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

Abstract

This paper proposes a new idea for dramatically increasing the efficiency of CO2 reduction to CH4 at Pt/C electrocatalysts with negligibly low overpotentials. Pt catalysts have typically been disregarded in favor of other metal catalysts for CO2 reduction due to their poor performances. However, our strategically‐designed, multi‐potential‐step method, using a membrane electrode assembly with Pt/C catalysts, allows CO2 to be electrocatalytically converted to CH4 at close to the theoretical electrode potential with a net faradaic efficiency of 59.8±9.7 %. This approach is relevant and important because it provides a method of simultaneously ameliorating CO2 buildup and generating useful products.

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

“…When potential sweeping in the negative direction, the signal of m / z 15 increased along with the reduction current from ∼0.2 V vs RHE, but the m / z -15 intensity decreased, and instead, the m / z -2 signal was detected from ∼0.1 V vs RHE under all the RH conditions. The MS-signal response to the applied potential was consistent with previous reports. − ,, It is experimentally known that the coverage of H ads located at the atop site on the Pt electrocatalyst determines whether the CH 4 generation reaction or the H 2 evolution reaction occurs preferentially. , Also, the gas chromatogram of the cathodic output gas during CO 2 reduction (Figure S2) revealed that only CH 4 was generated as a product. This result is supported by our previous experimental data from the mass-spectrum analysis and the test using isotopically labeled CO 2 ( 13 CO 2 ) gas .…”

“…The MSsignal response to the applied potential was consistent with previous reports. [43][44][45]47,48 It is experimentally known that the coverage of H ads located at the atop site on the Pt electrocatalyst determines whether the CH 4 generation reaction or the H 2 evolution reaction occurs preferentially. 43,48 Also, the gas chromatogram of the cathodic output gas during CO 2 reduction (Figure S2) revealed that only CH 4 was generated as a product.…”

“…[43][44][45]47,48 It is experimentally known that the coverage of H ads located at the atop site on the Pt electrocatalyst determines whether the CH 4 generation reaction or the H 2 evolution reaction occurs preferentially. 43,48 Also, the gas chromatogram of the cathodic output gas during CO 2 reduction (Figure S2) revealed that only CH 4 was generated as a product. This result is supported by our previous experimental data from the mass-spectrum analysis and the test using isotopically labeled CO 2 ( 13 CO 2 ) gas.…”

“…Because only CH 4 was obtained as a product from the CO 2 reduction, one possible cause that decreases the retention rate and accounts for the remaining Faradaic efficiency is the poisoning of Pt surface by the precursors of CH 4 formation (H ads and/or CO ads ). 48 Hence, when the practical application of this system is considered, it should be required to combine with the efficient less energy-intensive poisoning-elimination method proposed in our previous report. 44 Also, a different approach for the improvement of current density should be conducted in the future for the practical application.…”

“…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.…”