Unveiling the size effect of nitrogen-doped carbon-supported copper-based catalysts on nitrate-to-ammonia electroreduction

The electrocatalytic nitrate reduction reaction (NitRR) represents a promising approach toward achieving economically and environmentally sustainable ammonia. However, it remains a challenge to regulate the size effect of electrocatalysts to optimize the catalytic activity and ammonia selectivity. Herein, the Cu-based catalysts were tailored at the atomic level to exhibit a size gradient ranging from single-atom catalysts (SACs, 0.15-0.35 nm) to single-cluster catalysts (SCCs, 1.0-2.8 nm) and nanoparticles (NPs, 20-30 nm), with the aim of studying the size effect for the NO3--to-NH3 reduction reaction. Especially, the Cu SCCs exhibit enhanced metal-substrate and metal-metal interactions by taking advantageous features of Cu SACs and Cu NPs. Thus, Cu SCCs achieve exceptional electrocatalytic performance for the NitRR with a maximum Faradaic efficiency of ca. 96% and the largest yield rate of ca. 1.99 mg(NH3)center dot h(-1)center dot cm(-2) at -0.5 V vs. reversible hydrogen electrode (RHE). The theoretical calculation further reveals the size effect and coordination environment on the high catalytic activity and selectivity for the NitRR. This work provides a promising various size-controlled design strategy for aerogel-based catalysts effectively applied in various electrocatalytic reactions.