Intermolecular hydrogen bond modulating the selective coupling of protons and CO2 to CH4 over nitrogen-doped carbon layers modified cobalt

Abstract

Photocatalytic reduction of CO2 with H2O to CH4 is a promising route to migrate CO2 emission and complete the carbon neutrality goal. Nevertheless, one of the biggest challenges for this elegant strategy is that the coupling of the protons and CO2 to form CH4 is fiercely competed with proton-proton coupling to form H2, leading to extremely low CH4 selectivity. Herein, we designed and fabricated the nitrogen-doped carbon layers modified cobalt (N-C@Co) photocatalyst achieving the selective coupling of protons and CO2 to CH4 during photocatalytic reduction of CO2. The successful formation of intermolecular hydrogen bonds between the as-prepared N-C@Co and H2O molecule was found to suppress the mass transfer of the generated protons and promote the adsorption and activation of the CO2 molecule. More crucially, it was conducive to suppressing the desorption of the CO intermediate, which was typically deemed as the decisive species for CH4 generation. As a result, the H2 selectivity (9.0 %) and activity (17.3 µmol g−1) of the as-prepared N-C@Co were reduced by a factor of 9.3 and 17.6, respectively, as compared to that of bulk Co. The CH4 selectivity of N-C@Co was boosted 6.1 times from 13.3% of bulk Co to 81.3 % of N-C@Co with the generation rate of 155.7 μmol g−1 in 23 h. This work provides a new insight into the photocatalyst design for improving CH4 selectivity and suppressing the competing H2 and CO generation.