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2024
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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Kamal Hussien, M, Sabbah A, Qorbani M, Putikam R, Kholimatussadiah S, Tzou D-LM, Hammad Elsayed M, Lu Y-J, Wang Y-Y, Lee X-H, Lin T-Y, Thang NQ, Wu H-L, Haw S-C, Wu KC-W, Lin M-C, Chen K-H, Chen L-C.  2024.  Constructing B─N─P Bonds in Ultrathin Holey g-C3N4 for Regulating the Local Chemical Environment in Photocatalytic CO2 Reduction to CO, 2024. Small. n/a(n/a):2400724.: John Wiley & Sons, Ltd AbstractWebsite

Abstract The lack of intrinsic active sites for photocatalytic CO2 reduction reaction (CO2RR) and fast recombination rate of charge carriers are the main obstacles to achieving high photocatalytic activity. In this work, a novel phosphorus and boron binary-doped graphitic carbon nitride, highly porous material that exhibits powerful photocatalytic CO2 reduction activity, specifically toward selective CO generation, is disclosed. The coexistence of Lewis-acidic and Lewis-basic sites plays a key role in tuning the electronic structure, promoting charge distribution, extending light-harvesting ability, and promoting dissociation of excitons into active carriers. Porosity and dual dopants create local chemical environments that activate the pyridinic nitrogen atom between the phosphorus and boron atoms on the exposed surface, enabling it to function as an active site for CO2RR. The P?N?B triad is found to lower the activation barrier for reduction of CO2 by stabilizing the COOH reaction intermediate and altering the rate-determining step. As a result, CO yield increased to 22.45 µmol g?1 h?1 under visible light irradiation, which is ≈12 times larger than that of pristine graphitic carbon nitride. This study provides insights into the mechanism of charge carrier dynamics and active site determination, contributing to the understanding of the photocatalytic CO2RR mechanism.

Krishnamoorthy, V, Bangolla HK, Chen C-Y, Huang Y-T, Cheng C-M, Ulaganathan RK, Sankar R, Lee K-Y, Du H-Y, Chen L-C, Chen K-H, Chen R-S.  2024.  Efficient Hydrogen Evolution Reaction in 2H-MoS2 Basal Planes Enhanced by Surface Electron Accumulation, 2024. Catalysts. 14(1) Abstract

An innovative strategy has been developed to activate the basal planes in molybdenum disulfide (MoS2) to improve their electrocatalytic activity by controlling surface electron accumulation (SEA) through aging, annealing, and nitrogen-plasma treatments. The optimal hydrogen evolution reaction (HER) performance was obtained on the surface treated with nitrogen-plasma for 120 s. An overpotential of 0.20 V and a Tafel slope of 120 mV dec−1 were achieved for the optimized condition. The angle-resolved photoemission spectroscopy measurement confirmed the HER efficiency enhanced by the SEA conjugated with the sulfur vacancy active sites in the MoS2 basal planes. This study provides new insight into optimizing MoS2 catalysts for energy applications.

Qorbani, M, Chen K-H, Chen L-C.  2024.  Hybrid and Asymmetric Supercapacitors: Achieving Balanced Stored Charge across Electrode Materials, 2024. Small. n/a(n/a):2400558.: John Wiley & Sons, Ltd AbstractWebsite

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.

Kholimatussadiah, S, Hsu C-L, Ke S-W, Chou T-chin, Wu Y-F, Yakimova R, Kumatani A, Chen K-H, Chen L-C, Du H-Y.  2024.  In-situ observation of hydrogen nanobubbles formation on graphene surface by AFM-SECM, 2024. Electrochimica Acta. 493:144425. AbstractWebsite

Gas bubble evolution is an important phenomenon in many electrochemical processes and it is highly sensitive to the surface properties. Here we visualize the gas bubble dynamics on the surface of different graphene substrates during hydrogen evolution reaction (HER) using atomic force microscopy combined with scanning electrochemical microscopy. The low overpotential and low surface hydrophobicity of few-layer graphene formed on C-phase SiC causes the uniform distribution of hydrogen nanobubbles, which easily depart from the surface during the reaction. Conversely, the high overpotential and more hydrophobic surface of HOPG induces hydrogen bubbles to linger on the surface for an extended duration, leading to its accumulation and the subsequent formation of microbubbles. This in-situ nanoscale electrochemical mapping of hydrogen bubble dynamics provides new insight into electrocatalytic HER that occurs on non-metal electrodes.

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.

Chen, L, Chen W.  2024.  Applications Of X-ray Techniques To Nanomaterials For Energy Research. : World Scientific Publishing Company AbstractWebsite
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2023
Shown, I, Chen W-F, Chen K-H, Chen L-C.  2023.  Applications of X-ray Spectroscopy in Carbon Dioxide Reduction, 2023/08/30. Applications of X-ray Techniques to Nanomaterials for Energy Research. Volume 24:155-186.: WORLD SCIENTIFIC Abstract

The following sections are included: Introduction XAS for CO2 Reduction Electrochemical CO2 Reduction Photochemical CO2 Reduction Summary and Proposed Research Prospects Acknowledgments ReferencesThe following sections are included: Introduction XAS for CO2 Reduction Electrochemical CO2 Reduction Photochemical CO2 Reduction Summary and Proposed Research Prospects Acknowledgments References

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.

