Self-sensitization-induced protonation sites for weak-light-driven hydrogen evolution in coordination polymers

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The exploration on weak-light-driven catalysis is an important approach to reduce the dependence of photocatalysts on strong light and improve the efficiency of solar spectrum utilization. However, the reported photocatalysts typically necessitate high light intensity (e.g., exceeding 100 mW cm−2) for catalytic reactions, which cannot be achieved with natural solar light. Herein, a self-sensitization-induced strategy was employed to generate in-situ proton sites, enabling photocatalytic hydrogen evolution reaction (HER) even under low light intensity (10 mW cm−2). An indolocarbazole ligand (H2ICDB) was utilized to construct a paddle-wheel dicopper coordination polymer (CuICDB-DMF). By substituting the axially coordinated DMF with methanol or water, CuICDB-MeOH and CuICDB-H2O were obtained. Under weak-light irradiation (10 mW cm−2), CuICDB-H2O exhibited the highest photocatalytic HER rate of 838.4 μmol g−1 h−1 when compared to the other two counterparts. Remarkably, the substitution of axially coordinated H2O promotes charge separation and transfer efficiency through optimizing ligand-to-cluster charge transfer (LCCT) process. Moreover, density functional theory (DFT) calculations reveal that coordinated H2O substitution decreases the Gibbs free energy difference of the potential determining step (H2O* → OH* + H*) in CuICDB-H2O.