Electroless generation of nano-silver fern catalysts upon Cu foam as a highly effective bimetallic electrocatalyst design for ammonia electrosynthesis

Abstract

The electrocatalytic reduction of nitrate emerges as a valuable opportunity to remediate nitrate pollution while providing a sustainable pathway for ammonia electrosynthesis. Herein, a biomimetically nanostructured Cu/Ag bimetallic electrocatalyst was optimized by fine tuning metal ratios through an electroless galvanic replacement reaction. The bimetallic electrocatalyst with nano-fern structures was optimized at 2.9% w/w Ag loading that generated highly active catalytic centers upon the three-dimensional Cu substrate. The nano-fern catalytic centers were predominately Ag, but intercalation of Cu generated a versatile bimetallic electrocatalyst surface which accelerated nitrate to ammonia conversion. Nano-fern electrocatalytic domains synergized the first initial reduction step, when compared to the performance of the monometallic Cu, while the applied current density to the system modulated the second reduction of nitrite towards complete ammonia formation. Electrochemical characterization revealed that Ag addition to the Cu foam substrate reduced system resistance, boosting electron transfer capability. Limiting the liquid/air interface of the reaction solution maximizes aqueous ammonia retention in the system which in turn boosted product selectivity. With optimized synthesis and operational parameters, the Cu/Ag bimetallic electrocatalyst converted 96% of nitrate, with a 95% selectivity towards NH₃ formation in less than 60 min, highlighting groundbreaking performance for ammonia electrosynthesis via a galvanostatic based approach. Finally, such performance was maintained for ten consecutive ERN cycles, signifying great potential for continuous ERN treatment with the Cu/Ag bimetallic electrocatalyst.