Tag: stainless steel

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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

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Corrosion Protection

Corrosion is the chemical attack on a material leading eventually to its destruction if not stopped. It is caused by electrolytes, gases, solutions, or smelt. Corrosion occurs in different forms depending on the material under corrosive attack and the attacking agent. On metals, iron, for instance, its most visible manifestation is aerial or localized rust, such as needle holes in the surface. Crystalline corrosion of metals follows grain boundaries on surfaces. Corrosion is highly accelerated if the corroding material is in electrolytical contact with a more noble material. If this electrolytical contact is a liquid or humid substance, then corrosion is further accelerated. The reason is that the corroding material acts as anode (local cell) of a galvanic cell. Mechanical strain can accelerate corrosion as well.

A simple galvanic cell. The metal on the left side acts as anode and is dissolved into metal ions (M+). On the cathode water is transformed to hydrogen gas.

Corrosion protection is accomplished by coating the vulnerable material with corrosion resistant dense films. Such coating can be other metals such as zinc or chrome, as well as glazing, for example enamel. Protective paint is a wide-spread measure and is accomplished by adding pigments such as red (minium) or white lead, or organic substances. Tight plastic wrap is used as well. Iron is protected through transformation into stainless steel by adding chrome, nickel, etc.

The sacrificial anode is not a dissolving metal but soil or sewer organics. Microbes destroy these organics and produce CO2

If the material is exposed to water permanently, cathodic protection is frequently employed. To accomplish cathodic protection, the vulnerable material is connected to sacrificial anodes such as rods or plates that dissolve over time. Alternatively, directed current is used in many applications. Our patent pending solution provides a microbial anode that uses organic matter in soil or sewer as sacrificial anode. Instead of dissolving the metal, organic matter is degraded by microbes.

If a potentiostat is added to the galvanic cell, cathodic protection can be tailored to the protected material or the organics.

Besides metals, natural (wood, silk) and artificial polymers (plastics, rubber) can corrode as well. Softwood is generally more resistant than hardwood. Weak acids usually do no harm to wood. However, corrosion protection of wood is accomplished by painting or soaking it using protective agents. Artificial polymers rarely corrode as quickly as metals and if they do, a protective agent is mixed into the polymer formula at the time of its synthesis.