Manipulating local CO ₂ /H ₂ O ratio in electrocatalytic CO ₂ reduction toward multi‐carbon product

Abstract Electrocatalytic CO 2 reduction reaction (CO 2 RR) has been developed as a promising and attractive strategy to close the anthropogenic carbon cycle. Among various reduction products, multi‐carbon (C 2+ ) oxygenate and hydrocarbon compounds are desirable value‐added fuels or chemicals. Extensive researches have revealed the crucial role of local CO 2 and H 2 O concentrations (or the adsorption of *CO and *H) close to the electrode/catalyst surface in manipulating multi‐carbon generation pathways. In this mini reviews, we mainly summarized the recent progress of this field over the past five years. The modulating strategies for the hydrogen and carbon species ratio can be divided into three categories, i.e., catalyst morphology, electrolyte composition and mass transfer. The effectiveness of the aforementioned strategies in promoting multi‐carbon product selectivity was discussed in detail from the perspectives of tuning the local CO 2 and H 2 O concentrations and the subsequent thermodynamic‐ and kinetic‐controlled *CO and *H ratios. Finally, the critical challenges remaining in balancing the ratio of CO 2 and H 2 O as well as potential upgrading directions for future research are addressed.