In situ Grown Ni phosphate@Ni₁₂P₅ Nanorod Arrays as a Unique Core–Shell Architecture: Competitive Bifunctional Electrocatalysts for Urea Electrolysis at Large Current Densities

It is still a big challenge to develop active, stable, and easy-to-make bifunctional non-noble electrocatalysts for upshifting overall urea-assisted water splitting toward practical environmental applications at large current densities with lower cell voltages. In response, here we report a competitive bifunctional electrocatalyst that can catalyze both the urea oxidation reaction (UOR) and hydrogen evolution reaction (HER) by fabricating the in situ grown Ni phosphate (shell)-anchored Ni₁₂P₅ nanorod (core) arrays on the 3D Ni foam skeleton (named as Ni₁₂P₅/Ni-Pi/NF). Benefiting from the unique hierarchical core–shell nanorod architecture with abundant exposed active sites and improved electron and mass transfer efficiency, such elaborate binder-free arrays could act as a robust 3D UOR anode and can achieve 900 mA cm^–2 only at potentials of 1.378 V in 1.0 M KOH with 0.5 M urea. Additionally, this electrode also shows remarkable cathodic HER catalytic activities. Moreover, when constructing an alkaline electrolyzer using the bifunctional electrodes, the integrated system is capable of delivering the current density of 500 mA cm^–2 stably for over 6 h at a cell voltage as low as 1.662 V, which is 287 mV less than that for pure water splitting. As such, our result may become a significant step in developing an industrial electrolyzer for meaningful massive electrocatalytic hydrogen (H₂) production by urea-assisted water splitting.