Electrochemical reduction of CO2 is a value-added approach to both decrease the atmospheric emission of carbon-dioxide and to form valuable chemicals. We present a zero gap electrolyzer cell, which continuously converts gas phase CO2 to products without using any liquid catholyte. This is the first report of a multi-layer CO2 electrolyzer stack for scaling up the electrolysis process. CO formation with partial current densities above 250 mA cm−2 were achieved routinely, which was further increased to 300 mA cm−2 (with ~95 % Faradaic efficiency) by pressurizing the CO2 inlet (up to 10 bar). Evenly distributing the CO2 gas among the layers, the electrolyzer operates identically to the sum of multiple single-layer electrolyzer cells. When passing the CO2 gas through the layers consecutively, the CO2 conversion efficiency increased. The electrolyzer simultaneously provides high partial current density, low cell voltage (−3.0 V), high conversion efficiency (up to 40 %), and high selectivity for CO production.

A poly(aryl piperidinium)-based anion exchange membrane (PiperION) with high carbonate conductance is employed for CO₂ electrolysis to CO in conjunction with a tailored electrolyzer cell structure. This combination results in unprecedentedly high partial current densities in zero-gap cells (j_CO > 1.0 A cm⁻²), while maintaining high conversion (20–45%), selectivity (up to 90%) and low cell voltage (2.6–3.4 V).

Electrochemical CO₂ reduction (CO₂R) is an attractive option for storing renewable electricity and for the sustainable production of valuable chemicals and fuels. In this roadmap, we review recent progress in fundamental understanding, catalyst development, and in engineering and scale-up. We discuss the outstanding challenges towards commercialization of electrochemical CO₂R technology: energy efficiencies, selectivities, low current densities, and stability. We highlight the opportunities in establishing rigorous standards for benchmarking performance, advances in in operando characterization, the discovery of new materials towards high value products, the investigation of phenomena across multiple-length scales and the application of data science towards doing so. We hope that this collective perspective sparks new research activities that ultimately bring us a step closer towards establishing a low- or zero-emission carbon cycle.