Formation of Cu nanostructured electrode surfaces by an annealing–electroreduction procedure to achieve high-efficiency CO2 electroreduction

•An effective fibrous Cu electrode surface was proposed.•The Cu electrode surface contained a layered nanosphere–nanofiber structure.•A surface area of 458.1 cm2/cm2 was achieved.•The fibrous Cu electrode surface was high active for CO2 electroreduction.•A Faradaic efficiency of HCOO- yield reached 43% at low overpotentials.•The electrode surface is stable over 19 hours electrolysis compared to smooth Cu.

An effective fibrous Cu electrode surface, created using a procedure combining high-temperature annealing and electroreduction, is explored for CO2 reduction to produce useful fuels. The nanostructure of this Cu electrode surface contains a layer of nanofibers or nanofibers surrounded by kernels with 30–100 nm diameters. With a specific surface area as high as 458 cm2 per geometric electrode surface area, this nanostructured electrode is found to have a high activity toward CO2 reduction, indicated by its more positive reduction potentials and higher catalytic current density than a smooth Cu electrode. The Faradaic efficiency for HCOO− production is 43%, and the electrode surface remains stable during 19 h of electrolysis — better results than with smooth Cu under identical conditions.