Effect of copper doping in the TiO₂ film electrodes on the performance of photoelectrochemical biofuel cells

Cu-doped TiO₂ film electrodes are synthesized via sol–gel technique and physically characterized. The Cu-doped TiO₂ film electrodes is sensitized by tetrakis (4-carboxyphenyl) porphyrin and applied as a photoanode of a photoelectrochemical biofuel cell (PEBFC). The Cu/TiO₂-based PEBFCs show a short-circuit current (I_sc) of 75.9 μA, an open-circuit potential (V_oc) of 912 mV, a maximum power density (P_max) of 66.43 μW/cm² and an overall energy conversion efficiency (η) of 2.16%, respectively. The PEBFCs indicate improved photoelectric performances comparing the TiO₂-based PEBFC (I_sc: 72.5 μA, V_oc: 740 mV, P_max: 35.34 μW/cm², η: 1.52%). The Cu/TiO₂-based PEBFCs also indicate a higher incident photon-to-collected electron conversion efficiency (IPCE), which is probably due that the doped copper reduces the band gap of a wide-gap TiO₂ semiconductor as shown by ab initio band calculation. And the Cu/TiO₂-based PEBFC can provide long electron lifetime and decrease electron–hole pair recombination rate, which is responsible for the better performance in the Cu/TiO₂-based PEBFC than in the TiO₂-based PEBFC.