Energy conversion efficiency comparison of different aqueous and semi-aqueous CO₂ electroreduction systems

Abstract

An energy conversion efficiency index, that is independent of the anode reaction performance, is proposed for CO2 reduction in aqueous and semi-aqueous systems. The energy conversion efficiency of CO2 reduction...

Highly‐Efficient CO2 Electromethanation with Extremely Low Overpotentials on Pt/C Catalysts: Strategic Design of Multi‐Potential‐Step Method

“…The overpotentials of �0.3 V, �0.6 V, and �0.9 V are required for Au, Ag, and Cu electrocatalysts, respectively. [28] In contrast, when Pt is used, CO 2 is reduced around the theoretical electrode potential of the CO 2 reduction, and in many cases, it generates CO that strongly adsorbs on the Pt (CO ads ), [29][30][31] which is hard to remove or further reduced in aqueous solutions. [32,33] To transform the activity of Pt catalysts, we previously proposed and succeeded in the CO 2 electroreduction using a Pt-based catalyst in combination with a membrane electrode assembly (MEA).…”

“…Electrocatalysts, such as Au, Ag, Cu, etc., are well known as popular choices for experimental designs due to their CO 2 reduction activity, [3–27] although, these metals require high overpotentials. The overpotentials of $${\ge }$$ 0.3 V, $${\ge }$$ 0.6 V, and $${\ge }$$ 0.9 V are required for Au, Ag, and Cu electrocatalysts, respectively [28] . In contrast, when Pt is used, CO 2 is reduced around the theoretical electrode potential of the CO 2 reduction, and in many cases, it generates CO that strongly adsorbs on the Pt (CO ads ), [29–31] which is hard to remove or further reduced in aqueous solutions [32,33] .…”

Photo-assisted electrochemical CO2reduction at a boron-doped diamond cathode

“…Furthermore, CO 2 electrochemical reduction can be performed under ambient conditions, even at the industrial-scale. 3,12,13 In this case, to be competitive, this reaction must retain most of the energy in the final chemical product i.e., high energy conversion efficiency, or low activation energy for CO 2 , 14 and electrochemical (EC) and photoelectrochemical (PEC) approaches have been investigated for CO 2 reduction. 15 This may help produce energy with a lower environmental impact, [16][17][18] as in the case of hydrogen production from water electrolysis.…”

Influence of Water Molecules on CO2 Reduction at the Pt Electrocatalyst in the Membrane Electrode Assembly System

“…Moreover, it is not easy to obtain products by CO 2 electroreduction because experimentally high overpotentials are required to allow the CO 2 -reduction reaction. If the products are CO, HCOOH, and CH 4 , the overpotentials of ∼0.5, ∼1, and ∼1.5 V are known to be necessary, respectively. , This would be attributed to a reaction in which bent CO 2 anion radicals are formed by the first electron transfer to the linear CO 2 . , It has been reported that the required energy can be partially improved by the dynamic limitation of CO 2 molecules in the presence of surrounding hydrated cations and by increasing the specific surface area of the electrocatalyst. − …”

“…Consequently, we have recently succeeded in converting CO 2 into CH 4 with extremely low overpotentials (<0.1 V) by controlling the concentration of the CO 2 gas (to 2–7 vol %) to be fed to the cathode of the MEA containing Pt/C . It was also clarified that the CH 4 -formation reaction proceeds by a Langmuir–Hinshelwood mechanism associated with CO ads and adsorbed H (H ads ) when they are present on the Pt surface in the appropriate molar ratios. , Furthermore, the Faradaic efficiency of the CH 4 generation from the CO 2 reduction successfully increased up to ∼60% without any overpotentials thanks to optimization of the applied electrode potential as well as the electrocatalyst species. − The required overpotentials for the CH 4 production by CO 2 reduction have been reported to be ∼0 and ≥1.0 V for Pt and Cu electrocatalysts, respectively . Thus, the Pt electrocatalyst can selectively produce CH 4 from the CO 2 reduction around its thermodynamic equilibrium potential.…”