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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 behaviour of increasing the charge recombination gradually while shrinking the bandgap, here we present a series of polymers 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, which acts 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 enhancement of charge separation between D and A. As a result, the PITIC-ThF Pdots exhibit superior hydrogen evolution rates of 339.7 mmol g− 1 h− 1 (0.279 mol/h) and 4100 µmol g− 1 h− 1 (20.5 µmol/h) with visible (> 420 nm) and NIR (> 780 nm) light irradiation, respectively. Furthermore, PITIC-ThF Pdots exhibit a record-breaking apparent quantum yield (AQY) at 700 nm (4.76%). more...

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. more...

Most chemical vapor deposition methods for transition metal dichalcogenides use an extremely small amount of precursor to render large single-crystal flakes, which usually causes low coverage of the materials on the substrate. In this study, a self-capping vapor-liquid-solid reaction is proposed to fabricate large-grain, continuous MoS2 films. An intermediate liquid phase-Na2Mo2O7 is formed through a eutectic reaction of MoO3 and NaF, followed by being sulfurized into MoS2. The as-formed MoS2 seeds function as a capping layer that reduces the nucleation density and promotes lateral growth. By tuning the driving force of the reaction, large mono/bilayer (1.1 mm/200 μm) flakes or full-coverage films (with a record-high average grain size of 450 μm) can be grown on centimeter-scale substrates. The field-effect transistors fabricated from the full-coverage films show high mobility (33 and 49 cm2 V−1 s−1 for the mono and bilayer regions) and on/off ratio (1 ~ 5 × 108) across a 1.5 cm × 1.5 cm region., Here, the authors develop a self-capping vapour-liquid-solid reaction to fabricate large-grain continuous MoS2 films, whereby an intermediate liquid phase-Na2Mo2O7 is formed through a eutectic reaction of MoO3 and NaF, followed by sulphurisation into MoS2. more...

Designing highly conducting metal–organic frameworks (MOFs) is currently a subject of great interest for their potential applications in diverse areas encompassing energy storage and generation. Herein, a strategic design in which a metal–sulfur plane is integrated within a MOF to achieve high electrical conductivity, is successfully demonstrated. The MOF {[Cu2(6-Hmna)(6-mn)]·NH4}n (1, 6-Hmna = 6-mercaptonicotinic acid, 6-mn = 6-mercaptonicotinate), consisting of a two dimensional (–Cu–S–)n plane, is synthesized from the reaction of Cu(NO3)2, and 6,6′-dithiodinicotinic acid via the in situ cleavage of an S–S bond under hydrothermal conditions. A single crystal of the MOF is found to have a low activation energy (6 meV), small bandgap (1.34 eV) and a highest electrical conductivity (10.96 S cm−1) among MOFs for single crystal measurements. This approach provides an ideal roadmap for producing highly conductive MOFs with great potential for applications in batteries, thermoelectric, supercapacitors and related areas. more...

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. more...

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 Cu more...

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

The quest of earth-abundant bifunctional electrocatalysts for highly efficient oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is essential for clean and renewable energy systems. Herein, directed by the experimental analysis, we demonstrate layered nickel lithium phosphosulfide (NiLiP2S6) crystal as a highly efficient water-splitting catalyst in alkaline media. With strained lattice due to stacked layers as observed by TEM and electronic structure analysis performed by XPS showed mixed Ni2+,3+ oxidation states induced by addition of Li as a cation, NiLiP2S6 displays excellent OER (current density of 10 mA cm–2 showed an overpotential of 303 mV vs. RHE and a Tafel slope of 114 mV dec–1) and HER activity (current density of −10 mA cm–2 showed an overpotential of 184 mV vs. RHE and a Tafel slope of 94.5 mV dec–1). Finally, an alkaline media was employed to demonstrate the overall water splitting using NiLiP2S6 as both the anode and the cathode, which attained a 50 mA cm−2 current density at 1.68 V. This bimetallic phosphosulfide, together with long-term stability and enhanced intrinsic activity, shows enormous potential in water splitting applications. more...

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. more...

Pharmaceutical drugs' removal from wastewater by photocatalytic oxidation process is considered as an attractive approach and environmentally friendly solution. This report aims to appraise the practical application potential of Ag/g-C more...

