Showing papers by "Kuei-Hsien Chen published in 2022"
29 citations
TL;DR: In this article, a metal free modified g-C3N4 photocatalyst was synthesized by combining four different strategies in a one-pot thermal reaction: non-metal doping, porosity generation, functionalization with amino groups, and thermal oxidation etching.
29 citations
TL;DR: In this article , a two-step hydrothermal method was used to synthesize hollow bimetal oxides for energy storage in the field of energy storage due to their various oxidation states and synergistic interactions among multiple metal species.
27 citations
TL;DR: In this paper , the authors showed that the reconstructed and imperfect edge configurations enable CO 2 binding to form linear and bent molecules, and the consumed electron rate per edge atom is two orders of magnitude larger than the in-plane intrinsic defects.
Abstract: Abstract Ascertaining the function of in-plane intrinsic defects and edge atoms is necessary for developing efficient low-dimensional photocatalysts. We report the wireless photocatalytic CO 2 reduction to CH 4 over reconstructed edge atoms of monolayer 2H-WSe 2 artificial leaves. Our first-principles calculations demonstrate that reconstructed and imperfect edge configurations enable CO 2 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 WSe 2 –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 CO 2 reduction reactions.
24 citations
TL;DR: In this paper , the authors used effective and one-pot Heck coupling reactions under moderate reaction conditions to construct two new hybrid porous polymers (named OVS-P-TPA and OVSP-F HPPs) with high yield, based on silsesquioxane cage nanoparticles through the reaction of octavinylsilsesquioxanes (OVS) with different brominated pyrene (P-Br4), triphenylamine (TPA-Br3), and fluorene (F-Br2) as co-monomer units.
Abstract: In this study, we used effective and one-pot Heck coupling reactions under moderate reaction conditions to construct two new hybrid porous polymers (named OVS-P-TPA and OVS-P-F HPPs) with high yield, based on silsesquioxane cage nanoparticles through the reaction of octavinylsilsesquioxane (OVS) with different brominated pyrene (P-Br4), triphenylamine (TPA-Br3), and fluorene (F-Br2) as co-monomer units. The successful syntheses of both OVS-HPPs were tested using various instruments, such as X-ray photoelectron (XPS), solid-state 13C NMR, and Fourier transform infrared spectroscopy (FTIR) analyses. All spectroscopic data confirmed the successful incorporation and linkage of P, TPA, and F units into the POSS cage in order to form porous OVS-HPP materials. In addition, the thermogravimetric analysis (TGA) and N2 adsorption analyses revealed the thermal stabilities of OVS-P-F HPP (Td10 = 444 °C; char yield: 79 wt%), with a significant specific surface area of 375 m2 g–1 and a large pore volume of 0.69 cm3 g–1. According to electrochemical three-electrode performance, the OVS-P-F HPP precursor displayed superior capacitances of 292 F g−1 with a capacity retention of 99.8% compared to OVS-P-TPA HPP material. Interestingly, the OVS-P-TPA HPP showed a promising HER value of 701.9 µmol g−1 h−1, which is more than 12 times higher than that of OVS-P-F HPP (56.6 µmol g−1 h−1), based on photocatalytic experimental results.
15 citations
TL;DR: In this article , the effect of the local electronic structure on the reaction mechanism and electrochemical kinetics of Li-rich cathodes was investigated by combining operando quick scanning X-ray absorption spectroscopy with online gas chromatography.
Abstract: Li‐rich layered oxide cathodes with conventional transition metal cation and unique oxygen anion redox reactions deliver high capacities in Li‐ion batteries. However, the oxygen redox process causes the oxygen release, voltage fading/hysteresis, and sluggish electrochemical kinetics, which undermine the performance of these materials. By combining operando quick‐scanning X‐ray absorption spectroscopy with online gas chromatography, the effect of the local electronic structure is elucidated on the reaction mechanism and electrochemical kinetics of Li‐rich cathodes. The local electronic structure of Li‐rich cathodes varies with the excess Li (i.e., Li2MnO3 phase) and Ni contents. Compared to the Li‐rich cathodes with higher amounts of Li2MnO3 phase (high excess lithium content (HLC) cathode), those with lower Li2MnO3 contents (low excess lithium content (LLC) cathode) exhibit reversible anion redox reactions and suppressed voltage hysteresis. The cation oxidation process of LLC cathode is kinetically slower than that of HLC cathode and the cation oxidation potential is shifted, likely due to the local coordination associated with different Li/O ratios. The obtained insights into the effect of local electronic structure on the reaction mechanism and kinetics provide a better understanding and control of Li‐rich cathodes.
