Nickel oxynitride: A low overpotential, highly durable bifunctional electrocatalyst for efficient water-splitting

This study presents a simple soft urea technique for synthesizing nickel-based catalysts, focusing on the transition of NiO to NiON and finally to Ni3N. We conducted a detailed investigation into the catalytic activity of these nickel derivatives, employing techniques such as UV-Vis absorption spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy for thorough characterization. The results reveal that NiON outperforms the standard RuO2 catalyst, NiO and Ni3N, achieving an overpotential of 285 mV with a Tafel slope of 57 mV/dec at 10 mA/cm2 for the oxygen evolution reaction (OER) and a remarkable lower overpotential of 129 mV with a Tafel slope of 34 mV/dec for the hydrogen evolution reaction (HER). Notably, NiON demonstrates exceptional stability as a bifunctional catalyst for 14 h. In comparison with oxide (3.47 eV) and nitride phase (2.6 eV), nickel oxynitride possesses a lower optical band gap (2.2 eV). This study provides valuable insights into the roles of nitrogen and oxygen in nickel electrocatalysts, paving the way for enhanced efficiency in overall water splitting applications.