Hierarchically Structured Ni Nanotube Array-Based Integrated Electrodes for Water Splitting

The development of high-performance nonprecious electrocatalysts for overall water splitting has attracted increasing attention but remains a vital challenge. Herein, we report a ZnO-based template method to fabricate Ni nanotube arrays (NTAs) anchored on nickel foil for applications in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). On the basis of this precursor electrode, the three-dimensional NiSe₂ NTAs of unique sandwich-like coaxial structure have been fabricated by electrodeposition of NiSe₂ on Ni NTAs, which exhibits high performance toward the HER in both acidic and alkaline media. The method based on Ni NTAs can be readily extended to fabricate Ni₂P NTAs by gas–solid phosphorization for the HER, and NiFeO_<i>x</i> NTAs by anodic codeposition of Ni and Fe for the OER. Consequently, an alkaline electrolyzer has been constructed using NiFeO_<i>x</i> NTAs and NiSe₂ NTAs as anode and cathode, respectively, which can realize overall water splitting with a current density of 100 mA cm^–2 at an overpotential of 510 mV