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Shelke, AR, Wang H-T, Chiou J-W, Shown I, Sabbah A, Chen K-H, Teng S-A, Lin I-A, Lee C-C, Hsueh H-C, Liang Y-H, Du C-H, Yadav PL, Ray SC, Hsieh S-H, Pao C-W, Tsai H-M, Chen C-H, Chen K-H, Chen L-C, Pong W-F.  2022.  Bandgap Shrinkage and Charge Transfer in 2D Layered SnS2 Doped with V for Photocatalytic Efficiency Improvement. Small. n/a:2105076., Number n/a AbstractWebsite

Abstract Effects of electronic and atomic structures of V-doped 2D layered SnS2 are studied using X-ray spectroscopy for the development of photocatalytic/photovoltaic applications. Extended X-ray absorption fine structure measurements at V K-edge reveal the presence of VO and VS bonds which form the intercalation of tetrahedral OVS sites in the van der Waals (vdW) gap of SnS2 layers. X-ray absorption near-edge structure (XANES) reveals not only valence state of V dopant in SnS2 is ≈4+ but also the charge transfer (CT) from V to ligands, supported by V Lα,β resonant inelastic X-ray scattering. These results suggest V doping produces extra interlayer covalent interactions and additional conducting channels, which increase the electronic conductivity and CT. This gives rapid transport of photo-excited electrons and effective carrier separation in layered SnS2. Additionally, valence-band photoemission spectra and S K-edge XANES indicate that the density of states near/at valence-band maximum is shifted to lower binding energy in V-doped SnS2 compare to pristine SnS2 and exhibits band gap shrinkage. These findings support first-principles density functional theory calculations of the interstitially tetrahedral OVS site intercalated in the vdW gap, highlighting the CT from V to ligands in V-doped SnS2.

Lee, C-P, Chen W-F, Billo T, Lin Y-G, Fu F-Y, Samireddi S, Lee C-H, Hwang J-S, Chen K-H, Chen L-C.  2016.  Beaded stream-like CoSe2 nanoneedle array for efficient hydrogen evolution electrocatalysis, 2016. Journal of Materials Chemistry A. 4(12):4553-4561.: The Royal Society of Chemistry AbstractWebsite

The development of earth-abundant and efficient electrocatalysts for the hydrogen evolution reaction (HER) is one of the keys to success for future green energy systems using hydrogen fuel. Nanostructuring of electrocatalysts is a promising way to enhance their electrocatalytic performance in the HER. In this study, pure pyrite-type beaded stream-like cobalt diselenide (CoSe2) nanoneedles are directly formed on flexible titanium foils through treating a cobalt oxide (Co3O4) nanoneedle array template with selenium vapor. The beaded stream-like CoSe2 nanoneedle electrode can drive the HER at a current density of 20 mA cm−2 with a small overpotential of 125 mV. Moreover, the beaded stream-like CoSe2 nanoneedle electrode remains stable in an acidic electrolyte for 3000 cycles and continuously splits water over a period of 18 hours. The enhanced electrochemical activity is facilitated by the unique three-dimensional hierarchical structure, the highly accessible surface active sites, the improved charge transfer kinetics and the highly attractive force between water and the surface of the nanoneedles that exceeds the surface tension of water.

Lee, CP, Chen* WF, Billo T, Lin YG, Fu FY, Samireddi S, Lee CH, Hwang JS, Chen* LC, Chen* KH.  2016.  Beaded-stream-like CoSe2 nanoneedles array for efficient hydrogen evolution electrocatalysis. J. Mater. Chem. A . 4 :4553-4561.
Lin, YR, Tunuguntla V, Wei SY, Chen WC, Wong D, Lai CH, Liu LK, Chen LC, Chen KH.  2015.  Bifacial sodium-incorporated treatments: tailoring deep traps and enhancing carrier transport properties in Cu2ZnSnS4 solar cells. Nano Energy . 16:438.
Wong, DP, Suriyaprabha R, Yuvakumar R, Rajendran V, Chen YT, Hwang BJ, Chen LC, Chen KH.  2014.  Binder-free rice husk-based silicon-graphene composite as energy efficient Li-ion battery anodes. J. Mater. Chem. A. 2:13437-13441.
Dhara*, S, Chandra S, Magudapathy P, Kalavathi S, Panigrahi BK, Nair KGM, Sastry VS, Hsu CW, Wu CT, Chen KH, Chen LC.  2004.  Blue luminescence of Au nanoclusters embedded in silica matrix. J. Chem. Phys.. 121:12595-12599.
Dhara, SK, Datta A, Lan ZH, Chen* KH, Wang YL, Shen CS, Chen LC, Hsu CW, Lin HM, Chen CC.  2004.  Blue shift of yellow band in self-ion beam irradiated GaN nanowires. Appl. Phys. Lett.. 84:3486-3488.
Lo, HC, Wu JJ, Wen CY, Wong TS, Lin ST, Chen* KH, Chen LC.  2001.  Bonding characterization and nano-indentation study of the amorphous SiCxNy films with and without hydrogen incorporation. Diamond Relat. Mater.. 10:1916-1920.
Chattopadhyay, S, Chen* LC, Chien SC, Lin ST, Chen KH.  2002.  Bonding characterization, density measurement and thermal diffusivity studies of amorphous silicon carbon nitride and boron carbon nitride thin films. J. Appl. Phys.. 92:5150-5158.
Sabbah, A, Shown I, Qorbani M, Fu F-Y, Lin T-Y, Wu H-L, Chung P-W, Wu C-I, Santiago SRM, Shen J-L, Chen K-H, Chen L-C.  2022.  Boosting photocatalytic CO2 reduction in a ZnS/ZnIn2S4 heterostructure through strain-induced direct Z-scheme and a mechanistic study of molecular CO2 interaction thereon, 2022. Nano Energy. 93:106809. AbstractWebsite

