A Cu 2 O‐Pd dual active sites tandem catalyst enables efficient nitrate reduction to ammonia at low concentration

Abstract Electrochemical nitrate (NO 3 − ) reduction reaction (eNO 3 RR) to ammonia (NH 3 ) provides a promising route for both water conservation and green ammonia synthesis. Although various catalysts were designed for the eNO 3 RR and great achievements have been achieved, it is still a challenge to realize selective eNO 3 RR to NH 3 at low concentration for the competing hydrogen evolution reaction (HER) and poor mass transfer of NO 3 − . Herein, we designed a tandem catalyst of Pd nanoparticle loaded Cu 2 O hierarchical nanofiber (Pd‐Cu 2 O) to improve eNO 3 RR performance at low nitrate concentration. The Pd‐Cu 2 O shows a faraday efficiency (FE) of 95.80% and an ammonia selectivity of 97.34% at a comparatively low applied potential of −0.15 V versus RHE with low concentration. Besides, it exhibits excellent nitrate removal effects, the residual concentration of nitrate–N was only 7.22 ppm at −0.15 V. Electrochemical characterizations indicate that the abundant secondary heterojunction structures and the tandem effects of Pd‐Cu 2 O synergistically accelerate the transfer and conversion of NO 3 − and improve the dynamic of eNO 3 RR at low concentration. Furthermore, the operando electrochemical impedance spectroscopy (EIS) and density functional theory (DFT) calculations suggested the tandem effects of Pd‐Cu 2 O improved the adsorption of NO 3 − and *H and thus promoted the dynamics of eNO 3 RR at low concentration. The findings highlight the tandem effects of Pd‐Cu 2 O and provide an effective strategy for designing electrocatalysts that can be applied to low concentration and low applied potential conditions.