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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.

The mechanisms for O2 reduction and H2O/H2O2 formation on Co–corrin and Co–porphyrin cathode surfaces of the proton exchange membrane fuel cell (PEMFC) systems have been studied by hybrid Hartree–F...

Germanium tellurides and its pseudo binary compounds offer interesting properties that are important in thermoelectric and phase-change applications. Despite being a class of materials under scrutiny since its discovery, unique properties and functionalities kept on emerging in recent years. In this work, we observed another unique property of Ge-Sb-Te (GST) thin film that can be beneficial in its development for thermoelectric application. A rapid heating and quenching process of the GST film resulted in a metastable rock-salt cubic structure, exhibiting a unique electronic-transition-like behavior. Above the transition temperature at 150 °C, we observed a temperature-induced band modulation, corroborated with changes in its effective mass and valence band position that leads to favorable electronic and thermoelectric properties. Charge transfer between Sb and Te occurred, accompanied by a distorted cubic-to-cubic structural change. The interplay of the electronic and lattice structure born out of the co...

Interface engineering of CdS/CZTS(Se) is an important aspect of improving the performance of buffer/absorber heterojunction combination. It has been demonstrated that the crossover phenomenon due to the interface recombination can be drastically eliminated by interface modification. Therefore, in-depth studies across the CdS/CZTS(Se) junction properties, as well as effective optimization processes, are very crucial for achieving high-efficiency CZTSSe solar cells. Here, we present a comprehensive study on the effects of soft-baking (SB) temperature on the junction properties and the corresponding optoelectronic and interface-structural properties. Based on in-depth photoemission studies corroborated with structural and composition analysis, we concluded that interdiffusion and intermixing of CZTSSe and CdS phases occurred on the Cu-poor surface of CZTSSe at elevated SB temperatures, and the interface dipole moments induced by electrostatic potential fluctuation were thus significantly eliminated. In contrast, with low SB temperature, the CdS/CZTSSe heterojunction revealed very sharp interface with very short interdiffusion, forming interface dipole moments and drastically deteriorating device performance. These post thermal treatments also significantly suppress defect energy level of interface measured by admittance spectroscopy from 294 to 109 meV due to CdS/CZTSSe interdiffusion. Meanwhile, the interdiffusion effects on the shift of valence band maximum, conduction band minimum and band offset across the heterojunction of thermally treated CdS/CZTSSe interface are spatially resolved at the atomic scale by measuring the local density of states with cross-sectional scanning tunneling microscopy and spectroscopy. A significant enhancement in the power conversion efficiency from 4.88% to 8.48% is achieved by a facile interface engineering process allowing a sufficient intermixing of CdS/Cd and CZTSSe/Se phases without detrimental recombination centers.

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.

This work demonstrates the first example of interfacial manipulation in a hybrid photocatalyst based on poly(3-hexylthiophene-2,5-diyl) (P3HT) nanoparticle and graphene oxide (GO) bulk heterojunctions to efficiently reduce CO2 into selective industrial hydrocarbons under gas-phase reaction and visible-light illumination. High selectivity of chemical products (methanol and acetaldehyde) was observed. Moreover, the hybrid photocatalyst’s solar-to-fuel conversion efficiency was 13.5 times higher than that of pure GO. The increased production yield stems from the co-catalytic and sensitizing role of P3HT in the hybrid system due to its ability to extend light absorption to the visible range and improve interfacial charge transfer to GO. The hybrid P3HT-GO formed a type II heterojunction, and its static and dynamic exciton behaviors were examined using fluorescence spectroscopy and exciton lifetime mapping. A reduced fluorescence decay time was observed by interfacial manipulation for improved dispersion, indicating a more efficient charge transfer from the excited P3HT to GO. Thus, the conducting polymer nanoparticles, 2D nanocarbon, have demonstrated superior performance as a metal-free, non-toxic, low-cost, and scalable heterogeneous photocatalyst for CO2 reduction to solar fuel, a solid–gas system.

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.

Exploring electrocatalysts composed of earth-abundant elements for a highly efficient hydrogen evolution reaction (HER) is scientifically and technologically important for electrocatalytic water splitting. In this work, we report HER properties of acid treated pyrolyzed vitamin B12 supported on reduced graphene oxide (B12/G800A) that shows an extraordinarily enhanced catalytic activity with low overpotential (115 mV vs. RHE at 10 mA cm−2), which is better than that of most traditional nonprecious metal catalysts in acidic media. Stability tests through long-term potential cycles and at a constant current density confirm the exceptional durability of the catalyst. Notably, the B12/G800A catalyst exhibits extremely high turnover frequencies per cobalt site in acid, for example, 0.85 and 11.46 s−1 at overpotentials of 100 and 200 mV, respectively, which are higher than those reported for other scalable non-precious metal HER catalysts. Moreover, it has been conjectured that the covalency of Co–C and Co–N bonds affects HER activities by comparing the extended X-ray absorption fine structure (EXAFS) spectra of the B12/G800A. High-temperature treatment can modify the Co-corrin structure of B12 to form Co–C bonds along with Co–N, which broadens the band of cobalt, essentially lowering the d-band center from its Fermi level. The lower d-band center leads to a moderate hydrogen binding energy, which is favorable for hydrogen adsorption and desorption.

