A tandem catalyst with high CO2 capture capability to achieve a promoted CO2-to-CH4 electrochemical conversion

•A Cu-based tandem catalyst for high-efficiency CO2-to-CH4 electrochemical conversion was developed.•The Cu nanoparticles generated by electrochemical activation/reduction were the catalytic active sites.•The well-stabilized frameworks can guarantee a high capture capability of catalyst toward CO2.•The coupled carbon nanotubes were in favor of improving the selectivity towards CH4.•The key intermediates *CHO and *OCH3 for CH4 formation were confirmed.