Biohybrid architectures for efficient light-to-current conversion based on photosystem I within scalable 3D mesoporous electrodes†
The combination of advanced materials and defined surface design with complex proteins from natural photosynthesis is currently one of the major topics in the development of biohybrid systems and biophotovoltaic devices. In this study transparent mesoporous indium tin oxide (μITO) electrodes have been used in combination with the trimeric supercomplex photosystem I (PSI) from Thermosynechococcus elongatus and the small redox protein cytochrome c (cyt c) from horse heart to fabricate advanced and efficient photobiocathodes. The preparation of the μITO via spin coating allows easy scalability and ensures a defined increase in the electrochemically active surface area with accessibility for both proteins. Using these 3D electrodes up to 40 μm thickness, the immobilization of cyt c and PSI with full monolayer coverage and their electrical communication to the electrode can be achieved. Significant improvement can be made when the heterogenous electron transfer rate constant of cyt c with the electrode is increased by an appropriate surface treatment. The photocurrent follows linearly the thickness of the μITO and current densities of up to 150 μA cm−2 can be obtained without indications of a limitation. The internal quantum efficiency is determined to be 39% which demonstrates that the wiring of PSI via cyt c can be advantageously used in a system with high protein loading and efficient electron pathways inside 3D transparent conducting oxides.