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

Abstract

Electrochemical CO2 reduction reaction (CO2RR), which can convert CO2 into value-added products, is a renewable energy technology with great potential to help achieve natural carbon balance. However, the selectivity of value-added products in electrochemical CO2RR has always been a difficult problem to be solved. It not only requires the catalyst to adsorb enough CO2 for the subsequent reaction, but also needs to effectively modulate the CO2 reduction reaction pathway, so as to improve the selectivity of a particular product. Hence, a frameworks-stable Cu-based tandem catalyst coupled with carbon nanotubes (R-Cu-TAl-CNTs1) was synthesized, achieving a promoted CO2-to-CH4 electrochemical conversion. The well-stabilized frameworks in catalyst enabled it to maintain a high CO2 capture capability under electrochemical conditions to accumulate enough CO2 onto the surface of the catalyst and convert it to adsorbed state CO (*CO). The Cu nanoparticles obtained by a period of electrochemical activation/reduction, served as the catalytic active sites to further reduce *CO to CH4. And the adopted CNTs can accelerate the electron transfer during the reaction, further improve the CH4 selectivity over the tandem catalyst. The R-Cu-TAl-CNTs1 exhibited an excellent current density of 71 mA cm−2 at −1.76 V vs. RHE compared with R-Cu-TAl (57 mA cm−2). And the faradaic efficiency (FE) of CH4 over R-Cu-TAl-CNTs1 was up to 54%, nearly 2 times in comparison to that over R-Cu-TAl (30%) at −1.56 V vs. RHE. The CH4/C2H4 FE ratio over R-Cu-TAl-CNTs1 was up to 9.5, which was about 12 times compared to that over R-Cu-TAl. The in situ Fourier transform infrared spectroscopy (FTIR) investigated the dynamic evolution of the *CHO and *OCH3 intermediates in the reaction pathways of CH4 generation.