The present investigation mainly addresses the open circuit voltage (Voc) issue in kesterite based Cu2ZnSn(S,Se)4 solar cells by simply introducing alkali metal fluoride nanolayers (~ several nm NaF, or LiF) to lower the work functions of the front ITO contacts without conventional hole-blocking ZnO layers. Kelvin probe measurements confirmed that the work function of the front ITO decreases from 4.82 to 3.39 and 3.65 eV for NaF and LiF, respectively, resulting in beneficial band alignment for electron collection and/or hole blocking on top electrodes. Moreover, a 10.4% power conversion efficiency (~ 11.5% in the cell effective area) CZTSSe cell with improved Voc of up to 90 mV has been attained. This demonstration may provide a new direction of further boosting the performance of copper chalcogenide based solar cells as well.

A nonstoichiometric Si1− x Ge x with composition ratio dependent saturable absorption prepared by vaporized synthesis and chemical exfoliation is performed to passively mode-lock the Erbium-doped fiber laser (EDFL). The Si1− x Ge x with varied Ge/Si composition ratio from 3 to 16 exhibits tunable nonlinear modulation depth from 17% to 22%, where the Si1− x Ge x with the highest Ge content performs the largest nonlinear modulation depth. When operating the EDFL in the self-amplitude modulation region, the Si1− x Ge x with Ge/Si composition ratios of 3, 9, and 16 self-starts the EDFL pulsation with pulsewidths of 820, 760, and 730 fs. When operating the EDFL in high gain region, the self-phase modulation induced soliton compression dominates the repulsation of passively mode-locked EDFL, which slightly shrinks the EDFL pulsewidth from 346 to 338 fs. All these demonstrations are premier and important to explore the superior nonstoichiometric Si 1− x Ge x saturable absorbers for ultrafast fiber lasers.

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.

Applications of lithium ion battery have been hampered by a lack of ideal anode materials in terms of capacity and stability. The emergence of metal chalcogenide as a candidate material has reinvigorated the search of a low cost and high capacity material system. However, debate about the underlying mechanisms and overall appraisal of its usage in lithium ion battery system remains. Here, a comprehensive study on the energy storage mechanism of copper zinc tin sulfide (CZTS) nanowalls possessing ultrahigh rate capability (500 mAh g−1 charged within 60 s) is reported. Structural evolutions along with the accompanying changes in the oxidation state upon charge/discharge were monitored by ex-situ X-ray diffraction and X-ray photoelectron spectroscopy. During lithiation, lithium ion reacted with CZTS to form lithium sulfides. At the same time, a sequential conversion reactions of copper, zinc and tin sulfides enabled the CZTS nanowalls to achieve excellent electrochemical performance (1400 mAh g−1 at a current density of 1000 mA g−1 over 400 cycles). Multi-element metal chalcogenides in conjunction with an adhesion-enhancing seed layer and a rational nanostructure design hold the key to such ultrahigh capacity and stable anode materials for next generation energy storage devices.

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.

A heterobimetallic corrole complex, comprising oxygen reduction reaction (ORR) active non-precious metals Co and Fe with a corrole-N4 center (PhFCC), is successfully synthesized and used to prepare a dual-atom molecular catalyst (DAMC) through subsequent low-temperature pyrolysis. This low-temperature pyrolyzed electrocatalyst exhibited impressive ORR performance, with onset potentials of 0.86 and 0.94 V, and half-wave potentials of 0.75 and 0.85 V, under acidic and basic conditions, respectively. During potential cycling, this DAMC displayed half-wave potential losses of only 25 and 5 mV under acidic and alkaline conditions after 3000 cycles, respectively, demonstrating its excellent stability. Single-cell Nafion-based proton exchange membrane fuel cell performance using this DAMC as the cathode catalyst showed a maximum power density of 225 mW cm-2 , almost close to that of most metal-N4 macrocycle-based catalysts. The present study showed that preservation of the defined CoN4 structure along with the cocatalytic Fe-Cx site synergistically acted as a dual ORR active center to boost overall ORR performance. The development of DAMC from a heterobimetallic CoN4-macrocyclic system using low-temperature pyrolysis is also advantageous for practical applications.

