A photochemical cell with nano-porous TiO2 electrode sensitized by lignophenol under visible light irradiation

A photochemical solar cell sensitized with a lignophenol, which has been directly synthesized from lignocellulosics through the phase-separation system, on a nano-porous TiO2 film electrode was developed and improved by stirring, reflux and saturation in an acetone solution. Hinoki (Chamaecyparis obtusa)-lignophenol (p-cresol type, HKLC), Beech (Fagus crenata)-lignophenol (p-cresol type, BCLC), second derivatives-I of HKLC and BCLC (HKLC413, BCLC413) and second derivatives-II of HKLC and BCLC (HKLC443, BCLC443) were used as photo-sensitizers. The conversion of visible light from 150-W Xe lamp through a L41 UV cut filter into electricity was achieved with a sandwich-type cell consisted of FTO-glass-TiO2 film-lignophenol-electrolytes-Pt coated FTO. The open circuit photovoltage (Voc), the short-circuit photocurrent density (Isc), the fill factor (FF) and the photo-electricity conversion efficiency (η) for the cell with HKLC413 saturated on TiO2 electrode were estimated under 85.0 mW cm−2 visible light irradiation for 0.51 V, 10.23 mA cm−2, 0.59 and 3.61% respectively. On the other hand, the cell with HKLC saturated only on the surface of TiO2 electrode was estimated for η = 0.81%. Moreover, the amounts of HKLC413 and HKLC443 on the electrodes extracted by 1.0 M NaOH were larger than the amount of HKLC evaluated by UV–vis spectroscopy. After the extractions were carried out in NaOH, only both HKLC413 and HKLC443 were remained in electrodes with slight yellow appearances. These results indicated that lignophenols were adsorbed on the inner part of porous TiO2 electrodes. Consequently, the performances of these cells were strongly influenced by the molecular sizes and the structures of lignophenols.