Electrochemical CO2 reduction 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 CO2 reduction 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.

Electrochemistry has the potential to sustainably transform molecules with electrons supplied by renewable electricity. It is one of many solutions towards a more circular, sustainable and equitable society. To achieve this, collaboration between industry and research laboratories is a must. Atomistic understanding from fundamental experiments and modelling can be used to engineer optimized systems whereas limitations set by the scaled-up technology can direct the systems studied in the research laboratory. In this Primer, best practices to run clean laboratoryscale electrochemical systems and tips for the analysis of electrochemical data to improve accuracy and reproducibility are introduced. How characterization and modelling are indispensable in providing routes to garner further insights into atomistic and mechanistic details is discussed. Finally, important considerations regarding material and cell design for scaling up water electrolysis are highlighted and the role of hydrogen in our society's energy transition is discussed. The future of electrochemistry is bright and major breakthroughs will come with rigour and improvements in the collection, analysis, benchmarking and reporting of electrochemical water splitting data.

Copper is a unique catalyst for the electrochemical CO 2 reduction reaction (CO2RR) as it can produce multi-carbon products, such as ethylene and propanol. As practical electrolyzers will likely operate at elevated temperatures, the effect of reaction temperature on the product distribution and activity of CO2RR on copper is important to elucidate. In this study, we have performed electrolysis experiments at different reaction temperatures and potentials. We show that there are two distinct temperature regimes. From 18 up to ∼48 °C, C2+ products are produced with higher Faradaic efficiency, while methane and formic acid selectivity decreases and hydrogen selectivity stays approximately constant. From 48 to 70 °C, it was found that HER dominates and the activity of CO2RR decreases. Moreover, the CO2RR products produced in this higher temperature range are mainly the C1 products, namely, CO and HCOOH. We argue that CO surface coverage, local pH, and kinetics play an important role in the lower-temperature regime, while the second regime appears most likely to be related to structural changes in the copper surface.

Electrochemical reactions in general, and the CO 2 reduction reaction (CO2RR) in particular, are commonly studied at room temperature. However, practical electrolysers may use elevated temperatures. There is currently a lack of fundamental understanding of the effect of temperature on the CO2RR. Here, we performed temperature-dependent studies on the CO2RR on a relatively simple electrode material, namely gold, to obtain insights into how temperature influences this reaction and the competing hydrogen evolution reaction. A rotating ring disk electrode setup was used to show that the CO2RR activity and selectivity increased with temperature, and to obtain kinetic parameters such as the apparent activation energy and transfer coefficient. The magnitude of the temperature effect and the activation energy was affected by both the cation identity and concentration in the electrolyte. Moreover, the positive effect of temperature on the kinetics of the CO2RR was counteracted by the lower CO 2 solubility, making efficient mass transport even more important at higher temperatures.

Heterogenization of molecular catalysts for CO2 electroreduction has attracted significant research activity, due to the combined advantages of homogeneous and heterogeneous catalysts. In this work, we demonstrate the strong influence of the nature of the substrate on the selectivity and reactivity of electrocatalytic CO2 reduction, as well as on the stability of the studied immobilized indium(III) protoporphyrin IX, for electrosynthesis of formic acid. Additionally, we investigate strategies to improve the CO2 reduction by tuning the chemical functionality of the substrate surface by means of electrochemical and plasma treatment and by catalyst encapsulation in polymer membranes. We point out several underlying factors that affect the performance of electrocatalytic CO2 reduction. The insights gained here allow one to optimize heterogenized molecular systems for enhanced CO2 electroreduction without modification of the catalyst itself.