Oxygen Doping to Optimize Atomic Hydrogen Binding Energy on NiCoP for Highly Efficient Hydrogen Evolution

An outstanding hydrogen evolution electrocatalyst should have a free energy of adsorbed atomic hydrogen of approximately zero, which enables not only a fast proton/electron-transfer step but also rapid hydrogen release. An economic and industrially viable alternative approach for the optimization of atomic hydrogen binding energy is urgently needed. Herein, guided by density functional theory (DFT) calculations, it is theoretically demonstrated that oxygen doping in NiCoP can indeed optimize the atomic hydrogen binding energy (e.g., |ΔGH* | = 0.08, 0.12 eV on Co, P sites). To confirm this, NiCoP electrodes with controllable oxygen doping are designed and fabricated via alteration of the reducing atmosphere. Accordingly, an optimal oxygen-doped NiCoP (≈0.98% oxygen) nanowire array is found to exhibit the remarkably low hydrogen evolution reaction (HER) overpotential of 44 mV to drive 10 mA cm-2 and a small Tafel slope of 38.6 mV dec-1 , and long-term stability of 30 h in an alkaline medium. In neutral solution, only a 51 mV overpotential (@10 mA cm-2 ) is required, and the Tafel slope is 79.2 mV dec-1 . Meanwhile, in situ Raman spectra confirm the low formation overpotential (-30 mV) of NiCo-phosphate at the surface of ≈0.98% oxygen-doped NiCoP, which enables the material to show better HER performance.