11 citations
TL;DR: Although hematite (i.e., α-Fe2O3) has been widely investigated in photoelectrochemical water oxidation studies due to its high theoretical photocurrent density, it still suffers from serious surface charge recombination and low...
Abstract: Although hematite (i.e., α-Fe2O3) has been widely investigated in photoelectrochemical water oxidation studies due to its high theoretical photocurrent density, it still suffers from serious surface charge recombination and low...
8 citations
TL;DR: The phase evolution and thermoelectric properties of a series of Co(Ge 0.5Te0.5)3-Sbx (x = 0-0.20) compositions synthesized by mechanical alloying are reported in this paper .
Abstract: We report the phase evolution and thermoelectric properties of a series of Co(Ge0.5Te0.5)3-xSbx (x = 0-0.20) compositions synthesized by mechanical alloying. Pristine ternary Co(Ge0.5Te0.5)3 skutterudite crystallizes in the rhombohedral symmetry (R3̅), and Sb doping induces a structural transition to the cubic phase (ideal skutterudite, Im3̅). The Sb substitution increases the carrier concentration while maintaining a high thermopower even at higher doping levels owing to an increased effective mass. The exceptional electronic properties exhibited by Co(Ge0.5Te0.5)3 upon doping are attributed to the carrier transport from both the primary and secondary conduction bands, as shown by theoretical calculations. The enhanced electrical conductivity and high thermopower increase the power factor by more than 20 times. Because the dominant phonon propagation modes in binary skutterudites are associated with the vibrations of pnictogen rings, twisting the latter through the isoelectronic replacement of Sb4 rings with Ge2Te2 ones, as done in this study, can effectively reduce the thermal conductivity. This leads to an increase in the dimensionless figure-of-merit (zT) by a factor of 30, reaching 0.65 at 723 K for Co(Ge0.5Te0.5)2.9Sb0.1.
5 citations
4 citations
TL;DR: In this article, the effect of sputtering pressure on the thermoelectric properties of GeTe thin films was investigated and it was shown that the surface morphology of annealed GeTe films will change from cracks to voids with increasing sputtering pressures.
3 citations
TL;DR: In this article , a MoO3 nanolayer was applied as a sacrificial layer to optimize the quality of the interface between the CZTSSe and Mo back contact.
Abstract: Earth-abundant Cu2ZnSn(S,Se)4 (CZTSSe) is a promising nontoxic alternative compound for commercially available Cu(In,Ga)(S,Se)2 thin-film solar cells. In this study, a MoO3 nanolayer was applied as a sacrificial layer to optimize the quality of the interface between the CZTSSe and Mo back contact. MoO3 nanolayers can greatly improve CZTSSe grain growth and suppress the formation of some harmful secondary phases, especially the undesirable MoS(e)2. In terms of device performance, the series resistance was reduced from 1.83 to 1.54 Ω·cm2, and the fill factor was significantly enhanced from 42.67% to 52.12%. Additionally, MoO3 nanolayers improved CZTSSe absorber quality by lowering the defect energy levels from 228 to 148 meV. Furthermore, first-principles calculations demonstrate that the partial sulfoselenized MoO3 nanolayers may function as the (p-type) hole-selective contacts at Mo/CZTSSe interfaces, leading to an overall improvement in device performance. Lastly, a CZTSSe solar cell with about 26% improvement (compared with reference cells) in power conversion efficiency was achieved by inserting 5 nm MoO3 sacrificial layers.
TL;DR: In this article , a carbon-coated Cu2ZnSnS4 with a hierarchical 3D structure (CZTS@C) is used as an anode material for Li-ion batteries.
