From Waste to Energy and Fuel: Novel CuxNiy/CN catalysts from waste melamine resin for efficient nitrate reduction to ammonia

Abstract

The conversion of nitrate (NO3−) contaminants into ammonia (NH3) through electrochemical reduction presents a viable strategy for the dual purposes of wastewater purification and ammonia production. Meanwhile, dealing with hazardous heavy metals (Cu, Ni, etc.) in the electroplating industry is a global mandate, incurring substantial cost and consuming vast energy. This work integrates the treatment of Cu and Ni in electroplating wastewater with nitrate reduction reaction (NO3-RR) for sustainable fuel and electricity generation. A facile and cost-effective CuxNiy/CN catalyst, which represents CuNi alloy on nitrogen-doped carbon foam (CN), is developed from the waste electroplating water and melamine resin. Among various CuxNiy/CN catalysts, Cu0.5Ni0.5/CN exhibits enhanced NO3-RR performance with a high ammonia yield rate (1755 μg h-1 mgcat-1) and Faradaic efficiency (92.4%), which outcompetes to most of the reported catalysts. The performance of Cu0.5Ni0.5/CN in low nitrate concentration verifies the effectiveness of catalysts for potential industrial application. Theoretical calculations reveal that the reduced energy barrier facilitates the hydrogenation of *NO2 to *NO2H over Cu0.5Ni0.5/CN, favoring the subsequent reduction to NH3. A Zn-nitrate battery is designed for power generation with Cu0.5Ni0.5/CN catalyst, exhibiting a voltage of 1.36 V and power density of 1.51 mW cm–2. This study opens a new avenue to recycle both industrial (electroplating, nitrate) and domestic (melamine resin) wastes for sustainable fuel and power generation.