Layered MoS2 is considered as one of the most promising two-dimensional photocatalytic materials for hydrogen evolution and water splitting; however, the electronic structure at the MoS2-liquid interface is so far insufficiently resolved. Measuring and understanding the band offset at the surfaces of MoS2 are crucial for understanding catalytic reactions and to achieve further improvements in performance. Herein, the heterogeneous charge transfer behavior of MoS2 flakes of various layer numbers and sizes is addressed with high spatial resolution in organic solutions using the ferrocene/ferrocenium (Fc/Fc+) redox pair as a probe in near-field scanning electrochemical microscopy, i.e. in close nm probe-sample proximity. Redox mapping reveals an area and layer dependent reactivity for MoS2 with a detailed insight into the local processes as band offset and confinement of the faradaic current obtained. In combination with additional characterization methods, we deduce a band alignment occurring at the liquid-solid interface., Here, high-resolution atomic force microscopy and scanning electrochemical microscopy are used to investigate the electron transfer behaviour of layered MoS2 flakes in organic solutions, offering insights on the electronic band alignment at the solid-liquid interface. more...

Chemical alloying is a powerful approach to tune the electronic structure of semiconductors and has led to the synthesis of ternary and quaternary two-dimensional (2D) dichalcogenide semiconductor alloys (e.g., MoSSe₂, WSSe₂, etc.). To date, most of the studies have been focused on determining the chemical composition by evaluating the optical properties, primarily via photoluminescence and reflection spectroscopy of these materials in the 2D monolayer limit. However, a comprehensive study of alloying in multilayer films with direct measurement of electronic structure, combined with first-principles theory, is required for a complete understanding of this promising class of semiconductors. We have combined first-principles density functional theory calculations with experimental characterization of MoS_(2(1-x))Se_(2x) (where x ranges from 0 to 1) alloys using X-ray photoelectron spectroscopy to evaluate the valence and conduction band edge positions in each alloy. Moreover, our observations reveal that the valence band edge energies for molybdenum sulfide/selenide alloys increase as a function of increasing selenium concentration. These experimental results agree well with the results of density functional theory calculations showing a similar trend in calculated valence band edges. Our studies suggest that alloying is an effective technique for tuning the band edges of transition-metal dichalcogenides, with implications for applications such as solar cells and photoelectrochemical devices. more...

In this work, we study the effect of sputtering pressures on the thermoelectric properties of GeTe films. The working pressures were differentiated from 3 to 30 mTorr, and the as-deposited films were annealed at 623 K for 10 min in Ar atmosphere. The results show that the working pressure has a significant effect on the Ge content and crystalline size. The turning trend of the Seebeck coefficient with different sputtering pressures corresponds to the Ge content. The surface morphology of annealed film will change from cracks to voids with increasing sputtering pressure. This behavior can be explained by the growth mechanisms model. The voids and relatively low crystalline size of GeTe films affect to the reduction of the electrical conductivity. In addition, the void content decreased as film thickness was increased. Therefore, controlling the working pressures in the sputtering process and film thickness is important for the thermoelectric performance of GeTe thin film. In our work, we prove that the thermoelectric properties of GeTe films could be optimized effectively by simply tuning different sputtering conditions. more...

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-1h−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. more...

Among the lead-free thermoelectric material, germanium telluride (GeTe) has been extensively investigated due to its high thermoelectric performance (ZT) in mid-temperature; however, high p-type carrier density (∼1021 cm-3) hinder its suitability for higher ZT. In turn, to enhance the thermoelectric performance of the environmentally favorable GeTe, we explored that the Mo doping significantly optimizes the carrier concentration along with uniquely unveiled microcrystalline rods accompanying compact grain boundaries, high-density planar defects, and point defects effectuating all-frequency phonon scattering yields to lower down the thermal conductivity. Furthermore, Sb/Bi co-doping with Mo at the Ge sites predominantly reduces the carrier concentration and thermal conductivity to attain a higher ZT. The co-doping of Bi manifested a more prominent role in achieving the highest ZT of ∼2.3 at 673 K for the sample composition with Ge0.89Mo0.01Bi0.1Te. This study demonstrates an exciting hidden aspect of microstructural modification by forming highly dense microcrystalline rods (MCRs) through Mo and Sb/Bi doping to achieve high-performance in GeTe. more...

