April 2021 - Artificial carbon fixation contributes to closing the anthropogenic carbon cycle. However, large-scale conversion of CO2 into selective products remains a challenge. Coupled thermal–electrochemical catalysis could offer an attractive approach to upgrading CO2 into value-added products if selective electrocatalysts and integrated devices were developed. Here we identify a mechanistic route to selectively producing either CO or CH4 with high selectivity (>95%) using Ir–ceria-based catalysts in an intermediate-temperature (400 °C) CO2 electrolyser that operates at low overpotential and ambient pressure. We show that tuning of the Ir–O hybridization by controlling the Ir speciation can alter the catalyst surface chemical environment, enabling the stabilization of specific transition states for the production of either CO or CH4 during electrocatalysis. By achieving CO2 electrohydrogenation in tandem with light-alkane electrodehydrogenation, we further demonstrate that such an advanced electrolyser could be extended to the upgrade of different carbon resources in one-step, significantly enhancing the techno-economic feasibilty of the process.