Morphological and Electronic Dual Regulation of Cobalt-Nickel Bimetal Phosphide Heterostructures for Electrocatalytic Water Splitting.

Electrocatalytic water splitting is a key technology for production of the clean and sustainable hydrogen sources, which stores the abundant but impeded by the insufficient efficiency of the anode and cathode catalyst. Designing and constructing noble metal-free composite bifunctional electrocatalysts for promoting both cathodic hydrogen evolution and anodic oxygen evolution reactions is of great importance for water splitting. Here, the composition and morphology of a cobalt-nickel bimetal phosphide nanoparticles (NPs) embedded in a N-doped carbon nanotube hollow microspheres (NCNHMs) can effectively regulate the active sites and enhance the electronic transfer, resulting in the superior splitting efficiency. Owing to the synergistic effects between highly active Co-Ni bimetal phosphide NPs and NCNHMs, the as-prepared Co-Ni bimetal phosphide/NCNHMs show remarkable the electrochemical performance for water splitting compared with the Ni2P/NCNHMs. Therefore, the Ni1.4Co0.6P/NCNHMs through nitriding-phosphidation strategy derived from hollow Ni1.4-Co0.6-based metal organic framework (MOF) exhibit superior HER catalytic activity (= 87.9 mV at 10 mA cm-2 tested in 0.5 M H2SO4 and = 64.4 mV at 10 mA cm-2 tested in 1 M KOH) and OER catalytic activity (= 320.0 mV at 10 mA cm-2 tested in 1 M KOH), leading to excellent water splitting catalytic activity (= 1.55 V at 10 mA cm-2 tested in 1 M KOH). The density functional theory (DFT) simulations and experimental results reveal that the electro transfer from Co doping and coating with NCNHMs improve the electronic states, which could enhance the binding strength with H and therefore promote the electrocatalytic activity. The strong stability is related to the Co-Ni bimetal phosphide NPs surface protected by the NCNHMs.