Syum, Z, Billo T, Sabbah A, kumar Anbalagan A, Quadir S, Hailemariam AG, Sabhapathy P, Lee C-H, Wu H-L, Chen L-C, Chen K-H.  2023.  Enhancing the lithium-ion storage capability of Cu2ZnSnS4 anodes via a nitrogen-doped conductive support, 2023. Chemical Engineering Journal. 465:142786. AbstractWebsite

Achieving lithium-ion batteries with both excellent electrochemical performance and cycling stability is a top priority for their real-world applications. This work reports high-performance and stable Cu2ZnSnS4 (CZTS) anode materials encapsulated by nitrogen-doped carbon (CZTS@N-C) for advanced lithium-ion battery application. Ex-situ X-ray photoelectron spectroscopy and transmission electron microscopy revealed that the nitrogen-doped carbon network features a more conducive solid-electrolyte interphase that enables lower charge-transfer resistance and fast Li+ diffusion kinetics with negligible initial irreversible capacity loss. As a result, the CZTS@N-C electrode delivers a significantly enhanced capacity of 710 mAh g−1 with 73% capacity retention after 220 cycles at a current rate of 0.5 mA g−1 and superior rate performance compared to that of unmodified CZTS. Additionally, the study sheds light on the fast lithiation dynamics chemistry of CZTS@N-C through kinetics analysis, explored by in-situ Raman, ex-situ X-ray absorption, and in-situ electrochemical impedance. This study provides a new approach for fabricating high-performance, durable conductive polymer-encapsulated low-cost transition-metal-sulfide anode materials.

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.

Muthusamy, S, Sabbah A, Sabhapathy P, Chang Y-C, Billo T, Syum Z, Chen L-C, Chen K-H.  2023.  Modification of Conductive Carbon with N-Coordinated Fe−Co Dual-Metal Sites for Oxygen Reduction Reaction, 2023. ChemElectroChem. n/a(n/a):e202300272.: John Wiley & Sons, Ltd AbstractWebsite

Abstract Earth-abundant commercial conductive carbon materials are ideal electrocatalyst supports but cannot be directly utilized for single-atom catalysts owing to the lack of anchoring sites. Therefore, we employed crosslink polymerization to modify the conductive carbon surface with Fe?Co dual-site electrocatalysts for oxygen reduction reaction (ORR). First, metal-coordinated polyurea (PU) aerogels were prepared using via crosslinked polymerization at ambient temperature. Then, carbon-supported, atomically dispersed Fe?Co dual-atom sites (FeCoNC/BP) were formed by high-temperatures pyrolysis with a nitrogen source. FTIR and 13C NMR measurements showed PU linkages, while 15N NMR revealed metal?nitrogen coordination in the PU gels. Asymmetric, N-coordinated, and isolated Fe?Co active structures were found after pyrolysis using XAS and STEM. In alkaline media, FeCoNC/BP exhibited excellent ORR activity, with a E1/2 of 0.93?V vs. RHE, higher than that of Pt/C (20?%) (0.90?V), FeNC/BP (0.88?V), and CoNC/BP (0.85?V). An accelerated durability test (ADT) on FeCoNC/BP indicated good durability over 35000 cycles. FeCoNC/BP also showed moderate ORR and ADT performance in acidic media. The macro/mesoporous N-doped carbon structures enhanced the mass transport properties of the dual Fe?Co active-sites. Therefore, modifying carbon supports with nonprecious metal catalysts may be a cost-effective-strategy for sustained electrochemical energy conversion.

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)).

2022
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.

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.

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.

Bayikadi, KS, Imam S, Ubaid M, Aziz A, Chen K-H, Sankar R.  2022.  Effect of aliovalent substituted highly disordered GeTe compound's thermoelectric performance, 2022. 922:166221. AbstractWebsite

As a lead-free high-performance thermoelectric material, germanium telluride (GeTe) has recently been extensively studied for mid-temperature (500–800 K) applications. The carrier concentration and the thermal conductivity are reduced for vacancy-controlled GeTe compounds compared with pristine GeTe. We explored and optimized the Ge0.9−xSb0.1PxTe (x = 0.01–0.05) material's highest thermoelectric performance at elevated temperatures. Intrinsic Ge vacancy control and manipulation of Ge (+2) with Sb/P (+3) increased the charge contribution to power factor improvement to ∼42 µWcm−1 K−2 while minimizing the lattice thermal contribution to ∼0.4 W/mK. This resulted in an increase in thermoelectric performance of ∼2.4 @ 773 K for the Ge0.88Sb0.1P0.02Te sample. The inclusion of atomically disordered Sb/P ions considerably increases the scattering effects caused by the point defect, whereas stretched grain boundaries reveal the decreased lattice thermal contribution. The current work demonstrates the effectiveness of phosphorus as a co-dopant in increasing the average thermoelectric performance (ZTavg) value over the GeTe operating temperature range.