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. Photocatalytic reduction of CO2 to hydrocarbons is a promising route to both CO2 utilization and renewable fuel production. Here the authors identify that carbon-doped SnS2 possesses a high catalytic efficiency towards CO2 reduction owing to low photogenerated charge recombination rates. more...

Pharmaceutical drugs' removal from wastewater by photocatalytic oxidation process is considered as an attractive approach and environmentally friendly solution. This report aims to appraise the practical application potential of Ag/g-C3N4/ZnO nanorods toward the wastewater treatment of the pharmaceutical industry. The catalysts are synthesized by straightforward and environmentally-friendly strategies. Specifically, g-C3N4/ZnO nanorods heterostructure is constructed by a simple self-assembly method, and then Ag nanoparticles are decorated on g-C3N4/ZnO nanorods by a photoreduction route. The results show that three commercial drugs (paracetamol, amoxicillin, and cefalexin) with high concentration (40 mg L−1) are significantly degraded in the existence of a small dosage of Ag/g-C3N4/ZnO nanorods (0.08 g L−1). The Ag/g-C3N4/ZnO nanorods photocatalyst exhibits degradation performance of paracetamol higher 3.8, 1.8, 1.3 times than pristine g-C3N4, ZnO nanorods, and g-C3N4/ZnO nanorods. Furthermore, Ag/g-C3N4/ZnO nanorods have an excellent reusability and a chemical stability that achieved paracetamol degradation efficiency of 78% and remained chemical structure of the photocatalyst after five cycles. In addition, the photocatalytic mechanism explanation and comparison of photocatalytic drugs’ degradation ability have also been discussed in this study. more...

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. more...

A series of Sn added TiS2 (TiS2:Sn x ; x = 0, 0.05, 0.075 and 0.1) were prepared by solid state synthesis with subsequent annealing. The Sn atoms interacted with sulfur atoms in TiS2 and formed a trace amount of misfit layer (SnS)1+m(TiS2−δ)n compound with sulfur deficiency. A significant reduction in electrical resistivity with moderate decrease in the Seebeck coefficient was observed in Sn added TiS2. Hence, a maximum power factor of 1.71 mW/m-K2 at 373 K was obtained in TiS2:Sn0.05. In addition, the thermal conductivity was decreased with Sn addition and reached a minimum value of 2.11 W/m-K at 623 K in TiS2:Sn0.075, due to the impurity phase (misfit phase) and defects (excess Ti) scattering. The zT values increased from 0.08 in pristine TiS2 to an optimized value of 0.46 K at 623 K in TiS2:Sn0.05. more...

Understanding the role of the oxidation state of the Cu surface and surface-adsorbed intermediate species in electrochemical CO2 reduction is crucial for the development of selective CO2-to-fuel electrocatalysts. In this study, the electrochemical CO2 reduction mechanism over the Cu catalysts with various oxidation states was studied by using in situ surface-enhanced infrared absorption spectroscopy (SEIRAS), in situ soft X-ray absorption spectroscopy (Cu L-edge), and online gas chromatography measurements. The atop-adsorbed CO (COatop) intermediate is obtained on the electrodeposited Cu surface which primarily has the oxidation state of Cu(I). COatop is further reduced, followed by the formation of C1 product such as CH4. The residual bridge-adsorbed CO (CObridge) is formed on the as-prepared Cu surface with Cu(0) which inhibits hydrocarbon formation. In contrast, the CV-treated Cu electrode prepared by oxidizing the as-prepared Cu surface contains different amounts of Cu(I) and Cu(0) states. The major theme of this work is that in situ SEIRAS results show the coexistence of COatop and CObridge as the reaction intermediates during CO2 reduction and that the selectivity of CO2-to-ethylene conversion is further enhanced in the CV-treated Cu electrode. The Cu catalysts modulated by the electrochemical method exhibit different oxidation states and reaction intermediates as well as electrocatalytic properties. more...

