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Abstract With rising CO₂emissions and growing interests towards CO₂valorization, electrochemical CO₂reduction (eCO₂R) has emerged as a promising prospect for carbon recycling and chemical energy storage. Yet, product selectivity and electrocatalyst longevity persist as obstacles to the broad implementation of eCO₂R. A possible solution to ameliorate this challenge is to pulse the applied potential. However, it is currently unclear whether and how the trends and lessons obtained from the more conventional constant potential eCO₂R translate to pulsed potential eCO₂R. In this work, we report that the relationship between electrolyte concentration/composition and product distribution for pulsed potential eCO₂R is different from constant potential eCO₂R. In the case of constant potential eCO₂R, increasing KHCO₃concentration favors the formation of H₂and CH₄. In contrast, for pulsed potential eCO₂R, H₂formation is suppressed due to the periodic desorption of surface protons, while CH₄is still favored. In the case of KCl, increasing the concentration during constant potential eCO₂R does not affect product distribution, mainly producing H₂and CO. However, increasing KCl concentration during pulsed potential eCO₂R persistently suppresses H₂formation and greatly favors C₂products, reaching 71 % Faradaic efficiency. Collectively, these results provide new mechanistic insights into the pulsed eCO₂R mechanism within the context of proton‐donator ability and ionic conductivity. 

Abstract The electrochemical CO2 reduction reaction (CO2RR) has gathered widespread attention in the past decade as an enabling component to energy and fuel sustainability. Copper (Cu) is one of the few electrocatalysts that can convert CO2 to higher-order hydrocarbons. We report the CO2RR on polycrystalline Cu from 5 °C to 45 °C as a function of electrochemical potential. Our result shows that selectivity shifts toward CH4 at low temperature and H2 at high temperature at the potential values between −0.95 V and −1.25 V versus reversible hydrogen electrode (RHE). We analyze the activation energy for each product and discuss the possible underlying mechanism based on their potential dependence. The activation barrier of CH4 empirically obeys the Butler–Volmer equation, while C2H4 and CO show a non-trivial trend. Our result suggests that the CH4 production proceeds via a classical electrochemical pathway, likely the proton-coupled electron transfer of surface-saturated COad, while C2H4 is limited by a more complex process, likely involving surface adsorbates. Our measurement is consistent with the view that the adsorbate–adsorbate interaction dictates the C2+ selectivity.