Cu2ZnSnS4 (CZTS) nanoparticles (NPs) were prepared in a one-step microwave-assisted synthesis using a mixture of trioctylphosphine oxide (TOPO) and oleylamine (OLA) as solvent. The reaction medium was optimized by varying the TOPO and OLA ratios to control the CZTS NPs formation. The synthesized CZTS NPs were characterized by X-ray diffraction, Raman spectroscopy, UV–vis spectroscopy, and transmission electron microscopy techniques. High quality CZTS NPs with composition of Cu1.8Zn1.4SnS3.6, optimum size distribution in the range of 22±4 nm and band gap of around 1.5 eV were obtained using microwave assisted synthesis method with OLA:TOPO (1:1) as co-solvent. In the microwave assisted process, the reaction temperature and time has been reduced significantly to 165 °C and 10 min respectively, as compared with other wet chemical solvothermal hot injection/ surfactant based methods. Finally, CZTSSe solar cell fabricated from the selenized microwave-assisted CZTS NPs yielded an efficiency of 4.48%; therefore, the low cost of synthesis of this high quality CZTS NPs ink and the capability of spraying for large solar cell area is very attractive.

The spontaneous formation of surface electron accumulation (SEA) was observed in synthesized molybdenum diselenide (MoSe2) layered crystals with two-hexagonal (2 H) structure. An anomalously high electron concentration at the surface up to 1019 cm−3 is several orders of magnitude higher than that (3.6 × 1012 cm−3) of the inner bulk. The SEA is found to be generated easily by mechanical exfoliation and room temperature deselenization. Se-vacancies have been confirmed to be the major source resulting in SEA and n-type conductivity, and also the active sites for electrochemical catalysis in MoSe2. Noted that the SEA conjugated with the Se-vacancy-related surface defects enhances the electrochemical hydrogen evolution reaction (HER) activity substantially. The optimized HER efficiency with an overpotential at 0.17 V and Tafel slope at 60 mV/dec of the basal plane of 2 H-MoSe2 was achieved by the nitrogen plasma treatment, which has outperformed several nanostructures, thin films, and hybrid counterparts. This study reveals the intriguing surface-dominant electronic property and its effect on the HER enhancement of the basal plane, which is crucial for development of a stable, low-cost and highly efficient catalyst using 2 H-MoSe2.

The controlled growth of metal oxide nanostructures within hierarchically porous conductive carbon-based frameworks is critically important to achieving high volumetric performance and appropriate channel size for energy storage applications. Herein, we grow cobalt oxide (Co3O4) nanoflakes, using a sequential-electrodeposition process, into spherically porous sponge-like few-layer partially reduced graphene oxide (SrGO) synthesized by template-directed ordered assembly. Maximum specific/volumetric capacitances of 1112 F gCo3O4−1 (at 3.3 A gCo3O4−1), 178 F cm−3 (at 2.6 A cm−2), and 406 F gtotal−1 (at 1 A gtotal−1) and sensible rate capability (80% retention by increasing the charge/discharge current from 1 A g−1 to 16 A g−1) are obtained for the Co3O4 nanoflakes@SrGO hybrid electrodes. Besides, an asymmetric supercapacitor is made with the Co3O4[63%]@SrGO[37%] hybrid and activated carbon as a positive and a negative electrode, respectively. Electrochemical results indicate an energy density of 23.3 W h kg−1 at a high power density of 2300 W kg−1 (discharge time of about 42 s) and 62% retention even at a remarkable power density of 36 600 W kg−1 (discharge time of 1.6 s). Moreover, it shows excellent cycling stability with no decay after 20 000 charge/discharge cycles. This performance is attributed to the unique pore-sizes for an ion to channel into the porous structures, conductivity, and mechanical stability of the SrGO framework, which makes it promising for next-generation supercapacitors.

Kesterite-type Cu 2 ZnSnS 4 (CZTS) has been attracting a lot of attention in thin-film solar cells due to its relatively low cost, earth abundant and environmentally benign nature compared to its analog Cu(In, Ga)Se 2 materials. Until now, solution-based processes are considered as promising methodologies for mass production of CZTS materials for industrial demands. However, most material sources are highly toxic as well as dangerous. In this study, we proposed a facile and green synthesis strategy for the CZTS absorber by taking advantage of an ultrasonic spray technique where we adopted metallic nanopowders and ethanol as our nontoxic precursors as well as solvents, respectively. The phase formation and transition mechanism of the synthesized CZTS film are investigated through varying sulfurization temperatures and analyzed using X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. The solar cell device can be made at a scale as large as 20 × 20 mm 2 , and the cell shows a power conversion efficiency of 1.5%.

We present a systematic study in investigating the orientation characteristics of pentacene molecules grown on graphene substrates using polarized Raman spectroscopy. The substrate-induced orientation alignment of pentacene can be well distinguished through the polarized Raman spectra. Interestingly, we found that the nature of polycrystalline graphene not only provides efficient route to control molecular orientation, but also acts as an excellent template allowing conjugated molecules to stack accordingly. The relative orientation of the well-aligned pentacene molecules and the nearby graphene domains exhibits several preferred angles due to atomic interactions. This unique feature is further examined and verified by single domain graphene. Furthermore, polarized Raman spectroscopy contains abundant information allowing us to analyze the ordering level of pentacene films with various thicknesses, which provides insightful perspectives of manipulating molecular orientations with graphene and spatial orga...

