Electrochemical Reduction of CO2 to Formate in a Flow Cell on CuSx Grown by Atomic Layer Deposition

Transition metal chalcogenides (TMCs) are promising pre-catalysts in tuning the selectivity of electrochemical CO2 reduction (CO2R). Atomic Layer Deposition (ALD) enables well-controlled growth of thin TMC films on various gas diffusion electrodes. Herein we have studied the CO2R performance of ALD grown CuSx in a flow cell. The effects of electrode configuration, electrolyte concentration, temperature, and electrolysis time were carefully studied combined with pre- and post-electrolysis physico-chemical analyses of the films. The unique selectivity of sulfur doped Cu towards formate was retained with Faradaic efficiencies between 40 and 60%, but slow selectivity changes were observed over time. Major loss of the sulfur was encountered during initial 5 min reduction period and after that progressive formation of nanoparticles could be observed. Comparisons to ALD grown Cu thin film and CuSx modified Cu foam electrodes verified the importance of sulfur, and suggest that other electrocatalyst films could be easily realized with ALD.