Journal
CHEMICAL ENGINEERING JOURNAL
Volume 434, Issue -, Pages -Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.cej.2022.134765
Keywords
CO2RR; Cation exchange membrane; Membrane electrode assembly; Zero-gap; Cesium; Copper
Categories
Funding
- Young Scholar Fellowship Program [108-2636-E-007-006, 109-2636-E-007-006]
- Ministry of Science and Technology (MOST) in Taiwan
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By regulating the rate of proton transport and modifying the sulfonic acid side chains with alkali metal cations, the hydrogen evolution reaction (HER) is suppressed, leading to significantly improved CO2 reduction reaction (CO2RR) efficiency.
Direct gas phase electrolysis using a membrane electrode assembly (MEA) reactor has been recognized as a promising direction for large scale continuous CO2 conversion. The so called zero-gap CO2 reduction was however seldom achieved when proton is the main charge carrier in the system due to the overwhelmed competing hydrogen evolution reaction (HER) taking place at the cathode. In this work, the suppression of HER is achieved by regulating the rate of proton transport through the membrane electrolytes and is realized by the modification of the sulfonic acid side chains with alkali metal cations. The MEA's CO2 reduction reaction (CO2RR) faradaic efficiency (CO2RR-FE) is significantly improved as the alkali cations are varied sequentially from Li to Cs. Such improvement is attributed to the significantly hindered proton transport in the Cs-MEA, as reflected by the substantially larger high frequency resistance (HFR), which leads to enhanced competitive adsorption of CO2 on the copper catalyst. In addition, the Cs-MEA showed the highest robustness for both the membrane cations and the copper cathode against leaching and corrosion. Moreover, the observed phase transition of copper metal into faceted cuprous oxide crystals exposing low index surfaces also favors CO2RR over HER. The collective desirable properties of the Cs-MEA result in the best CO2RR performance, exhibiting a maximum CO2RR-FE of 0.44% at-1.2 V vs RHE and a space time yield (STY) of 1.06 mmol.h(-1).g(cat)(-1) for methane (CH4) and 2.02 mmol.h(-1).g(cat)(-1) for carbon monoxide (CO).
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