Kuei-Hsien Chen

Ascertaining the function of in-plane intrinsic defects and edge atoms is necessary for developing efficient low-dimensional photocatalysts. We report the wireless photocatalytic CO2 reduction to CH4 over reconstructed edge atoms of monolayer 2H-WSe2 artificial leaves. Our first-principles calculations demonstrate that reconstructed and imperfect edge configurations enable CO2 binding to form linear and bent molecules. Experimental results show that the solar-to-fuel quantum efficiency is a reciprocal function of the flake size. It also indicates that the consumed electron rate per edge atom is two orders of magnitude larger than the in-plane intrinsic defects. Further, nanoscale redox mapping at the monolayer WSe2–liquid interface confirms that the edge is the most preferred region for charge transfer. Our results pave the way for designing a new class of monolayer transition metal dichalcogenides with reconstructed edges as a non-precious co-catalyst for wired or wireless hydrogen evolution or CO2 reduction reactions.

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.

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Solar cells based on kesterite Cu2ZnSnSe4 (CZTSe) compounds with earth-abundant elements are highly desirable for the low-cost and high-efficiency production of renewable energy. However, the occurrence of intrinsic defects substantially impairs the photovoltaic properties of CZTSe. Herein, a cation substitution method to control and passivate the defect states in bandgap of kesterite CZTSe by incorporating Ag ions is introduced. Intensity-dependent low-temperature photoluminescence measurements show that Ag incorporation can reduce the density and depth of intrinsic defects in CZTSe. The results reveal that 10% Ag-alloyed CZTSe provides the shallowest defect states and less nonradiative recombination. It is also confirmed by first-principles calculations that Ag incorporation enables the formation and suppresses the beneficial and detrimental defects, respectively. Based on the theoretical results, the observed subband photoluminescence peaks can be assigned to the intrinsic point and cluster defects. The best power conversion efficiency of 10.2% is achieved for the 10% Ag-alloyed CZTSe cell, along with an enhanced open-circuit voltage. These results open up a new avenue for further improving the performances of CZTSe-based device via defect engineering.