A cadmium sulfide (CdS) layer with a thickness of 37±5 nm is deposited onto a Cu2ZnSn(SSe)4 absorber layer using Cd(NO3)2 precursor at pH 11.8 via chemical bath deposition. Full devices fabricated with the thin CdS layer show improved champion efficiency of 6.97%, compared with the 5.91% efficiency of the control device, which can be attributed to the increased current density from reduced light reflection in the visible region and enhanced charge collection in the shorter wavelength region.

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.

BiCuTeO is a promising thermoelectric material owing to its intrinsically low thermal conductivity and high carrier concentration. This study investigated the influence of stoichiometric oxygen deficiencies on the thermoelectric performance of BiCuTeO. Bulk BiCuTeO1−x (0.16 ≥ x) samples were prepared by a conventional solid state reaction and pelleted by hot pressing. Synchrotron X-ray diffraction, electron probe X-ray microanalysis, scanning electron microscopy, and transmission electron microscopy characterized the samples. A maximum value of 1.06 was achieved for the dimensionless figure of merit ZT at 673 K for BiCuTeO0.88, which is approximately 49% better than the current maximal ZT value for BiCuTeO. The power factor was noticeably improved owing to increases in the electrical conductivity and Seebeck coefficient. Moreover, the optimal oxygen deficiency could introduce nanoparticles, resulting in reduced thermal conductivity. The findings will be important for the future development of metal oxide thermoelectric materials for use in practical thermoelectric devices.

Gas-phase photocatalytic reactions to convert carbon dioxide and water into oxygen and hydrocarbons are the foundation of life on earth. However, the efficiency of photosynthesis is relatively low (~1%), which leaves much room for artificial photosynthesis to reach the benchmark of the solar cells (>15%). In this work, carbon implanted SnS2 thin films (C–SnS2) were prepared to study photocatalytic activity and adsorbate-catalyst surface interactions during CO2 photoreduction. The electron density distribution in C–SnS2 and its contribution toward the photogenerated charge transfer process has been analyzed by the angle-dependent X-ray absorption near-edge structure (XANES) study. The C–SnS2 surface affinity toward the CO2 molecule was monitored by in-situ dark current and Raman spectroscopy measurements. By optimizing the dose during ion implantation, SnS2 thin film with 1 wt% carbon incorporation shows 108 times enhancement in the CO2 conversion efficiency and more than 89% product selectivity toward CH4 formation compared with the as-grown SnS2 without carbon incorporation. The improved photocatalytic activity can be ascribed to enhanced light harvesting, pronounced charge-transfer between SnS2 and carbon with improved carrier separation and the availability of highly active carbon sites that serve as favorable CO2 adsorption sites.

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.

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.

Manipulating the nature of defects and carrier dynamics in kesterite Cu2ZnSnS4 (CZTS) solar cells is challenging because of the complex behavior of defects. Among the various strategies used to reduce the defect levels, sodium-incorporated CZTS absorbers are effective and beneficial for defect passivation. In this study, we proposed a bifacial sodium-incorporated treatment (BSIT) in CZTS for the control of defect levels. The defect energy levels of the absorber measured by admittance spectroscopy decrease from 263 to 112 meV with increasing Na contents. In addition, impedance measurements of the sample after the BSIT showed an improved carrier dynamics with a prolonged minority carrier lifetime from 0.9 to 1.8 μs. This suggests that the post treatment of NaF diffused from the top and bottom surfaces of the CZTS absorbers is beneficial for carrier transport behaviors. Our results demonstrated that by manipulating the sodium content in the BSIT, defect passivation and effective reduction of carrier recombination can be attained, resulting in enhanced CZTS device performance from 4.1% to 5.6%.

Biobased materials capable of transforming into selective proton-exchange composite membranes (PEMs) are highly favored for use in direct methanol fuel cells (DMFCs) because of their low cost and abundance. Here, a polysaccharide and a clay have been functionalized together to make a highly proton selective PEM. Use of chitosan and clay composites ensured limited methanol crossover and thereby high measured performance via efficient fuel convertibility. In this study, sulfonated natural nanocomposite PEMs made of chitosan and sodium–montmorillonite (CS-MMT) were characterized for their water swelling, proton conductivity and methanol permeability parameters. The CS-MMT membrane with a proton conductivity of 4.92 × 10–2 S cm–1 and a power density of 45 mW/cm2 showed a measured methanol crossover current density (J) of

A non-toxic sol–gel spin coating approach is one of the attractive routes to achieve high atom economy, good quality Cu2ZnSnS4 (CZTS) thin films. In this paper, we introduce 1,3-dimethyl-2-imadazolidinone as a solvent for the preparation of highly viscous, homogeneous, nontoxic CZTS ink that eliminates the need for the use of additional binders or additives to disperse the precursors. In addition, we further report the annealing of the spin coated CZTS thin film in 6% diluted H2S gas with an externally supplied tin and sulfur environment to suppress the loss of tin from the thin-film surface and to enhance the device performance. CZTS grain sizes greater than 0.7 μm have been achieved with no detectable presence of carbon rich layers or layers containing fine grain sizes at the Mo/CZTS interface. An efficiency of 5.67% for the champion device fabricated here has been achieved with an open circuit voltage of 0.58 V, a short current density of 18.48 mA cm−2, and a fill factor of 53.14%.

