在眾多半導體材料中，具備窄能隙(~1.1 eV)與適當傳導帶位置的矽，被視為光陰極產氫材料中的主力發展之對象。為了更進一步提升電子電洞對分離以及表面電催化能力，如何在半導體光電極表面以具電化學催化活性之共觸媒修飾，有效提升其氫氣產生速率，一直為此領域所關注之議題。
有鑑於此，本研究採用p型半導體矽作為光電極，引進石墨烯於其表面使建立石墨烯/p-型矽蕭基接面，進而提升其光電極之電子電洞對分離能力，同時可以減緩原生氧化層的增長；此外，本研究首度提出於石墨烯/p-型矽光電極表面，利用蕭基接面增益光沉積製程來合成鉑奈米粒子作為共觸媒，進而增加其產氫速率。相較於一般光沉積製程，從光學電子顯微鏡與感應耦合電漿原子發射光譜分析結果，顯示蕭基接面增益光沉積製程能在相同反應條件下達到更高的鉑沉積量，表示石墨烯/p-型矽蕭基接面能有效提升電子電洞對快速分離以避免其再結合。利用光沉積還原機制，可合理推論蕭基接面增益光沉積製程所合成之鉑奈米粒子，能精準沉積在光電子最佳傳遞路徑之活性位置，並進一步抑制光電子再結合的可能，達到提升整體產氫反應速率。本研究中亦利用蕭基接面增益光沉積對光源強度之依存性，藉由調控光源強度、光照時間及溶液濃度等參數去調控鉑奈米粒子之尺寸、含量以及覆蓋率，並結合掃描電子顯微鏡、感應耦合電漿原子發射光譜、線性掃描伏安法以及電化學阻抗分析等分析技術，製備可應用於在光催化水分解的高效能鉑奈米粒子修飾石墨烯/p-型矽蕭基接面平台。本研究實驗結果顯示出在標準太陽光模擬器(AM 1.5 & 100 mW/cm2)條件照射下，在以光沉積法製備鉑奈米粒子修飾石墨烯/p-型矽蕭基接面光電極於水溶液系統(pH=0)下，起始電位可正偏移至0.27 V，並於0 V (vs. RHE)之光電流可達19.08 mA/cm2，高於在相同條件下無光電流產生之純矽元件以及使用含浸法所製備之鉑奈米粒子系統(0.417 mA/cm2)，且具有120小時之穩定度。本研究提出一種蕭基接面增益光沉積製程，並成功應用在製備高效能水分解光觸媒電極。

Photoelectrochemical (PEC) water splitting is a promising method to directly convert solar energy into hydrogen generation without any carbon emission and air pollution. With its narrow band gap and suitable conduction band position, silicon has been considered as one of the most ideal photocathodes among the numerous semiconductor materials.
Herein, in this work, graphene and silicon were delicately assembled to form the Schottky junction based device. It can not only separate the charge carriers rapidly but also inhibit the growth of silicon native oxide. In addition, Pt nanoparticles (Pt NPs) were selectively photodeposited to modify the graphene/p-Si electrode by Schottky junction. Through the Auger Electron Spectroscopy, it is noticeable that the Pt NPs decorated by photodeposition method were inclined to be reduced on the graphene/p-Si side, instead of bare p-Si. It shows Pt NPs could be more efficiently reduced on the active sites of electrocatalysis, which are also the same sites for catalyzing the hydrogen evolution reaction under illumination. Meanwhile, particle sizes, loading, and distribution of co-catalyst can be easily and precisely controlled by Schottky junction enhanced photodeposition. The results were analyzed by SEM, ICP-AES, LSV and EIS to confirm the optimal parameters. Also, the bare silicon device showed no photo-response under 1 Sun simulation at 0 V(vs. RHE), but the photocurrent density of Pt NPs decorated graphene/p-Si device increased to 19.08 mA/cm2. The onset potential positively shifted to 0.27 V and the stability remained for 120 hours. The performance of the device has surpassed the values from devices of bare silicon or with Pt co-catalysts decorated by impregnation method. These results provide an evidence to support that the photo-induced charge separation of p-Si could be enhanced by introducing the graphene/p-Si Schottky junction.

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