Abd Samad Nur Azimah, Lai Chin Wei, Lau Kung Shiuh, Abd Hamid Sharifah Bee
Nanotechnology & Catalysis Research Centre (NANOCAT), 3rd Floor, Block A, Institute of Postgraduate Studies (IPS), University of Malaya, 50603 Kuala Lumpur, Malaysia.
Materials (Basel). 2016 Nov 22;9(11):937. doi: 10.3390/ma9110937.
Efficient solar driven photoelectrochemical (PEC) response by enhancing charge separation has attracted great interest in the hydrogen generation application. The formation of one-dimensional ZnO nanorod structure without bundling is essential for high efficiency in PEC response. In this present research work, ZnO nanorod with an average 500 nm in length and average diameter of about 75 nm was successfully formed via electrodeposition method in 0.05 mM ZnCl₂ and 0.1 M KCl electrolyte at 1 V for 60 min under 70 °C condition. Continuous efforts have been exerted to further improve the solar driven PEC response by incorporating an optimum content of TiO₂ into ZnO nanorod using dip-coating technique. It was found that 0.25 at % of TiO₂ loaded on ZnO nanorod film demonstrated a maximum photocurrent density of 19.78 mA/cm² (with V vs. Ag/AgCl) under UV illumination and 14.75 mA/cm² (with V vs. Ag/AgCl) under solar illumination with photoconversion efficiency ~2.9% (UV illumination) and ~4.3% (solar illumination). This performance was approximately 3-4 times higher than ZnO film itself. An enhancement of photocurrent density and photoconversion efficiency occurred due to the sufficient Ti element within TiO₂-ZnO nanorod film, which acted as an effective mediator to trap the photo-induced electrons and minimize the recombination of charge carriers. Besides, phenomenon of charge-separation effect at type-II band alignment of Zn and Ti could further enhance the charge carrier transportation during illumination.
通过增强电荷分离实现高效的太阳能驱动光电化学（PEC）响应在制氢应用中引起了极大的关注。形成无束状的一维ZnO纳米棒结构对于PEC响应的高效率至关重要。在本研究工作中，通过电沉积法在70°C条件下于0.05 mM ZnCl₂和0.1 M KCl电解液中，以1 V电压沉积60分钟，成功制备了平均长度为500 nm、平均直径约为75 nm的ZnO纳米棒。通过浸涂技术将最佳含量的TiO₂掺入ZnO纳米棒中，不断努力进一步改善太阳能驱动的PEC响应。结果发现，负载在ZnO纳米棒薄膜上0.25 at%的TiO₂在紫外光照射下表现出最大光电流密度为19.78 mA/cm²（相对于Ag/AgCl），在太阳光照射下为14.75 mA/cm²（相对于Ag/AgCl），光转换效率约为2.9%（紫外光照射）和约4.3%（太阳光照射）。该性能比ZnO薄膜本身高出约3 - 4倍。由于TiO₂ - ZnO纳米棒薄膜中存在足够的Ti元素，其作为有效的介质捕获光生电子并使电荷载流子的复合最小化，从而实现了光电流密度和光转换效率的提高。此外，Zn和Ti的II型能带排列处的电荷分离效应现象可进一步增强光照期间的电荷载流子传输。
