Efficient Recycling of Dilute Nitrate to Ammonia Using Cu Nanowire Electrocatalyst

Electrochemical reduction of nitrate provides a sustainable route for the recycling of waste nitrate to valuable ammonia when powered by electricity from renewable sources. Development of such a process requires efficient electrocatalysts that can facilitate high single-pass conversion of dilute nitrate to ammonia. Here we report a Cu nanowire electrocatalyst for nitrate reduction that was prepared by growing Cu nanowires with tunable morphology and density on a Cu foam substrate. Compared with the Cu foam, the Cu nanowires created new catalytic sites and greatly enhanced the activity and selectivity for nitrate reduction to ammonia. As a result, the optimized Cu nanowire electrode showed a 3-fold increase in the nitrate reduction activity with a 90% Faradaic efficiency for ammonia production at a low overpotential of −0.1 V vs RHE in an electrolyte containing 5 mM nitrate, which is attributed to the high catalytic surface area with an appropriate combination of Cu(100) and Cu(111) facets. The electrode was further tested for continuous nitrate electrolysis using a flow cell, which achieved a 76% single-pass conversion of nitrate with a 93% ammonia Faradaic efficiency, demonstrating great promise for applications in wastewater treatment and sustainable ammonia production.