Watt-level power density of direct borohydride fuel cells enabled by electrode local-environment and mass transport regulations

The electrode mass transport limitation during borohydride oxidation reaction (BOR) involving three-phase interfaces greatly deteriorates the performance and energy efficiency of direct sodium borohydride fuel cells (DBFCs). Here we develope a hierarchical structure electrode (HSE) strategy via dispersing Pd clusters on needle-structured CoP-O nanoarrays in situ grown on optimized macro-porous nickel foam (NF), to enhance the solution/gas transport, catalyst utilization and across electrode conductivity, and meanwhile to regulate the OH^–-enrichment local environments at the anode of DBFC. The fabricated Pd@CoP-O/NF HSE exhibits excellent BOR catalytic activity featuring a rather low overpotential of 433 mV at 1 A cm⁻² and an electron transfer number up to 7.8, and particularly an extra-high power density of 1.23 W cm⁻² under O₂ conditions. The watt-level power density of DBFCs is achieved by the adsorption regulations of H*/OH^– species on the catalyst and the effective separation and dissipation of bubbles from electrode, which provides an alternative but highly promising pathway for DBFC applications.