Hydrogen Generation from Water Splitting on Non-polar GaN Surface

• Main Author: 張正明
• Other Authors: 蔡明剛
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/47266877593901418827

碩士 === 國立臺灣師範大學 === 化學系 === 101 === A theoretical study is carried out to investigate hydrogen generation on non-polar GaN surface through water molecules decomposition. The various catalytic pathways are explored and the corresponding reaction barriers are calculated. Co-catalysts, Pt and Rh, are also taken into account in the computational models in order to understand the subsequent effect in hydrogen molecule formation and catalytic reaction barriers resulted from the presence of metal elements. The theoretical insights collected through the analysis on both transition metal elements could be helpful for the further co-catalyst development. Two types of models for the description of co-catalyst are introduced in the current study. The first model is metal atoms being physically absorbed on surface while the other one is embedding the metal atoms in the vacant sites of GaN materials. The catalytic mechanisms of Pt and Rh were also different. Hydrogen atom favored to bond with Pt with the additional hydrogen atom interacting with PtH intermediate. Rh element played more significant role of catalyzing the H-H bond formation especially the embedded Rh was found to have a lowest reaction barrier. However, the current study could not clarify if the bottleneck step happens at a thermodynamic step or kinetic step. The first barrier of splitting water is 0.042eV however the second barrier is quite high as more than 6 eV. The direct generation of breaking water into H2 and O2 is inaccessible without the external assistance, e.g. photon or applied voltage. Interestedly, the coupling of two OH radicals absorbed on the surface may lead to the formation O-O bond and formed HOOH. The breaking HO bond in HOOH may be another potential pathway for the source of H atoms.