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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
Hammad Elsayed, M, Abdellah M, Alhakemy AZ, Mekhemer IMA, Aboubakr AEA, Chen B-H, Sabbah A, Lin K-H, Chiu W-S, Lin S-J, Chu C-Y, Lu C-H, Yang S-D, Mohamed MG, Kuo S-W, Hung C-H, Chen L-C, Chen K-H, Chou H-H.  2024.  Overcoming small-bandgap charge recombination in visible and NIR-light-driven hydrogen evolution by engineering the polymer photocatalyst structure, 2024. Nature Communications. 15(1):707. AbstractWebsite

Designing an organic polymer photocatalyst for efficient hydrogen evolution with visible and near-infrared (NIR) light activity is still a major challenge. Unlike the common behavior of gradually increasing the charge recombination while shrinking the bandgap, we present here a series of polymer nanoparticles (Pdots) based on ITIC and BTIC units with different π-linkers between the acceptor-donor-acceptor (A-D-A) repeated moieties of the polymer. These polymers act as an efficient single polymer photocatalyst for H2 evolution under both visible and NIR light, without combining or hybridizing with other materials. Importantly, the difluorothiophene (ThF) π-linker facilitates the charge transfer between acceptors of different repeated moieties (A-D-A-(π-Linker)-A-D-A), leading to the enhancement of charge separation between D and A. As a result, the PITIC-ThF Pdots exhibit superior hydrogen evolution rates of 279 µmol/h and 20.5 µmol/h with visible (>420 nm) and NIR (>780 nm) light irradiation, respectively. Furthermore, PITIC-ThF Pdots exhibit a promising apparent quantum yield (AQY) at 700 nm (4.76%).

Krishnamoorthy, V, Sabhapathy P, Raghunath P, Huang C-Y, Sabbah A, Kamal Hussien M, Syum Z, Muthusamy S, Lin M-C, Wu H-L, Chen R-S, Chen K-H, Chen L-C.  2024.  Synergistic Electronic Interaction of Nitrogen Coordinated Fe-Sn Double-Atom Sites: An Efficient Electrocatalyst for Oxygen Reduction Reaction, 2024. Small Methods. n/a(n/a):2301674.: John Wiley & Sons, Ltd AbstractWebsite

Abstract Double-atom site catalysts (DASs) have emerged as a recent trend in the oxygen reduction reaction (ORR), thereby modifying the intermediate adsorption energies and increasing the activity. However, the lack of an efficient dual atom site to improve activity and durability has limited these catalysts from widespread application. Herein, the nitrogen-coordinated iron and tin-based DASs (Fe-Sn-N/C) catalyst are synthesized for ORR. This catalyst has a high activity with ORR half-wave potentials (E1/2) of 0.92 V in alkaline, which is higher than those of the state-of-the-art Pt/C (E1/2 = 0.83 V), Fe-N/C (E1/2 = 0.83 V), and Sn-N/C (E1/2 = 0.77 V). Scanning electron transmission microscopy analysis confirmed the atomically distributed Fe and Sn sites on the N-doped carbon network. X-ray absorption spectroscopy analysis revealed the charge transfer between Fe and Sn. Both experimental and theoretical results indicate that the Sn with Fe-NC (Fe-Sn-N/C) induces charge redistribution, weakening the binding strength of oxygenated intermediates and leading to improved ORR activity. This study provides the synergistic effects of DASs catalysts and addresses the impacts of P-block elements on d-block transition metals in ORR.

Sabhapathy, P, Raghunath P, Sabbah A, Shown I, Bayikadi KS, Xie R-K, Krishnamoorthy V, Lin M-C, Chen K-H, Chen L-C.  2023.  Axial Chlorine Induced Electron Delocalization in Atomically Dispersed FeN4 Electrocatalyst for Oxygen Reduction Reaction with Improved Hydrogen Peroxide Tolerance, 2023. Small. :2303598.: John Wiley & Sons, Ltd AbstractWebsite

