 – 6

1 kW – 1 MW

Residential storage

Learn more about EES in the EU in the next post.

(Jon Martin, 2019)

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EU market summary for energy storage

Electrical energy storage (EES) is not only a vital component in the reliable operation of modern electrical grids, but also a focal point of the global renewable energy transition. It has been often suggested that EES technologies could be the missing piece to eliminating the technical hurdles facing the implementation of intermittent renewable energy sources. In the following blog posts, selected EES markets within the European Union will be evaluated in detail.

With over 80 MW of installed wind and solar capacity, Germany is by far the leading EU nation in the renewable energy transition. However, experts have argued that Germany’s need for widespread industrial scale energy storage is unlikely to materialize in any significant quantity for up to 20-years. This is due to a number of factors. Germany’s geographic location and abundance of connections to neighbouring power grids makes exporting any electricity fluctuations relatively easy. Additionally, when Germany reaches its 2020 targets for wind and solar capacity (46 GW and 52 GW, respectively) the supply at a given time would generally not exceed 55 GW. Nearly all of this would be consumed domestically, with no/little need for storage.

When evaluating energy storage in the UK, a different story emerges. Being an isolated island nation there is considerably more focus on energy independence to go along with their low-carbon energy goals. However, the existing regulatory environment is cumbersome, and poses barriers significant enough to substantially inhibit the transition to a low-carbon energy sector – including EES. The UK government has acknowledged the existence of regulatory barriers and pledged to address them. As part of this effort, a restructuring of their power market to a capacity-based market is already underway. The outlook for EES in the UK is promising, there is considerable pressure from not only industry, but also the public and the government to continue developing EES facilities at industrial scale.

Italy, once heavily hydro-powered, has grown to rely on natural gas, coal, and oil for 50% of it’s electricity (gas representing 34% alone). The introduction of a solar FIT in 2005 lead to significant growth in the solar industry (Italy now ranks 2nd in per capita solar capacity globally) before the program ended in July 2014. In recent years there has been notable growth in electro-chemical EES capacity (~84 MW installed), primarily driven by a single large-scale project by TERNA, Italy’s transmission system operator (TSO). This capacity has made Italy the leader in EES capacity in the EU, however the market is to-date dominated by the large TSOs.

However, the combination of a reliance on imported natural gas, over 500,000 PV systems no longer collecting FIT premiums, and increasing electricity rates presents a unique market opportunity for residential power-to-gas in Italy.
Denmark is aggressively pursing a 100-percent renewable target for all sectors by 2050. While there is still no official roadmap policy on how they will get there, they have essentially narrowed it down to one of two scenario: a biomass-based scenario, or a wind + hydrogen based scenario. Under the hydrogen-based scenario there would be widespread investment to expand wind capacity and couple this capacity with hydrogen power-to-gas systems for bulk energy storage. With the Danish expertise and embodied investment in wind energy, one would expect that the future Danish energy system would be build around this strength, and hence require significant power-to-gas investment.

The renewable energy industry in Spain has completed stagnated due to retroactive policy changes and taxes on consumption of solar generated electricity introduced in 2015. The implementation of the Royal Decree 900/2015 on self-consumption has rendered PV systems unprofitable, and added additional fees and taxes for the use of EES devices. No evidence was found to suggest a market for energy storage will materialize in Spain in the near future.

The final country investigated was the Netherlands, which has been criticized by the EU for its lack of progress on renewable energy targets. With only 10% of Dutch electricity coming from renewable sources, there is currently little demand for large-scale EES. While the Netherlands may be lagging behind on renewable electricity targets, they have been a leader in EV penetration; a trend that will continue and see 1-million EVs on Dutch roads by 2025. In parallel with the EV growth, there has been a large surge in sub-100kW Li-ion installations for storing energy at electric vehicle (EV) charging stations. It is expected that these applications will continue to be the primary focus of EES in the Netherlands.

Similar to Italy, the Dutch rely heavily on natural gas for energy within their homes. This fact, coupled with an ever-increasing focus on energy independent and efficient houses could make the Netherlands a prime market for residential power-to-gas technologies.

Read more about electrical energy storage here.

Jon Martin, 2019

(Photo: NASA)