Rational design of bifunctional Co5.47N/MoN-NF electrocatalyst for efficient hydrazine-assisted hydrogen production with ultra-high hydrazine electrochemical utilization efficiency

Hydrazine (N 2 H 4 )-assisted water electrolysis represents a promising technology for efficient green hydrogen production. The primary challenge lies in developing efficient and stable electrocatalysts while maximizing the electrochemical utilization of N 2 H 4 . Herein, we report the synthesis of bifunctional ultrathin Co 5.47 N/MoN nanosheets supported on Ni foam (Co 5.47 N/MoN-NF) via a two-step hydrothermal process followed by ammonia treatment. The Co 5.47 N/MoN-NF catalyst exhibits outstanding electrocatalytic performance, achieving high current densities of 500 and 1000 mA cm −2 at applied potentials of −255 and 52 mV for hydrogen evolution reaction (HER) and hydrazine oxidation reaction (HzOR), respectively. Notably, it also demonstrates excellent stability, maintaining a current density of 500 mA cm −2 for ∼760 h during HER and 1000 mA cm −2 for ∼240 h during HzOR without any observable performance degradation. Electrochemical in situ Raman spectroscopy confirms that the catalyst maintains its active metal nitride phase during HzOR, while electrochemical in situ infrared analysis reveals the displacement of H 2 O molecules by OH⁻ species within the electrical double layer, offering mechanistic insights into the reaction process. Further studies reveal that the spontaneous decomposition of N 2 H 4 leads to significant reactant waste, making it essential to develop rational strategies to improve its electrochemical utilization efficiency (η). Specifically, the controlled addition of thiourea can enhance η of N 2 H 4 up to 98 %, enabling near-complete electrochemical utilization of N 2 H 4 . These findings offer valuable insights into the design of bifunctional electrocatalysts for industrial applications and present effective strategies to maximize the electrochemical utilization of N 2 H 4 . Hydrazine (N 2 H 4 )-assisted water electrolysis is a promising technology for efficient green hydrogen production. The controlled addition of thiourea can significantly enhance the electrochemical utilization efficiency of N 2 H 4 , reaching up to 98 %, thereby enabling near-complete electrochemical utilization of N 2 H 4 . • The Co 5.47 N/MoN-NF catalyst exhibits outstanding electrocatalytic HER and HzOR activity and stability. • Electrochemical in situ Raman spectroscopy confirms that the catalyst maintains its active metal nitride phase during HzOR. • Electrochemical in situ infrared analysis provides valuable insights into the role of OH⁻ species. • The controlled addition of thiourea can enhance electrochemical utilization efficiency of N 2 H 4 up to 98 %.