Trimetallic Carbon-Supported Catalysts for Borohydride Oxidation and Oxygen Reduction in Alkaline Solutions

Abstract

Borohydrides present a particularly attractive option for alkaline liquid fuel systems, having high energy densities, a low standard potential for its oxidation, and good stability in alkaline conditions. A key area in the success of a fuel cell utilizing borohydride is the development of an anode, which can make use of the full 8-electron oxidation, directly oxidising the borohydride with as little of the undesired hydrolysis reaction occurring as possible. This is in addition to the common requirements of high activity, high stability, good electronic conductivity and effective transport of reactants and products. Here we present new studies on the oxidation of borohydride and reduction of oxygen in alkaline media under various conditions for a selection of trimetallic carbon-supported catalysts based on Pd, prepared by quick and straightforward synthetic routes. The prepared catalysts were characterised by cyclic voltammetry, chronoamperometry, and RDE based procedures. Notably, PdAuNi/C prepared via a NaBH4-2-propanol complex presents highly dispersed trimetallic alloy particles, as determined by XRD, XPS and TEM. The best performing electrodes under characterisation conditions were tested in a direct borohydride fuel cell under several different conditions. The influence of experimental parameters (temperature, borohydride concentration, as well as NaOH concentration) on the electrical behaviour of the fuel cell were studied and optimized. These results show that Pd-based trimetallic catalysts supported on carbon provide a ready route to successfully operate borohydride based fuel cells. Acknowledgements: A. Elsheikh acknowledges a Newton-Mosharafa Scholarship (Reference no. NMJ8/15) for funding. The Portuguese Foundation for Science and Technology (FCT, Portugal) is acknowledged for PhD grant no. SFRH/BD/137470/2018 (R.C.P. Oliveira), contract no. IST-ID/156/2018 (B. Šljukić) and contract no. IF/01084/2014/CP1214/CT0003 under IF2014 Programme (D.M.F. Santos). Keywords: Palladium, trimetallic catalysts, nanomaterials, borohydride oxidation, oxygen reduction, fuel cell, kinetic parameters.