Understanding cation effects in electrochemical CO₂ reduction

Abstract

Field-sensitive electrochemical reactions are controlled by electrode charging which is sensitive to the size of the electrolyte containing cations.

Hydroxide Is Not a Promoter of C2+ Product Formation in the Electrochemical Reduction of CO on Copper

“…This is in contradiction to the data presented in Figure c. We note that the lack of specific adsorption of C‐Na + is confirmed by the lack of Stark tuning of any bands associated with the crown ether (Figure S10). Another commonly invoked mechanism to explain the cation effect is the modification of the interfacial electric field due to the different cation sizes . However, we do not observe any detectable change in the Stark tuning rate in adsorbed CO on Cu in the Na + concentration range of 0.1 to 1 m (30–33 cm −1 V −1 ; Figure S11).…”

“…The lack of change in the Stark tuning rate of adsorbed CO on Pt at different pH values, that is, H + concentrations, has been reported recently by Koper and co‐workers . This is likely because that the concentration of cations in neither the bulk nor the diffuse layer has any significant impact on the Helmholtz capacitance, as suggested by a recent computational study . The average electric field between the OHP and the electrode surface within the framework of the GCS model does not change appreciably in the Na + concentration range investigated in this work, and thus cannot explain the enhanced production of C 2+ products in the CORR at higher Na + concentrations.…”

“…According to the classical Gouy‐Chapman‐Stern (GCS) model, cations reside at the outer Helmholtz plane (OHP) and the diffuse layer . Thus, a higher cation concentration of cations in the electrolyte could increase the density of cations at the OHP, which may induce a stronger electrostatic field at the interface . Strong field has recently been proposed to stabilize the key intermediate of CO 2 electroreduction and lower the energy barrier of C 2 product formation .…”

Iron Porphyrin Allows Fast and Selective Electrocatalytic Conversion of CO2 to CO in a Flow Cell

“…Comparative electrolysis at 50 mA cm −2 (Figure S15) led to a 390 mV overpotential decrease along with a slight CO selectivity increase and an EE gain of 8 %, as summarized in Table . As recently suggested by Chan et al., cations having the smallest hydration radius, which is inversely proportional to the ionic radius, may lead to the strongest interfacial electric field, favoring CO 2 adsorption at catalytic sites.…”

“…Besides increasingt he electrolyte salt concentration and temperature, it was recently shown that the cation size of the electrolyte may also impact the catalytic performance. [33,34] Using a0 .5 m CsHCO 3 as electrolyte solution( see Figure S14 and Table S2), as ignificant performance increasew as obtained with ac urrent density of 9mAcm À2 at 270 mV overpotential (99.9 %C Os electivity)a nd ac urrent density (at h = 870 )o f 83.7 mA cm À2 (97.6 %s electivity), av alue two times larger than the one obtained using a0 .5 m NaHCO 3 solution.C omparative electrolysis at 50 mA cm À2 ( Figure S15) led to a3 90 mV overpotentiald ecrease along with as light CO selectivity increase and an EE gain of 8%,a ss ummarizedi nT able 1. As recently suggestedb yC han et al, [34] cations having the smallest hydration radius, which is inversely proportional to the ionic radius, may lead to the strongest interfacial electric field, favoring CO 2 adsorptionatc atalytic sites.…”