Rather than just focusing on the catalyst itself in the electrocatalytic CO 2 reduction reaction (eCO 2 RR), as previously reviewed elsewhere, we herein extend the discussion to the special topic of the microenvironment around the electrocatalytic center and present a comprehensive overview of recent research progress. We categorize the microenvironment based on the components relevant to electrocatalytic active sites, i.e., the catalyst surface, substrate, co-reactants, electrolyte, membrane, and reactor. Supported by most of the reported articles, the relevant factors affecting the catalytic performance of eCO 2 RR are then discussed in detail, and existing challenges and potential solutions are mentioned. Perspectives for the future research on eCO 2 RR, including the integration of different microenvironment factors, the extension to industrial application by coupling with carbon capture and conversion, and separation of products, are also discussed.

Rather than just focusing on the catalyst itself in the electrocatalytic CO 2 reduction reaction (eCO 2 RR), as previously reviewed elsewhere, we herein extend the discussion to the special topic of the microenvironment around the electrocatalytic center and present a comprehensive overview of recent research progress. We categorize the microenvironment based on the components relevant to electrocatalytic active sites, i.e., the catalyst surface, substrate, co-reactants, electrolyte, membrane, and reactor. Supported by most of the reported articles, the relevant factors affecting the catalytic performance of eCO 2 RR are then discussed in detail, and existing challenges and potential solutions are mentioned. Perspectives for the future research on eCO 2 RR, including the integration of different microenvironment factors, the extension to industrial application by coupling with carbon capture and conversion, and separation of products, are also discussed.

A simple method was proposed to activate alkaline Cu(OH) 2 with an acidic ionomer, Nafion, to regulate its surface microenvironment, including hydrophobicity and local basicity. In particular, the direct complete neutralization reaction between Cu(OH) 2 and Nafion in aqueous solution induces the exposing of vast anions which can exclude the in-situ-formed hydroxides and raise the local basicity. Remarkably, the optimal Nafionactivated Cu(OH) 2 -derived Cu can efficiently suppress the hydrogen evolution reaction (HER) and improve the selectivity for multi-carbon products in the CO 2 electroreduction reaction (eCO 2 RR). The H 2 Faradaic efficiency (FE) decreased to 11% at a current density of 300 mA/cm 2 (−0.76 V vs. RHE) in a flow cell, while the bare one with H 2 had an FE of 40%. The total eCO 2 RR FE reaches as high as 83%, along with an evidently increased C 2 H 4 FE of 44% as compared with the bare one (24%), and good stability (8000 s), surpassing that of most of the reported Cu(OH) 2 -derived Cu. The experimental and theoretical results both show that the strong hydrophobicity and high local basicity jointly boosted the eCO 2 RR as acquired by felicitously introducing ionomer on the Cu (OH) 2 -derived Cu surface.