Kuei-Hsien Chen

Abstract An electrochemical capacitor configuration extends its operational potential window by leveraging diverse charge storage mechanisms on the positive and negative electrodes. Beyond harnessing capacitive, pseudocapacitive, or Faradaic energy storage mechanisms and enhancing electrochemical performance at high rates, achieving a balance of stored charge across electrodes poses a significant challenge over a wide range of charge?discharge currents or sweep rates. Consequently, fabricating hybrid and asymmetric supercapacitors demands precise electrochemical evaluations of electrode materials and the development of a reliable methodology. This work provides an overview of fundamental aspects related to charge-storage mechanisms and electrochemical methods, aiming to discern the contribution of each process. Subsequently, the electrochemical properties, including the working potential windows, rate capability profiles, and stabilities, of various families of electrode materials are explored. It is then demonstrated, how charge balancing between electrodes falters across a broad range of charge?discharge currents or sweep rates. Finally, a methodology for achieving charge balance in hybrid and asymmetric supercapacitors is proposed, outlining multiple conditions dependent on loaded mass and charge?discharge current. Two step-by-step tutorials and model examples for applying this methodology are also provided. The proposed methodology is anticipated to stimulate continued dialogue among researchers, fostering advancements in achieving stable and high-performance supercapacitor devices.

BiCuTeO is a promising thermoelectric material owing to its intrinsically low thermal conductivity and high carrier concentration. This study investigated the influence of stoichiometric oxygen deficiencies on the thermoelectric performance of BiCuTeO. Bulk BiCuTeO1−x (0.16 ≥ x) samples were prepared by a conventional solid state reaction and pelleted by hot pressing. Synchrotron X-ray diffraction, electron probe X-ray microanalysis, scanning electron microscopy, and transmission electron microscopy characterized the samples. A maximum value of 1.06 was achieved for the dimensionless figure of merit ZT at 673 K for BiCuTeO0.88, which is approximately 49% better than the current maximal ZT value for BiCuTeO. The power factor was noticeably improved owing to increases in the electrical conductivity and Seebeck coefficient. Moreover, the optimal oxygen deficiency could introduce nanoparticles, resulting in reduced thermal conductivity. The findings will be important for the future development of metal oxide thermoelectric materials for use in practical thermoelectric devices.

Exploring electrocatalysts composed of earth-abundant elements for a highly efficient hydrogen evolution reaction (HER) is scientifically and technologically important for electrocatalytic water splitting. In this work, we report HER properties of acid treated pyrolyzed vitamin B12 supported on reduced graphene oxide (B12/G800A) that shows an extraordinarily enhanced catalytic activity with low overpotential (115 mV vs. RHE at 10 mA cm−2), which is better than that of most traditional nonprecious metal catalysts in acidic media. Stability tests through long-term potential cycles and at a constant current density confirm the exceptional durability of the catalyst. Notably, the B12/G800A catalyst exhibits extremely high turnover frequencies per cobalt site in acid, for example, 0.85 and 11.46 s−1 at overpotentials of 100 and 200 mV, respectively, which are higher than those reported for other scalable non-precious metal HER catalysts. Moreover, it has been conjectured that the covalency of Co–C and Co–N bonds affects HER activities by comparing the extended X-ray absorption fine structure (EXAFS) spectra of the B12/G800A. High-temperature treatment can modify the Co-corrin structure of B12 to form Co–C bonds along with Co–N, which broadens the band of cobalt, essentially lowering the d-band center from its Fermi level. The lower d-band center leads to a moderate hydrogen binding energy, which is favorable for hydrogen adsorption and desorption.

Pharmaceutical drugs' removal from wastewater by photocatalytic oxidation process is considered as an attractive approach and environmentally friendly solution. This report aims to appraise the practical application potential of Ag/g-C3N4/ZnO nanorods toward the wastewater treatment of the pharmaceutical industry. The catalysts are synthesized by straightforward and environmentally-friendly strategies. Specifically, g-C3N4/ZnO nanorods heterostructure is constructed by a simple self-assembly method, and then Ag nanoparticles are decorated on g-C3N4/ZnO nanorods by a photoreduction route. The results show that three commercial drugs (paracetamol, amoxicillin, and cefalexin) with high concentration (40 mg L−1) are significantly degraded in the existence of a small dosage of Ag/g-C3N4/ZnO nanorods (0.08 g L−1). The Ag/g-C3N4/ZnO nanorods photocatalyst exhibits degradation performance of paracetamol higher 3.8, 1.8, 1.3 times than pristine g-C3N4, ZnO nanorods, and g-C3N4/ZnO nanorods. Furthermore, Ag/g-C3N4/ZnO nanorods have an excellent reusability and a chemical stability that achieved paracetamol degradation efficiency of 78% and remained chemical structure of the photocatalyst after five cycles. In addition, the photocatalytic mechanism explanation and comparison of photocatalytic drugs’ degradation ability have also been discussed in this study.