Photocatalytic activity of a 2D copper porphyrin metal–organic framework for visible light overall water splitting†

A 2D copper tetrakis(4-carboxyphenyl)porphyrin metal–organic framework has been prepared and used as a photocatalyst for overall water splitting, measuring under visible light irradiation (λ > 450 nm) under one sun power conditions a H₂ production rate of 120 μmol_H2 g_catalyst⁻¹ h⁻¹ that is among the highest ever reported. While the 2D Cu porphyrin MOF undergoes substantial degradation in 3 h upon UV irradiation (320–380 nm) in the presence of air, it appears to be photostable under the conditions of the overall water splitting and visible light exposure, exhibiting similar temporal profiles for H₂ and O₂ evolution. Photocurrent experiments and band energy measurements indicate that the photocatalytic efficiency derives from an efficient charge separation in the visible region (apparent electron charge extraction efficiency at 540 nm of 0.1%) and adequate alignment of the redox potential of the conduction (−0.59 V vs. NHE) and valence (+1.48 V vs. NHE) bands for water splitting.