Germanium antimony telluride (GeSbTe or GST), a popular material in optical and non-volatile memory devices, attracted renewed attention due to its potential for thermoelectric applications. In this study, we have employed a two-stage engineering process to enhance the thermoelectric properties of GeTe-rich GeSbTe. First, we introduced vacancy into the material by modifying the germanium content without disrupting the crystal structure. This influenced the electronic properties of the GeTe-rich GeSbTe and improved the overall dimensionless figure of merit, zT, from 0.7 to 1.1. Second, we rapidly cooled the material after annealing, further enhancing the zT value from 1.1 to 1.48 – one of the highest values reported for this material. In-depth studies suggest that disorder in the crystal structure was created via rapid cooling enhanced phonon scattering and effectively reduced the thermal conductivity, which, in turn, enhanced the thermoelectric performance.

We demonstrated the catalytic growth of m-axial InxGa1−xN (0.10 ≤ x ≤ 0.17) nanocolumn arrays with high crystallinity on silicon substrates using metal–organic chemical vapor deposition with trimethylindium (TMIn), triethylgallium (TEGa), and ammonia as precursors. The high quality of InGaN nanocolumns (NCs) were believed to be due to the utilization of TEGa that achieved less carbon impurities and offered more comparable vapor pressure with that of TMIn at low temperature. In addition, these NCs were grown in non-polar m-axis, which the internal electric field of the InGaN that often deteriorates the device performances might be able to be eliminated. Furthermore, the bandgap of this InGaN can be modulated from UV to visible region simply by tuning the ratio of the precursor during the fabrication. Our results suggest an approach to the fabrication of large-area NCs with a tunable bandgap on a silicon substrate by the standard MOCVD method that offers an immense opportunity for electronic and photonic applications and allows the scale-up from a research laboratory to industrial scale.

Rice husks, often neglected and considered as waste, contain constituents that could be of a potential use in advanced material applications. In this study, rice husks were used as a source of silicon dioxide for the synthesis of silicon nanoparticles (Si NPs) through magnesiothermic reduction process. The Si NPs were further used to prepare a binder-free composite system comprising Si NPs and graphene as an anode material for lithium ion battery system (LiBs). The composite system fabricated from rice husk-based Si NPs (RH-Si NPs) yielded an initial capacity of 1000 mA h g−1 at high applied current density of 1000 mA g−1. This study opens up the use of waste materials such as rice husk as a sustainable source of key components in advanced technology applications.

Template-free and direct-grown poly(3,4-ethylenedioxythiophene) nanowires/carbon cloth (PEDOT-NWs/CC) nanocomposite is successfully fabricated via electrochemical polymerization for hierarchical supercapacitor electrodes in neutral aqueous electrolyte of Na 2 SO 4 . The uniform distribution of PEDOT-NWs with 60–80 nm in diameter and several microns in length, and their characteristics of infrared absorption are determined by SEM and FTIR, respectively. The electrochemical impedance analysis is performed to probe the diffusion characteristics of PEDOT-NWs/CC electrode. Moreover, high gravimetric capacitance of 256.1 F g −1 at a specific energy of 182.1 Wh kg −1 and a specific power of 13.1 kW kg −1 is obtained under a wide operated potential of 1.6 V. These results clearly present a cost-effective and simple method of fabrication of the nanostructured polymers with enormous potential in flexible energy storage device applications.

Current research has demonstrated the combination of the high theoretical capacity offered by silicon nanoparticles (Si NPs) with graphene-based matrices in order to produce a high energy density and stable lithium ion battery system. However, Si NPs do not mix well with graphene oxide aqueous suspensions and thus create severe segregation of the materials. In this letter, we propose a simple, cost-effective and commercially-viable solvent exchange process to improve the interaction of the Si NPs in poor solvent environments such as in aqueous media. Using N-methylpyrrolidone (NMP) to disperse the Si NPs and followed by a solvent exchange process, we are able to improve the dispersion and stability of Si NPs in aqueous graphene oxide aqueous suspension. Consequently, this also improves the output and the stability of the lithium ion battery using the aforementioned composite system.

Production of hydrogen from water electrolysis has stimulated the search of sustainable electrocatalysts as possible alternatives. Recently, cobalt phosphide (CoP) and molybdenum phosphide (MoP) received great attention owing to their superior catalytic activity and stability towards the hydrogen evolution reaction (HER) which rivals platinum catalysts. In this study, we synthesize and study a series of catalysts based on hybrids of CoP and MoP with different Co/Mo ratio. The HER activity shows a volcano shape and reaches a maximum for Co/Mo = 1. Tafel analysis indicates a change in the dominating step of Volmer–Hyrovský mechanism. Interestingly, X-ray diffraction patterns confirmed a major ternary interstitial hexagonal CoMoP 2 crystal phase is formed which enhances the electrochemical activity.

