Boosting Electrochemical Nitrate-Ammonia Conversion Via Organic Ligands-Tuned Proton Transfer

Abstract

Electrochemical nitrate (NO3-) reduction reaction (NO3-RR) offers an ideal route to harvest ammonia (NH3) under ambient conditions. Despite recent advances in Cu-based NO3-RR electrocatalysts, their synthesis heavily relies on the regulation of adsorption strength towards nitrogen-containing intermediates, and other important factors are ignored (i.e., the proton transfer rate). Here, we select Cu nanoparticles (NPs) as model catalysts to investigate whether and how the proton transfer rate impacts the NO3-RR kinetics. The results indicate that the proton transfer is involved in the rate-determining step (RDS) of NO3-RR, and the weak water dissociation ability of Cu leads to slow proton transfer rate and consequently sluggish NO3-RR kinetics. To this end, we enhance the water dissociation ability of Cu NPs by incorporating uncoordinated carboxylate ligands to enable rapid proton transfer, which in turn boosts the hydrogenation of key intermediates for reducing the overall energy barrier of NO3-RR. As a result, Cu NPs with the ligands display a maximum NH3 yield rate of 496.4 mmol h-1 gcat-1, outperforming counterpart without ligands. This work not only deepens our knowledge on the NO3-RR mechanism, but also offers new guidelines for the smart design of efficient electrocatalysts.