| Energy challenges have inspired the use of inexpensive and effective materials for mass production of clean fuels from solar energy. Photoelectrochemical cells employing semiconducting materials have attracted considerable interest for directly converting sunlight into storable chemical fuel(hydrogen) via water-splitting. Currently, the research about the photoelectrodes in the photoelectrochemical cell is focusing on exploring the new materials and new mechanism with an aim to increase the photoelectric conversion efficiency. Ferroelectric materials have good ferroelectric, piezoelectric, pyroelectric and optical properties. Ferroelectric materials have spontaneous polarizations which can be flipped. Ferroelectric films form obvious depolarization field after poling, which can separate the photo-generated carriers. This character makes them to be one kind of candidates for photoelectrodes. In addition, widespread concerns were focused on semiconductors decorated with noble metals due to their excellent catalytic activity. Based on above background, we performed the following two works in this thesis:(1) The bimetallic Ag-Pt catalyst leads to the significant enhancement of photoelectrochemical activity for the Pb Ti O3 film photocathode deposited on ITO-coated quartz substrates. Ag particles contacting on Pb Ti O3 surface are used to enhance the visible utilization due to its surface plasmon resonance effect and the formation of the favorable energy level between Ag and Pb Ti O3 for efficient electron-extraction. The Pt which residues on the Ag particle surface prepared via galvanic replacement reaction has an excellent catalytic effect on the water reduction. Consequently, the photocurrent for the Pb Ti O3 photocathode enhanced significantly from 60 to 202 m A/cm2 under zero potential vs. saturated calomel electrode and 100 m W/cm2 Xe lamp illumination, and increased further to 234 m A/cm2 by poling the Pb Ti O3 film. The corresponding increase in energy conversion efficiency was from 0.06% to 0.13%.(2) On the basis of the first work, we chose the np+-Si photocathode as the research object. We found that its photoelectrochemical properties including the saturation current and the open circuit voltage can be improved greatly, due to the passivation of surface Al2O3 thin layer. In addition, we deposited Ag and Pt particles by electrodeposition method and Ag-Pt bimetallic particles by a galvanic replacement reaction, on the Al2O3-np+-Si photocathode surface. We found that the saturation current of the samples did not change significantly after the deposition of Ag, Ag-Pt and Pt nanoparticles, but the on-set potential increased obviously. The sample with Pt nanoparticles has the highest on-set potential which reaches 0.53 V vs. RHE. The energy conversion efficiency of this sample is up to 7.1%, which can be calculated from its photocurrent-potential data. We also give an explanation that the effect of Ag-Pt is not superior to pure Pt on improving the water splitting activity of Al2O3-np+-Si photocathode. |
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