Pulsed electro-catalysis enables effective conversion of low-concentration nitrate to ammonia over Cu2O@Pd tandem catalyst

Electro-catalytic conversion of nitrate (NO3-) to ammonia (NH3) via the Nitrate Reduction to Ammonia (NORA) process represents a promising strategy for both ammonia synthesis and environmental remediation. Despite its potential, the efficiency of low-concentration NORA is often hindered by mass transfer limitations, competing byproducts (N2 and NO2-), and side reactions such as hydrogen evolution. This study introduces a novel pulsed electro-synthesis technique that alternates the potential to periodically accumulate and transform NO2- intermediates near a Cu2O@Pd electrode, enhancing the NORA process. Compared with that under potentiostatic conditions, the Cu2O@Pd electrodes exhibited a higher NORA activity under the optimized pulsed condition, where a NH3-N Faradaic efficiency (FE) of 81.2%, a yield rate of 1.08 mg h-1 cm-2 and a selectivity efficiency (SE) of 81.5%, were achieved. In-situ characterization revealed an enhancement mechanism characterized by optimized adsorption of the key *NO intermediate, followed by the hydrogenation path "*N → *NH → *NH2→ *NH3". Further investigations indicated the electro-catalytic synergies between Pd sites and Cu species, where the Pd atoms were the reaction sites for the H adsorption while the Cu species were responsible for the NO3- activation. This research offers a novel insight into a method of enhancing low-concentration NORA. Ammonia (NH3) is an important chemical feedstock. The nitrate (NO3-) electro-reduction to ammonia (NORA) presents the great advantage in improving NH3 production. However, the efficiency of low-concentration NORA (<10 mM) is limited by the slow mass-transfer and competitive hydrogen evolution reaction. Pulsed electro-catalysis systems can overcome the limitation and improve the conversion efficiency of low-concentration nitrate to ammonia. Herein, we develop a pulsed NH3 electro-synthesis method with alternating potential for the periodical accumulation and conversion of the NO2- intermediates in the vicinity of a Cu2O@Pd electrode during the NORA. In-situ characterization uncovers the enhancement mechanism and the electro-catalytic synergies.