Nonnoble metal catalysts are low-cost alternatives to Pt for the oxygen reduction reactions (ORRs), which have been studied for various applications in electrocatalytic systems. Among them, transition metal complexes, characterized by a redox-active single-metal-atom with biomimetic ligands, such as pyrolyzed cobalt–nitrogen–carbon (Co–Nx/C), have attracted considerable attention. Therefore, we reported the ORR mechanism of pyrolyzed Vitamin B12 using operando X-ray absorption spectroscopy coupled with electrochemical impedance spectroscopy, which enables operando monitoring of the oxygen binding site on the metal center. Our results revealed the preferential adsorption of oxygen at the Co2+ center, with end-on coordination forming a Co2+-oxo species. Furthermore, the charge transfer mechanism between the catalyst and reactant enables further Co–O species formation. These experimental findings, corroborated with first-principle calculations, provide insight into metal active-site geometry and structural evolution during ORR, which could be used for developing material design strategies for high-performance electrocatalysts for fuel cell applications., Understanding active-site geometry and structural evolution during electrocatalysis is important for further development. Here the authors use operando X-ray absorption spectroscopy combined with electrochemical impedance spectroscopy to investigate single atom catalysts derived from Vitamin B12. more...

We have demonstrated a nonlinear behavior for the bandgap opening of doped graphene by controlling the concentration of B and N co-dopants. X-ray absorption and emission spectra reveal that the ban ... more...

Tin-based composites are promising anode materials for high-performance lithium-ion batteries (LIBs); however, insufficient conductivity, as well as fatal volume expansion during cycling lead to poor electrochemical reversibility and cycling stability. In this work, we demonstrate the lithium-ion storage behaviors of SnS2 anode material deposited on different electrode supports. The SnS2 grown on 3D hierarchical carbon nanotube-carbon cloth composites (SnS2-CNT-CC) shows superior capacity retention and cycle stability, compared to that on planar Mo sheets and carbon cloth. The specific capacity of SnS2 on Mo, CC, and CNT-CC is around 240, 840, and 1250 g−1, respectively. The SnS2-CNT-CC electrode outperforms in the cyclic performance and rate capability compared to other electrode configurations due to the multi-electron pathway and high surface area derived from 3D hierarchical CNT-CC electrode support. Furthermore, a significant decrease in the charge transfer resistance is observed by utilizing 3D hierarchical CNT-CC electrode support. The use of 3D hierarchical structures as electrode support could be the best alternative to enhance the electrochemical performances for the next generation LIBs. more...

The conversion of CO2 into hydrocarbon fuels via the photocatalytic reaction route is considered a potential strategy to concurrently address serious energy crisis and greenhouse gas emission problems. Nevertheless, the generation of long-chain hydrocarbon products (Cn, n ≥ 2) from the visible-light-reactive photocatalytic CO2 reduction has also been considering a contemporary challenge. Herein, we indicate that Ag nanoparticles (Ag NPs) loaded gC3N4/ZnO nanorods heterojunction (Ag-gC3N4/ZnO NRs abbreviation) has extended photoactive range and enhanced specific surface area. The combination of Ag NPs and gC3N4/ZnO NRs significantly enhances photocatalytic CO2 reduction efficiency to form the acetone product. Detail, the acetone production efficiency of Ag-gC3N4/ZnO NRs is 8.4 and 7.5 times higher than pure ZnO NRs and gC3N4/ZnO NRs at the same condition, respectively. This study represents a potential approach toward higher-energy-value hydrocarbons production and greenhouse gas emission mitigation. more...

