Photodeposition of Co-Based Oxygen Evolution Catalysts on α-Fe2O3 Photoanodes

被引:192
作者
McDonald, Kenneth J. [1 ]
Choi, Kyoung-Shin [1 ]
机构
[1] Purdue Univ, Dept Chem, W Lafayette, IN 47907 USA
基金
美国国家科学基金会;
关键词
iron oxide; photoelectrochemical cell; photoelectrolysis; oxygen evolution catalyst; photodeposition; RAY PHOTOELECTRON-SPECTROSCOPY; IRON-OXIDE ELECTRODES; WATER OXIDATION; SEMICONDUCTOR ELECTRODES; EVOLVING CATALYST; THIN-FILMS; COBALT; HEMATITE; PHOSPHATE; XPS;
D O I
10.1021/cm1020614
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Cobalt-based oxygen evolution catalysts containing phosphates (Co-Pi OEC) were photochemically deposited onto the surface of n-type alpha-Fe2O3 electrodes to enhance solar O-2 production. alpha-Fe2O3 films used in this study were prepared by electrodepositing Fe films followed by thermal oxidation at 500 degrees C. The use of a nonaqueous plating solution made it possible to deposit adherent and uniform Fe films, which is difficult to achieve in an aqueous medium. Photodeposition of Co-Pi OEC was carried out by using photogenerated holes in the valence band of alpha-Fe2O3 to oxidize Co2+ ions to Co3+ ions in a phosphate buffer solution, which resulted in the precipitation of Co-Pi OEC on the alpha-Fe2O3 surface. Two different deposition conditions, open circuit (OC) and short circuit (SC) conditions, were studied comparatively to understand their effect on the growth and composition of Co-Pi OEC deposits. The results showed that the SC condition where the photoreduction reaction is physically separated from the photo-oxidation reaction significantly increased the yield and nucleation density of Co-Pi OECs, resulting in a better coverage of the alpha-Fe2O3 surface with Co-Pi OEC nanoparticles. X-ray photoelectron spectroscopy showed that the OC condition resulted in a higher Co2+/Co3+ ratio in the Co-Pi OEC deposits than the SC condition. This difference in composition is due to the simultaneous photoreduction occurring on the a-Fe2O3 surface under OC conditions. Co-Pi OEC improved the photocurrent of alpha-Fe2O3 electrodes more than Co2+ ions simply adsorbed on the alpha-Fe2O3 surface and the Co-Pi OEC deposited under SC conditions resulted in the most pronounced photocurrent enhancement. These results demonstrate the advantages of creating a SC condition for photodeposition of Co-Pi OECs. O-2 detection measurements show that the presence of photodeposited Co-Pi OEC on the alpha-Fe2O3 surface not only increases the total amount of photocurrent generated by facilitating electron hole pair separation but also increases the photocurrent to O-2 conversion efficiency by improving O-2 evolution kinetics.
引用
收藏
页码:1686 / 1693
页数:8
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