Multielectron transportation of polyoxometalate-grafted metalloporphyrin coordination frameworks for selective CO2-to-CH4 photoconversion

Photocatalytic CO2 reduction into energy carriers is of utmost importance due to the rising concentrations of CO2 and the depleting energy resource. However, the highly selective generation of desirable hydrocarbon fuel, such as methane (CH4), from CO2 remains extremely challenging. Herein, we present two stable polyoxometalate-grafted metalloporphyrin coordination frameworks (POMCFs), which are constructed with reductive Zn-e-Keggin clusters and photosensitive tetrakis(4-carboxylphenyl)porphyrin (H2TCPP) linkers, exhibiting high selectivity (>96%) for CH4 formation in a photocatalytic CO2-reduction system. To our knowledge, the high CH4 selectivity of POMCFs has surpassed all of the reported coordination-framework-based heterogeneous photocatalysts for CO2-to-CH4 conversion. Significantly, the introduction of a Zn-epsilon-keggin cluster with strong reducing ability is the important origin for POMCFs to obtain high photocatalytic selectivity for CH4 formation, considering that eight Mo-V atoms can theoretically donate eight electrons to fulfill the multielectron reduction process of CO2-to-CH4 transformation.