Solar photoreduction of CO2 to produce value added hydrocarbons is highly desirable to tackle environmental and energy issues. [1-2] Despite the great improvement in the efficiency and cost of solar cells, the efficiency in artificial photosynthesis is much lower than the >15% of solar cells. Recent progress in 2D chalcogenides with tunable bandgap and layer numbers offers great opportunity for the investigation in this field. In this work, thin film and powder SnS2 have been synthesized for the study. Hydrothermal synthesis of carbon-containing SnS2 exhibits a highly active photocatalytic conversion of CO2 to selective hydrocarbons under visible-light irradiation. Overall, the carbon doping in the SnS2 nanostructure plays a key role and significantly enhance the visible light photocatalytic activity with a photochemical quantum efficiency above 0.7%. [3-4] Meanwhile, Thin film SnS2 has been grown for the mechanism study. By carbon-ion implantation of the thin film, we observed enhanced CO2 reduction under solar illumination. Other FTIR, Raman, NMR, BET, SECM, and synchrotron based facilities including APXPS and XAS have been used to investigate this issue. 1. Shown, H.C. Hsu, Y.C. Chang, C.H. Lin, P.K. Roy, A. Ganguly, C.H. Wang, J.K. Chang, C.I. Wu, L.C. Chen, K.H. Chen, Nano Letters 14, 6097-6103 (2014). 2. Billo, F.Y. Fu, P. Raghunath, I. Shown, W.F. Chen, H.T. Lien, T.H. Shen, J.F. Lee, M. C. Lin, J.S. Hwang, C.H. Lee, L.C. Chen, and K.H. Chen, Small 14, 1702928 (2018). 3. Shown, S. Samireddi, Y.C. Chang, R. Putikam, P.H. Chang, A. Sabbah, F.Y. Fu, W.F. Chen, C.I. Wu, T.Y. Yu, P.W. Chung, M.C. Lin, L.C. Chen, and K.H. Chen, Nature Comm. 9, 169 (2018). 4. T. Billo, I. Shown, A.K. Anbalagan, T.A. Effendi, A. Sabbah, F.Y. Fu, C.M. Chu, W.Y. Woon, R.S. Chen, C.H. Lee, K.H. Chen, L.C. Chen, Nano Energy 72, 104717 (2020). more...

Solar photoreduction of CO2 to produce value added hydrocarbons is highly desirable to tackle environmental and energy issues. [1-2] Despite the great improvement in the efficiency and cost of solar cells, the efficiency in artificial photosynthesis is much lower than the >15% of solar cells. Recent progress in 2D chalcogenides with tunable bandgap and layer numbers offers great opportunity for the investigation in this field. In this work, thin film and powder SnS2 have been synthesized for the study. Hydrothermal synthesis of carbon-containing SnS2 exhibits a highly active photocatalytic conversion of CO2 to selective hydrocarbons under visible-light irradiation. Overall, the carbon doping in the SnS2 nanostructure plays a key role and significantly enhance the visible light photocatalytic activity with a photochemical quantum efficiency above 0.7%. [3-4] Meanwhile, Thin film SnS2 has been grown for the mechanism study. By carbon-ion implantation of the thin film, we observed enhanced CO2 reduction under solar illumination. Other FTIR, Raman, NMR, BET, SECM, and synchrotron based facilities including APXPS and XAS have been used to investigate this issue. 1. Shown, H.C. Hsu, Y.C. Chang, C.H. Lin, P.K. Roy, A. Ganguly, C.H. Wang, J.K. Chang, C.I. Wu, L.C. Chen, K.H. Chen, Nano Letters 14, 6097-6103 (2014). 2. Billo, F.Y. Fu, P. Raghunath, I. Shown, W.F. Chen, H.T. Lien, T.H. Shen, J.F. Lee, M. C. Lin, J.S. Hwang, C.H. Lee, L.C. Chen, and K.H. Chen, Small 14, 1702928 (2018). 3. Shown, S. Samireddi, Y.C. Chang, R. Putikam, P.H. Chang, A. Sabbah, F.Y. Fu, W.F. Chen, C.I. Wu, T.Y. Yu, P.W. Chung, M.C. Lin, L.C. Chen, and K.H. Chen, Nature Comm. 9, 169 (2018). 4. Y. Fu, I. Shown, C.H. Li, P. Raghunath, T.Y. Lin, T. Billo, H.L. Wu, C.I. Wu, P.W. Chung, M.C. Lin, L.C. Chen, and K.H. Chen, ACS Appl. Mater. & Interface 11, 28 (2019). more...

(Invited) Photocatalytic CO2 conversion to hydrocarbon fuels, which makes solar energy harvesting and CO2 reduction reaction (CO2RR) simultaneously, is a killing two birds with one stone approach to solving the energy and environmental problems. However, challenges are the low photon-to-fuel conversion efficiency of the photocatalysts and lack of the product selectivity. Recently, 2D-layered nanomaterials with defect engineering, e.g. the carbon interstitial-doped SnS2 nanosheets [Nature Comm. 9, 169 (2018)], have shown promise for CO2RR. Here, I will present a different case, MoS2 with vacancies controlled by plasma. Productivity and selectivity of CO2RR were found to be dependent strongly with the different Mo/S ratios of the MoS2 of single to few layers. Orders-of-magnitude enhancement in productivity and selectivity of C2 product over 97% has been obtained. The role and interplay of the defects and the hosting materials, and their effects on the adsorption of CO2 and subsequent CO2RR, studied by the near-ambient pressure X-ray photoemission spectroscopy, along with density functional theory will be discussed. more...

