Sub‐Nanometer‐Scale Cu₉S₅ Enables Efficiently Electrochemical Nitrate Reduction to Ammonia

Abstract The sub‐nanometer is a key feature size in materials science. Unlike single‐atom and nanomaterials, size effects and inter‐component cooperative actions in sub‐nanomaterials will effective on its performance is more significant. Here, 0.95 nm ordered arrangement Cu 9 S 5 sub‐nanowires (Cu 9 S 5 SNWs) are synthesized through the co‐assembly effect of inorganic nuclei (Cu 9 S 5 ) and clusters (phosphotungstic acid‐PTA), achieving a significant increase in the specific surface area of the sample and ≈100% atomic exposure rate, which is the key to its high catalytic activity. PTA clusters not only act as a “charge transfer station” to accelerate the inter‐component electron transfer process, but also facilitate the dissociation of water and provide more hydrogen protons, thus dramatically facilitating the electrocatalytic process. The experimental results show that the Cu 9 S 5 SNWs exhibited excellent nitrate reduction reaction (NO 3 − RR) properties. The Faraday efficiency (FE) of NO 3 − RR is 90.4% at the optimum potential −0.3 V RHE (reversible hydrogen electrode) and the ammonia production is as high as 0.37 mmol h −1 cm −2 , which is superior to most reported electrocatalysts. In addition, the Zn‐NO 3 − liquid‐flow battery devices assembled using Cu 9 S 5 SNWs as electrode materials show excellent application results. This work provides a reference for the design of highly efficient sub‐nanoscale NO 3 − RR electrocatalysts.