Electrochemical CO₂ reduction: Implications of electrocatalyst's surface hydroxyl groups

Electrochemical CO₂ reduction (ECCO₂R) is a viable and promising approach for converting the greenhouse gas carbon dioxide into useful chemicals and fuels. Electrochemical activity and product selectivity are essential for this purpose. The ECCO₂R can lead to the formation of a wide variety of by-products, which is primarily dictated by the nature of electrocatalysts. Surface modification of electrocatalysts with oxide and/or hydroxide moieties can be a simple yet effective strategy to improve activity and selectivity of the ECCO₂R process. This article attempts to review and identify relationship between the surface hydroxylation of electrocatalysts and the product selectivity. Impact of electrocatalyst's surface modification with oxide/hydroxide on activity, product selectivity, intermediate stability, plausible mechanism and catalyst evolution during the ECCO₂R is highlighted by focusing on select and representative research findings. The review finds that the product selectivity is highly dependent not only on the presence of OH group on the electrocatalysts' surfaces but also the type and distribution of the group. Moreover, the selectivity can be tuned by introducing and controlling the density of surface OH. Future perspectives and challenges are also emphasized.