Facet Selectivity of Carbon Dioxide Electroreduction to HCOOH on a Zn Catalyst

Metallic zinc, regarded as the typical CO selectivity catalyst in CO₂ electroreduction, can also exhibit HCOOH selectivity, but the real reasons for HCOOH selectivity remain somewhat unclear. Here, density functional theory calculations were initially employed to elucidate that the Zn(002) facet exhibited the most favorable adsorption energy for the critical HCOO* intermediate in HCOOH formation. Then, the Zn catalyst with a predominant (002) facet was prepared and exhibited a maximum HCOOH Faradaic efficiency of 90%, a partial current density of 40 mA cm^-2 and excellent stability without deactivation (<5% productivity change) during 20 h of operation. Comprehensive theoretical analysis further revealed that the pronounced selectivity toward HCOOH production predominantly stemmed from the significantly reduced reaction energy barrier for the CO₂ electroreduction pathway to HCOOH on the Zn(002) facet, as compared to the competing pathways leading to CO and H₂ formation.