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 (Ni3N‐VN/NF and Ni2P‐VP2/NF) as coupled hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalysts for efficient overall water splitting is demonstrated. The heterointerface in Ni3N‐VN has a suitable H* absorption energy, being favorable for enhancing HER activity with onset overpotential (ηonset) 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 Ni2P‐VP2 with oxide species can give enhanced activity with ηonset 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 Ni3N‐VN/NF and Ni2P‐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.

The hydrogen evolution reaction (HER) in the neutral medium can avoid the problems caused by strong acid (bases) media and thus is promising for practical application. The suitable catalyst in the neutral medium for HER requires good conductivity for decreasing ohm resistance, porous structures for weakening diffusion resistance, and plentiful active sites, but its synthesis remains a challenge. Here, the 2D MoP/MoS 2 heterostructure nanosheets rather than common anion doping supported on carbon cloth (CC) was designed to meet the above criteria. The catalyst only needs a low overpotential of 96 mV to achieve a current density of 10 mA cm −2 (η 10 ) for HER in the neutral medium (without iR correction), which is much lower than 199 mV of the bare MoS 2 . The good performance is ascribed to plentiful active sites on the heterointerface of MoP/MoS 2 for activating H 2 O, good conductivity of MoP and CC for electron transfer, and pores surrounded by MoP/MoS 2 facilitating mass transfer as shown by XPS and density functional theory calculations. The catalyst also exhibits outstanding activity in alkaline (η 10 of 54 mV) and acid (η 10 of 69 mV) media. The cells by coupling the MoP/MoS 2 cathode with a NiFe-LDH anode can deliver a current density of 10 mA cm −2 at 1.51 V in 1 M KOH and 1.98 V in 1 M PBS. The effective overall water splitting can be driven by a solar panel (1.51 V), implying its ability to store solar energy as H 2 energy.

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We have reported the synthesis of hierarchical whisker-on-sheet (HWS) NiCoP anchored on Ni foam with adjustable surface structure for efficient hydrogen evolution reaction (HER). The HWS NiCoP was obtained by controllable phosphidation of HWS Ni-Co-carbonates hydroxide precursor grown on Ni foam (NF). The experimental parameters were optimally tuned to understand the formation process of the precursor and to regulate the microstructure of the materials. The test results indicated that the HWS NiCoP/NF can produce a current density of 10 mA cm-2 (η10) at a low overpotential of 59 mV and a current density of 100 mA cm-2 (η100) at an overpotential of 220 mV for HER. Notably, upon surface activation with KOH, the HER performance of HWS NiCoP/NF could be dramatically enhanced with η10 and η100 values of 42 mV and 141 mV, respectively. The HWS NiCoP/NF showed a superior performance to NiCoP displaying other morphologies (sheets and wires etc.) The good performance of HWS NiCoP/NF should be attributed to their special whisker-on-sheet structures that are favourable for effective contact with the electrolyte. Also, hydrated metals can be formed on surface after the alkali treatment step, which is beneficial to moderate the bonding to hydrogen and thus, improve the HER activity. The present study will be indicative toward the construction of highly-efficient HER catalysts by regulating the structure of the materials.