|Problems of sustainable energy resource and environmental cleaning were introduced, and a concept given to solve these issues. BioPhotoChemical Cell (BPCC) was proposed comprising a mesoporous n-semiconductor (SC, here TiO2) film photoanode coated on a conducting glass and an O2-reducing cathode capable if completely and efficiently photodecomposing biomass and its wastes in an aqueous solution involving also solid suspensions under solar UV-light irradiation with simultaneous electrical power generation. The principle and the mechanism were interpreted by a Schottky junction on a nanostructured n-SC thin film soaked in a biomass aqueous solution. The electrical power was presented by open circuit photovoltage, short circuit photocurrent, and Fill Factor (FF). Remarkably high quantum efficiencies (QEs) for the photocomposition were obtained. External QE based on total incident UV-light exceeding 2 (=200%) and internal QE based on activating UV photons exceeding 20 (2000%) were interpreted by an autooxidation mechanism of the photoactivated biomass.