The development of photocatalytic systems with high activity to trigger CO2 reduction into formic acid (FA, HCOOH), which is regarded as a promising hydrogen storage compound, is an attractive option for simultaneously solving energy and environmental problems. The effects of heteroatom doping as well as the confinement of Pd alloy nanoparticles (NPs) on an amine-functionalized Fe-based metal organic framework (Fe3-MOF) were investigated. The substitution of different metals in the metal cluster nodes significantly changed the CO2 adsorption capacity as well as the CO2 activation properties under visible light irradiation, with Mn2+ doping particularly improving the performance of both. The confinement of PdAu NPs inhibited electron–hole recombination by efficiently trapping excited electrons and then promoting photocatalytic FA production. By optimizing the parameters, a high FA production of 725 μmol·g–1 can be achieved after 24 h, which is 3.6 times greater than that obtained with unmodified Fe3-MOF. The results of the present study have the potential to greatly enrich the applications of MOF-based photocatalysts with the aim of developing economical CO2-mediated hydrogen storage energy cycling.

The effects of depositing Pd alloy nanoparticles (NPs) on an amine-functionalized Fe-metal organic framework (MOF; MIL-88B-NH2) were investigated, with the aim of developing a photo-switchable bifunctional catalyst for hydrogen storage/delivery mediated by CO2/formic acid (FA). The highly dispersed PdAg NPs promoted photocatalytic FA synthesis from CO2 under visible light and inhibited electron-hole recombination by efficiently trapping excited electrons. The release of H2 via the dehydrogenation of FA upon heating was efficiently catalyzed by the electron-rich Pd species generated by alloying with Ag. These Pd species acted as crucial active centers associated with amine-functionalized moieties in the linker groups of the Fe-MOF.