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Characterization of Graphite/ZnO Schottky Barriers Formed on Polar and Nonpolar ZnO Surfaces
摘要： The authors demonstrate that the electrical properties of Schottky junctions fabricated by the deposition of colloidal graphite strongly depend on the crystallographic orientation of the ZnO substrate. The current-voltage, capacitance-voltage, and impedance measurements indicate that near-ideal Schottky junctions form on c-plane, while on a- and m-plane the junctions are laterally inhomogeneous. This behavior is assigned to higher concentration of native point defects in the near-surface region of nonpolar ZnO substrates. The authors further present an extended equivalent circuit model, which corresponds to actual structure of the junctions, and sheds light on their electrical transport properties.
关键词： impedance spectroscopy,graphite,equivalent circuit,ZnO,crystal polarity,Schottky contact
更新于2025-09-23 15:21:01
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Graphite Supported Stainless-Steel Electrode for the Degradation of Azo Dye Orange G by Fenton Reactions: Effect of Photo-Irradiation
摘要： An electrode, stainless steel supported on graphite, was used for the degradation of hazardous organic compounds, azo dye Orange G (OG), using the photoelectro- Fenton (PEF) process. Results showed that the applied current controlled the electrogeneration rate of both ferrous ion and hydrogen peroxide, which in turn affected the dye degradation kinetics. At an applied current density of 45 μA cm?2, the SS-graphite electrode yielded a molar ?H2O2(cid:2)=?Fe2t(cid:2) ratio of 3.6, which was optimal for dye degradation. Under otherwise identical conditions, UV irradiation significantly enhanced OG degradation, i.e., PEF is more effective than electro-Fenton (EF) process. At the optimal applied current density of 45 μA cm?2, or optimal molar ?H2O2(cid:2)=?Fe2t(cid:2) of 3.6, OG decolorization and total organic carbon removal were 83% (in 3 h) and 55% (in 7 h), versus 75% (in 3 h) and 20% (in 7 h) by PEF and EF, respectively. OG degradation by both PEF and EF processes followed the pseudo first-order kinetics, which suggested the major role of OH radical in OG decolorization.
关键词： Stainless steel,Graphite,Orange G,Photo-electro-Fenton (FEF),Steady-state approximation,Decolorization
更新于2025-09-23 15:21:01
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Carbon coated-Cu nanoparticles as a cocatalyst of g-C3N4 for enhanced photocatalytic H2 evolution activity under visible-light irradiation
摘要： The photocatalytic H2 evolution is an important technology to solve the energy crisis. The hydrogen evolution rate of the g-C3N4 system in triethanolamine solution as sacrificial agent is obvious higher than in methanol solution. But up to now, most of the Cu nanoparticles as cocatalyst of g-C3N4 photocatalytic systems for hydrogen evolution are performed in methanol solution because Cu nanoparticles are unstable in triethanolamine solution. Here, carbon coated-Cu nanoparticles as cocatalyst of g-C3N4 composites (Cu@C/g-C3N4) were prepared by simple two-steps technology of annealing then grinding. The compositions, morphology and optical and photoelectrochemical (PEC) properties of the composites were characterized by means of physicochemical techniques. The prepared composition was used to generate hydrogen under visible light irradiation in triethanolamine solution. The results displayed that the hydrogen evolution rate of the optimal Cu@C/g-C3N4 was up to 265.1 μmol g-1 h-1 that is close to the activity of 0.5% Pt/g-C3N4, and after four repeated reactions, the photocatalytic activity decreased only by about 15%. The good photocatalytic activity and stability result from Cu nanoparticles increase the transfer efficiency of charge carriers by trapping the photogenerated electrons produced by g-C3N4 and the protective effect of carbon layer on Cu nanoparticles.
关键词： Cu nanoparticles,Visible-light,Graphite carbon nitride,Photocatalytic H2 evolution,Carbon coating layer
更新于2025-09-23 15:21:01
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A Hydrogen Peroxide Sensor Based on Catalytically Active Systems Rua??RuO2 Obtained by High-Speed Laser Synthesis
摘要： There is a need for simple and economical chemical sensors for monitoring the concentration of hydrogen peroxide in biological media. In this work, we demonstrate the possibility of using for this purpose catalytically active ruthenium compounds obtained by high-speed laser synthesis on the surface of a graphite electrode.
关键词： Ru–RuO2,graphite electrode,catalytically active systems,hydrogen peroxide sensor,high-speed laser synthesis
更新于2025-09-23 15:19:57
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Characterization of form-stable phase-change material for solar photovoltaic cooling
摘要： Solar PV panel cooling is essential to achieve maximum efficiency of PV modules. Phase-change material (PCM) is one of the prominent options to cool the panel and reduce the temperature, since PCMs have low thermal conductivity. Expanded graphite particles are used to enrich the structure and stability as well as to increase the thermal properties. In the present research work, polyethylene glycol (PEG) 1000 is used as a base material and expanded graphite for inclusive particle. A novel form-stable PEG1000/EG composite PCM mixture is prepared, using impregnation and dispersion method. Expanded graphite and PEG1000/EG sample phase compositions are investigated, using X-ray diffraction technique. No new peak is identified in the composite PCM sample. The surface morphology and structure of EG and PEG1000/EG are investigated, using scanning electron microscopy (SEM). Chemical stability analysis is done by Fourier-transform infrared spectroscopy. Thermal properties of the prepared composite PCMs are analysed by differential scanning calorimetry, thermogravimetric analysis (TGA) and KD2 pro analyser. Results show that addition of EG in various propositions (5%, 10% and 15%) enhances the thermal conductivity of PCM samples from 0.3654 to 1.7866 W mK?1, while melting point and latent heat of fusion of PCM samples are getting reduced. TGA thermographs are used to investigate the thermal stability of the composite PCM samples. TGA curves show that loss of mass happens above the operating temperature, and it is varied with different mass ratios of EG. Characterization of the prepared composite PCM samples is compared and found that PEG1000-85%/EG-15% is the best form-stable PCM, suitable for cooling the solar PV panel as well as to improve the electrical efficiency coupled with a decrease of temperature in the range of 35 °C to 40 °C.
