Tip-Enhanced Electric Fields on Dendritic Copper Accelerate Water Dissociation for Selective Nitrate-To-Ammonia Electroreduction

Electrocatalytic nitrate reduction reaction (NO₃RR) presents a sustainable strategy for concurrently remediating nitrate (NO₃^–) pollution and producing valuable ammonia (NH₃). However, its practical application is hindered by sluggish kinetics, particularly on copper (Cu)-based catalysts, which often suffer from inefficient water dissociation, leading to low NH₃ selectivity and accumulation of toxic nitrite byproducts. Here, we report the design of copper nanodendrites (Cu NDs) as highly effective NO₃RR electrocatalysts. We demonstrate that the sharp tips of the Cu NDs generate localized and intense electric fields. These tip-enhanced fields drive the enrichment of hydrated potassium ions, which in turn significantly accelerates the water dissociation step, ensuring a sufficient supply of active hydrogen (H*) for deep hydrogenation. As a result, the Cu ND catalyst achieves an exceptional NH₃ yield rate of 2.58 mmol h^–1 cm^–2 and a Faradaic efficiency (FE) of 96.91% at −0.6 V versus reversible hydrogen electrode. Remarkably, the catalyst exhibits outstanding durability, maintaining over 96% NH₃ FE during a 300 h continuous test. In a membrane electrode assembly designed for practical application, the FE of NH₃ surpasses 90% for over 100 h. Furthermore, we demonstrate a scalable product separation process using air stripping, recovering nearly 98% of the produced NH₃ and converting over 80% into high-purity NH₄Cl and NH₃·H₂O. This work presents a catalyst design strategy that overcomes a key kinetic bottleneck in the NO₃RR and bridges the gap between fundamental catalysis and practical application.