Carbon dioxide conversion into valuable chemicals using solar light considered an ideal goal in renewable energy studies. For the purpose of effective photocatalytic materials, a large number of strategies have been studied. Coupling of semiconductors is considered one of the best approaches to design a good photocatalyst for producing selective solar fuels. In this study, we fabricate ZnO/ Co(OH)2 model heterogeneous catalysts for CO2 reduction under visible light irradiation. Firstly, Three ZnO samples with different morphologies and surface area were fabricated by varying preparation methods. It is found that ZnO nanoflakes with a high ratio of {0002} facets possess a higher conversion rate yielding Methanol, Acetaldehyde, and Acetone as the major products of photocatalytic CO2 reduction in a continuous flow gas-phase reaction condition. The obtained ZnO nanoflakes were then treated to form the heterostructure of ZnO/Co(OH)2. When the mass ratio between hexagonal-phased ZnO and Co(OH)2 is varied, the composite catalyst shows selective methanol formation as a major product compared to pristine ZnO phases. The synthesized samples were characterized by means of a multi techniques approach involving powder X-ray diffraction, scanning electron microscopy coupled with energy dispersive X-ray analysis, transmission electron microscopy, Photoluminescence, UV-Visible diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, and surface area measurements. In conclusion, the results can not only provide the importance indication about the influence of {0002} facets of ZnO, but also demonstrated a strategy for the selective formation of hydrocarbons over the heterostructure semiconductors of ZnO/Co(OH)2 nanocomposites. more...

Lithium-ion batteries (LIBs) function as power sources in various environments and the effect of temperature is one of the major factors which limits the performance and proper operations in in cold climates or high altitude areas and in space applications. Hence, the poor charge/discharge rate and short lifetime of LIBs in low-temperature areas have restricted its application for electric vehicle (EV) or a hybrid EV. In this work, copper zinc tin sulfide (CZTS) thin-film anode materials with different mixtures of electrolytes has been prepared to study the electrochemical performance at low-temperature environments. The CZTS anode, prepared from EC/DEC/DMC electrolyte has demonstrated higher efficiency and reversible capacity at -10 oC as compared to the binary electrolyte obtained from EC/DEC electrolyte. The performance of the electrolyte at different temperature ranges and the corresponding electrochemical performance of CZTS electrode is systematically analyzed. The Kinetics and surface morphology of the as-prepared CZTS anode has been analyzed using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS) and Scanning electron microscope (SEM) respectively. As compared to the room temperature capacity, the CZTS has demonstrated outstanding capacity retention around 55.3 % at -10 oC in the ternary solvent electrolyte mixtures after 100 cycles at 500 mA/g current density. However, in the binary EC-DEC based electrode, a rapid capacity degradation with a capacity retention of only around 27.2 % of the room temperature capacity has been observed at the same experimental conditions. This method could be an alternative approach to study the effect of electrolyte and the performance of the anode materials in the design of thin-film micro-batteries for next-generation sub-zero temperature applications. The detail characterization and experimental results with the future perspective of this study will be discussed here. more...

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Designing highly conducting metal–organic frameworks (MOFs) is currently a subject of great interest for their potential applications in diverse areas encompassing energy storage and generation. Herein, a strategic design in which a metal–sulfur plane is integrated within a MOF to achieve high electrical conductivity, is successfully demonstrated. The MOF {[Cu2(6-Hmna)(6-mn)]·NH4}n (1, 6-Hmna = 6-mercaptonicotinic acid, 6-mn = 6-mercaptonicotinate), consisting of a two dimensional (–Cu–S–)n plane, is synthesized from the reaction of Cu(NO3)2, and 6,6′-dithiodinicotinic acid via the in situ cleavage of an S–S bond under hydrothermal conditions. A single crystal of the MOF is found to have a low activation energy (6 meV), small bandgap (1.34 eV) and a highest electrical conductivity (10.96 S cm−1) among MOFs for single crystal measurements. This approach provides an ideal roadmap for producing highly conductive MOFs with great potential for applications in batteries, thermoelectric, supercapacitors and related areas., Metal–organic frameworks that contain metal–sulfur chains have been demonstrated to exhibit good electrical conductivity. Here, the authors integrate a 2D metal–sulfur plane into a metal–organic framework, reporting a single crystal with a high conductivity of 10.96 S/cm. more...

