Kay Andreas, Cesar Ilkay, Grätzel Michael
Institut des sciences et ingénierie chimiques, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland.
J Am Chem Soc. 2006 Dec 13;128(49):15714-21. doi: 10.1021/ja064380l.
Thin films of silicon-doped Fe2O3 were deposited by APCVD (atmospheric pressure chemical vapor deposition) from Fe(CO)5 and TEOS (tetraethoxysilane) on SnO2-coated glass at 415 degrees C. HRSEM reveals a highly developed dendritic nanostructure of 500 nm thickness having a feature size of only 10-20 nm at the surface. Real surface area determination by dye adsorption yields a roughness factor of 21. XRD shows the films to be pure hematite with strong preferential orientation of the [110] axis vertical to the substrate, induced by silicon doping. Under illumination in 1 M NaOH, water is oxidized at the Fe2O3 electrode with higher efficiency (IPCE = 42% at 370 nm and 2.2 mA/cm2 in AM 1.5 G sunlight of 1000 W/m2 at 1.23 VRHE) than at the best reported single crystalline Fe2O3 electrodes. This unprecedented efficiency is in part attributed to the dendritic nanostructure which minimizes the distance photogenerated holes have to diffuse to reach the Fe2O3/electrolyte interface while still allowing efficient light absorption. Part of the gain in efficiency is obtained by depositing a thin insulating SiO2 interfacial layer between the SnO2 substrate and the Fe2O3 film and a catalytic cobalt monolayer on the Fe2O3 surface. A mechanistic model for water photooxidation is presented, involving stepwise accumulation of four holes by two vicinal iron or cobalt surface sites.
通过常压化学气相沉积（APCVD），在415摄氏度下，以五羰基铁（Fe(CO)5）和四乙氧基硅烷（TEOS）为原料，在涂有SnO2的玻璃上沉积了硅掺杂的Fe2O3薄膜。高分辨率扫描电子显微镜（HRSEM）显示，薄膜具有高度发达的树枝状纳米结构，厚度为500纳米，表面特征尺寸仅为10 - 20纳米。通过染料吸附测定实际表面积，粗糙度因子为21。X射线衍射（XRD）表明，薄膜为纯赤铁矿，由于硅掺杂，[110]轴垂直于基底具有强烈的择优取向。在1 M NaOH溶液中光照下，Fe2O3电极上水的氧化效率（在370纳米处的入射光电流转换效率（IPCE）= 42%，在1.23 VRHE下1000 W/m2的AM 1.5 G太阳光中为2.2 mA/cm2）高于报道的最佳单晶Fe2O3电极。这种前所未有的效率部分归因于树枝状纳米结构，它使光生空穴扩散到Fe2O3/电解质界面的距离最小化，同时仍能实现高效的光吸收。通过在SnO2基底和Fe2O3薄膜之间沉积一层薄的绝缘SiO2界面层以及在Fe2O3表面沉积一层催化钴单层，可获得部分效率提升。本文提出了一个水光氧化的机理模型，涉及两个相邻的铁或钴表面位点逐步积累四个空穴。
