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).

Solar-driven carbon dioxide (CO2) conversion to fuels and high value chemicals can contribute to the better utilization of renewable energy sources. Photosynthetic (PS), photocatalytic (PC), photoelectrochemical (PEC), and photovoltaic plus electrochemical (PV + EC) approaches are intensively studied strategies. We aimed to compare the performance of these approaches using unified metrics, as well as to highlight representative studies with outstanding performance in a given aspect. Most importantly, a statistical analysis was carried out to compare the differences in activity, selectivity, and durability of the various approaches, and the underlying causes are discussed in detail. Several interesting trends were found: (i) only the minority of the studies present comprehensive metrics; (ii) the CO2 reduction products and their relative amount vary across the different approaches, (iii) only the PV + EC approach is likely to lead to industrial technologies in the mid-term future. Lastly, a brief perspective on new directions is given to stimulate discussion and future research activity.

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.