We synthesized a bismuth-rich bismuth sulfide (Bi2+xS3) to improve the electrical conductivity. A percolated composite was obtained by mixing Bi2+xS3 with commercial Bi2S3 so that the other thermoelectric parameters were not compromised. The Bi2+xS3 acted as a conductive percolating channel within the Bi2S3 matrix. This percolation approach retained the high Seebeck coefficient of the Bi2S3 matrix while improving the electrical conductivity. A dimensionless figure of merit (zT) up to five times that of the pure Bi2S3 sample was achieved. more...

The photoconduction properties of (non-polar) m-plane and (polar) c-plane ZnO thin films epitaxially grown on relatively lattice-matched LiGaO2 substrates by chemical vapor deposition have been investigated and compared. Structural and photoluminescence characterizations indicate that the c-plane ZnO films possess higher crystallinity than the m-plane ZnO films. Owing to their superior crystallinity and lower dark current, the c-plane ZnO films exhibit significantly higher optimal sensitivity (S = 4650) to ultraviolet light than the m-plane ZnO films (S = 10). However, in terms of photocurrent generation efficiency, the m-plane ZnO films exhibit over one order of magnitude higher responsivity (R = 0.05–3.2 A W−1) than the c-plane ZnO films (R = 0.009–0.035 A W−1) in the light intensity range 1.6–320 W m−2. The probable mechanisms causing the aforementioned differences based on surface-dominant photoconduction and bulk-dominant structural and photoluminescence properties are also discussed. more...

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., Photocatalytic reduction of CO2 to hydrocarbons is a promising route to both CO2 utilization and renewable fuel production. Here the authors identify that carbon-doped SnS2 possesses a high catalytic efficiency towards CO2 reduction owing to low photogenerated charge recombination rates. more...

Flexible supercapacitors, a state-of-the-art material, have emerged with the potential to enable major advances in for cutting-edge electronic applications. Flexible supercapacitors are governed by the fundamentals standard for the conventional capacitors but provide high flexibility, high charge storage and low resistance of electro active materials to achieve high capacitance performance. Conducting polymers (CPs) are among the most potential pseudocapacitor materials for the foundation of flexible supercapacitors, motivating the existing energy storage devices toward the future advanced flexible electronic applications due to their high redox active-specific capacitance and inherent elastic polymeric nature. This review focuses on different types of CPs-based supercapacitor, the relevant fabrication methods and designing concepts. It describes recent developments and remaining challenges in this field, and its impact on the future direction of flexible supercapacitor materials and relevant device fabrications. more...

Secondary ion mass spectrometry (SIMS) with 520 keV A u 400 4 + projectiles operating in event-by-event bombardment/detection mode was applied to investigate pyrolized mixtures of catalyst (vitamin B12) and carbon supports (carbon black). The specimens are alternative cathode materials to platinum for fuel cells. The goal was to understand the effect of temperature on the chemical environment of the catalytically active sites formed on the carbon supports during pyrolysis. The A u 400 4 + projectiles probed the samples one-at-a-time in a stochastic manner and the resulting secondary ions from the individual impacts were recorded separately. The coincidental methodology allows one to compile mass spectra comprising selectively the secondary ions from the impacts on the active sites, extracting the local molecular information of the active sites within a nanodomain (∼10 3 nm 3 ). The detection of CoN 4 C x − suggests Co-N 4 be the moiety retained from the pyrolized vitamin B12 in the presence of the carbon black. Variations in the local chemical environment of the active sites as a function of pyrolysis temperature were also observed. Additionally, we could quantify the dispersion of the active sites among the carbon supports, a measure providing a direction for future device optimization. more...