A Guideline to Determine Faradaic Efficiency in Electrochemical CO 2 Reduction

T he electrochemical CO 2 reduction reaction (eCO 2 RR) using renewable electricity to produce different valueadded chemicals is a promising approach to mitigate CO 2 emission.[1][2][3][4] Four parameters are primarily used to evaluate the performance of a catalyst: (a) current density, (b) overpotential, (c) faradaic efficiency (FE), and (d) durability.To ensure the reproducibility of all these parameters and a fair comparison with different catalysts, they should be measured accurately and reliably.While previous articles have discussed how to reliably report overpotential, 5 and iR compensation in detail, 6 there is a lack of literature comprehensively covering key details related to the analysis of liquid and gaseous products in eCO 2 RR, which is crucial for the authentic calculation of FE.Reporting FE in an authentic manner needs careful attention as incomplete analyses of parameters that are used to calculate FE may result in its overestimation or underestimation.This would lead to a serious problem when comparing newer values with existing reports.To address this issue, we provide a comprehensive guideline on the accurate calculation of FE based on our experimental observations and previous reports.Definition.The FE is a measurement of selectivity of a particular product formed during eCO 2 RR.It is mathematically calculated as follows: Q Q FE(%) 100