Enhanced electroreduction of low-concentration nitrate using a Cu-Pd bimetallic cathode system: Performance evaluation, mechanism analysis, and potential applications
Mu Yuan, Jun Sun, Yongli Wu, Min Zheng, Chenhao Sheng, Chao Wu, Qinian Wang
Abstract
Copper (Cu) is a widely recognized cathode for the electrochemical reduction of nitrate (NO 3 - ). Nevertheless, its practical applications are currently restricted due to limited activity and selectivity, particularly at low NO 3 - concentrations. Herein, a Cu-Pd bimetallic cathode system was designed for NO 3 - reduction reaction with low NO 3 - concentrations (≤40 mg-N L −1 ). In this system, a Cu nanowire array cathode was utilized for NO 3 - reduction, while a Pd/C particle cathode was employed for NO 2 - reduction with H 2 generated in situ from a polypyrrole electrode. Due to the improved mass transfer and active sites derived from Pd/C particle cathode, along with the synergistic effects of NO 3 - reduction and NO 2 - reduction, the constructed Cu-Pd bimetallic cathode system achieved a 7.32-fold increase in NO 3 – removal rate and a 1.70-fold increase in NH 4 + selectivity compared to the traditional Cu cathode. This performance surpassed that of many other state-of-the-art Cu-based cathodes under similar conditions. Moreover, the Cu-Pd bimetallic cathode system displayed high reusability, and extremely low Cu and Pd leaching. Additionally, it showed strong resistance to environmental factors and can adapt to a wide pH range (3−9) and various NO 3 - concentrations (10–40 mg-N L −1 ). The electron spin resonance and scavenger experiments confirmed that both direct electron transfer and indirect reduction by atomic H* were involved in the NO 3 - removal process, with indirect reduction playing a more significant role. Overall, our findings guide the design of superior catalytic systems for NO 3 - removal to enhance the activity and selectivity of NO 3 - reduction for efficient water purification .