Abstract Atomically dispersed iron sites on nitrogen-doped carbon (Fe-NC) are the most active Pt-group-metal-free catalysts for oxygen reduction reaction (ORR). However, due to oxidative corrosion and the Fenton reaction, Fe-NC catalysts are insufficiently active and stable. Herein, w e demonstrated that the axial Cl-modified Fe-NC (Cl-Fe-NC) electrocatalyst is active and stable for the ORR in acidic conditions with high H2O2 tolerance. The Cl-Fe-NC exhibits excellent ORR activity, with a high half-wave potential (E1/2) of 0.82 V versus a reversible hydrogen electrode (RHE), comparable to Pt/C (E1/2 = 0.85 V versus RHE) and better than Fe-NC (E1/2 = 0.79 V versus RHE). X-ray absorption spectroscopy analysis confirms that chlorine is axially integrated into the FeN4. More interestingly, compared to Fe-NC, the Fenton reaction is markedly suppressed in Cl-Fe-NC. In situ electrochemical impedance spectroscopy reveals that Cl-Fe-NC provides efficient electron transfer and faster reaction kinetics than Fe-NC. Density functional theory calculations reveal that incorporating Cl into FeN4 can drive the electron density delocalization of the FeN4 site, leading to a moderate adsorption free energy of OH* (?GOH*), d-band center, and a high onset potential, and promotes the direct four-electron-transfer ORR with weak H2O2 binding ability compared to Cl-free FeN4, indicating superior intrinsic ORR activity.

Muthusamy, S, Sabhapathy P, Raghunath P, Sabbah A, Chang Y-C, Krishnamoorthy V, Ho T-T, Chiou J-W, Lin M-C, Chen L-C, Chen K-H.  2023.  Mimicking Metalloenzyme Microenvironments in the Transition Metal-Single Atom Catalysts for Electrochemical Hydrogen Peroxide Synthesis in an Acidic Medium, 2023. Small Methods. :2300234.: John Wiley & Sons, Ltd AbstractWebsite

Abstract Electrochemical reduction of oxygen into hydrogen peroxide in an acidic medium offers an energy-efficient and green H2O2 synthesis as an alternative to the energy-intensive anthraquinone process. Unfortunately, high overpotential, low production rates, and fierce competition from traditional four-electron reduction limit it. In this study, a metalloenzyme-like active structure is mimicked in carbon-based single-atom electrocatalysts for oxygen reduction to H2O2. Using a carbonization strategy, the primary electronic structure of the metal center with nitrogen and oxygen coordination is modulated, followed by epoxy oxygen functionalities close to the metal active sites. In an acidic medium, CoNOC active structures proceed with greater than 98% H2O2 selectivity (2e?/2H+) rather than CoNC active sites that are selective to H2O (4e?/4H+). Among all MNOC (M = Fe, Co, Mn, and Ni) single-atom electrocatalysts, the CoNOC is the most selective (> 98%) for H2O2 production, with a mass activity of 10 A g?1 at 0.60 V vs. RHE. X-ray absorption spectroscopy is used to identify the formation of unsymmetrical MNOC active structures. Experimental results are also compared to density functional theory calculations, which revealed that the structure-activity relationship of the epoxy-surrounded CoNOC active structure reaches optimum (?G*OOH) binding energies for high selectivity.

Kamal Hussien, M, Sabbah A, Qorbani M, Hammad Elsayed M, Quadir S, Raghunath P, Tzou D-LM, Haw S-C, Chou H-H, Thang NQ, Lin M-C, Chen L-C, Chen K-H.  2023.  Numerous defects induced by exfoliation of boron-doped g-C3N4 towards active sites modulation for highly efficient solar-to-fuel conversion, 2023. Materials Today Sustainability. 22:100359. AbstractWebsite

Graphitic carbon nitride (CN) has emerged as a highly promising material in the photocatalysis field. However, its bulk structure suffers from a lack of active sites, limiting its practical application. Herein, a boron-doped CN (BCN) was prepared by a green gas-blowing-assisted thermal polymerization and then subjected to different exfoliation processes in order to delaminate the layered structure and tune the surface-active sites. A thorough comparative study shows that thermal exfoliation creates unsaturated nitrogen sites and induces the formation of interconnected layers that act as an electron diffusion channel for better charge transport. Furthermore, the thermally exfoliated BCN is rich in structural disorders that serve as dissociation defects for photoinduced charge carriers with a low exciton binding energy of 27 meV. Experimental results supported by theoretical calculations show that the nitrogen adjacent to boron is activated by the surrounding surface amino groups and the perforated texture to serve as an active adsorption site towards CO2 and H2O. Consequently, the exfoliated BCN acts as an outstanding bifunctional photocatalyst towards CO2 reduction into CO (40.41 μmol g−1 h−1) and prominent hydrogen evolution (4740 μmol g−1 h−1, 12.2% apparent quantum yield (AQY)).

