Mediator-free solar energy conversion by the artificially installed thylakoid membrane on the functionalized electrode

Here we report an effective solar energy conversion using a whole thylakoid membrane chemically installed on the anthraquinone-modified glassy carbon (GC) electrode. A mixed monolayer of anthraquinone and carboxyphenyl on the GC surface was formed prior to the thylakoid bioconjugation via reductive C-C coupling. Thus prepared electrodes showed higher photocurrent than those without an anthraquinone layer. Two main electron transfer pathways have been identified from the blocking experiments with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), an inhibitor of QB site in photosystem II (PSII) and with paraquat, a possible electron acceptor of FA/FB site in photosystem I (PSI). 41% photocurrent follows the normal electron transfer pathway from FA/FB to the electrode via anthraquinone. The remaining 59% directly flows from QA (or QB) to the electrode also via anthraquinone. From the complete solar cell that was constructed in combination with an oxygen reduction cathode, the maximum power density of 0.27 μW/cm2 with current density of 0.63 μA/cm2 under one sun illumination was obtained. The turnover frequency was calculated to be 10 water molecule oxidation per PSII unit per second, indicating that the thylakoid membrane on the surface maintained its activity. This work provides a simple and reliable method to photoenergy conversion using thylakoid membranes.