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.