Significance Using electricity to reduce CO ₂ or CO back into valuable liquid fuels can revolutionize the way we produce chemicals/fuels. However, there are two types of impurity challenges involved: Different liquid products were typically cogenerated on Cu catalysts; in addition, those generated liquid fuels were inevitably mixed with ion impurities in liquid electrolytes. By integrating the rational design of Cu nanocube catalyst and porous solid electrolyte reactor, we report a direct and continuous generation of high-purity acetic acid solutions via electrochemical CO reduction.