Qorbani, M, Sabbah A, Lai Y-R, Kholimatussadiah S, Quadir S, Huang C-Y, Shown I, Huang Y-F, Hayashi M, Chen K-H, Chen L-C.  2022.  Atomistic insights into highly active reconstructed edges of monolayer 2H-WSe2 photocatalyst, 2022. Nature Communications. 13(1):1256. AbstractWebsite

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.

Fu, F-Y, Fan C-C, Qorbani M, Huang C-Y, Kuo P-C, Hwang J-S, Shu G-J, Chang S-M, Wu H-L, Wu C-I, Chen K-H, Chen L-C.  2022.  Selective CO2-to-CO photoreduction over an orthophosphate semiconductor via the direct Z-scheme heterojunction of Ag3PO4 quantum dots decorated on SnS2 nanosheets, 2022. Sustainable Energy & Fuels. 6(19):4418-4428.: The Royal Society of Chemistry AbstractWebsite

Direct Z-scheme heterojunctions are widely used for photocatalytic water splitting and CO2 reduction due to facilitating well-separated photogenerated charge carriers and spatial isolation of redox reactions. Here, using a facile two-step hydrothermal and ion-exchange method, we uniformly decorate silver orthophosphate (i.e., Ag3PO4) quantum dots with an average characteristic size of ∼10 nm over tin(iv) sulphide (i.e., SnS2) nanosheets to form a 0D/2D heterojunction. The direct Z-scheme mechanism, i.e. charge transport for efficient electron (from SnS2) and hole (from Ag3PO4) recombination, is confirmed by the following experiments: (i) ultraviolet and X-ray photoelectron spectroscopies; (ii) photodeposition of Pt and PbO2 nanoparticles on reduction and oxidation sites, respectively; (iii) in situ X-ray photoelectron spectroscopy; and (iv) electron paramagnetic resonance spectroscopy. Owing to the photoreduction properties of Ag3PO4 with orthophosphate vacancies, Z-scheme charge carrier transfer, and efficient exciton dissociation, an optimized heterojunction shows a high CO2-to-CO reduction yield of 18.3 μmol g−1 h−1 with an illustrious selectivity of ∼95% under light illumination, which is about 3.0 and 47.8 times larger than that of Ag3PO4 and SnS2, respectively. The carbon source for the CO product is verified using a 13CO2 isotopic experiment. Moreover, by tracing the peak at ∼1190 cm−1 in the dark and under light irradiation, in situ diffuse reflectance infrared Fourier transform spectroscopy demonstrates that the CO2 reduction pathway goes through the COOH* intermediate.

Kamal Hussien, M, Sabbah A, Qorbani M, Hammad Elsayed M, Raghunath P, Lin T-Y, Quadir S, Wang H-Y, Wu H-L, Tzou D-LM, Lin M-C, Chung P-W, Chou H-H, Chen L-C, Chen K-H.  2021.  Metal-free four-in-one modification of g-C3N4 for superior photocatalytic CO2 reduction and H2 evolution, 2021. Chemical Engineering Journal. :132853. AbstractWebsite

Utilization of g-C3N4 as a single photocatalyst material without combination with other semiconductor remains challenging. Herein, we report a facile green method for synthesizing a metal free modified g-C3N4 photocatalyst. The modification process combines four different strategies in a one-pot thermal reaction: non-metal doping, porosity generation, functionalization with amino groups, and thermal oxidation etching. The as-prepared amino-functionalized ultrathin nanoporous boron-doped g-C3N4 exhibited a high specific surface area of 143.2 m2 g−1 which resulted in abundant adsorption sites for CO2 and water molecules. The surface amino groups act as Lewis basic sites to adsorb acidic CO2 molecules, which can also serve as active sites to facilitate hydrogen generation. Besides, the simultaneous use of ammonium chloride as a dynamic gas bubble template along with thermal oxidation etching efficiently boosts the delamination of the g-C3N4 layers to produce ultrathin sheets; this leads to stronger light–matter interactions and efficient charge generation. Consequently, the newly modified g-C3N4 achieved selective gas-phase CO2 reduction into CO with a production yield of 21.95 µmol g-1, in the absence of any cocatalyst. Moreover, a high hydrogen generation rate of 3800 µmol g-1 h-1 and prominent apparent quantum yield of 10.6% were recorded. This work opens up a new avenue to explore different rational modifications of g-C3N4 nanosheets for the efficient production of clean energy.

