Single-Atom Copper Anchored on Defective Layered Double Hydroxides Enables High-Efficiency Electrochemical Nitrate Reduction to Ammonia

Abstract

The electrochemical reduction of nitrate ions (NO3–) to ammonia (NH3) offers a sustainable and environmentally route for the recycling of nitrogen. However, the electrochemical nitrate reduction reaction (NO3RR) is limited by complex eight-electron transfer kinetics and the competing hydrogen evolution reaction (HER), resulting in low Faradaic efficiency and poor NH3 selectivity. Herein, we successfully synthesized a non-noble-metal Cu/CoAl-LDH-xh catalyst via an ion-exchange engineering strategy, in which monodispersed copper single atoms were anchored onto the aluminum metal defect sites of tannic acid-etched cobalt–aluminum layered double hydroxide (LDH). In situ spectroscopic characterization and density functional theory (DFT) calculations reveal that the presence of Co sites combined with the introduction of copper single atoms establishes an electron transfer channel, thereby promoting surface electron redistribution. The synergistic interaction between Co and Cu active sites optimizes the H* kinetics and mitigates the imbalance between H* supply and consumption typically encountered in single-site configurations. Such cooperation effectively suppresses the competing hydrogen evolution reaction (HER) and lowers the energy barrier for the dehydration-hydrogenation of *HNOH, thereby driving the efficient conversion of nitrate to ammonia. Under low-concentration nitrate conditions, this catalyst exhibits outstanding nitrate reduction performance, achieving a Faradaic efficiency exceeding 98% and an ammonia selectivity over 80%, which surpasses most reported non-noble-metal catalysts as well as some noble-metal-based counterparts. These findings offer profound insights into the design and application of single-atom-anchored metal hydroxides, particularly in advancing the electrocatalytic conversion of nitrate to ammonia.