A nanostructured bifunctional Pd/C gas-diffusion electrode for metal-air batteries

Designing a bifunctional air electrode which catalyses both the oxygen reduction and oxygen evolution reactions is an essential part of progress towards fully rechargeable metal-air batteries, such as the iron-air battery which is environmentally friendly, low cost, and does not suffer risk of thermal runaway like lithium-ion batteries. This paper reports the development of a lightweight carbon-based bifunctional air electrode, catalysed by a small (0.5 mg cm-2) loading of 30 wt.% palladium on carbon. The Pd-catalysed air electrode showed good bifunctional activity, with 0.53 V potential difference between oxygen reduction and evolution. The Pd/C air electrode showed improved catalytic activity at high current densities (≥ 50 mA cm-2) and enhanced durability compared with two commercial Pt/C air electrodes produced by Gaskatel GmbH and Johnson Matthey. A stable oxygen evolution potential was maintained over 1,000 charge-discharge cycles

Improving the stability and discharge capacity of nanostructured Fe₂O₃/C anodes for iron-air batteries and investigation of 1-octhanethiol as an electrolyte additive

Iron-based aqueous batteries, such as the iron-air and nickel-iron chemistries, are limited by passivation and hydrogen evolution at the iron anode, especially at high current densities. In this paper, strategies to minimise these issues are investigated with iron electrodes composed of 20–50 nm Fe2O3 nanoparticles produced by the Adams and Oxalate methods. The strategies include ball milling the Fe2O3 with Ketjenblack carbon to improve conductivity, addition of bismuth sulphide to the electrode and 1-octanethiol to the electrolyte, and addition of potassium carbonate as a pore-forming agent. The ratio of Fe/C in the electrode and the 1-octanethiol additive have the greatest impact on the electrode capacity. The Fe/C ratio should be below 2.0 to ensure conductivity of the discharged electrode. The presence of 1-octanethiol can protect the electrodes from passivation during discharge; at very high 2C discharge rates adding 1-octanethiol increases the electrode specific capacity from 17 to 171 mAh/gFe. The synthesis method and use of pore former do not have a significant effect on the capacity. In all electrodes, the Fe2O3 nanoparticles are in the same crystalline phase after cycling and do not undergo significant crystal growth and passivation, demonstrating the stability and suitability of these materials for iron-based batteries.</p

A high-performance, bifunctional oxygen electrode catalysed with palladium and nickel-iron hexacyanoferrate

The development of air-breathing cathodes, which utilise atmospheric oxygen, enables the construction of lightweight, high energy density metal-air batteries and fuel cells. Air electrodes can be very lightweight and thin because the active material, oxygen, does not need to be stored inside the cell. However, air electrodes are restricted by poor reaction kinetics and low activity of many catalysts towards the oxygen evolution and reduction reactions. In addition, it is a challenge to maintain chemical and mechanical stability of the catalyst and supporting materials at oxidising currents under the strong alkaline conditions commonly used,and gas evolution. This paper reports a novel bifunctional oxygen electrode with remarkable stability, able to perform at current densities up to 1,000 mA cm-2 and withstand 3,000 cycles continuously. The electrode is catalysed by a mixture of Pd/C and mixed nickel-iron hexocyanoferrate, which have high activities towards the ORR and OER reactions, respectively.<br/

A rechargeable, aqueous iron air battery with nanostructured electrodes capable of high energy density operation

In order to decrease the global dependence on fossil fuels, high energy density, rechargeable batteries with high charge capacity are required for mobile applications and efficient utilization of intermittent sources of renewable energy. Metal-air batteries are promising due to their high theoretical energy density. In particular, the iron-air battery, with a maximum specific energy output of 764 W h kg-1Fe, represents a low cost possibility. This paper considers an iron-air battery with nanocomposite electrodes, which achieves an energy density of 453 W h kg-1Fe and a maximum charge capacity of 814 mA h g-1Fe when cycled at a current density of 10 mA cm-2, with a cell voltage of 0.76 V. The cell was manufactured by 3D printing, allowing rapid modifications and improvements to be implemented before an optimized prototype can be manufactured using traditional computer numerical control machining

A comparison of Pd/C, perovskite, and Ni-Fe hexacyanoferrate bifunctional oxygen catalysts, at different loadings and catalyst layer thicknesses on an oxygen gas diffusion electrode

Air electrode development is one of the most challenging steps in the design of lightweight and efficient metal-air batteries and fuel cells. The best performing oxygen catalysts often contain precious metals at a high manufacturing cost. In this paper, two low-cost catalysts for the oxygen reduction (ORR) and evolution reactions (OER), based on LSFCO perovskite and Ni-Fe hexacyanoferrate, were compared with a precious metal palladium catalyst on carbon (Pd/C). LSFCO/C showed the best all-round performance as a single bifunctional catalyst but Pd/C had the strongest ORR activity. Ni-Fe hexacyanoferrate is straightforward to manufacture in industrial quantities, and is more active for the OER than palladium and LSFCO perovskite at small loadings &lt; 5 mg cm-2. By mixing a small loading of Pd/C with Ni-Fe hexacyanoferrate, lower overpotentials for both the ORR and OER can be reached, with the difference in potential between the two reactions being only 0.62 V at a current density of 20 mA cm-2. The effect of catalyst loading of each catalyst on the gas-diffusion electrode was studied, and rotating disk voltammetry was used to study the catalytic behavior of the Ni-Fe hexacyanoferrate catalyst.</p

Effect of 1-Octanethiol as an electrolyte additive on the performance of the iron-air battery electrodes

It has recently been established that 1-octanethiol in the electrolyte can allow iron-electrodes to be discharged at higher rates. However, the effect of thiol additives on the air-electrode, has not yet been studied. The effect of solvated thiols on the surface positive electrode reaction is of prime importance if these are to be used in an iron-air battery. This work shows that the air-electrode catalyst is poisoned by the presence of octanethiol, with the oxygen reduction overpotential at the air-electrode increasing with time of exposure to the solution and increased 1-octanethiol concentration in the range 0-0.1 mol dm-3. Post-mortem XPS analysis were performed over the used air-electrodes suggesting the adsorption of sulphur-species over the catalyst surface, reducing its performance. Therefore, although sulphur-based additives may be suitable for nickel-iron batteries they are not recommended for iron-air batteries except in concentrations well below 10 ×10-3 mol dm-3