Fabrication of hematite photoanode for solar water splitting by using pulsed laser deposition
Chih-ping Yen (嚴治平)1,2*, Yan-jin Li (李彥瑾)3, Shr-jie Luo (羅士傑)3, Jyhpyng Wang (汪治平)1,2,4, Chung-jen Tseng (曾重仁)3, Szu-yuan Chen (陳賜原)1,4
1Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, Taiwan
2Department of Physics, National Taiwan University, Taipei, Taiwan
3Department of Mechanical Engineering, National Central University, Jhongli, Taiwan
4Department of Physics, National Central University, Jhongli, Taiwan
* presenting author:Chih-Ping Yen, email:d97222014@ntu.edu.tw
Solar hydrogen production is promising as a clean and sustainable energy source. An ideal material for solar water splitting should have the properties such as proper band edge positions, small band gap for good light harvesting, good electron and hole transport characteristics, high electrochemical charge-transfer rate, and high chemical stability. For hematite, however, the low electron mobility, short hole diffusion length, and sluggish oxygen evolution reaction impose severe limitation on its application, although it possesses a suitable band gap and good chemical stability. These shortcomings could be overcome by (1) employment of n-type doping to increase electron conductivity and to create a depletion region for effective separation of electrons and holes and (2) fabrication of a nano-porous structure in the hematite film to increase its electrochemically active surface area.
In this work, we used pulsed laser deposition in an atmosphere consisting of nitrogen and oxygen gases to prepare Ti-doped α-Fe2O3 (hematite) thin films composed of an array of nanorods formed by stacking of nanoparticles on FTO substrates. The films were annealed in situ during and after deposition at 500 oC for 4 hours in total. The target-to-substrate distance, argon gas pressure, and oxygen gas pressure were optimized to maximize simultaneously the specific surface area and electron-doping concentration of the hematite film, leading to a high photocurrent density. The dependences of the film characteristics on these control parameters could be explained by cooperative control over nanoparticle formation and oxygen dissipation in the ablation plume to attain the desire mesoscopic morphology and defect identity.

Keywords: solar water splitting, defect chemistry, hematite photoanode, pulsed laser deposition