Acceleration of the charge transfer rate for efficient photocatalytic hydrogen production via adjusting modulator and introducing electronic bridge dual strategies

The technology of photolysis water hydrogen evolution driven by solar energy is considered promising to alleviate the energy crisis. However, the low separation and transfer efficiency of photogenerated charge carriers is still one of the challenges leading to the inferior efficiency of photocatalysis. In this paper, alkyl n-hexanoic acid (HA) and aryl benzoic acid (BA) were used as modulators to synthesize HA-PCN-224 and BA-PCN-224 by solvothermal method, in which TCPP linker was coordinated with Zr-O clusters in accompany with part of reserved modulators, respectively. The photocatalytic hydrogen evolution activity of HA-PCN-224 (225.29 mu mol center dot g- 1 center dot h-1) was 2.86 times as that of BA-PCN-224 (78.78 mu mol center dot g- 1 center dot h-1), which should be ascribed to the higher conductivity confirmed by the electrochemical impedance spectroscopy (EIS). Subsequently, the sample HA-PCN-224(Pd) was synthesized by introducing PdII into the porphyrin center. The Photoluminescence (PL), photocurrent response (it), Mott-Schottky characterization, and density functional theory (DFT) calculations show that HA-PCN-224(Pd) has excellent electrical conductivity and unique PdII electron bridge, which can significantly accelerate the carrier separation and transfer efficiency. Surprisingly, with the help of PdII as an electron bridge, the photocatalytic hydrogen production activity of HA-PCN-224(Pd) is as high as 20411.32 mu mol center dot g- 1 center dot h-1, which is about 90.60 times as that of the original HA-PCN-224. This work provides us with a novel avenue to modulate the conductivity of MOFs via adjusting monocarboxylic acid regulators and introduce unique PdII as the effective electron bridge to promote excellent separation and transfer efficiency of charge carriers for the application in solar energy-related fields.