Incorporating porphyrin-Pt in light-harvesting metal-organic frameworks for enhanced visible light-driven hydrogen production

Abstract

Molecular catalysts for H2-evolution are of interest for their integration into light-harvesting complexes for photocatalytic water splitting. Here, we report the meso-tetra (4-carboxyphenyl) porphine [(TCPP)PtII] complex as a molecular H2-evolving photocatalyst using chloranilic acid (CA) as a sacrificial electron donor, the choice of which is critical to the stability of the photocatalyst. When triethanolamine was used, [(TCPP)PtII] decomposed to form Pt nanoparticles. Density functional theory calculations together with evidence from electrochemical and spectroscopic analyses suggested that the catalysis was possibly initiated by a proton-coupled electron transfer (PCET) to form [(TCPP)PtI]-N-H, followed by another electron injection and protonation to form a [(TCPP)PtII-hydride]-N-H intermediate that can release H2. As the whole catalytic cycle involves the injection of multiple electrons, a light-harvesting network should be helpful by providing multiple photo-induced electrons. Thus, we integrated this molecular catalyst into a light-harvesting metal-organic framework to boost its activity by ~830 times. This work presents a mechanistic study of the photocatalytic H2 evolution and energy transfer and highlights the importance of a light-harvesting network for multiple electron injections.