Morphological and Electronic Tuning of Ni₂P through Iron Doping toward Highly Efficient Water Splitting

Abstract

Efficient water electrolysis for hydrogen production constitutes a key segment for the upcoming hydrogen economy, but has been impeded by the lack of high-performance and low-cost electrocatalysts for, ideally, simultaneously expediting the kinetics of both hydrogen and oxygen evolution reactions (HER and OER). In this study, the favored binding energetics of OER and HER reaction intermediates on iron-doped nickel phosphides are first predicted by density functional theory (DFT) simulations, and then experimentally verified through the fabrication of Fe-doped Ni2P nanoparticles embedded in carbon nanotubes using metal–organic framework (MOF) arrays on nickel foam as the structural template. Systematic investigations on the effect of phosphorization and Fe doping reveal that while the former endows a larger benefit on OER than on HER, the latter enables not only modulating the electronic structure, but also tuning the micromorphology of the catalyst, synergistically leading to both enhanced HER and OER. As a result, extraordinary performances of constant water electrolysis are demonstrated requiring only a cell voltage of 1.66 V to afford a current density of 500 mA cm–2, far outperforming the benchmark electrode couple composed of Pt/C and RuO2. Postelectrolysis characterizations combined with DFT inspection further reveal that while the Fe-doped Ni2P species are mostly retained after prolonged HER, they are in situ converted to Fe/P-doped γ-NiOOH during OER, serving as the actual OER active sites with high activity.