Coupling Curvature and Hydrophobicity: A Counterintuitive Strategy for Efficient Electroreduction of Nitrate into Ammonia.

Abstract

The electrochemical upcycling of nitrate (NO₃^-) to ammonia (NH₃) holds promise for synergizing both wastewater treatment and NH₃ synthesis. Efficient stripping of gaseous products (NH₃, H₂, and N₂) from electrocatalysts is crucial for continuous and stable electrochemical reactions. This study evaluated a layered electrocatalyst structure using copper (Cu) dendrites to enable a high curvature and hydrophobicity and achieve a stratified liquid contact at the gas-liquid interface of the electrocatalyst layer. As such, gaseous product desorption or displacement from electrocatalysts was enhanced due to the separation of a wetted reaction zone and a nonwetted zone for gas transfer. Consequently, this electrocatalyst structure yielded a 2.9-fold boost in per-active-site activity compared with that with a low curvature and high hydrophilic counterpart. Moreover, a NH₃ Faradaic efficiency of 90.9 ± 2.3% was achieved with nearly 100% NO₃^- conversion. This high-curvature hydrophobic Cu dendrite was further integrated with a gas-extraction membrane, which demonstrated a comparable NH₃ yield from the real reverse osmosis retentate brine.