NiSe₂‑Nanooctahedronas an EfficientElectrocatalyst for Overall Water Splitting

Hydrogen production through electrocatalysis has attracted much attention due to negligible environmental pollution by using renewable electrical energy. To bring electrolysis technology to cost parity, a nonprecious, stable, and earth-abundant transition-metal-based bifunctional catalyst is desired for overall water splitting. Herein, we report the synthesis of NiSe₂ nanoparticles using a simple, template-free, and single-step solvothermal method by varying the reaction medium, i.e., either water or propanol or their mixture. Using the ethylenediaminetetraacetic acid (EDTA) as a structure-directing agent, nanooctahedron-shaped NiSe₂ particles are synthesized for the first time. The nanosized NiSe₂ octahedron is demonstrated as a potential bifunctional electrocatalyst for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in an alkaline medium. For hydrogen evolution, a small overpotential of 119 mV is needed to generate a current density of 10 mA cm^–2, whereas 345 mV overpotential is required for oxygen evolution reaction delivering a current density of 50 mA cm^–2. Furthermore, the electrolyzer with NiSe₂-nanooctahedrons as an electrocatalyst delivers 10 mA cm^–2 at a cell voltage of 1.55 V for overall water splitting and shows excellent stability with a negligible change in current density in 20 h.