Development of Bimetallic PdNi Electrocatalysts toward Mitigation of Catalyst Poisoning in Direct Borohydride Fuel Cells

Abstract

Cost-effective and highly active borohydride oxidation reaction (BOR) electrocatalysts are crucial for the advancement of direct borohydride fuel cells (DBFCs). Noble-metal electrocatalysts, such as Pd, are used as benchmark electrocatalysts because of their superior BOR activity. However, Pd suffers from catalyst poisoning because of strong binding with BHx intermediates at a high BOR overpotential, making it unsuitable for high DBFC performance, whereas Ni exhibits a low degree of catalyst poisoning because of a relatively weak binding of BHx intermediates. Density functional theory (DFT) calculations indicate a lowering of H- and OH-binding energies on bimetallic PdNi surfaces in comparison to their individual counterparts, thereby freeing more sites for BH4 adsorption that is crucial for a high BOR rate. The as-synthesized bimetallic PdNi/C electrocatalyst exhibits higher current densities at a BH4 concentration range of 50-500 mM than Pd/C and Ni/C. A DBFC unit with a pH-gradientenabled microscale bipolar interface employing PdNi/C, Pt/C, and H2O2 as the anode, cathode, and oxidant, respectively, exhibits a power density of 466 +/- 1.5 mW/cm(2) at 1.5 V, a peak power density of 630 +/- 2 mW/cm(2) at 1.1 V, with an open-circuit voltage of 1.95 +/- 0.01 V. Our bimetallic alloy electrocatalyst shows high DBFC performance, providing a pathway for the development of suitable BOR electrocatalysts.