Selective Borohydride Oxidation Reaction on Nickel Catalyst with Anion and Cation Exchange Ionomer for High‐Performance Direct Borohydride Fuel Cells

Abstract Direct borohydride fuel cells (DBFCs) operate with liquid H₂O₂ and a high‐energy‐density NaBH₄ solution. A facile, direct synthesis method using a non‐noble nickel catalyst for the DBFC anode is shown. The complex anode reaction with an anion‐exchange ionomer (AEI) and a cation‐exchange ionomer (CEI) is evaluated in half‐cell and single‐cell configurations. The ionomer type produces high (AEI) or low local pH (CEI) at the active site of the catalyst in the single‐cell configuration, generating different catalytic reactions. The performance of the nickel catalyst is compared to that of a palladium catalyst. The selective catalytic activities for the borohydride oxidation reaction and hydrogen oxidation reaction are the key parameters for achieving good performance. Furthermore, fuel utilization and H₂ evolution measurement in a single‐cell configuration provide more information on the complex anode reaction in the DBFC. The nickel catalyst with CEI on nickel foam (NiF@CEI‐Ni) shows the highest DBFC peak power density (0.59 W cm⁻²) with a non‐noble metal anode catalyst.