CuNi alloy for hydrazine oxidation assisted energy-saving urea production via proton exchange membranes

Nitrate (NO 3 - ) and hydrazine (N 2 H 4 ) are common nitrogen pollutants in groundwater. The electrochemical method can be used to synthesize the added product urea while treating N-pollution. Therefore, the development of sufficiently efficient electrosynthesis urea systems and efficient electrocatalysts is of great significance, but also challenging. In this paper, CuNi alloy nanosheets (Cu x Ni y /CF) on copper foam surface were synthesized by electrodeposition , and C-N coupled hydrazine oxidation (HzOR) system was constructed by proton exchange membrane (PEM). Cu and Ni in CuNi alloy act as double active sites and react with C-N coupling reaction and HzOR respectively. At −0.5 V potential, the Faraday efficiency of Cu 8 Ni 2 /CF for C-N coupling reaction is 51.66 %, and the urea yield is 254.09 μg h −1 cm −2 . At the same time, HzOR with low thermodynamic oxidation potential can quickly produce excess H + to supply protons to the cathode for C-N coupling reaction, thus significantly promoting the forward C-N coupling reaction. Cu 1 Ni 9 /CF also showed significant activity in the oxidation reaction of N 2 H 4 in KOH electrolyte. Therefore, we assembled a Cu 1 Ni 9 (+) || Cu 8 Ni 2 (-) electrolytic cell , which only needs 0.23 V working voltage up to 150 mA cm −2 , and can convert NO 3 - and CO 2 to urea at a power consumption of 5.09 kWh kg −1 while converting N 2 H 4 . Energy saving 37.6 % compared to conventional C-N coupled OER electrolytic system (about 8.16 kWh kg −1 urea). It can greatly reduce the cost of urea production, make the price of fertilizer and chemical raw materials more competitive, and promote the development of agriculture and chemical industry while reducing greenhouse gas emissions and nitrogen pollutants in the ecological environment. This study reports a promising and effective strategy for the synthesis of urea and treatment of N contaminants at a small operating voltage. • HzOR works by providing proton-assisted C-N coupling reactions in PEM. • Bifunctional Cu x Ni y /CF catalyst has two active sites to promote anode and cathode reaction. • The C-N coupling-HzOR system shows ideal economic profitability.