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

Electrochemical nitrate reduction reaction (NO 3 RR) provides a promising route for the denitrification of wastewater and sustainable NH 3 production but requires active and selective electrocatalysts. Here, we demonstrate a rigorous design of a tandem electrocatalyst for efficient conversion of NO 3 – to NH 3 . 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 NO 3 RR 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 NO 3 RR to NH 3, suggesting a tandem mechanism that involves NO 3 – reduction to NO 2 – on Cu and solution transfer and further reduction of NO 2 – to NH 3 on Co-based sites. When operated in a flow cell, the Cu/Co(OH) 2 catalyst achieved 100% single-pass conversion of dilute NO 3 – solution to NH 3 at low overpotentials.