Constructing a multisite catalyst for achieving efficient and highly selective borohydride oxidation reaction

It is crucial to develop efficient and inexpensive borohydride oxidation reduction (BOR) electrocatalysts for the practical application of direct borohydride fuel cells (DBFCs). However, until now, there is still rare electrocatalyst that can simultaneously achieve a high BOR rate, high faradaic efficiency, and low BOR onset potential. In this work, we reported an efficient multisite catalyst CoFe&AuC, with a peak power density of 580 mW/cm² in DBFC (Air as oxidant), which is 2.8 and 4.3 times higher than CoFe&C (210 mW/cm²) and AuC (136 mW/cm²), respectively. Meanwhile, CoFe&AuC also shows a peak power density of 1371 mW/cm² in DBFC with O₂ used as an oxidant. Notably, CoFe&AuC exhibits a high electron transfer number (5.4) and fuel efficiency (65.6 %), suggesting the high selectivity for BOR. In situ spectroscopy combined with density functional theory (DFT) calculations indicate that the enhanced BOR activity can be attributed to the tandem effect between different components: the rapid adsorption and initial oxidation of BH₄^- to BH₃ species on CoFe LDH and the further oxidation of BH₃ species on Au nanoparticles, which efficiently break the bottleneck of Au catalyzing BH₄^-. This work provides a novel pathway for designing multisite electrocatalysts with high BOR activity and selectivity.