In-situ surface structural reconstruction of NiMoO4 for efficient 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.