Browsing by Author "Chang, Sun-Tang"

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On the Reduction of O-2 on Cathode Surfaces of Co-Corrin and Co-Porphyrin: A Computational and Experimental Study on Their Relative Efficiencies in H2O/H2O2 Formation
(2020-02-27)
Huang, Wen-Fei
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Chang, Sun-Tang
;
Huang, Hsin-Chih
;
Wang, Chen-Hao
;
Chen, Li-Chyong
The mechanisms for O-2 reduction and H2P/H2O2 formation on Co-corrin and Co-porphyrin cathode surfaces of the proton exchange membrane fuel cell (PEMFC) systems have been studied by hybrid Hartree-Fock/density functional theory (B3LYP) calculations with the LANL2DZ basis set. The calculations show that the reduced Co-corrin with a single negative charge (Co-corrin(-)) is more reactive than the neutral Co-corrin and the doubly charged Co-corrin(2-). Both O-2 and O adsorptions are most stable on Co-corrin(-), rather than Co-corrin or Co-corrin(2-). The potential energy profiles show that the decomposition of O-2 on both Co-corrin and Co-corrin(-) can take place energetically favorably without thermal activation. The formation of H2O and H2O2 are predicted to occur by two separate reaction paths: the HO path and the HOO path. The HO path with H2O as the predominant product on the reduced Co-corrin(-) surface, the energetically favored surface, under operational cathodic conditions, which is consistent with recent experimental findings, wherein the PEMFCs with pyrolyzed vitamin B12 containing Co-corrin as catalysts loaded at the cathode, can deliver up to 14.5 A cm(-3) at 0.8 V with IR compensation. A similar calculation performed for a Co-porphyrin system shows a significantly less efficient O-2 reduction, consistent with the experiment results of the PEMFC power output studies.
Role of Tin Chloride in Tin-Rich Mixed-Halide Perovskites Applied as Mesoscopic Solar Cells with a Carbon Counter Electrode
(2016-12)
Tsai, Cheng-Min
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Wu, Hui-Ping
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Chang, Sun-Tang
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Huang, Chi-Feng
;
Wang, Chia-Hsin
We report the synthesis and characterization of alloyed Sn Pb methylammonium mixed-halide perovskites (CH3NH3SnyPb1-yI3-xClx) to extend light harvesting toward the near infrared region for carbon-based mesoscopic solar cells free of organic hole-transport layers. The proportions of Sn in perovskites are well controlled by mixing tin chloride (SnCl2) and lead iodide (Pbl(2)) in varied stoichiometric ratios (y = 0-1). SnCl2 plays a key role in modifying the lattice structure of the perovskite, showing anomalous optical and optoelectronic properties; upon increasing the concentration of SnC2, the variation of the band gap and band energy differed from those of the Snl(2) precursor. The CH3NH3SnyPb1-yI3-xClx devices showed enhanced photovoltaic performance upon increasing the proportion of SnCl2 until y = 0.75, consistent with the corresponding potential energy levels. The photovoltaic performance was further improved upon adding 30 mol % tin fluoride (SnF2) with device configuration FTO/TiO2/Al2O3/NiO/C, producing the best power conversion efficiency, 5.13%, with great reproducibility and intrinsic stability.
Vitalizing fuel cells with vitamins: pyrolyzed vitamin B12 as a non-precious catalyst for enhanced oxygen reduction reaction of polymer electrolyte fuel cells
(2012-01-01)
Chang, Sun-Tang
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Wang, Chen-Hao
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Du, He-Yun
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Hsu, Hsin-Cheng
;
Kang, Chih-Ming
The limited natural abundance and high cost of Pt has been a major barrier in its applications for hydrogen or methanol fuel cells. In this work, based on the pyrolyzed corrin structure of vitamin B12 (py-B12/C), it is reported to produce superior catalytic activity in the oxygen reduction reaction (ORR) with an electron transfer number of 3.90, which is very close to the ideal case of 4. The H-2-O-2 fuel cell using py-B12/C provides a maximum power density of 370 mW cm(-2) and a current density of 0.720 A cm(-2) at 0.5 V at 70 degrees C. Calculations based on density functional theory suggests that the corrin complex with a low-symmetric structure offers a much preferable path for the ORR, which is not applicable to the porphyrin with a high-symmetric structure. The long-term stability and high ORR activity of py-B12/C make it a viable candidate as a Pt-substitute in the ORR.