Effect of Electrolyte Composition and Concentration on Pulsed Potential Electrochemical CO₂ Reduction

Abstract

With rising CO2 emissions and growing interests towards CO2 valorization, electrochemical CO2 reduction (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 KHCO3 concentration favors the formation of H2 and CH4. In contrast, for pulsed potential eCO2R, H2 formation is suppressed due to the periodic desorption of surface protons, while CH4 is still favored. In the case of KCl, increasing the concentration during constant potential eCO2R does not affect product distribution, mainly producing H2 and CO. However, increasing KCl concentration during pulsed potential eCO2R persistently suppresses H2 formation and greatly favors C2 products, 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.

Bayesian Optimization of Electrochemical Devices for Electrons-to-Molecules Conversions: The Case of Pulsed CO2 Electroreduction

“…For these experiments, the active voltage was set to 3 V and the resting voltage set to 1.1 V, leading to an active total current density of 200-240 mA cm -2 . Our results show that FECO can be improved when appropriate pulsed potentials are applied [Figure 1(B)], as previously demonstrated in other reactor configurations 56,69,76,[81][82][83] . These initial results serve as a baseline for determining the optimal combination of active and resting pulse durations using BO.…”

“…[69][70][71] More specifically, previous studies have shown that the use of dynamic voltage pulses can control selectivity and/or stability of CO2 electroreduction. 56,[72][73][74][75][76][77][78][79][80][81][82][83][84] All of these studies used a systematic approach to determine optimal operation conditions leading to large information gaps between the tested experimental conditions and possibly suboptimal parameter selection. In this study, we leverage these previous findings to demonstrate the use of BO to rapidly optimize the dynamic operating conditions in industrially relevant zero-gap electrochemical conversion devices.…”

Chemoselective, Metal-free, (Hetero)Arene Electroreduction Enabled by Rapid Alternating Polarity

“…Consistent with these findings are literature reports of CO2 or CO reduction using pulsed potential instead of DC that produce less H2. [30][31][32][33][34][35] Collectively, these experiments support the mechanism summarized in Figure 2C.…”

“…Borderline cases also exist when Ered,arene is close to Ered,FG, and such cases were exemplified in the reduction of 31 and 32. In accord with this simple rubric, when a functional group is more easily reducible, the method is unable to favor the reduction of (hetero)arenes (33)(34)(35).…”

Dynamic Boundary Layer Simulation of Pulsed CO2 Electrolysis on a Copper Catalyst

“…This result is consistent with prior experimental studies for pulsed CO 2 R on Cu that demonstrated improved CH 4 selectivity with increasing buffer electrolyte concentration. 42 The transient microenvironment accessed by pulsing a highly concentrated buffer solution is one of high CO 2 concentration, high overpotential, and low pH. These conditions are ideal for CH 4 formation, which primarily occurs at high overpotentials and is enhanced by the higher proton activities at low pHs.…”