New benchmark for water photooxidation by nanostructured α-Fe2O3 films
New benchmark for water photooxidation by nanostructured α-Fe2O3 films
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DOI：
10.1021/ja064380l
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发表时间：
2006-12-13
影响因子：
15
通讯作者：
Graetzel, Michael
中科院分区：
文献类型：
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作者：
Kay, Andreas;Cesar, Ilkay;Graetzel, Michael
通过APCVD（大气压化学气相沉积）由Fe（CO）（5）和TEOS（四乙氧基硅烷）在415 ℃下在SnO 2涂覆的玻璃上沉积硅掺杂的Fe 2 O3薄膜。HRSEM揭示了一个高度发达的树枝状纳米结构的500 nm的厚度，在表面上的特征尺寸只有1020 nm。通过染料吸附测定的真实的表面积得到粗糙度因子为21。X射线衍射分析表明，薄膜为纯赤铁矿，具有垂直于衬底的[110]轴的强择优取向，这是由硅掺杂引起的。在1 M NaOH中的照射下，水在Fe 2 O3电极处的氧化效率（在1.23 V-RHE下在1000 W/m（2）的AM 1.5 G阳光下在370 nm和2.2 mA/cm（2）下的IPCE = 42%）高于最佳报道的单晶Fe 2 O3电极。这种前所未有的效率部分归因于树枝状纳米结构，其最小化了光生空穴必须扩散以到达Fe 2 O3/电解质界面的距离，同时仍然允许有效的光吸收。部分的效率增益是通过在SnO 2衬底和Fe 2 O3膜之间沉积薄的绝缘SiO2界面层和在Fe 2 O3表面上的催化钴单层而获得的。提出了一个水光氧化的机理模型，涉及由两个相邻的铁或钴表面位点逐步积累四个空穴。
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 1020 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/cm(2) in AM 1.5 G sunlight of 1000 W/m(2) at 1.23 V-RHE) 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.