The Electrochemical Preparation Of Cuprous Oxide Film Which Is Applied In Photo-catalysis And Photo-voltaic Conversion

As a promising p-type semiconductor, cuprous oxide can be widely applied inphoto-catalysis and photo-voltaic conversion because its band structure is corresponding tothe wave length of visible light. However, the energy of visible light is low, so thephoto-generated electron-hole pairs in cuprous oxide can easily recombine, which resultsin the low quantum efficiency of cuprous oxide. Therefore, it’s of great significance toexplore the proper methods, as well as to investigate the interaction mechanism ofpreparation conditions, properties and performance of cuprous oxide.The quantum efficiency of cuprous oxide can be improved either by the energy barrierof cuprous oxide based heterojunction or by quantum confinement effect resulted bydecrement of crystallites size. So in this work cuprous oxide film was prepared viaelectrochemical methods, including anodization and electro-deposition. The technicalconditions in the preparation were investigated and the effect mechanism of which wasdiscussed. The properties of the as-prepared cuprous oxide film on photo-catalysis andphoto-voltaic conversion were studied.1. Cuprous oxide film was prepared with anodization+hydrolysis/reduction methods.The influences of technique parameters to the anodization, such as the pH value and theconcentration of electrolyte, the anodization current, the temperature and agitation werestudied. When copper was anodized in acidic solution, cuprous chloride film can form onthe surface of anode, which can be converted into cuprous oxide by hydrolysis of hydrogenperoxide solution under light illumination, the cuprous oxide film was porous andcomposing with nano crystallites. When copper was anodized in alkaline solution, copperhydroxide film can form on the anode, which can be converted into cuprous oxide bythermal reduction in reducing atmosphere or reacting with glucose solution. The kinetic and thermodynamic models of the electric double layer on the anode were established, themorphology and composition of the anode’s surface was characterized, and thecorresponding electrochemical data was analysed. According to these results, it was foundthat high pH value facilitate the formation of cupric hydroxide both kinetically andthermodynamically. By increasing the electrolyte concentration can also promote thegeneration of cupric hydroxide.2. The cuprous oxide films presented high catalytic activity, which was attributed tothe copper/cuprous oxide heterojunction. The photo-generated electron-hole pairs can beeffectively separated, and meanwhile the recombination of electron-hole pairs can beimpeded due to the inter electric field between copper substrate and cuprous oxide film.The cuprous oxide film can degrade methyl orange by60%~70%in90minutes, and thecuprous oxide film can also photo-catalytically accelerate the oxidized decolourization rateof organic dyes such as methylene blue. The photo-catalytic elimination of alga anddegradation of organic pollutants in river water sample by cuprous oxide film wascharacterized, the elimination rate of cyanophyta, chlorophyta and other alga were100%,100%and90.9%in4hours, and the degradation rate of total carbon, phosphorus andnitrogen in4hours were10.6%,55.4%and18.4%, respectively. The cuprous oxide filmalso presented high catalytic activity in the oxygen evolution reaction from water splitting,the evolved oxygen was172.90~233.27μmol per milligram of cuprous oxide. Theevolution of oxygen was resulted by the bending of band structure of cuprous oxide. Theremaining hydrogen cation resulted in the acidization of water. The film post-treated withhydrolysis reaction posessed the best catalytic activity per unit mass, which was attributedto the surface area and quantum confinement effect.3. By adding complexing agents in the electrolyte, the preferred orientation ofcrystallites of the electro-deposited cuprous oxide film on indium tin oxide conductingglass was controlled. Cuprous oxide film of cubic crystallite was prepared by addingEDTA-Na, and film of octahedral crystallites was prepared by adding lactic acid. Theeffect of complexing agents was discussed. It was found that the stability constant ofcopper-based complex compound can obviously influence the deposition potential ofcuprous oxide, and the potential can significantly alter the growth priority of differentplanes, which resulted in oriented growth of cuprous oxide grains. The quantitative relationships between the stability constant and the deposition potential of differentcomplexing agents, as well as the relationship between the potential and the formationenergy of microcrystalline cuprous oxide’s (110),(111) and (200) planes were calculated,respectively. The maximal output power of photovoltaic cell composed of cuprous oxidefilm of octahedral crystallites was2.37mW/cm2, while the maximal output power ofphotovoltaic cell composed of cubic crystallites was1.81mW/cm2. The octahedralcrystallites have more dangling bonds and intrinsic spot defects, which results in the higherquantum efficiency.4. Nano-crystalline cuprous oxide films were prepared by electro-deposition, withsurfactats micelles or vesicles as the templetes. The influence mechanism of surfactant tothe size of crystallites was investigated. The crystalline size of cuprous oxide film wasbetween20~50nm by adding sodium dodecyl sulfate or polyethylene glycol octylphenolether into the electrolyte. The photo-voltaic conversion property of the as-prepared cuprousoxide film was significantly improved because of the decreasing of crystalline size. Themaximal output power of photovoltaic cell composed of cuprous oxide film prepared byadding1.9g/L and3.6g/L of sodium dodecyl sulfate templetes reached3.88mW/cm2and3.94mW/cm2，respectively. The maximal output power of photovoltaic cell composed ofcuprous oxide film prepared by adding polyethylene glycol octylphenol ether vesicletemplate was10.64mW/cm2.The primary innovations in this work include:1. Anodization+hydrolysis/reduction methods were designed to prepare cuprousoxide film on Cu substrate. The cuprous oxide presented high photo-catalytic activity. Thecuprous oxide was applied as the photo-catalyst for the oxygen evolution reaction fromwater splitting under visible light, without any co-catalyst and sacrificial agent.2. The shape and size of electro-deposited cuprous oxide crystallite was controlled byadding complexing agents and surfactant micelle and vesicle templates. The as-preparednano-crystalline cuprous oxide film presented remarkable photo-voltaic property.