化石燃料的使用導致了日益嚴重的全球溫室效應，危害性氣體副產物的劇增也造就了許多新興疾病與傷害，同時因消耗速度遠超行成所需時間所帶來的能源危機隱患不允許我們滿足於現況，前述種種使的新的綠色能源與配套能源應用技術的開發迫在眉睫。氫氣因無汙染性、易獲取性、豐富性、高燃燒熱、可持續性與可再生成為了優異的綠色能源並已廣泛應用，也因此氫氣感測器之研究也成為熱門研究主題。
二氧化鈦因獨特的電學、光學、催化和氣敏特性，具有無毒、低成本和惡劣環境下高穩定性等優點成為較有潛力的氫氣感測材料候選者，而透過還原退火製程對其進行能帶隙調節，將之轉變成能帶隙較小且具備更優異載流子特性、電性能和光學性能之黑色二氧化鈦為提升其氣體感測性能有效且熱門的方針，不僅如此，本研究亦結合陣列化製程技術，透過提升感氣層之比表面積近一步提升所開發之元件的響應性能，並且透過一氧化碳大氣還原退火技術有效規避了當前黑色二氧化鈦最主流之製備方法氫化法所面臨的設備侷限以及實驗安全性隱患。
本研究成功透過一氧化碳大氣還原退火技術製備了具優秀載流子特性、電性能和光學性能之黑色二氧化鈦，並達到提升室溫二氧化鈦氫氣感測器響應能力之實驗目的，由旋塗法製備得到之薄膜狀感氣層黑色二氧化鈦感測器(Sp-750℃)相比由相同製程得之白色二氧化鈦感測器(Sp-W-TiO2)有著顯著的性能提升，由2%提升至304%，並具備優異的靈敏度、應答時間、恢復時間、選擇性和穩定性；隨後本團隊近一步透過陣列化技術對感氣材料之比表面積以及電性能進行優化，並成功提升元件之效能，由水熱法製備得到之黑色二氧化鈦陣列感測器(Hy-750℃)具備傑出的1050%響應值，相比相同製程得到之白色二氧化鈦陣列感測器(Hy-W-TiO2)僅具備25%之響應值，Hy-750℃亦具備優異的靈敏度、應答時間、恢復時間、選擇性和穩定性。

Nowadays, environmental pollution and energy crisis are the major problems challenging our world. Hydrogen (H2), is renewable and free of carbon emission, which can play crucial role in securing energy and reducing greenhouse effect. H2 having 120 MJ/Kg energy density that is three times that of diesel or gasoline is a promising next generation green energy source. The use of H2 as energy source can also overcome air pollution and depletion of fossil fuels issues. Nevertheless, H2 is flammable and highly explosive when its concentration greater than 4% that needs great attention in storing large amount of H2 gas. Therefore, quick detection of H2 leakage at ultralow concentration is very important. Hence, development of H2 gas sensor is mandatory.
Titanium dioxide (TiO2) is one kind of metal oxides semiconductor having wide bandgap that is being applied various areas such photocatalysis, solar cells, lithium-ion battery, gas sensors, and photodetectors due to its chemical stability, eco-friendliness, structural, optical and transportation properties. Various types of TiO2 based gas sensor have been developed and exhibited excellent gas sensing performance toward different gases. However, their practical applicability suffers from one or more of the following limitation: high working temperature, low selectivity, slow response, stability and reproducibility. Therefore, looking for strategy that overcome the abovementioned limitations is necessary.
Recently, black TiO2 has got huge consideration in different fields such as CO2 reduction, water evaporation, organic pollutant treatment and water splitting due to its high oxygen vacancy. However, there is no study reported on gas sensing property of black TiO2 to date. Therefore, development of black TiO2 based gas sensor that having excellent sensing performance is important.
Hence, in this work, black TiO2 nanoforest based H2 gas sensor was synthesized by simple and facile spin coating method for the first time. The synthesized sample was systematically characterized. The H2 gas sensing property of the developed black TiO2 nanoforest based sensor was investigated at room temperature. Its practical applications were evaluated in terms of selectivity, cyclic and long-term stability. The findings showed that the developed sensor possesses outstanding hydrogen sensing property (304%). Besides, it exhibited excellent selectivity, cyclic and long-term stability that are crucial for real applications sensor. Moreover, the developed sensor presented almost the same sensor response in wide range of relative humidity confirming its promising candidacy to be used real application of H2 gas detection and monitoring in environmental remediation.
Nevertheless, we are not satisfied with its sensitivity. Thus, we proposed a strategy to overcome this issue. Different researchers have found out that controlling morphology directionally growing them can improve their properties for various applications. Accordingly, black TiO2 nanoforest was synthesized by simple and facile hydrothermal method for the first time. Its H2 gas sensing property was investigated at room temperature. The applicability of the sensor in real life was also studied. The results revealed that the fabricated black TiO2 nanoforest based sensor exhibits outstanding H2 gas sensing performance of 1050% sensor response toward 500 ppm H2 gas. Besides, it also presented excellent selectivity, cyclic and long term stability that are very crucial for real applications. Moreover, the developed sensor showed similar H2 gas sensing performance in wide range of environmental conditions that confirms its candidacy practical application of H2 gas monitoring. Therefore, this study paves way in development of black TiO2 nanoforest based sensors by easy, cost-efficient and facile method that could play significant role various areas of environmental remediation.

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