Asymmetric Pulsed Electrolysis Enhances Nitrate-to-Ammonia Electroreduction via Optimizing the Local Reaction Microenvironment

Pulsed electrolysis is widely regarded as a promising strategy for enhancing the performance of the electrocatalytic nitrate reduction reaction (NO₃^-RR). However, research on the effect of symmetric and asymmetric pulsed electrolysis on the NO₃^-RR remains elusive. Here, the CuMn alloy serves as a model catalyst to systematically investigate the impact of symmetric and asymmetric pulsed electrolysis on the performance of NO₃^-RR. A series of operando measurements and control experiments indicate that a suitable asymmetric pulsed electrolysis can optimize the local microenvironment of the NO₃^-RR, including optimizing the coverage of NO₃^-, enhancing the generation of key N-containing intermediates, and inhibiting the hydrogen evolution reaction, thereby improving the Faradaic efficiency and yield rate of NH₃. Consequently, the Faradaic efficiency and yield rate of NH₃ for the optimal asymmetric pulsed electrolysis between a less negative potential time of 2 s and a more negative potential time of 4 s are 94.03% and 9.13 mg h^-1 cm^-2, respectively, which are 1.42-fold and 2.10-fold higher than those of static electrolysis. Moreover, the Faradaic efficiency of NH₃ for the optimal asymmetric pulsed electrolysis was 66.32% at a lower concentration of NO₃^- (2000 ppm), which is 1.73-fold higher than that of static electrolysis, indicating that the performance of asymmetric pulsed electrolysis is further enhanced in the lower concentration of NO₃^-, further confirming that asymmetric pulsed electrolysis is a feasible strategy to improve the performance of the NO₃^-RR.