Copper serves as the benchmark “standard” in the search for an active, selective, and stable monometallic electrocatalyst that can sustain the conversion of CO2 into chemical fuels more reduced than CO or HCOOH at appreciable reaction rates. The intrinsic ability of Cu to facilitate the production of oxygenates and hydrocarbons from CO2 reduction (CO2R) remains unsurpassed among unalloyed transition metals. The non-nobility of Cu, however, poses tactical challenges in the acquisition of atomic-level information from electrochemical surface science investigations. Evaluation schemes for the electrocatalytic performance of Cu are often patterned after analogous methodologies designed for Pt, the catalyst par excellence for many reductive transformations involving hydrogen. Pre- and post-catalysis surface interrogations appear suitable for Pt but are inadequate for Cu in the context of CO2R. The susceptibility of Cu toward surface reconstruction during CO2R makes in situ methods ineffectual, especially when carried out beyond the dynamic range of critical reaction parameters. This review describes the need for the seriatim implementation of operando methods in CO2R research, i.e. the consecutive execution of analytical techniques that examine the electrode surface during the electrocatalytic reaction. The use of the CO intermediate as an analytical surrogate for CO2 in alkaline medium is exploited to illustrate various operando strategies that can ascertain the surface structure, product profile, surface-vs-solution concentration dependence of reaction rates, and surface coordination modes of surface-bound species at well-defined Cu electrodes.
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