Bamboo-shaped CNTs in which oxygen was incorporated were directly grown on carbon cloth (O-BCNT-CC) by microwave plasma-enhanced chemical vapor deposition. Mixed precursors CH 4 /H 2 /N 2 /O 2 were introduced during the growth process. For comparison, bamboo-shaped CNTs without incorporated oxygen were prepared herein (BCNT-CC). Then, platinum catalysts were prepared on the as-grown O-BCNT-CC (Pt/O-BCNT-CC) and the as-grown BCNT-CC (Pt/BCNT-CC). According to TEM-EELS oxygen mapping, O atoms were uniformly distributed on the O-BCNT surface. Methanol oxidation was performed using Pt/O-BCNT-CC and Pt/BCNT-CC in 1 M methanol and 1 M sulfuric acid by cyclic voltammetry. In the initial cycle, the peak current density of Pt/O-BCNT-CC was almost equal to that of Pt/BCNT, indicating that both had nearly equal activities in the beginning. After 300 cycles, the peak current of Pt/BCNT-CC was reduced to half of the initial peak current owing to platinum-poisoning; however, the peak current of Pt/O-BCNT-CC decayed less. In Pt/O-BCNT-CC, the oxygen-containing functional groups affect the orientation index of crystalline Pt, providing a means of oxidizing methanol and stabilizing Pt catalysts for the long-term.

The overall enhancement of poly(3-hexylthiophene): [6,6]-phenyl C61-butyric acid methyl ester based organic solar cell with a thin layer of bathocuproine (BCP) inserted between active layers and aluminum (Al) cathodes was investigated. X-ray and ultraviolet photoemission spectroscopy show that no reaction occurs at the active layer/BCP interface and 2 nm of BCP could effectively suppress the chemical reactions between Al and active layers. Atomic force microscope images also indicate that BCP layers can provide smoother contact surfaces with Al cathodes and suppress the generation of shunt leakage, resulting in larger V oc and better power conversion efficiency of devices.

Non-precious metal catalysts of the oxygen reduction reaction are highly favored for use in polymer electrolyte fuel cells (PEFC) because of their relatively low cost. Here, a new carbon-black-supported pyrolyzed Co-corrole (py-Co-corrole/C) catalyst of the oxygen reduction reaction (ORR) in a PEFC cathode is demonstrated to have high catalytic performance. The py-Co-corrole/C at 700 °C exhibits optimized ORR activity and participates in a direct four-electron reduction pathway for the reduction of O2 to H2O. The H2-O2 PEFC test of py-Co-corrole/C in the cathode reveals a maximum power density of 275 mW cm−2, which yields a higher performance and a lower Co loading than previous studies of Co-based catalysts for PEFCs. The enhancement of the ORR activity of py-Co-corrole/C is attributable to the four-coordinated Co-corrole structure and the oxidation state of the central cobalt.

This work demonstrates the directly grown graphene-like carbon nanowall (GNW)–carbon nanotube (CNT)–polyacrylonitrile-based carbon fiber (CF) paper structure for use as a highly efficient supercapacitor. The CF was prepared by electrospinning, and was then treated by carbonization. The CNTs were directly grown on the CF paper by microwave plasma-enhanced chemical vapor deposition using CH4/H2 precursors at 800 °C. The GNW was further reconstructed onto the CNT surface by microwave plasma-enhanced chemical vapor deposition using CH4/H2 precursors at 1500 °C (GNW–CNT/CF). Electrochemical measurements demonstrate that the capacitance of the GNW–CNT/CF electrode is around 176 F g− 1 at a charging/discharging current density of 0.5 mA/cm2. The stand-up structure of GNW–CNT/CF has a high capacitance, attributable to its large surface area, high electrical conductivity and direct growth with low energy-loss. This novel stand-up structure of GNW–CNT/CF with a high surface area and low electron-transfer resistance has great potential for developing a revolutionary new class of nanostructured electrodes in supercapacitors or other energy-conversion applications.

In this Letter, we investigated the effect of the molecular stacking orientation on the open circuit voltage (VOC) of pentacene-based organic solar cells. Two functionalized pentacenes, namely, 6,13-diphenyl-pentacene (DP-penta) and 6,13-dibiphenyl-4-yl-pentacene (DB-penta), were utilized. Different molecular stacking orientations of the pentacene derivatives from the pristine pentacene were identified by angle-dependent near-edge X-ray absorption fine structure measurements. It is concluded that pentacene molecules stand up on the substrate surface, while both functionalized pentacenes lie down. A significant increase of the VOC from 0.28 to 0.83 V can be achieved upon the utilization of functionalized pentacene, owing to the modulation of molecular stacking orientation, which induced a vacuum-level shift.

