Fundamental Insights into Photoelectrocatalytic Hydrogen Production with a Hole-Transport Bismuth Metal-Organic Framework

Solar fuels production is a cornerstone in the development of emerging sustainable energy conversion and storage technologies. Light-induced H-2 production from water represents one of the most crucial challenges to produce renewable fuel. Metal-organic frameworks (MOFs) are being investigated in this process, due to the ability to assemble new structures with the use of suitable photoactive building blocks. However, the identification of the reaction intermediates remains elusive, having negative impacts in the design of more efficient materials. Here, we report the synthesis and characterization of a new MOF prepared with the use of bismuth and dithieno[3,2-b:2',3'-d]thiophene-2,6-dicarboxylic acid (DTTDC), an electron-rich linker with hole transport ability. By combining theoretical studies and time-resolved spectroscopies, such as core hole clock and laser flash photolysis measurements, we have completed a comprehensive study at different time scales (fs to ms) to determine the effect of competitive reactions on the overall H-2 production. We detect the formation of an intermediate radical anion upon reaction of photogenerated holes with an electron donor, which plays a key role in the photoelectrocatalytic processes. These results shed new light on the use of MOFs for solar fuel production.