Morphology and composition-controllable synthesis of copper sulfide nanocrystals for electrochemical reduction of CO2 to HCOOH

Abstract Electrochemical conversion of CO2 into value-added chemicals such as formic acid (HCOOH) has gained tremendous interests. Sulfide-derived copper has been shown recently to be selective for HCOOH production. However, the rich composition and morphology variation of copper sulfides on their electrochemical CO2 reduction have yet to be investigated. Herein, we report a simple ethylene glycol solvothermal route to synthesize copper sulfides nanocrystals, with their morphology and composition varied by tuning the Cu/S feed ratio and reaction temperatures. When being applied to the electrochemical reduction of CO2 to HCOOH, CuS nanoflowers exhibited high Faradic efficiency (∼ 52%) due to its high S content and specific morphology, compared to their more Cu-rich counterparts.