| Energy crisis and environmental pollution are two challenges that limiting thesustainable development of human society and economy in the21st century. To addressthese challenges, developing new clean energy technologies have become a broadconsensus in today’s world. Since the semiconductor photocatalytic technology capableof capturing abundant solar energy for producing clean energy，which has beenconsidered to be one of possible solutions to counter energy crisis and environmentalpollution. With continued investment in photocatalysis in recent decades, photocatalysisresearch (such as photocatalytic water splitting, photocatalytic degradation of pollutants)has attracted considerable attention, and this research field has gradually developed intoan interdiscipline that involving chemistry, physics, materials, environmental and otherrelated disciplines. For developing practical photocatalytic technology, the presentphotocatalysis research has focused on several directions, such as exploration ofphotocatalytic mechanism, development of new photocatalysts and combination ofphotocatalytic technology and other energy technology.On the basis of new trends of photocatalysis research, the object of the dissertationis to develop photocatalysts for capturing solar energy and investigate theirphotoelectrocatalytic activities for exploring the potential application value in newenergy field. In the dissertation, we have synthesized several kinds of nanostructuredTiO2-based, WO3-based and BiVO4-based photocatalysts via electrochemical deposition,solvothermal technique and drop-casting method, and systematically investigated theirphotoelectrocatalytic activities．In general, the main content of this dissertation includestwo parts:(1) By combining the photocatalytic mechanism of semiconductors with theelectrocatalytic mechanism of anode catalysts in diret methanol fuel cell (DMFC), wechosen TiO2nanotubes array (TiO2NTs) as Ni nanoparticles, Pt nanoparticles and PtNialloy nanoparticles support material for methanol oxidation. After systematicallyinvestigated the electrocatalytic and photoelectrocatalytic activities of Ni/TiO2NTs,Pt/TiO2NTs, PtNi/TiO2NTs and PtNi/C-TiO2NTs, a new kind of fuel cellconcept-photo-assisted diret methanol fuel cell was propound based on the obtainedresults;(2) To develop photoanodes for water oxidation, nanostructured WO3andBiVO4films were respectively synthesized on FTO glass substrates by solvothermaltechnique and drop-casting method. In addition, Bi2S3/WO3heterojunction film and W and Mo doped BiVO4film were synthesized in present work to improve thephotoelectrochemical activities of obtained WO3and BiVO4films. The main results areas follows：①The TiO2nanotubes prepared via electrochemical anodic oxidation have wellordered array-structure and large specific surface area, which could provide not onlyabundant penetrated channel for metal ions depositing but also large space for methanoloxidation reactions. Thus, TiO2NTs are suitable for supporting anode catalysts in diretmethanol fuel cell. In addition, it is found that the morphology and structure ofTiO2NTs are unchanged after carbon doping, but the carbon doped TiO2NTs(C-TiO2NTs) have better conductivity and stronger catalyst-support interaction, whichare advantageous for supporting catalysts. After pulse electrodepositing, evenlydispersed Ni nanoparticles, Pt nanoparticles and PtNi alloy nanoparticles withappropriate size were respectively deposited on TiO2NTs or C-TiO2NTs to formNi/TiO2NTs, Pt/TiO2NTs, PtNi/TiO2NTs, PtNi/C-TiO2NTs composite catalysts.②At certain potential, the Ni nanoparticles of Ni/TiO2NTs can be converted intoNiOOH, which are active for methanol oxidation reactions. Compared to the catalyticperformance without illumination, Ni/TiO2NTs show enhanced catalytic activity andstability for methanol oxidation under illumination, which can be attributed to theinteraction of electro-catalysis and photo-catalysis of Ni/TiO2NTs composite catalysts.Meanwhile, when Ni(OH)2formed in the composite at certain potential, p-n junctionsare formed at the interface between Ni(OH)2and TiO2NTs, which may accelerate andimprove the oxidation rates of methanol and CO-like intermediates.③Since Pt incorporating Ni to form PtNi alloy can produce more abundantoxygen-donating species OHadsto oxidate methanol and the intermediates,PtNi/TiO2NTs have higher catalytic activity compared with Pt/TiO2NTs for methanoloxidation. Photoelectrochemical measurements show that Pt/TiO2NTs andPtNi/TiO2NTs both have higher catalytic activity and stability for methanol oxidationunder illumination due to the photo-assisting functions. In addition, it reveals that PtNialloy nanoparticles supported on C-TiO2NTs have higher catalytic performance thanthat supported on TiO2NTs, which was primarily ascribed to carbon doped TiO2NTs(C-TiO2NTs) have better conductivity and stronger catalyst-support interaction.④Based on the photoelectrochemical performances of Ni/TiO2NTs, Pt/TiO2NTs,PtNi/TiO2NTs and PtNi/C-TiO2NTs, a new kind of fuel cell concept─photo-assisteddiret methanol fuel cell (PDMFC) was propound in present work. In the PDMFC, the solar light serves as assistant energy to accelerate the oxidation of rates of methanol andintermediates. Thus, both solar energy and methanol chemical energy could be finallyconverted into electric energy in the PDMFC.⑤Different nanostructured WO3films were synthesized on FTO glass substrateusing a solvothermal method with diffrerent volume ratios of water to ethanol. TheWO3nanoprism arrays film with thickness of2μm, was synthesized atVwater:Vethanol=3:3showed the better photoelectrochemical activity than the sheetlikestructures produced using other Vwater:Vethanol. To improve the photoelectrochemicalactivity of WO3nanoprism arrays film, Bi2S3/WO3heterojunction films were designedby coupling WO3films with varying amounts of urchin-like Bi2S3nanospheres. Aftercoating a single layer of Bi2S3on top of the WO3film, the resulting Bi2S3/WO3heterojunction film showed enhanced photoelectrochemical activity. In presen work, theoptimal number of Bi2S3layers for coupling with the WO3film was found to be3layers(the nominal thickness of the Bi2S3layer was estimated to be approximately3μm),which had the highest photocurrent density and IPCE values. The origin of enhancedphotoelectrochemical activity of the Bi2S3/WO3heterojunction film was primarilyascribed to the band potential matching between WO3and Bi2S3, which is advantageousfor charge separation.(6) Nanostructured BiVO4films were synthesized on FTO glass substrate using asimple drop-casting method. Synthesis parameters such as the amount of polyethyleneglycol600(PEG-600) and the precursor solution drying time are investigated tooptimize the morphology and structure of films for photoelectrochemical wateroxidation. The BiVO4films consisting of nanoflakes with an average thickness of20nm and length of2μm were synthesized from a precursor solution containing Bi3+, V3+and PEG-600with a Bi: V: PEG-600volume ratio of2:2:1, dried at135°C for55min.Photoelectrochemical measurements show that the BiVO4nanoflake array films havehigher photoelectrochemical activity than the BiVO4nanoparticle films. Additionally,the nanoflake arrays were tested after incorporating W and Mo to enhance thephotoelectrochemical activity. The2%W,6%Mo co-doped BiVO4nanoflake array filmsdemonstrate the best photoelectrochemical activity with photocurrent densities about2times higher than the un-doped BiVO4nanoflake films and greater than thephotocurrents of individually Mo doped or W doped BiVO4films. The origin ofenhanced photoelectrochemical activity for the co-doped film may be due to theimproved conductivity through the BiVO4or slightly enhanced water oxidation kinetics. The study in the dissertation could provide some references to develop efficientand new photocatalytic materials, and inspire relative research fields to explore newtheory and direction．... |
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