Nickel Oxynitride Bifunctional Catalyst with Nitrogen-Induced Defect for Efficient Ammonia Splitting toward Hydrogen Production

The transition to sustainable energy highlights the need for efficient green hydrogen production, with ammonia emerging as a promising hydrogen carrier due to its transport and storage capabilities. The US Department of Energy has recognized it as the most pipeline-compatible option for large scale transport distribution. Overcoming the sluggish kinetics of the ammonia oxidation reaction (AOR) remains a crucial challenge for advancing this technology. This study reports a bifunctional Ni-based catalyst, focusing on the transformation from nickel oxide (NiO) to nickel oxynitride (NiOxNy), synthesized by the soft urea method for ammonia splitting. Nitrogen incorporation into the NiO lattice induces defects, leading to a band gap narrowing in NiOxNy (2.15 eV) compared to pristine NiO (3.8 eV), as evidenced by the Tauc plot derived from UV−vis absorption spectroscopy. The presence of active sites, which play a crucial role in determining catalytic activity, was found to be 0.611 mmol/gcatalyst. The NiOxNy exhibits superior performance compared to NiO, metallic Ni, and standard RuO2, with an AOR overpotential of 1.357 V vs SHE and a Tafel slope of 54.14 mV dec−1 at 10 mA cm−2. For the hydrogen evolution reaction (HER), it also outperforms the benchmark Pt/C, exhibiting a lower overpotential of 151 mV vs SHE and a Tafel slope of 93.55 mV dec−1. Additionally, the catalyst demonstrates better long-term stability as a bifunctional catalyst for 12 h. These finding highlights that nitrogen-induced structural modifications improve electrical conductivity and generate defect-rich surfaces, facilitating efficient hydrogen adsorption and desorption, thereby advancing hydrogen production technologies.