Pure-Water-Fed Forward-Bias Bipolar Membrane CO Electrolyzer.

Coupling renewable electricity to reduce carbon dioxide (CO) electrochemically into carbon feedstocks offers a promising pathway to produce chemical fuels sustainably. While there has been success in developing materials and theory for CO reduction, the widespread deployment of CO electrolyzers has been hindered by challenges in the reactor design and operational stability due to CO crossover and (bi)carbonate salt precipitation. Herein, we design asymmetrical bipolar membranes assembled into a zero-gap CO electrolyzer fed with pure water, solving both challenges. By investigating and optimizing the anion-exchange-layer thickness, cathode differential pressure, and cell temperature, the forward-bias bipolar membrane CO electrolyzer achieves a CO faradic efficiency over 80% with a partial current density over 200 mA cm at less than 3.0 V with negligible CO crossover. In addition, this electrolyzer achieves 0.61 and 2.1 mV h decay rates at 150 and 300 mA cm for 200 and 100 h, respectively. Postmortem analysis indicates that the deterioration of catalyst/polymer-electrolyte interfaces resulted from catalyst structural change, and ionomer degradation at reductive potential shows the decay mechanism. All these results point to the future research direction and show a promising pathway to deploy CO electrolyzers at scale for industrial applications.