Lin, Y.-G.Y.-G.LinHsu, Y.-K.Y.-K.HsuBasilio, A.M.A.M.BasilioChen, Y.-T.Y.-T.ChenChen, K.-H.K.-H.ChenYIT-TSONG CHEN2020-06-182020-06-18201410944087https://scholars.lib.ntu.edu.tw/handle/123456789/503240Hydrogen generation through direct photoelectrolysis of water was studied using photoelectrochemical cells made of different facets of free-standing polar GaN system. To build the fundamental understanding at the differences of surface photochemistry afforded by the GaN {0001} and {000 -1} polar surfaces, we correlated the relationship between the surface structure and photoelectrochemical performance on the different polar facets. The photoelectrochemical measurements clearly revealed that the Ga-polar surface had a more negative onset potential relative to the N-polar surface due to the much negative flat-band potential. At more positive applied voltages, however, the N-polar surface yielded much higher photocurrent with conversion efficiency of 0.61% compared to that of 0.55% by using the Ga-polar surface. The reason could be attributed to the variation in the band structure of the different polar facets via Mott- Schottky analyses. Based on this work, understanding the facet effect on photoelectrochemical activity can provide a blueprint for the design of materials in solar hydrogen applications. © 2013 Optical Society of America.[SDGs]SDG7Energy conversion; Gallium nitride; Hydrogen production; Solar power generation; Surface structure; Flat-band potentials; Hydrogen generations; Photoelectrochemical measurements; Photoelectrochemical performance; Photoelectrochemicals; Photoelectrolysis; Schottky analysis; Surface photochemistry; Applied voltages; Electrochemistryjournal article10.1364/OE.22.000A21