Phosphorus-doped cobalt oxide constructs high and low valence Cobalt: Efficient synergistic catalytic electrooxidation of sodium borohydride

Abstract

Low-cost, high-performance electrode materials for mitigating hydrogen release are urgently needed for anodes of direct borohydride fuel cells (DBFC). Herein, CoP-CoOx with both high (Co2+/3+) and low (Coδ+) valence cobalt is successfully constructed by regulating the Co valence state by P and O and achieves efficient catalysis of NaBH4 electrooxidation. Coδ+ has an extremely strong ability to break B-H bonds, and Co2+/3+ is near the grain boundaries to provide strong adsorption of electronegative reactants and uneven stress on B-H bonds. Benefiting from the synergistic effect of high and low valence cobalt, and the unique inner hole structure of material induced by the phosphorylation process, the direct sodium borohydride-hydrogen peroxide fuel cells (DBHPFC) assembled with CoP-CoOx as anodes can reach a maximum power density of 280 mW cm−2 at room temperature. Meanwhile, high phosphorus doping is effective in improving fuel utilization. This work provides a cost-effective, highly-active anode engineering strategy for DBFC and attracts attention to the valence state of cobalt-based materials in the field of catalytic NaBH4 electrooxidation.