Direct formate anion exchange membrane fuel cells with a PdAu bimetallic nanoparticle anode electrocatalyst obtained by metal vapor synthesis

Abstract

Fuels can be produced from the electrochemical reduction of industrial waste CO₂ (e-fuels) using renewable energy and hence are an attractive option for the storage of renewable energy in a chemical form. The energy stored in the e-Fuel may be recovered on-demand using a direct fuel cell thus completing a carbon neutral cycle. Anion exchange membrane fuel cells (AEMFCs) are versatile devices that can be fed by both a gaseous fuel such as H₂ and with liquid fuels (e.g. alcohols, formate, hydrazine, NaBH₄). Formate is a molecule that can be easily obtained by the electrochemical reduction of CO₂ with high selectivity. Efficient re-transformation of the energy stored in the chemical bonds into electrical energy requires the development of efficient and stable electrocatalysts. Palladium alloy catalysts are highly active under alkaline conditions when Pd is mixed with more oxophilic transition metals. Here we report that enhanced activity and stability can be obtained with Au–Pd alloy nanoparticles when compared to a Pd catalyst. Both catalysts are prepared by a metal vapour synthesis method. We show that the key to enhanced performance is the partial segregation of Au to the NP surface that increases oxophilicity and favours the adsorption and transfer of OH⁻ species to the active Pd sites. This enhanced activity translates to high power densities and performance stability when employed in AEMFCs fed with aqueous potassium formate fuel (Peak power density of 0.14 W cm⁻², energy efficiency of 33%, faradaic efficiency of 80%).