Abstract: The widespread use of energy storage technologies has created a high demand for the development of novel anode materials in Li-ion batteries (LIBs) with high areal capacity and faster electron-transfer kinetics. In this work, carbon-coated Cu2ZnSnS4 with a hierarchical 3D structure (CZTS@C) is used as an anode material for LIBs. The CZTS@C microstructures with enhanced electrical conductivity and improved Li-ion diffusivity exhibit high areal and gravimetric capacities of 2.45 mA h/cm2 and 1366 mA h/g, respectively. The areal capacity achieved in the present study is higher than that of previously reported CZTS-based materials. Moreover, in situ X-ray diffraction results show that lithium ions are stored in CZTS through the insertion reaction, followed by the alloying and conversion reactions at ∼1 V. The structural evolution of Li2S and Cu–Sn/Cu–Zn alloy phases occurs during the conversion and alloying reactions. The present work provides a cost-effective and simple method to prepare bulk CZTS and highlights the conformal carbon coating over CZTS, which can enhance the electrical and ionic conductivities of CZTS materials and increase the mass loading (1–2.3 mg/cm2). The improved stability and rate capability of CZTS@C anode materials can therefore be achieved.
TL;DR: In this paper , a flexible broadband photodetector based on a hybrid of two nanomaterials having complementary ranges of absorption offers the possibility for better wearable sensors, which can detect signals from domestic appliances such as air conditioner remotes, laser pointers and cellphone flashlights.
Abstract: Hybrids of two-dimensional (2D) and 0D nanomaterials offer a wider spectrum of properties than their counterparts. Here, we choose a molybdenum disulfide and NaGdF4:Yb3+, Er3+ upconversion nanoparticle (MoS2-UCNP) nanocomposite (NC) on graphene (G)-coated polydimethylsiloxane (PDMS) and silica/silicon (SiO2/Si) substrates as broadband photodetectors (PDs). The band gap (∼680 nm) limited response of pure MoS2 is broadened by the infrared (980 nm) absorbing UCNPs. Identically fabricated PDs on PDMS and SiO2/Si showed the highest photoresponsivity of 26.18 and 84.52 AW–1, respectively, under 661 nm laser illumination at a density of 1 mW/cm2 at 1 V bias. The MoS2-UCNPs/Graphene/SiO2/Si PD (SiO2/Si PD) showed a response time of ∼100 ms compared to ∼3 s for the PDMS-based PD. The PDMS-based PD showed a reasonably stable photocurrent, decaying by ∼39%, under 250 repetitive cycles of 6.25% bending strain; a maximum decrease of ∼40% of the photocurrent was observed under the 11.11% bending strain compared to the as-prepared flat PD. Both devices could detect signals from domestic appliances such as air conditioner remotes, laser pointers, and cellphone flashlights. The flexible PD based on a hybrid of two nanomaterials having complementary ranges of absorption offers the possibility for better wearable sensors.
TL;DR: In this paper , a combination of neutron diffraction and synchrotron-based X-ray absorption techniques was implemented to investigate the relationships among cation disorder, defect concentration, overall long-range crystallographic order, and local atomic-scale structure for (AgxCu1-x)2ZnSnSe4 (ACZTSe) material.
Abstract: Understanding the nature of and controlling the cation disorder in kesterite-based absorber materials remain a crucial challenge for improving their photovoltaic (PV) performances. Herein, the combination of neutron diffraction and synchrotron-based X-ray absorption techniques was implemented to investigate the relationships among cation disorder, defect concentration, overall long-range crystallographic order, and local atomic-scale structure for (AgxCu1–x)2ZnSnSe4 (ACZTSe) material. The joint Rietveld refinement technique was used to directly reveal the effect of cation substitution and quantify the concentration of defects in Ag-alloyed stoichiometric and nonstoichiometric Cu2ZnSnSe4 (CZTSe). The results showed that 10%-Ag-alloyed nonstoichiometric ACZTSe had the lowest concentration of detrimental antisite CuZn defects (∼8 × 1019 defects per cm–3), which was two times lower than pristine and five times lower than the stoichiometric compositions. Moreover, Ag incorporation maintained the concentrations of beneficial Cu vacancies (VCu) and antisite ZnCu defects to >2 × 1020 defects per cm–3. X-ray absorption measurements were performed to verify the degree of disorder through the changes in bond length and coordination number. Therefore, the incorporation of Ag into the CZTSe lattice could control the distribution of antisite defects, in the form of short- and long-range site disorder. This study paves the way to systematically understand and further improve the properties of kesterite-based materials for different energy applications.
