Complete Single-Pass Conversion of Dilute Nitrate to Ammonia Using Cu/Co(OH)2 Tandem Electrocatalyst

Electrochemical nitrate reduction reaction (NO3RR) provides a promising route for the denitrification of wastewater and sustainable NH3 production but requires active and selective electrocatalysts. Here, we demonstrate a rigorous design of a tandem electrocatalyst for efficient conversion of NO3– to NH3. Based on the screening of tandem components, a catalyst coupling Cu and Co(OH)2 with an optimal ratio and tandem architecture was developed to promote and balance the activities of sequential NO3RR steps on different active sites. Compared to counterpart catalysts including Cu, Co(OH)2, and Cu–Co alloy, the Cu/Co(OH)2 catalyst with separated phases showed much higher activity and selectivity for the NO3RR to NH3, suggesting a tandem mechanism that involves NO3– reduction to NO2– on Cu and solution transfer and further reduction of NO2– to NH3 on Co-based sites. When operated in a flow cell, the Cu/Co(OH)2 catalyst achieved 100% single-pass conversion of dilute NO3– solution to NH3 at low overpotentials.