Valiyaveettil, SM, Nguyen D-L, Wong DP, Hsing C-R, Paradis-Fortin L, Qorbani M, Sabbah A, Chou T-L, Wu K-K, Rathinam V, Wei C-M, Chen L-C, Chen K-H.  2022.  Enhanced Thermoelectric Performance in Ternary Skutterudite Co(Ge0.5Te0.5)3 via Band Engineering, 2022. Inorganic Chemistry. : American Chemical Society AbstractWebsite

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Valiyaveettil, SM, Qorbani M, Hsing C-R, Chou T-L, Paradis-Fortin L, Sabbah A, Srivastava D, Nguyen D-L, Ho T-T, Billo T, Ganesan P, Wei C-M, Chen L-C, Chen K-H.  2022.  Enhanced thermoelectric performance of skutterudite Co1−yNiySn1.5Te1.5−x with switchable conduction behavior, 2022. Materials Today Physics. 28:100889. AbstractWebsite

A fine control of carriers in solids is the most essential thing while exploring any functionality. For a ternary skutterudite like CoSn1·5Te1.5−x, which has been recently recognized as a potential material for thermoelectric conversion, the dominant carrier could be either electrons or holes via chemically tuning the quaternary Sn2Te2 rings in the structure. Both theoretical calculation and different spectroscopic probes, such as X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) were employed to unveil the conduction type switching details. On the other hand, a Ni-for-Co substitution was applied to enhance electronic transport, and thereby the thermoelectric power factor. Thanks to the substantial cut-off of lattice thermal conductivity by the characteristic Sn2Te2 rings in the skutterudite structure, ultimately a 70-fold increase in the dimensionless figure-of-merit (zT) is achieved at 723 K with the nominal composition Co0·95Ni0·05Sn1·5Te1.5.

Venugopal, B, Syum Z, Yu S-Y, Sabbah A, Shown I, Chu C-W, Chen L-C, Lee C-H, Wu H-L, Chen K-H.  2022.  Enhancing the Areal Capacity and Stability of Cu2ZnSnS4 Anode Materials by Carbon Coating: Mechanistic and Structural Studies During Lithiation and Delithiation, 2022. ACS Omega. 7(11):9152-9163.: American Chemical Society AbstractWebsite

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Ho, T-T, Jokar E, Quadir S, Chen R-S, Liu F-C, Cheng-YingChen, Chen K-H, Chen L-C.  2022.  Enhancing the photovoltaic properties of SnS-Based solar cells by crystallographic orientation engineering, 2022. Solar Energy Materials and Solar Cells. 236:111499. AbstractWebsite

Tin monosulfide (SnS) is a promising light-harvesting material for solar cell applications, owing to its potential for large-scale production, cost-effectiveness, eco-friendly source materials, and long-term stability. However, SnS crystallizes in an orthorhombic structure, which results in a highly anisotropic charge transport behavior. Tailoring the crystallographic orientation of the SnS absorber layer plays a critical role in the enhancement of the transfer of charge carriers and the power conversion efficiency (PCE). By controlling the substrate tilting angle and temperature ramp rate in vapor transport deposition, the crystal growth orientation was tuned to a preferred direction which significantly suppressed the unfavorable (040) crystallographic plane. Through the combination of these two approaches, the PCE could be increased from 0.11% to 2%. The effect of the tilting angle was numerically simulated to investigate its role in controlling the film uniformity and directing the film growth. In addition, the correlation between the texture coefficient of the (040) plane and the charge transport properties was determined by a combination of analytical methods such as device performance studies, electrochemical impedance spectroscopy, along with transient photovoltage, space-charge-limited current, and dark current measurements. These techniques were blended together to prove that the marked improvement in PCE can be ascribed to a reduced charge recombination (in both SnS bulk and interfaces) and an enhanced hole mobility.

Ho, T-T, Yang Z-L, Fu F-Y, Jokar E, Hsu H-C, Liu P-C, Quadir S, Cheng-YingChen, Chiu Y-P, Wu C-I, Chen K-H, Chen L-C.  2022.  Modulation and Direct Mapping of the Interfacial Band Alignment of an Eco-Friendly Zinc-Tin-Oxide Buffer Layer in SnS Solar Cells, 2022. ACS Applied Energy MaterialsACS Applied Energy Materials. 5(11):14531-14540.: American Chemical Society AbstractWebsite
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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.

Quadir, S, Qorbani M, Sabbah A, Wu T-S, kumar Anbalagan A, Chen W-T, Valiyaveettil SM, Thong H-T, Wang C-W, Cheng-YingChen, Lee C-H, Chen K-H, Chen L-C.  2022.  Short- and Long-Range Cation Disorder in (AgxCu1–x)2ZnSnSe4 Kesterites, 2022. Chemistry of Materials. : American Chemical Society AbstractWebsite

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