Publication date: 15th December 2025
The electrochemical carbon dioxide reduction reaction (CO2RR), which converts CO2 to valuable fuels and chemicals with electricity from renewable sources, is attracting attention. However, CO2RR has a critical issue of low product selectivity due to the complex reaction pathways. Most previous studies focused on electrode optimization and achieved a certain increase in selectivity, but have not yet overcome the problem. In this context, the modulation of electrolytes has recently been focused on, and the cation effect is particularly in the spotlight1). Although intermediate stabilization has been reported to be a major cation effect 2), the hypothesis is mainly supported by theoretical calculation; thus, experimental evidence is desired.
Here, we focused on high-concentration electrolytes, which have been reported to alter CO2RR selectivity 3), expecting a pronounced cation effect to enable the experimental observation of reaction intermediates under the influence of cations. In this work, we demonstrate that increasing electrolyte concentration enhances ethylene (C2H4) selectivity. Moreover, a pronounced dependence on the cation species was observed, with C2H4 selectivity increasing in the order of Li⁺ < K⁺ < Na⁺. In situ surface-enhanced infrared spectroscopy (SEIRAS) suggests that key reaction intermediates, such as CO2,ad are effectively stabilized by cations, and that the degree of stabilization depends on the cation species. Moreover, it was confirmed that COad (a key reaction intermediate in the dimerization step) is localized within the Na+ system, further assisting C2H4 formation. At the conference, we will discuss how cation-induced changes in intermediate conditions correlate with the enhanced C2H4 selectivity.
This work was supported by JSPS KAKENHI Grant-in-Aid for Early-Career Scientists( grant no. 22K14542) , JST under the ASPIRE program( grant no. JPMJAP2422) and NEDO under the Intensive Support Program for Young Promising Researchers (grant no. JPMJAP20004).
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