Selective and Efficient Reduction of Carbon Dioxide to Carbon Monoxide on Oxide‐Derived Nanostructured Silver Electrocatalysts

Abstract

In this work, the selective electrocatalytic reduction of carbon dioxide to carbon monoxide on oxide‐derived silver electrocatalysts is presented. By a simple synthesis technique, the overall high faradaic efficiency for CO production on the oxide‐derived Ag was shifted by more than 400 mV towards a lower overpotential compared to that of untreated Ag. Notably, the Ag resulting from Ag oxide is capable of electrochemically reducing CO2 to CO with approximately 80 % catalytic selectivity at a moderate overpotential of 0.49 V, which is much higher than that (ca. 4 %) of untreated Ag under identical conditions. Electrokinetic studies show that the improved catalytic activity is ascribed to the enhanced stabilization of COOH. intermediate. Furthermore, highly nanostructured Ag is likely able to create a high local pH near the catalyst surface, which may also facilitate the catalytic activity for the reduction of CO2 with suppressed H2 evolution.

Understanding the Heterogeneous Electrocatalytic Reduction of Carbon Dioxide on Oxide‐Derived Catalysts

“…According to DFT calculations on Cu(100) surfaces, the energy barrier of ethanol formation is 0.2 eV higher than that of ethylene formation . This is, interestingly, in agreement with the observation that Faradaic efficiency of ethanol is lower than that of ethylene on different kinds of monometallic Cu catalysts ,,,,,…”

“…OD−Ag catalysts also showed improvement over their native polycrystalline counterparts. At −0.8 V vs. RHE, OD−Ag is reported to produce CO with 89 % Faradaic efficiency at −1.15 mA/cm 2 total geometric current density compared to native polycrystalline Ag which produces CO with 4.1 % efficiency at ∼−0.5 mA/cm 2 total geometric current density . The roughness factor of the surface was not reported in this study, making normalization difficult.…”

Progress in development of electrocatalyst for CO2 conversion to selective CO production

“…Subsequently, OD‐Ag catalysts exhibited significantly improved performances compared to polycrystalline Ag counterparts . A typically larger overpotential is required on the bulk Ag surface compared with that of Au due to the weaker binding energy of *COOH on Ag, however, similarly low overpotentials were achieved on OD‐Ag electrocatalysts.…”

“…The performance of a nanostructured catalyst is determined not only by its active sites and modified intrinsic activities, but also by its peripheral condition gained from structure modification. Nanostructure may cause the partial limitation of the diffusion process and hinder the neutralization reaction for OH − generated near the surface (by *COOH to *CO step), resulting in a high local pH at the electrode/electrolyte interface . The increasing local pH would contribute to the suppressed HER.…”

“…This led to avoid the high pH conditions, which can cause the mass transport limitation of CO 2 and consequently decrease selectivity of CO 2 RR . Interestingly, however, it has been observed that increasing (local) pH rather helps favor CO 2 RR over HER due to peripherally decreasing H + concentration on the electrode . These results indicate that the impact of pH should also be considered from the kinetics standpoint of HER, which is the spontaneously competing reaction of CO 2 ‐to‐CO in the aqueous electrolyte.…”