TiO $_2$薄层对水中III-V纳米线断裂的鲁棒保护
Robust Protection of III-V Nanowires in Water Splitting by a Thin Compact TiO$_2$ Layer
摘要：
具有合适能带结构和强陷光能力的窄带隙III-V族半导体纳米线（NWs）是高效低成本太阳能水分解系统的理想材料。然而，由于它们的纳米尺寸，它们比薄膜对应物遭受更严重的电解质溶液腐蚀。因此，短期耐久性是将这些NW用于实际水裂解应用的主要障碍。在这里，我们首次证明了通过原子层沉积法沉积的致密TiO $_2$薄层（约7 nm厚）可以为III-V族纳米线提供强大的保护。在大气环境中储存14个月后，被保护的GaAs纳米线保持其光致发光强度的91.4%，这表明TiO $_2$层是无针孔的。作为水裂解的光电阴极，它们表现出比未保护的光电阴极高45%的光电流密度和高达91%的法拉第效率，并且在窄带隙III-V NW光电极中保持了创纪录的高稳定性能;在强酸电解质溶液（pH = 1）中进行67小时的光电化学稳定性测试反应后，它们没有显示出明显的腐蚀迹象，这与35小时后完全失效的未受保护的NW形成鲜明对比。这些发现提供了一种有效的方法来提高III-V NW基光电极的稳定性和性能，这对于基于太阳能的水裂解系统中的实际应用非常重要。
英文摘要：
Narrow-bandgap III-V semiconductor nanowires (NWs) with a suitable band structure and strong light-trapping ability are ideal for high-efficiency low-cost solar water-splitting systems. However, due to their nanoscale dimension, they suffer more severe corrosion by the electrolyte solution than the thin-film counterparts. Thus, short-term durability is the major obstacle for using these NWs for practical water splitting applications. Here, we demonstrated for the first time that a thin layer (~7 nm thick) of compact TiO$_2$ deposited by atomic layer deposition can provide robust protection to III-V NWs. The protected GaAs NWs maintain 91.4% of its photoluminescence intensity after 14 months of storage in ambient atmosphere, which suggests the TiO$_2$ layer is pinhole-free. Working as a photocathode for water splitting, they exhibited a 45% larger photocurrent density compared with un-protected counterparts and a high Faraday efficiency of 91%, and can also maintain a record-long highly-stable performance among narrow-bandgap III-V NW photoelectrodes; after 67 hours photoelectrochemical stability test reaction in strong acid electrolyte solution (pH = 1), they show no apparent indication of corrosion, which is in stark contrast to the un-protected NWs that are fully failed after 35-hours. These findings provide an effective way to enhance both stability and performance of III-V NW based photoelectrodes, which are highly important for practical applications in solar-energy-based water splitting systems.
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