Venugopal, B, Shown I, Samireddi S, Syum Z, Krishnamoorthy V, Wu H-L, Chu C-W, Lee C-H, Chen L-C, Chen K-H.  2021.  Microstructural intra-granular cracking in Cu2ZnSnS4@C thin-film anode enhanced the electrochemical performance in lithium-ion battery applications, 2021. Materials Advances. 2(17):5672-5685.: RSC AbstractWebsite

Cu2ZnSnS4 (CZTS) has demonstrated excellent performance as an anode material for lithium-ion batteries. However, the repeated lithiation and delithiation create a cracking pattern and lead to island formation in the thin-film electrode, resulting in a capacity fading over cycling in lithium-ion batteries (LIB's). In order to control this crack behaviour, we introduce carbon into CZTS thin-films by a hydrothermal method to form CZTS@C composite. CZTS@C significantly reduced the crack pattern formation on the electrode surface as well as improved the conductivity of the CZTS@C electrode. At the early stages of lithiation and delithiation, the volume expansion and contraction of Li–CZTS@C create intra-granular cracking only at the surface level, and it offers a high capacity of about 785 mA h g−1 after 150 cycles at 1000 mA g−1 charging rate, excellent rate capability (942 mA h g−1, 678 mA h g−1 and 435 mA h g−1 at 500 mA g−1, 2000 mA g−1 and 5000 mA g−1), and superior cyclability (925 mA h g−1 even after 200 cycles at 500 mA g−1). The excellent electrochemical performance at high-current rates can be attributed to intra-granular cracking together with carbon coating that provides a short transportation length for both lithium ions and electrons. Moreover, the controlled cracking pattern formation in CZTS@C facilitates faster reaction kinetics, which open up a new solution for the development of high-power thin-film anodes for next-generation LIBs applications.

Huang, Y-F, Liao K-W, Fahmi FRZ, Modak VA, Tsai S-H, Ke S-W, Wang C-H, Chen L-C, Chen K-H.  2021.  Thickness-Dependent Photocatalysis of Ultra-Thin MoS2 Film for Visible-Light-Driven CO2 Reduction. Catalysts. 11, Number 11 AbstractWebsite

The thickness of transition metal dichalcogenides (TMDs) plays a key role in enhancing their photocatalytic CO2 reduction activity. However, the optimum thickness of the layered TMDs that is required to achieve sufficient light absorption and excellent crystallinity has still not been definitively determined. In this work, ultra-thin molybdenum disulfide films (MoS2TF) with 25 nm thickness presented remarkable photocatalytic activity, and the product yield increased by about 2.3 times. The photocatalytic mechanism corresponding to the TMDs’ thickness was also proposed. This work demonstrates that the thickness optimization of TMDs provides a cogent direction for the design of high-performance photocatalysts.

Roy, P, Kumar, Haider G, Chou T-chin, Chen K-H, Chen L-C, Chen Y-F, Liang C-T.  2019.  Ultrasensitive Gas Sensors Based on Vertical Graphene Nanowalls/SiC/Si Heterostructure, 2019. ACS SensorsACS Sensors. 4(2):406-412.: American Chemical Society AbstractWebsite
K.P.O., M, Shown I, Chen L-C, Chen K-H, Tai Y.  2018.  Flexible sensor for dopamine detection fabricated by the direct growth of α-Fe2O3 nanoparticles on carbon cloth, 2018. Applied Surface Science. 427:387-395. AbstractWebsite

