本研究使用氮化鎵薄膜系列半導體作為工作電極應用於光電化學系統裂解水產氫氣與還原甲酸，氮化鎵薄膜系列半導體普遍被認定為具有穩定的化學特性且具有良好的抗腐蝕能力，且氮化鎵薄膜系列工作電極能帶跨越水的氧化還原電位與二氧化碳的還原電位，因此在選擇特定的對電極下，氮化鎵薄膜系列工作電極能夠同時藉由電解水產生氫氣、氧氣與甲酸等產物，因此本論文進一步使用氮化鋁鎵薄膜成長在氮化鎵上，形成一個具有高載子遷移率的異質結構元件作為工作電極，改善未摻雜之氮化鎵半導體作為工作電極光電流不足的缺點。
首先，為了探討海水作為電解液於光電化學系統中的影響性，我們分別利用四種不同濃度的水與1莫爾濃度食鹽水溶液作為電解液，使用本實驗室目前最熟悉且最穩定的n型氮化鎵作為工作電極，分別以全新的試片於五種電解液下電解；經由實驗發現，四種濃度之海水電解液中最穩定且光電流最高者為濃度58.50‰的2.90mA/cm2，但是若
與將工作電極置於去離子水配置的1.00M食鹽水溶液相比，其光電流相差了4.97mA/cm2，此結果顯示將工作電極至於食鹽水溶液中比較有利於離子的傳輸。
為了改善工作電極置於海水中光電流過低的問題，我們藉由質子交換膜將工作電極與對電極之電解液區隔之方式，將工作電極的電解液替換成1.00M食鹽水溶液，且對電極電解液同時改變為純海水、1.00M氯化鈉鹽度之海水與1.50M氯化鈉鹽度之海水，藉由將工作電極置於相對較少雜質之1.00M食鹽水溶液進而提升光電流大小的同時，於對電極使用不同濃度的海水，同時探討金屬錫片裸露在不同濃度海水電解液下產生氫氣與甲酸產量的比較；結果證明，由於高濃度的海水對於二氧化碳的溶解度較低，使高濃度海水較利於產氫氣，另外相對低濃度的純海水，由於其對於二氧化碳的溶解度較高，使甲酸產量較多，同時降低了氫氣的產量。
另外我們將工作電極分別置入氮化鋁鎵/氮化鎵異質結構與u型氮化鎵，由長時間電壓時間曲線、IPCE與實驗後工作電極表面形貌得知，雖然氮化鋁鎵/氮化鎵異質結構具有二維度電子氣之特性，但是其在光電化學實驗初始受限於表層薄膜氮化鋁鎵吸光波段為325nm以內，導致光電流低於參考試片u型氮化鎵，然而經由光生電洞的光蝕刻後，氮化鋁鎵/氮化鎵的氮化鋁鎵薄膜由於只有18nm導致大部分皆被蝕刻，但是相對粗糙的蝕刻表面與液面上工作電極尚保留的2DEG使氮化鋁鎵/氮化鎵的光電流提升。
最後我們模擬了將太陽能電池串接於工作電極上，成功的利用多晶矽太陽能電池產生的1.16V偏壓於光陽極，將氮化鋁鎵/氮化鎵異質結構的平均光電流大小從未偏壓的1.35mA/cm2提升至6.19 mA/cm2，u型氮化鎵則為從未偏壓的1.05 mA/cm2提升至5.00 mA/cm2。

In this study, we explored the effects of gallium nitride(GaN)-based film semiconductor as the photoelectodes to generate hydrogen and facilitate reduction carbon dioxide to formic acid in electrolytes of sodium chloride solution and seawater. First, in order to investigate the effects of different concentration seawater as the electrolytes, we used N-type GaN as the photoanode, which is provided with stability, and chaged the different concentration seawater into 17.23 salt ppt, 33.87 salt ppt (pure), 58.50 salt ppt, 87.40 salt ppt, and 1M sodium chloride solution as the electrolytes. The results indicated that the highest photocurrent in four different concentrations seawater is 58.50 salt ppt with 2.13 mA/〖cm〗^2. However, the photocurrent (7.10 mA/〖cm〗^2) of 1M sodium chloride solution of electrolyte was much higher than the electrolyte of seawater was found when took the sodium chloride solution to consideration. Second, in order to improve the low photocurrent in electrolyte of seawater, we changed the electrolyte in the photoanode side to 1M sodium chloride solution and maintained the counter electrode electrolyte as the different concentration seawater by the advantage of nafion. Furthermore, we used the AlGaN/GaN heterostructure and GaN, which was processed by ICP, as the photoanode. The results indicated that putting the counter electrode in different concentration seawater, PEC system can product less formic acid in higher concentration seawater and result in more hydrogen generation. Moreover, the AlGaN/GaN heterostructure as the photoanode could enhance the photocurrent by the layer of 18 nm AlGaN and 2DEG in compare with u-GaN(ICP). In the end, we took the solar cell as the power supplier rather than the Potentiostat. In the situation of the AlGaN/GaN heterostructure and u-GaN(ICP) as the photoanode, we successfully enhanced the photocurrent from 1.35 mA/〖cm〗^2 and 1.05 mA/〖cm〗^2 to 6.19 mA/〖cm〗^2 and 5.00 mA/〖cm〗^2 in contribution to the additional bias of solar cell.

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