In-situ surface structural reconstruction of NiMoO4 for efficient overall water splitting

[Display omitted] •Molybdenum of P-NiMoOx dissolute and hydroxyls layers form during HER.•NiMoO4 transforms into highly active NiOOH during OER.•Ultra-low voltage of 1.55 V to afford 100 mA cm−2 for overall water splitting. NiMoO4 is generally considered as stable substrates rather than participating in the catalysis of overall water splitting. However, when NiMoO4 based catalysts applied in alkaline oxidation/reduction conditions, the in-situ formed surface oxide hydroxides/hydroxyls will further simultaneously enhance oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) via such especial surface structural reconstruction. Here self-supported NiMoO4 is constructed by one-step hydrothermal for OER, followed by vapor deposition method, hierarchical catalyst consisting of monocrystalline P-NiMoOx nanorods decorated by CoP-Co2P nanoparticles (denoted as CoPx/P-NiMoOx) is designed for HER. During OER, surface NiMoO4 in-situ transforms into highly active NiOOH. The reconstructed NiOOH/NiMoO4 exhibits outstanding OER performance (overpotentials of 207 and 266 mV at 10 and 100 mA·cm−2). As HER proceeds, electro-reduction promotes dissolution of molybdenum, meanwhile, hydroxyls from dissociated H2O molecules coupled with exposed nickel sites form amorphous hydroxyls layers at surface dissolution sites. The reconstructed amorphous-hydroxyls/CoPx/P-NiMoOx catalyst possesses highly efficient HER activity (overpotentials of 9 and 67 mV at 10 and 100 mA·cm−2). Additionally, the integrating water splitting system requires only 1.55 V to reach 100 mA·cm−2 with excellent stability.