AbstractPorous α-Fe2O3 nanoparticles are directly grown on acid treated carbon cloth (ACC) using a simple hydrothermal method (denoted as ACC-α-Fe2O3) for employment as a flexible and wearable electrochemical electrode. The catalytic activity of ACC-α-Fe2O3 allowing the detection of dopamine (DA) is systematically investigated. The results showed that the ACC-α-Fe2O3 electrode exhibits impressive electrochemical sensitivity, stability and selectivity for the detection of DA. The detection limit determined with the amperometric method appears to be around 50nM with a linear range of 0.074–113μM. The impressive DA sensing ability of the as prepared ACC-α-Fe2O3 electrode is due to the good electrochemical behavior and high electroactive surface area (19.96cm2) of α-Fe2O3 nanoparticles anchored on the highly conductive ACC. It is worth noting that such remarkable sensing properties can be maintained even when the electrode is in a folded configuration.

Chang, CK, Kataria S, Kuo CC, Ganguli A, Wang BY, Hwang JY, Huang KJ, Yang WH, Wang SB, Chuang CH, Chen M, Huang CI, Pong WF, Song KJ, Chang SJ, Guo J, Tai Y, Tsujimoto M, Isoda S, Chen CW, Chen LC, Chen KH.  2013.  Band gap engineering of chemical vapor deposited graphene by in-situ BN doping. ACS Nano. 7:1333-1341.
Liu, YL, Yu CC, Fang CY, Chen HL, Chen CW, Kuo CC, Chang CK, Chen LC, Chen KH.  2013.  Using optical anisotropy as a quality factor to rapidly characterize structural qualities of large-area graphene films. Analytical Chemistry.
Aravind, K, Su YW, Chun DS, Kuo W, Wu CS, Chang-Liao KS, Chen KH, Chen LC, Chen CD.  2012.  Magnetic-field and temperature dependence of the energy gap in InN nanobelt. AIP Advances. 2:012155.
Karlsson, KF, Amloy S, Chen YT, Chen KH, Hsu HC, Hsiao CL, Chen LC, Holtz PO.  2012.  Polarized emission and excitonic fine structure energies of InGaN quantum dots. Physica B-Condensed Matter. 407:1553.
Huang, H-C, Shown I, Chang S-T, Hsu H-C, Du H-Y, Kuo M-C, Wong K-T, Wang S-F, Wang C-H, Chen L-C, Chen K-H.  2012.  Pyrolyzed Cobalt Corrole as a Potential Non-Precious Catalyst for Fuel Cells. Adv. Funct. Mater.. 22:3500–3508.
Chang, ST, Wang CH, Du HY, Hsu HC, Kang CM, Chen CC, Wu CS, Yen SC, Huang WF, Chen LC, Lin MC, Chen KH.  2012.  Vitalizing fuel cells with a vitamin: pyrolyzed vitamin B12 as non-precious catalyst for enhanced oxygen reduction reaction. Energy & Environ. Sci.. 5:5305-5314.
Hsu, CW, A.Ganguly, Chen CP, Kuo CC, Paskov PP, Holtz PO, Chen KH, Chen LC.  2011.  Optical properties of functionalized GaN nanowires. J. Appl. Phys.. 109:053523.
Hwang, JS, Kao MC, Shiu JM, Fan CN, Ye SC, Yu WS, Lin TY, Chattopadhyay S, Chen LC, Chen KH.  2011.  Photocurrent mapping in high efficiency radial p-n junction silicon nanowire solar cells using atomic force microscopy. J. Phys. Chem. C. 115:21981-21986.
Amloy, S, Chen YT, Karlsson KF, Chen KH, Hsu HC, Hsiao CL, C.Chen L, Holtz* PO.  2011.  Polarization resolved fine structure splitting of zero-dimensional InGaN excitons. Phys. Rev. B. 83:201307.
Hu, MS, Kuo CC, Wu CT, Chen CW, Ang PK, Loh KP, Chen KH, Chen LC.  2011.  The production of SiC nanowalls sheathed with a few layers of strained graphene and their use in heterogeneous catalysis and sensing applications. Carbon. 49:4911-4919.
Kataria, S, Liu TW, Hsiao CL, Dhara S, Chen LC, Chen KH, Dash S, Tyagi AK.  2010.  Growth orientation dependent hardness for epitaxial wurtzite InN films. J. Nanosci. Nanotechnol.. 10:5170-5174.