Electrochemical Reduction of CO₂ into Tunable Syngas Production by Regulating the Crystal Facets of Earth-Abundant Zn Catalyst

The electrochemical reduction of CO₂ to syngas with a tunable CO/H₂ ratio is regarded as an economical and promising method for the future. Herein, a series of earth-abundant Zn catalysts with different crystal facet ratios of Zn(002) to Zn(101) in the bulk phase have been prepared on electrochemically polished Cu foam by the electrochemical deposition method. The Zn catalyst with more (101) crystal facets show good electrochemical activity for the CO₂ reduction reaction (CO₂RR) to CO and that with more (002) crystal facets favor the hydrogen evolution reaction. The linear relationship between the crystal facet ratio of Zn(101) to Zn(002) and the Faradaic efficiency (FE) of CO₂RR to CO has been revealed for the first time. The prepared catalyst with more (101) facets show greater than 85% FE to syngas at -0.9 V (vs reversible hydrogen electrode) in aqueous electrolyte, with tunable CO/H₂ ratios ranging from 0.2 to 2.31 that can be used in existing industrial systems. Meanwhile, the mechanism of electroreduction of CO₂ on the Zn electrode has been studied by in situ infrared absorption spectroscopy. The highly selective role of the Zn(101) crystal facet in the CO₂RR to CO has been evidenced by density functional theory calculations.