The limited natural abundance and high cost of Pt has been a major barrier in its applications for hydrogen or methanol fuel cells. In this work, based on the pyrolyzed corrin structure of vitamin B12 (py-B12/C), it is reported to produce superior catalytic activity in the oxygen reduction reaction (ORR) with an electron transfer number of 3.90, which is very close to the ideal case of 4. The H2–O2fuel cell using py-B12/C provides a maximum power density of 370 mW cm−2 and a current density of 0.720 A cm−2 at 0.5 V at 70 °C. Calculations based on density functional theory suggests that the corrin complex with a low-symmetric structure offers a much preferable path for the ORR, which is not applicable to the porphyrin with a high-symmetric structure. The long-term stability and high ORR activity of py-B12/C make it a viable candidate as a Pt-substitute in the ORR.

This study demonstrates the feasibility of platinum-free catalysts, which exhibit not only a high activity in the oxygen reduction reaction (ORR) but also a high tolerance of methanol. A cobalt (II) tetramethoxyphenylporphyrin (CoTMPP) precursor was dispersed in N,N-dimethylmethanamide (DMF), which was ultrasonically stirred for 30 min to yield a homogeneous solution, and then filtered to remove the solvent. The CoTMPP precipitate was pyrolyzed at temperatures of 300, 500, 700 and 900 °C in N 2 atmosphere. Raman spectra include strong peaks at 1330 and 1550 cm − 1 , which are associated with the D- and G-peaks of pyrolyzed CoTMPP above 500 °C, revealing that the original porphyrin structure of CoTMPP yields a network structure of poly-aromatic hydrocarbons upon the pyrolysis. Pyrolyzed CoTMPP loaded on carbon blacks (CoTMPP/C) at 700 °C exhibits a higher ORR activity than other various pyrolysis temperatures. In a methanol-containing solution, pyrolyzed CoTMPP/C preferentially undergoes the ORR rather than the methanol oxidation reaction, and so exhibits a high tolerance of methanol. Pyrolyzed CoTMPP has the pyrrolic nitrogen, and part of the cobalt-containing nitrogen chelate is cleaved and bound to other atoms, forming Co―N x ―C y (x + y = 4), which are responsible for the ORR activity and the high tolerance of methanol.

We propose a nanostructured near infrared photodetector based on indium nitride (InN) nanorod/poly(3-hexylthiophene) hybrids. The current–voltage characteristic of the hybrid device demonstrates the typical p–n heterojunction diode behavior, consisting of p-type polymer and n-type InN nanorods. The device shows a photoresponse range of 900–1260 nm under various reverse biases. An external quantum efficiency of 3.4% at 900 nm operated at −10 V reverse bias was obtained, which is comparable with devices based on lead sulfide and lead selenide hybrid systems.

Solvent effects on the bulk heterojunction of poly(3-hexylthiophene) (P3HT) and single-walled carbon nanotubes (SWNTs) have been studied. Not only the morphology of P3HT but also the SWNT dispersion in P3HT matrix show strong dependence on the solvents. Atomic force microscopy images suggest that P3HT forms poor crystal structure in chloroform but better in solvents that have relatively high boiling points such as chlorobenzene, toluene, and o-xylene. However, the results of quench rate of photoluminescence and the exciton lifetime decay rate in SWNT/P3HT indicate that a good SWNT dispersion can only be obtained in chloroform and chlorobenzene cases. This suggests that more effective interfaces can be formed when these two solvents are used and thus leads to enhanced charge separation rate, which eventually will benefit the photovoltaic performance. Our photovoltaic demonstration further confirms the idea and suggests that using chlorobenzene for preparation of SWNT/P3HT photovoltaic devices will give mor...

This review will give a brief introduction to the growth and characterization methods of both binary and ternary compounds, in particular those exhibiting one-dimensionality, of the family to orient the readers about the material system to be discussed. A section will deal with the size and shape selection in group III nitride nanomaterials with a stress on intriguing morphologies such as nanowires, nanotips, and nanobelts. Complex structures, such as hierarchical and core-shell structures, will be introduced. Optical, electrical, and mechanical property, such as hardness, will be discussed in a greater detail, distinguishing the bulk from the nano wherever possible. Available models of electrical conduction and photoconduction in nanomaterials and their dependence on the actual size of the objects will be presented and compared. Optical properties of ensemble and single nanostructures, wherever possible, will be addressed in detail. The section on application will focus mainly on the sensor applications,...

