Browsing by Author "Hwang, Bing Joe"

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Creation of 3D Textured Graphene/Si Schottky Junction Photocathode for Enhanced Photo-Electrochemical Efficiency and Stability
(2019-08-01)
Ku, Che-Kuei
;
Wu, Po-Hsieh
;
Chung, Cheng-Chu
;
Chen, Chun-Chi
;
Tsai, Kaijie
This work presents a novel photo-electrochemical architecture based on the 3D pyramid-like graphene/p-Si Schottky junctions. Overcoming the conventional transfer technique by which only planar graphene/Si Schottky junctions are currently available, this work demonstrates the 3D pyramid-like graphene/p-Si Schottky junction photocathode, which greatly enhances light harvesting efficiency and exhibits promising photo-electrochemical performance for hydrogen generation. The formation of 3D pyramid-like graphene/p-Si Schottky junctions exhibits enhanced electrochemical activity and promotes charge separation efficiency compared with the bare pyramid Si surface without graphene. The inherent chemical inertness of graphene significantly improves the operational stability of 3D graphene/p-Si Schottky junction photo-electrochemical cells. The 3D pyramid-like graphene/p-Si Schottky junction photocathode delivers an onset potential of 0.41 V and a saturated photocurrent density of -32.5 mA cm(-2) at 0 V (vs RHE) with excellent stability comparable to values reported for textured or nanostructured p-Si photocathodes coated with ultrathin oxide layers by the conventional atomic layer deposition technique. These results suggest that the formation of graphene/Si Schottky junctions with a 3D architecture is a promising approach to improve the performance and durability of Si-based photo-electrochemical systems for water splitting or solar-to-fuel conversion.
New proton conducting membranes with high retention of protic ionic liquids
(2011)
Ye, Yun Sheng
;
Cheng, Ming Yao
;
Tseng, Ji Yong
;
Liang, Gao-Wei
;
Rick, John
New proton conducting membranes, exhibiting a high proton conductivity (10(-2) S cm(-1), without humidification at 160 degrees C), based on the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate (BMIm-BF(4)) were investigated. The incorporation of a similar initial IL loading was found to reduce the proton conductivity loss of a sulfonated polydiacetylene based membrane, i.e. SPDA70-IL70 by 19.2% and IL-based Nafion by 64.6%; additionally, the SPDA70-IL70 was able to maintain a proton conductivity of more than 10(-3) S cm(-1) after centrifugation. The introduction of both a cross-linked structure and a high degree of sulfonation into the polymer matrix, resulted in significant improvements to the membranes' thermal properties, the dispersion of ionic domains, and the retention of IL-together with a reduction of proton conductivity loss. The membranes, which have a high degree of sulfonation with thermally cross-linkable diacetylene in the polymer's main chain, avoid the drawback of poor miscibility commonly associated with sulfonated polymers and cross-linking agents. When the composite membrane was used in a H(2)/O(2) fuel cell without humidification at 100 degrees C, a power density > 250 mA cm(-2) was achieved together with a maximum current denisty of 122 mW cm(-2).
Synthesis and characterization of new sulfonated polytriazole proton exchange membrane by click reaction for direct methanol fuel cells (DMFCs)
(2011-11-01)
Huang, Yao Jheng
;
Ye, Yun Sheng
;
Yen, Ying Chieh
;
Tsai, Li Duan
;
Hwang, Bing Joe
Sulfonated polytriazole (SPTA) in which the acidic sulfonic acid and basic triazole groups act as physical crosslinking sites within a polymer backbone has been successfully prepared, for use as a proton exchange membrane, using the click reaction. The acid-base interactions of the SPTA membranes leads to the formation of well-dispersed ionic clusters and the random distribution of ion channels with good connectivity resulting in lower methanol permeabilities at ambient temperatures and similar or higher proton conductivities than Nafion 117 at 80 degrees C in conditions of near zero relative humidity. Proton conductivities (sigma) of 0.149 S cm(-1) at 80 degrees C and 9 x 10(-5) S cm(-1) in anhydrous conditions together with low methanol permeability (P) at 0.1 x 10(-6) cm(2) s(-1) that are comparable or superior to Nafion 117 (sigma(T=80) : 0.151 S cm(-1); sigma(RH=0) : 3 x 10(-5) S cm(-1); P(T=30): 1.31 x 10(-6) cm(2) s(-1)) were achieved. Additionally, the selectivity of SPTA is approximately four times higher than that of Nafion 117, thus it may have potential for use in direct methanol fuel cells (DMFCs). Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.