Controllable orientation-dependent crystal growth of high-index faceted dendritic NiC_0.2 nanosheets as high-performance bifunctional electrocatalysts for overall water splitting

Developing highly active, non-noble-metal electrocatalysts for both H₂ and O₂ evolution reactions (HER and OER, respectively) still remains a great challenge. Herein, we report a facile route for the controllable orientation-dependent crystal growth of {20} high-index faceted dendritic hexagonal NiC_x nanosheets on Ni-coated copper foil, with an optimized carbon content of 16.7 at%, by a mild electrodeposition approach. Impressively, the as-prepared material (denoted as d-NiC_0.2NS/Ni/CF) shows remarkable catalytic activity (with overpotentials of 121 mV and 228 mV at 10 mA cm⁻² for the HER and OER, respectively), simultaneously giving a nearly 100% faradaic yield and affording superior catalytic stability (beyond 100 h) as a bifunctional electrocatalyst for both the HER and OER in basic media. The achieved ultrahigh catalytic performance of d-NiC_0.2NS/Ni/CF is primarily attributed to its dendritic nanosheet morphology, optimized 16.7 at% carbon content, and fully exposed {20} high-index facets, which lead to improved mass/electron transport capability and fully exposed active sites. In comparison with the other non-noble-metal electrocatalysts developed to date, we provide a controllable and mild strategy to fabricate high-performance nickel-carbide-based electrocatalysts for advanced applications.