Facet-Engineered Cu Nanoflake Electrocatalysts for Efficient Nitrate-to-Ammonia Conversion

Electrochemical nitrate reduction reaction (NO3RR) provides a promising approach for recycling nitrate from wastewater into ammonia, but its practical implementation requires catalysts capable of efficient and selective nitrate-to-ammonia conversion. Here we report Cu nanoflakes grown on Cu foam with tunable morphology and facet exposure as efficient catalysts for NO3RR to NH3. Compared with their Cu nanowire counterparts, the Cu nanoflakes showed a 5-fold higher NO3RR current density with an 81% Faradaic efficiency for NH3 production at a low overpotential of 0.15 V vs RHE. This performance arises from a 3-fold enhancement in intrinsic activity, enabled by an optimal ratio and synergy between exposed Cu(100) and Cu(111) facets, which facilitate a tandem pathway involving nitrate-to-nitrite conversion followed by nitrite reduction to ammonia. The Cu nanoflake electrode was further evaluated in a single-pass flow-cell configuration for continuous NO3RR electrolysis, achieving ∼97% NH3 Faradaic efficiency at 0 V vs RHE across varying nitrate concentrations and sustaining stable performance over ∼100 h of operation. These results establish facet engineering as an effective strategy for designing Cu-based NO3RR catalysts for nitrate remediation and sustainable ammonia production.