Impact of the Anode Catalyst Layer Design on the Performance of H2O2-Direct Borohydride Fuel Cells

Pt and Pd electrocatalysts are active for the complex 8-electron borohydride oxidation reaction (BOR), but the completeness of the electrochemical reaction is compromised by the formation of byproducts, including unreacted H-2. We probe how combining the two electrocatalysts might improve the overall BOR activity. Five catalyst layer compositions are compared by rotating disk electrode (RDE) voltammetry and as the anode in hydrogen-peroxide direct borohydride fuel cells (H2O2-DBFCs): Pt/C, Pd/C, a Pt/C + Pd/C mixture, and graded layers of Pt/C and Pd/C as Pt/C|Pd/C or Pd/C|Pt/C. The RDE results show distinct mechanistic pathways for Pt and Pd, electrodes, but that the mixtures and Pt/C|Pd/C graded electrodes lead to better BOR activity than Pt or Pd alone. Similarly, the graded anodes in H2O2-DBFC outperform the ones with pure Pt/C or Pd/C under several operational conditions due to synergy between Pt and Pd. The Pt and Pd appear to serve as cooperative electrocatalysts, with their combination leading to less deleterious H2 escape than cells with Pt-only electrodes, and higher electrochemical performance than cells with Pd-only electrodes. We conclude that catalyst layers with graded compositions are promising electrode architectures for DBFCs. (c) The Author(s) 2019. Published by ECS.