Protonated polyaniline (PANI) is directly polymerized on Nafion 117 (N117), forming a composite membrane, to act as a methanol-blocking layer to reduce the methanol crossover in the direct methanol fuel cell (DMFC), which is beneficial for the DMFC operating at high methanol concentration. The PANI layer grown on the N117 with a thickness of 100 nm has an electrical conductivity of 13.2 S cm −1 . The methanol permeability of the PANI/N117 membrane is reduced to 59% of that of the N117 alone, suggesting that the PANI/N117 can effectively reduce the methanol crossover in the DMFC. Comparison of membrane-electrode-assemblies (MEA) using the conventional N117 and the newly developed PANI/N117 composite shows that the PANI/N117-based MEA outputs higher power at high methanol concentration, while the output power of the N117-based MEA is reduced at high methanol concentration due to the methanol crossover. The maximum power density of the PANI/N117-based MEA at 60 °C is 70 mW cm −2 at 6 M methanol solution, which is double the N117-based MEA at the same methanol concentration. The resistance of PANI/N117 composite membrane is reduced at elevated methanol concentration, due to the hydrogen bonding between methanol and PANI pushes the polymer chains apart. It is concluded that the PANI/N117-based MEA performs well at elevated methanol concentration, which is suitable for the long-term operation of the DMFC.

article i nfo Electrophoretic deposition technique was successfully utilized to deposit the PtRu nanoparticles on carbon nanotubes, which were directly grown on carbon cloths (CNTs/CC). We applied an external dc field to drive the PtRu nanoparticles, which were surrounded by negatively charged glycolate in an ethylene glycol process, toward the positively biased CNTs. Systematic studies to achieve optimal size and loading amount by varying the bias potential and deposition time have been carried out. An average PtRu particle size of 2.08 nm with catalytic activity of 1.6 A/cm 2 /mg in electro-oxidation methanol could be achieved, which is highly desirable for fuel cell applications.

Combinations of different aromatic polymers and organic solvents have been studied as dispersing agents for preparing single-walled carbon nanotubes solutions, using optical absorbance, photoluminescence-excitation mapping, computer modeling, and electron microscopic imaging to characterize the solutions. Both the polymer structure and solvent used strongly influence the dispersion of the nanotubes, leading in some cases to very high selectivity in terms of diameter and chiral angle. The highest selectivities are observed using toluene with the rigid polymers PFO-BT and PFO to suspend isolated nanotubes. The specific nanotube species selected are also dependent on the solvent used and can be adjusted by the use of THF or xylene. Where the structure has more flexible conformations, the polymers are shown to be less selective but show an enhanced overall solubilization of nanotube material. When chloroform is used as the solvent, there is a large increase in the overall solubilization, but the nanotubes are suspended as bundles rather than as isolated tubes which leads to a quenching of their photoluminescence.

This study demonstrated the feasibility of a high-performance membrane-electrode-assembly (MEA), with low electrocatalyst loading on carbon nanotubes (CNTs) grown directly on carbon cloth as an anode. The direct growth of CNTs was synthesized by microwave plasma-enhanced chemical vapor deposition using CH4/H2/N2 as precursors. The cyclic voltammetry and electrochemical impedance measurements with 1 mM Fe(CN)63−/4− redox reaction reveal a fast electron transport and a low resistance of charge transfer on the direct growth of CNT. The electrocatalysts, platinum and ruthenium, were coated on CNTs by sputtering to form Pt-Ru/CNTs-CC with carbon cloth for CC. Pt-Ru electrocatalysts are uniformly dispersed on the CNT, as indicated by high-resolution scanning electron microscopy (HRSEM) and transmission electron microscopy (TEM), because the nitrogen doped in the CNT acts as active sites for capturing electrocatalysts. The MEA, the sandwiched structure which comprises 0.4 mg cm−2 Pt-Ru/CNTs-CC as the anode, 3.0 mg cm−2 Pt black as the cathode and Nafion 117 membrane at the center, performs very well in a direct methanol fuel cell (DMFC) test. The micro-structural MEA analysis shows that the thin electrocatalyst layer is uniform, with good interfacial continuity between membrane and the gas diffusion layer.

A hierarchical carbon nanotube-polypyrrole (CNT-PPy) core-shell composite was fabricated by growing CNTs directly on carbon cloth (CC) as a skeleton followed by electropolymerization of PPy with controlled polymerization time. Direct fabrication of electroactive (CNT-PPy) materials on the flexible CC electrode could reduce the interfacial resistance between the electrode and electrolyte and improve the ion diffusion. The supercapacitor electrode based on optimized PPy/CNT-CC exhibits excellent electrochemical performance, with the highest gravimetric capacitance being roughly 1038 F g(-1) per active mass of PPy and up to 486.1 F g(-1) per active mass of the PPy/CNT composite. Notably, excellent flexibility and cycle stability up to 10 000 cycles with only 18 % capacitance loss was achieved. At the same time, the fabricated asymmetric supercapacitor (PPy/CNT-CC∥CNT-CC) shows the maximum power density of 10 962 W kg(-1) at an energy density of 3.9 Wh kg(-1) under the operating potential of 1.4 V. The overall high cycle stability and high performance of the fabricated PPy/CNT-CC flexible electrode is due to the novel binder-free direct growth process.