Preparation Of Au Modified Oxidizing Material And Their Photoelectrochemistry Water Splitting

Solar induced water splitting has been regarded as one of the most attractive routes in view of the abundant and renewable nature of solar and water resources. Photoelectrochemical cell(PEC) is a kind of photoelectrochemical devices which convert solar energy directly into chemical energy and storage using the semiconductor and the electrolyte. And which has some advantages such as the convenient preparation technology, environmentally friendly and low cost. Composition and structure of photoelectrode affect the light absorption, the utilization of electronic collection and transmission, which decided the photoelectrochemical properties of the PEC. Therefore, improving the photoelectrochemical properties of photoelectrodes is the key to improve the efficiency light conversion factors of PEC. The surface plasmon resonance(SPR) effect of noble metal can expand the response range of incident light, increase of absorption of the incident, increase light electron in the electrode of light transmission rate, prolong the life of electronic, and inhibit photoproduction electronic-hole composite, etc. In this paper, Au decorated oxide photoanodes were prepared, and the absorption of visible light was enhanced and the combination of photogenerated electron-holes was suppressed. Therefore, the activity of photoelectrode was improved.The main researchs contents are as follows:(1) WO3 nanoparticles with diameter around 100 nm were synthesised via hydrothermal method, and the WO3 film used as photoanode substrate was prepared via a blade coating process. Au nanoparticles sol prepared by NaBH4 reduction of HAuCl4, was modified onto WO3 photoanode surface through drop-coating. According to experimental result, when content of Au reached 0.34 at %, the photocurrent density was 0.44 mA·cm-2 at 1.0 V vs Ag/AgCl as much as 3.7 times of WO3 photoanode(0.12 mA·cm-2 at 1.0 V vs Ag/AgCl). Au modified photoanode could remarkably increase photoelectrichemical properties because of the SPR of Au nanoparticles through improving absorption of visible light, increasing photogenerated carriers density, improving electron transport rate and promoting separation of photogenerated electronic-hole on the surface.(2) WO3 nanorod array was fabricated on the conductive surface of FTO via one-step hydrothermal process. The influence of different volume ratio of ethanol to water onWO3 thin film morphology was also studied According to experimental result, water can help to fabricate WO3 nanorod, while ethanol can help to grow WO3 nanorod directly on FTO. When the volume ratio of ethanol to water was 5:5, and the calcination temperature is 500 oC, WO3 thin film exhibited the best photoelectrichemical properties. Different content of Au nanoparticle modified WO3 nanorod was fabricated via photoreduction method, the photocurrent density of Au/WO3-2 photoanode reached 1.24 mA·cm-2 at 1.0 V vs Ag/AgCl, which was as much as 71% improvement of WO3 nanorod photoanode(0.726 mA·cm-2 at 1.0 V vs Ag/AgCl). Because the SPR effect of Au nanoparticles can expand the light absorption area to the visible region, enhance absorption of visible light, improve electron transport rate, promote separation of photogenerated electronic-hole and improve photoelectric conversion efficiency. The SPR of Au nanoparticles can also reduce the Fermi level, which can accelearate the kinetic of redox reaction. Au modified WO3 photoanodes have photoelectric response at 0 V vs Ag/AgCl, while WO3 has photoelectric response until 0.4 V, and this was proved by calculating the potential of flat belt through Mott-Schottky.(3) ZnO nanorod array(ZNR) growth on FTO was prepared via chemical bath method and then modified by Au nanoparticles to form Au-ZnO nanorod photoanode(ZNRA). Further studies show the load of Au nanoparticles could influence the water splitting performance of ZNRA. As the load of Au nanoparticles increased from 0 at % to 2.6 at %, the photocurrent density is 0.24 mA·cm-2(1.0 V vs Ag/AgCl), which is around 4 times of bare ZNR(0.065 mA·cm-2 at 1.0 V vs Ag/AgCl). When the load of Au nanoparticles increased further, it may form more recombination centers on the interface between Au nanoparticles and ZnO nanorod, which would be the recombination center of photogenerated electronic-holes, and then lead to the detriorate of the photoelectrochemical properties. At the same time, the more load of Au, the higher stability of the photoanode, which due to the light fastness of Au nanoparticles.