Anion‐Modulated HER and OER Activities of 3D Ni–V‐Based Interstitial Compound Heterojunctions for High‐Efficiency and Stable Overall Water Splitting

Overall water splitting driven by a low voltage is crucial for practical H₂ evolution, but it is challenging. Herein, anion-modulation of 3D Ni-V-based transition metal interstitial compound (TMIC) heterojunctions supported on nickel foam (Ni₃ N-VN/NF and Ni₂ P-VP₂ /NF) as coupled hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalysts for efficient overall water splitting is demonstrated. The heterointerface in Ni₃ N-VN has a suitable H* absorption energy, being favorable for enhancing HER activity with onset overpotential (η_onset ) of zero and Tafel slope of 37 mV dec^-1 in 1 m KOH (close to that of Pt/C/NF). For the OER, the synergy of Ni₂ P-VP₂ with oxide species can give enhanced activity with η_onset of 220 mV and Tafel slope of 49 mV dec^-1 . The good activity is ascribed to heterointerface for activating the intermediates, good conductivity of TMICs for electron-transfer, and porous structure facilitation of mass-transport. Additionally, the minimal mutual influence of Ni₃ N-VN/NF and Ni₂ P-VP₂ /NF allows easy coupling for efficient overall water splitting with a low driving voltage (≥1.43 V), a voltage of 1.51 V at 10 mA cm^-2 , and remarkable durability for 100 h. It can be driven by a solar cell (1.5 V), indicating its potential to store intermittent energy.