Employing direct Z-scheme semiconductor heterostructures in photocatalysis offers efficient charge carrier separation and isolation of both redox reactions, thus beneficial to reduce CO2 into solar fuels. Here, a ZnS/ZnIn2S4 heterostructure, comprising cubic ZnS nanocrystals on hexagonal ZnIn2S4 (ZIS) nanosheets, is successfully fabricated in a single-pot hydrothermal approach. The composite ZnS/ZnIn2S4 exhibits microstrain at its interface with an electric field favorable for Z-scheme. At an optimum ratio of Zn:In (~ 1:0.5), an excellent photochemical quantum efficiency of around 0.8% is reached, nearly 200-fold boost compared with pristine ZnS. Electronic levels and band alignments are deduced from ultraviolet photoemission spectroscopy and UV-Vis. Evidence of the direct Z-scheme and carrier dynamics is verified by photo-reduction experiment, along with photoluminescence (PL) and time-resolved PL. Finally, diffuse-reflectance infrared Fourier transformed spectroscopy explores the CO2 and related intermediate species adsorbed on the catalyst during the photocatalytic reaction. This microstrain-induced direct Z-scheme approach opens a new pathway for developing next-generation photocatalysts for CO2 reduction.

Jarwal, B, Abbas S, Chou T-L, Vailyaveettil SM, Kumar A, Quadir S, Ho T-T, Wong DP, Chen L-C, Chen K-H.  2024.  Boosting Thermoelectric Performance in Nanocrystalline Ternary Skutterudite Thin Films through Metallic CoTe2 Integration, 2024. ACS Applied Materials & InterfacesACS Applied Materials & Interfaces. 16(12):14770-14780.: American Chemical Society AbstractWebsite
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Fang, WC, Huang* JH, Chen LC, Su YO, H.Chen K, Sun CL.  2006.  Carbon nanotubes directly grown on Ti electrodes and enhancement in their electrochemical properties by nitric acid treatment. Electrochemical and Solid-State Lett.. 9:A5.
Chen*, KH, Wong TS, Wang CT, Chen LC, Ma KJ.  2001.  Carbon nanotubes growth by rapid thermal processing. Diamond and Related Materials. 10:1810-1813.
Shown, I, Samireddi S, Chang Y-C, Putikam R, Chang P-H, Sabbah A, Fu F-Y, Chen W-F, Wu C-I, Yu T-Y, Chung P-W, Lin MC, Chen L-C, Chen K-H.  2018.  Carbon-doped SnS2 nanostructure as a high-efficiency solar fuel catalyst under visible light, 2018. Nature Communications. 9(1):169. AbstractWebsite

Photocatalytic formation of hydrocarbons using solar energy via artificial photosynthesis is a highly desirable renewable-energy source for replacing conventional fossil fuels. Using an l-cysteine-based hydrothermal process, here we synthesize a carbon-doped SnS2 (SnS2-C) metal dichalcogenide nanostructure, which exhibits a highly active and selective photocatalytic conversion of CO2 to hydrocarbons under visible-light. The interstitial carbon doping induced microstrain in the SnS2 lattice, resulting in different photophysical properties as compared with undoped SnS2. This SnS2-C photocatalyst significantly enhances the CO2 reduction activity under visible light, attaining a photochemical quantum efficiency of above 0.7%. The SnS2-C photocatalyst represents an important contribution towards high quantum efficiency artificial photosynthesis based on gas phase photocatalytic CO2 reduction under visible light, where the in situ carbon-doped SnS2 nanostructure improves the stability and the light harvesting and charge separation efficiency, and significantly enhances the photocatalytic activity.

