Electrochemical Conversion, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Hahn-Meitner-Platz 1, 14109, Berlin, Germany.
Institut für Chemie & Biochemie, Freie Universität Berlin, 14195, Berlin, Germany.
Nat Commun. 2023 Apr 12;14(1):2062. doi: 10.1038/s41467-023-37520-x.
Membrane electrode assemblies enable CO electrolysis at industrially relevant rates, yet their operational stability is often limited by formation of solid precipitates in the cathode pores, triggered by cation crossover from the anolyte due to imperfect ion exclusion by anion exchange membranes. Here we show that anolyte concentration affects the degree of cation movement through the membranes, and this substantially influences the behaviors of copper catalysts in catholyte-free CO electrolysers. Systematic variation of the anolyte (KOH or KHCO) ionic strength produced a distinct switch in selectivity between either predominantly CO or C products (mainly CH) which closely correlated with the quantity of alkali metal cation (K) crossover, suggesting cations play a key role in C-C coupling reaction pathways even in cells without discrete liquid catholytes. Operando X-ray absorption and quasi in situ X-ray photoelectron spectroscopy revealed that the Cu surface speciation showed a strong dependence on the anolyte concentration, wherein dilute anolytes resulted in a mixture of Cu and Cu surface species, while concentrated anolytes led to exclusively Cu under similar testing conditions. These results show that even in catholyte-free cells, cation effects (including unintentional ones) significantly influence reaction pathways, important to consider in future development of catalysts and devices.
膜电极组件能够以工业相关的速率进行 CO 电解，但它们的运行稳定性通常受到阴极孔中固体沉淀物形成的限制，这是由于阴离子交换膜对阳离子的不完全排斥作用，导致来自阳极电解液的阳离子穿过膜迁移而引发的。在这里，我们表明阳极电解液浓度会影响阳离子通过膜的迁移程度，这会极大地影响无阴极电解液 CO 电解槽中铜催化剂的行为。通过系统地改变阳极电解液（KOH 或 KHCO）的离子强度，在主要生成 CO 或 C 产物（主要是 CH）之间产生了明显的选择性转变，这与碱金属阳离子（K）穿过膜的数量密切相关，这表明即使在没有离散液态阴极的电池中，阳离子在 C-C 偶联反应途径中也起着关键作用。在位 X 射线吸收和拟原位 X 射线光电子能谱揭示了 Cu 表面的物种组成强烈依赖于阳极电解液的浓度，其中稀阳极电解液导致 Cu 和 Cu 表面物种的混合物，而浓阳极电解液则在类似的测试条件下导致仅存在 Cu。这些结果表明，即使在无阴极电解液的电池中，阳离子的影响（包括非故意的影响）也会显著影响反应途径，这对于未来催化剂和设备的开发非常重要。
