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 < 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. (C) 2018 The Electrochemical Society.