TL;DR: In this paper , the quaternary Sn2Te2 rings in the structure of a ternary skutterudite were chemically tuned to enhance the conduction type switching details, and a Ni-for-Co substitution was applied to enhance electronic transport.
TL;DR: In this article , an n-type mixed anion Co4Ge6Te6 skutterudite was converted into a p-type material through partial substitution of Fe for Co.
TL;DR: Direct Z-scheme heterojunctions are widely used for photocatalytic water splitting and CO2 reduction by facilitating well-separated photogenerated charge carriers and spatial isolation of redox reactions as discussed by the authors .
Abstract: Direct Z-scheme heterojunctions are widely used for photocatalytic water splitting and CO2 reduction by facilitating well-separated photogenerated charge carriers and spatial isolation of redox reactions. Here, using a facile two-step...
TL;DR: In this article , a single crystalline nature of Co-GaN nanowires was identified, and a small expansion in the lattice constant due to implantation-induced stress effect was observed, which was recovered by thermal annealing.
Abstract: GaN nanowires (NWs) grown on silicon via atmospheric pressure chemical vapor deposition were doped with Cobalt (Co) by ion implantation, with a high dose concentration of 4 × 1016 cm−2, corresponding to an average atomic percentage of ~3.85%, and annealed after the implantation. Co-doped GaN showed optimum structural properties when annealed at 700 °C for 6 min in NH3 ambience. From scanning electron microscopy, X-ray diffraction, high resolution transmission electron microscope, and energy dispersive X-ray spectroscopy measurements and analyses, the single crystalline nature of Co-GaN NWs was identified. Slight expansion in the lattice constant of Co-GaN NWs due to the implantation-induced stress effect was observed, which was recovered by thermal annealing. Co-GaN NWs exhibited ferromagnetism as per the superconducting quantum interference device (SQUID) measurement. Hysteretic curves with Hc (coercivity) of 502.5 Oe at 5 K and 201.3 Oe at 300 K were obtained. Applied with a magnetic field of 100 Oe, the transition point between paramagnetic property and ferromagnetic property was determined at 332 K. Interesting structural and conducive magnetic properties show the potential of Co-doped GaN nanowires for the next optoelectronic, electronic, spintronic, sensing, optical, and related applications.
TL;DR: In this article , a dinitrosyl iron complex (1-N3MDA) was explored as a molecular precursor for one-pot photosynthesis of a cubic Fe@Fe3O4 core-shell nanoparticle well-dispersed in an N-doping carbonaceous polymer (NZVI@NC).
Abstract: Nanoscale zerovalent iron (NZVI) features potential application to biomedicine, (electro-/photo)catalysis, and environmental remediation. However, multiple-synthetic steps and limited ZVI content prompt the development of a novel strategy for efficient preparation of NZVI composites. Herein, a dinitrosyl iron complex [(N3MDA)Fe(NO)2] (1-N3MDA) was explored as a molecular precursor for one-pot photosynthesis of a cubic Fe@Fe3O4 core-shell nanoparticle (ZVI% = 60%) well-dispersed in an N-doping carbonaceous polymer (NZVI@NC). Upon photolysis of 1-N3MDA, photosensitizer Eosin Y, and sacrificial reductant TEA, the α-diimine N3MDA and noninnocent NO ligands (1) enable the slow reduction of 1-N3MDA into an unstable [(N3MDA)Fe(NO)2]- species, (2) serve as a capping reagent for controlled nucleation of zerovalent Fe atom into Fe nanoparticle, and (3) promote the polymerization of degraded Eosin Y with N3MDA yielding an N-doping carbonaceous matrix in NZVI@NC. This discovery of a one-pot photosynthetic process for NZVI@NC inspires continued efforts on its application to photolytic water splitting and ferroptotic chemotherapy in the near future.
TL;DR: In this article , the authors explored and optimized the Ge0.9−xSb0.1PxTe (x = 0.01-0.05) material's highest thermoelectric performance at elevated temperatures.