Facet-Selective Bromide Adsorption at High-index Facets of Copper Sulfides for Improved Electrochemical Nitrogen Reduction Activity and Selectivity

Electrochemical nitrogen reduction reaction (eNRR) is a promising sustainable alternative to the energy-intensive Haber–Bosch process for ammonia (NH₃) synthesis. However, simultaneously achieving high activity and selectivity remains challenging due to competing hydrogen evolution reaction (HER). In this study, a series of copper sulfide catalysts were investigated for eNRR under ambient conditions. Copper sulfides featuring highly crystalline low-index (1 1 1) facets exhibited significant NH₃ production; however, the presence of high-index facets led to a reduction in Faradaic efficiency (F.E.) due to their higher activity toward the competing HER. To mitigate this intrinsic trade-off between activity and selectivity, bromide ions were introduced to selectively adsorb onto the high-index planes, effectively suppressing HER. Optimizing the bromide ion coverage on CuSₓ catalysts resulted…