Ultrathin Co_0.5NiS Nanosheets for Hydrazine Oxidation Assisted Nitrite Reduction

Abstract Nitrite (NO₂⁻) and hydrazine (N₂H₄) are common N‐pollutants in groundwater. The electrochemical method can realize the treatment of N‐pollutants and the synthesis of energy substance ammonia (NH₃). Designing and synthesizing efficient electrocatalysts is of great significance. Herein, ultrathin Co_0.5NiS nanosheets attached on nickel foam (Co_0.5NiS‐NSs/NF) are synthesized via cyanogel‐NaBH₄ hydrolysis process and succedent sulfurization approach. Owing to the ultrathin nanosheet structure and the interaction between Ni and Co, Co_0.5NiS‐NSs/NF exhibits high activity for NO₂⁻ reduction reaction (NO₂⁻RR), in which the Faraday efficiency is 92.2% and the NH₃ yield is 0.25 mmol h⁻¹ cm⁻² at −0.15 V potential. Meanwhile, Co_0.5NiS‐NSs/NF also displays remarkable activity for N₂H₄ oxidation reaction in KOH electrolyte. Therefore, a symmetrical Co_0.5NiS‐NSs/NF||Co_0.5NiS‐NSs/NF electrolyzer is assembled, which only needs the operating voltage of 0.36 V to reach 10 mA cm⁻² for NO₂⁻‐to‐NH₃ conversion in the presence of N₂H₄. This work reports a promising and efficient strategy for NH₃ production at a small operating voltage and treatment of the N‐pollutants.