Chen*, LC, Chang SW, Chang CS, Wen CY, Wu J-J, Chen YF, Huang YS, Chen KH.  2001.  Catalyst-free growth of transparent SiCN nanorods. J. Phys. & Chem. of Solids. 62:1567-1576.
Chen*, C-C, Yeh C-C, Chen CH, Yu MY, Liu HL, Wu JJ, Chen KH, Chen LC, Peng JY, Chen YF.  2001.  Catalytic growth and characterization of gallium nitride nanowires. J. Am. Chem. Soc.. 123:2791-2798.
Li, CC, Lin RJ, Lin HP, Chang CC, Lin YK, Chen LC, Chen KH.  2011.  Catalytic performance of plate-type Cu/Fe nanocomposites on ZnO nanorods for oxidative steam reforming of methanol. Chem. Comm.. 47:1473-1475.
Muto*, S, Dhara SK, Datta A, Hsu CW, Wu CT, Shen CH, Chen LC, Chen KH, Wang YL, Tanabe T, Maruyama T, Lin HM, Chen CC.  2004.  Characterization of nanodome on GaN nanowires formed with Ga ion irradiation. Mater. Trans.. 45:435-439.
Huang, LW, Chang CK, Chien FC, Chen KH, Chen P, Chen FR, Chang CS.  2014.  Characterization of the cleaning process on a transferred graphene. J. Vac. Sci. Tech. A . 32:050601.
Wei-ChaoChen, Tunuguntla V, Min-HsuehChiu, Lian-JiunLi, Shown I, Lee C-H, Hwang J-S, Chen L-C, Chen K-H.  2017.  Co-solvent effect on microwave-assisted Cu2ZnSnS4 nanoparticles synthesis for thin film solar cell. Solar Energy Materials and Solar Cells. 161:416-423.
Fahimi, Z, Moradlou O, Sabbah A, Chen K-H, Chen L-C, Qorbani M.  2022.  Co3V2O8 hollow spheres with mesoporous walls as high-capacitance electrode for hybrid supercapacitor device, 2022. 436:135225. AbstractWebsite

Bimetal oxides are promising materials in the field of energy storage due to their various oxidation states, synergistic interactions among multiple metal species, and stability. In this work, Co3V2O8 hollow spheres are synthesized by a two-step hydrothermal method: (i) synthesis of V2O5 spheres and (ii) partial replacement of V by Co through the Kirkendall effect. As an electrode, it shows an extrinsic pseudocapacitive charge-storage mechanism due to different oxidation states of V and Co ions. Because of the low crystallinity degree of the mesoporous wall and high accessible surface area of hollow spheres, the optimum Co3V2O8 electrode reaches a high specific capacitance of 2376F g−1 at a current density of 2 A g−1, which is more than two times higher than the top reported values, and a rate capability retention of ∼80% at 20 A g−1. Using Co3V2O8, activated carbon, and KOH as positive, negative electrodes, and electrolyte, respectively, a hybrid supercapacitor device presents maximum energy and power densities of 59.2 Wh kg−1 and 36.6 kW kg−1, respectively. Further, the aqueous supercapacitor device shows superior structural and electrochemical stabilities after 10,000 galvanostatic charge–discharge cycles because of the arrays of voids in the orthorhombic crystal structure of Co3V2O8 that can decrease the volume expansion/shrinkage during the intercalation/deintercalation processes. Our results provide a platform for exploring bimetallic Co and V-based oxides, hydroxides, and sulfides nanostructures as promising energy storage materials in the future.

Deliwala, S, Goldman J, Chen KH, Lu C-Z, Mazur E.  1994.  Coherent Anti-Stokes Raman Spectroscopy of Infrared Multiphoton Excited Molecules. J. Chem. Phys.. 101:8517-8528.
Chen, KH, Wu JJ, Chen LC, Wen C-Y, Kichambare PD, Tarntair FG, Kuo PF, Chang SW, Chen YF.  2000.  Comparative studies in field emission properties of carbon-based materials. Diamond & Related Materials. 9:1249-1256.
Ray, SC, Pao CW, Tsai HM, Chiou JW, Pong* WF, Chen CW, Tsai M-H, Papakonstantinou P, Chen LC, Chen KH.  2007.  A comparative study of the electronic structures of oxygen- and chlorinetreated nitrogenated carbon nanotubes by X-ray absorption and scanning photoelectron microscopy. Appl. Phys. Lett.. 91:202102.
Chen*, RS, Tsai HY, Chan CH, Huang YS, Chen YT, Chen KH, Chen LC.  2015.  Comparison of CVD- and MBE-grown GaN nanowires: crystallinity, photoluminescence, and photoconductivity. J. Electronic Mater. . 44 :177.