Tunable B-Doped Cobalt Phosphide Nanosheets Engineered via Phosphorus Activation of Co-MOFs for High Efficiency Alkaline Water-Splitting.

Introducing secondary heteroatoms and simultaneous in situ surface modification can enhance electrocatalysts by affecting their porosity for adjusting electrochemically active surface area (ECSA), number of active sites, and electronic properties, thus mitigating the sluggish kinetics of oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline media. Here, mesoporous 3D heterostructures of boron-doped cobalt phosphide@nitrogen-doped carbon nanosheet network arrays are successfully grown on Ni foam as free-standing bifunctional electrocatalysts with controlled phosphorous levels (B-CoP@NC/NF, x = 0.25, 0.5, and 1). Boron doping induces the Co active sites to bind O* and OOH* intermediates. Meanwhile, an optimal phosphorous content also leads to ideal adsorption strength at each reaction step, satisfying the Sabatier principle well. The optimal B-CoP@NC/NF requires low overpotentials of 248 mV for OER and 95 mV for HER with long-term stability. The B-CoP@NC/NF (+/-) electrolyzer exhibits a low cell potential of 1.59 V at 10 mA cm for overall water-splitting, with superior activity compared to the RuO/NF(+)//20%Pt/NF(-) electrolyzer at high current densities above 50 mA cm. Such exceptional bifunctional activities are attributed to the modulated electronic structure, lower charge-transfer resistance, higher ECSA, and inductive effect of B-doping, thus boosting both OER and HER activities in alkaline media.