FABRICATION OF NANOSTRUCTURED α-Fe_2O_3 FILMS FOR SOLAR-DRIVEN HYDROGEN GENERATION USING HYBRID HEATING

摘要

Electrodeposited thin films of Fe were oxidised using a novel conventional/microwave hybrid heating method. The photo-performance of hematite electrodes was investigated and the results are compared with regards to the amount of microwave power applied. The findings showed significant improvement in the performance of hematite electrodes when microwave heating was used. The genuine 'microwave effect' observed in this case is confirmed by using hybrid heating experiments at identical time-temperature profiles. The photocurrent density obtained at 0.23 V vs. V_(Ag/AgCl) increased significantly from 7 to 126 μA.cm~(-2) when microwave power was raised from 0 to 300 W. The films prepared by pure conventional annealing showed high recombination and photocurrent onset of around 0.4 V vs V_(Ag/AgCl) while the onset showed a negative shift to 0.1 V vs V_(Ag/AgCl) for the hybrid samples. The results obtained from Raman spectroscopy indicated a highly defective crystalline nature for the conventionally-annealed samples while microwave-assisted annealing resulted in fewer defects in the oxygen sublattice of hematite structure. It suggests that microwave heating improves surface properties of hematite films thus enhancing the photoelectrochemical performance of the photoelectrodes. Hybrid heating was found to provide a unique opportunity to control/tailor the oxidation kinetics and in turn the photo-performance of hematite electrodes using microwave power.