The electrochemical reduction of CO₂ is a promising route to convert carbon emissions into valuable chemicals and fuels. In electrolyzers producing multi-carbon products, 70%–95% of the supplied CO₂ is converted to (bi)carbonates, limiting the carbon efficiency of electrochemical CO₂ conversion. These (bi)carbonate anions can be lost to the aqueous electrolyte, converted back to gaseous CO₂ and diluted in the anode tail gas, and/or combined with alkali metal cations from the electrolyte to form solid salt precipitates. Here, we report a microchanneled solid electrolyte that allows for the recapture and recycling of (bi)carbonate ions before reaching the anode, reducing CO₂ loss to ∼3%. We demonstrate CO₂ electroreduction to multi-carbon products with 77% selectivity without the use of alkali metal cations, by incorporating fixed quaternary ammonium cations. This system simultaneously achieves near-zero CO₂ loss, high selectivity toward multi-carbon products, and stable operation at an industrially relevant current density over 200 h.

_{CO 2}的电化学还原是将碳排放物转化为有价值的化学品和燃料的有前景的途径。在生产多碳产品的电解槽中，70%–95% 的供应 CO ₂被转化为碳酸氢盐，限制了电化学 CO ₂转化的碳效率。这些碳酸(氢)根阴离子可以损失到含水电解质中，转化回气态CO ₂并在阳极尾气中稀释，和/或与来自电解质的碱金属阳离子结合形成固体盐沉淀物。在这里，我们报告了一种微通道固体电解质，它可以在到达阳极之前重新捕获和循环碳酸氢根离子，从而将 CO ₂损失降低至 3%。我们展示了 CO₂通过加入固定的季铵阳离子，在不使用碱金属阳离子的情况下，以 77% 的选择性电还原成多碳产物。该系统同时实现了近乎零的CO ₂损失、对多碳产物的高选择性以及在工业相关电流密度下200小时以上的稳定运行。