Dynamic Reconstruction and Microenvironment Modulation of a Pd-Doped CuS Electrocatalyst for Nearly Unity-Efficiency Ammonia Electrosynthesis from Nitrate

Copper-based catalysts are known for their high ammonia selectivity in the electrochemical nitrate reduction reaction (NO₃RR), yet the underlying mechanisms of this selectivity remain insufficiently understood and warrant further investigation. This study employs single-atom palladium-doped copper sulfide (Pd₁/CuS) as a model precatalyst to elucidate the mechanisms driving its high selectivity. Comprehensive characterization reveals that Pd₁/CuS undergoes in situ transformation into Cu while maintaining isolated palladium sites. The activated catalyst achieves near-unity (∼100%) selectivity for ammonia at -0.5 V vs RHE, along with high yield rates that significantly surpass those of the undoped catalyst, maintaining over 98.2% selectivity across 15 consecutive cycles. Mechanistic studies using in situ spectroscopies, theoretical calculations, and ab initio molecular dynamics simulations demonstrate that the incorporation of Pd promotes the partial desolvation of hydrated alkali ions, enhances water dissociation, improves intermediate adsorption in NO₃RR, and facilitates proton transfer by strengthening the hydrogen-bond network while thermodynamically suppressing the recombination of adsorbed protons (*H). These effects synergistically promote the ammonia-selective pathway. This work provides fundamental insights into the relationship between dynamic structural evolution and catalytic performance in the NO₃RR, advancing the rational design of high-selectivity copper-based catalysts.