Double sulfur vacancies by lithium tuning enhance CO2 electroreduction to n-propanol

Electrochemical CO2 reduction can produce valuable products with high energy densities but the process is plagued by poor selectivities and low yields. Propanol represents a challenging product to obtain due to the complicated C-3 forming mechanism that requires both stabilization of *C-2 intermediates and subsequent C-1-C-2 coupling. Herein, density function theory calculations revealed that double sulfur vacancies formed on hexagonal copper sulfide can feature as efficient electrocatalytic centers for stabilizing both CO* and OCCO* dimer, and further CO-OCCO coupling to form C-3 species, which cannot be realized on CuS with single or no sulfur vacancies. The double sulfur vacancies were then experimentally synthesized by an electrochemical lithium tuning strategy, during which the density of sulfur vacancies was well-tuned by the charge/discharge cycle number. The double sulfur vacancy-rich CuS catalyst exhibited a Faradaic efficiency toward n-propanol of 15.41% at -1.05V versus reversible hydrogen electrode in H-cells, and a high partial current density of 9.9mAcm(-2) at -0.85V in flow-cells, comparable to the best reported electrochemical CO2 reduction toward n-propanol. Our work suggests an attractive approach to create anion vacancy pairs as catalytic centers for multi-carbon-products. Electrochemical CO2 reduction to the valuable n-propanol is challenging due to the complicated C-3 forming mechanism. Here, authors demonstrate double sulfur vacancies formed on hexagonal copper sulfide can serve as efficient electrocatalytic centers.