Polymeric Benzothiadiazole, Benzooxadiazole, and Benzoselenadiazole Photocathodes for Photocatalytic Oxygen Reduction to Hydrogen Peroxide

Visible-light-driven semiconductor photoelectrodes are promising new devices for on-demand photocathodic generation of hydrogen peroxide. Herein, the fabrication of organic polymeric photocathodes employing poly(4,7-di(thiophen-2-yl)benzo[c][1,2,5]thiadiazole) (pThBTD), and comparatively seven other related derivatives is reported. The monomer dithienobenzodithiazole can be directly polymerized on an electrode via two methods: electropolymerization or iodine-vapor-assisted polymerization. Both give polymers with wide visible light absorption and suitable stability for photoelectrodes. These methods yield different active layer morphologies, with electropolymerization yielding photocathodes with better performance. Critical issues affecting oxygen reduction photocurrents are evaluated, namely thickness, wettability, and pH. Photocathodic oxygen reduction currents, as well as photovoltages, are among the highest reported for an organic photoelectrocatalyst, and pThBTD films can stably produce H2O2 with high faradaic yield over at least 8 h. This work shows that single-component organic semiconductor devices can be highly competitive versus more complex heterostructures and that such low-bandgap organic polymers can afford remarkable stability.