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

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 Cu₉S₅ sub-nanowires (Cu₉S₅ SNWs) are synthesized through the co-assembly effect of inorganic nuclei (Cu₉S₅) 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 Cu₉S₅ SNWs exhibited excellent nitrate reduction reaction (NO₃⁻RR) properties. The Faraday efficiency (FE) of NO₃⁻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-NO₃⁻ liquid-flow battery devices assembled using Cu₉S₅ SNWs as electrode materials show excellent application results. This work provides a reference for the design of highly efficient sub-nanoscale NO₃⁻RR electrocatalysts.