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Porphyrins have been widely used in designing photocatalyst systems. However, finding an effective strategy to improve the intrinsic photocatalytic activity of porphyrin molecules remains a challenge. Here, two new porphyrins, meso-tetra(5-carboxyfuryl)porphyrin (H2TCFP) and meso-tetra(5-carboxythienyl)porphyrin (H2TCTP), were successfully synthesized and compared with meso-tetra(m-carboxyphenyl)porphyrin (H2TmCPP), to clarify the influence of the organic unit bridging the carboxyl acid group with the porphine ring on the photocatalytic activity of porphyrin for H2 evolution from water splitting. The H2 evolution rates of 10.8 mmol g−1 h−1 observed for H2TCFP and 9.7 mmol g−1 h−1 for H2TCTP are both larger than 8.0 mmol g−1 h−1 observed for H2TmCTP under optimal conditions. The best photocatalytic activity observed for H2TCFP was investigated through experiments and density functional theory (DFT) calculations and was interpreted in terms of the combined effect of several key factors of the entire photocatalytic process, including the high absorptivity of UV light, high separation efficiency of photogenerated carriers, and low Gibbs energy required for associated water splitting. Meanwhile, the concentration-dependent performance of photocatalytic activity was analyzed and attributed to the aggregation and light-bleaching effect exerted on porphyrins. [ABSTRACT FROM AUTHOR]

The electronic state of metallic centers plays a crucial role in electrocatalytic reactions such as oxygen evolution reaction (OER), which usually require high-valence transition metallic centers. Herein, we propose an organic ligand coordination strategy to modulate the electronic state of metallic centers in NiFe LDH, by introducing three different organic linkers including 2,6-naphthaleneducarboxylic acid, 4,4′-bipyridine, and 1H-1,2,3-triazole on the surface of NiFe LDH to derive atomic-layered metal–organic framework (NiFe LDH@MOF). Experimental results indicate that the electronic structure of metal centers in the composite was modified after the coordination of organic linker, among which the most amount of high-valence state was for Fe species in the 1H-1,2,3-triazole involved catalysts (NiFe LDH@MOF-3). Density functional theory (DFT) calculations further demonstrate that the 1H-1,2,3-triazole linkers around Fe centers optimized the d-band center together with the beneficial Gibbs free energy of the intermediate. Therefore, NiFe LDH@MOF-3 exhibited a superior electrocatalytic OER performance with a low overpotential of 242 mV to achieve a current density of 100 mA cm−2, a small Tafel slope of 32.3 mV dec−1. This work provides a general strategy for the modulation of the electronic structure of metallic centers using organic linker coordination to achieve a high-performance electrocatalyst. [ABSTRACT FROM AUTHOR]