Urea-Functionalized Silver Catalyst toward Efficient and Robust CO₂ Electrolysis with Relieved Reliance on Alkali Cations

Abstract

We report a new strategy to improve the reactivity and durability of a membrane electrode assembly (MEA)-type electrolyzer for CO2 electrolysis to CO by modifying the silver catalyst layer with urea. Our experimental and theoretical results show that mixing urea with the silver catalyst can promote electrochemical CO2 reduction (CO2R), relieve limitations of alkali cation transport from the anolyte, and mitigate salt precipitation in the gas diffusion electrode in long-term stability tests. In a 10 mM KHCO3 anolyte, the urea-modified Ag catalyst achieved CO selectivity 1.3 times better with energy efficiency 2.8-fold better than an untreated Ag catalyst, and operated stably at 100 mA cm–2 with a faradaic efficiency for CO above 85% for 200 h. Our work provides an alternative approach to fabricating catalyst interfaces in MEAs by modifying the catalyst structure and the local reaction environment for critical electrochemical applications such as CO2 electrolysis and fuel cells.

How membrane characteristics influence the performance of CO2 and CO electrolysis

“…[190][191][192][193] Despite AEM demonstrating excellent CO (2) E efficiency and product selectivity, 23 few studies focus on the chemical/alkaline stability of the AEMs from a CO (2) E perspective. At present, most of the CO (2) E studies are conducted for less than 200 h 43,67,[194][195][196][197] with only a few long-term studies available between 1000-4000 h. 198,199 However, Yin et al 87 investigated this and found o5% degradation of cationic groups in their AEM (QAPPT) after a 100 h CO 2 E test on an Au/C-based MEA electrolyzer.…”

Strategies for the mitigation of salt precipitation in zero-gap CO2 electrolyzers producing CO

“…Most works therefore chose the salt concentration either for optimal elctrochemical performance or for durability, depending on the scope of the study. Most publications reporting longterm tests (>100 h) use low anolyte salt concentation between 0.01 -0.1 M. However, it is reported that utilizing low salt concentrations only delays the formation of precipitates in the cathode and even with anolyte concentrations of 10 mM significant precipitation is observed after a few days, if no further measures are taken 8,23 . In addition to electrolyte concentration, the electrolyte composition also influences the precipitation behavior.…”

“…For instance, functional groups of the anion exchange polymers can compensate the co-catalytic effect of the alkali metal cations 40,41 . Furthermore, Garg et al reported improved performance and durability by functionalizing the Ag catalyst layer with urea (200 hours operation at 100 mA•cm -², Faradaic efficiency of ~85%, with 10 mM KHCO3 anolyte) 23 .…”

“…Most publications reporting long-term tests (>100 h) use low anolyte salt concentration between 0.01-0.1 M. However, it is reported that utilizing low salt concentrations only delays the formation of precipitates in the cathode and even with anolyte concentrations of 10 mM signicant precipitation is observed aer a few days, if no further measures are taken. 8,23 In addition to electrolyte concentration, the electrolyte composition also inuences the precipitation behavior. The most commonly investigated electrolytes consist of either OH − , HCO 3 − or CO 3 2− as anions and either Li + , Na + , K + , Rb + or Cs + as cations.…”

Advancing integrated CO2 electrochemical conversion with amine-based CO2 capture: a review

“…30 In a zero-gap membrane electrode assembly configuration, the (bi) carbonates are also prone to precipitate at electrode pores, block CO 2 diffusion to the catalytically active surface, and severely degrade the overall cell performance. 7,31,32 These technical issues constitute the significant challenges faced by the practical deployment of gas-fed CO 2 electrochemical conversion at a large scale.…”