关键词： PEG1000 PCM material,Solar PV cooling,Expanded graphite,Thermal storage,DSC,Characterization
更新于2025-09-23 15:19:57
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Plasma chemistry produced during laser ablation of graphite in air, argon, helium and nitrogen
摘要： Laser-induced plasma chemistry produced during the ablation of graphite targets at atmospheric pressure in air, argon, helium and nitrogen was studied through time-resolved atomic and molecular emission spectroscopy. The plasma plume and plasma chemistry were generated by focusing a 6-mm diameter, 212 mJ, 1064-nm nanosecond Nd:YAG laser to a spot size of about 1 mm diameter over graphite samples of 99.9% pureness. The atomic emissions C I 247.86 nm, N I 821.50 nm and O I 777.19 nm, and the molecular bands C2 (473.71 nm) and CN (359.04 nm and 388.30 nm) were monitored as a function of time (0.2 to 220 μs). While the C I and C2 emissions followed a near-exponential decay, the CN emission in air and nitrogen showed an emission behavior characterized by two local maxima at 0.2 μs and 20-30 μs after the plasma ignition. The first maximum was explained by the early plasma chemistry produced by the ablated carbon species and the confining background gas, whereas the second maximum was attributed to atomic recombination and shock wave-induced excitation of the plasma plume. Two main effects were observed when the ablation was produced in different background gases. First, the presence of oxygen (≈21%) in air had a negligible effect on atomic lines; however, the CN emission intensity and lifetime were significantly reduced in comparison with an atmosphere of 100% nitrogen. This was attributed to the reduction of nitrogen species as reaction partners during the plasma chemistry in air. Secondly, due to the assumed higher plasma temperature in Ar, this gas favored the emission intensity and lifetime of atomic species but hindered the formation of C2 species. Because the collection optics of the emission spectroscopy system was configured in backscatter mode, which integrates over the entire plasma volume and gate time without spatial resolution, the time-resolved behavior of the plasma emissions were only related to the number density of emitters but not to specific locations in the plasma volume.
关键词： Atomic-molecular emissions,Laser-induced breakdown spectroscopy,Plasma chemistry,Graphite
更新于2025-09-23 15:19:57
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Disorder in H <sup>+</sup> -irradiated HOPG: effect of impinging energy and dose on Raman D-band splitting and surface topography
摘要： Disorder was induced in pristine highly oriented pyrolytic graphite (HOPG) by irradiation with H+ ions with energies of 0.4 MeV and 1 MeV, and doses of 1014 ions/cm2 and 1016 ions/cm2. Raman spectroscopy was used as the main technique to characterize different samples and gain new insights on the splitting of the D band into two components (D1 and D2), trying to correlate this feature of the vibrational spectrum with the impinging energy and dose. An increased ID2/IG ratio in comparison with ID1/IG was observed in the irradiated samples. This behavior indicates that the impinging energy mainly affects the D1 component, while the D2 component is strongly dominated by the dose. We expect a larger contribution of defects (originating from the rupture of C–C sp2 symmetry through the formation of C–H sp3 bonds) to the D2 component than to the D1 component. SQUID measurements of the irradiated samples showed an enhancement in the normalized remanence, as well as an increment in coercivity compared to pristine HOPG, consistent with H+-induced point-like defects as well as C–H bonds. AFM scanning after Raman and SQUID characterization showed a distribution of surface defects, which were ascribed to the burst of hydrogen blisters formed as a consequence of the irradiation process. The results presented in this work contribute to the current trend in nanotechnology in areas devoted to the control of properties by defect engineering in carbon-based materials.
关键词： ion–solid interactions,highly oriented pyrolytic graphite (HOPG),topography,Raman spectroscopy,disorder
更新于2025-09-19 17:15:36
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Graphite lithiation and capacity fade monitoring of lithium ion batteries using optical fibers
摘要： Increasing the e?ciency and safety of battery management systems may require internal monitoring of lithium ion batteries. In this work, we present an analysis of the interaction between ?ber-optic evanescent wave sensors (FOEWS) and graphite particles within a lithium ion battery over multiple cycles. Through slow charging and long rest periods, the FOEWS signal has shown sensitivity to lithium concentration at the surface of graphite particles by demonstrating a response to the slow di?usion of lithium ions within graphite particles during rest periods (i.e. relaxation of the electrode). The slope of the FOEWS signal during a full charge is found to exhibit three distinct peaks that occur within lithiated graphite's stage transitions zones IV, III and II. Deviation from the observed three peak trend correlates with signi?cant battery capacity fade and thus indicate the sensors ability to detect capacity fade in real-time. During experiments, signi?cant deviations in the slope during charging occurred at about ~5% SOC and minor disturbances to the slope were observed at ~80% SOC, which supports limiting the depth of charge and discharge to avoid accelerated capacity fade. These results deepen our understanding of the FOEWS's interaction with lithium ion batteries and supports the development of algorithms that optimize the control and monitoring of graphite lithiation with the aim of achieving safer operation as well as maximizing capacity and battery life.
关键词： Optical ?ber sensor,Lithium ion battery,State of charge,Graphite,Capacity fade,Signal analysis
更新于2025-09-19 17:13:59
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Double-Mesoscopic Hole-Transport-Material-Free Perovskite Solar Cells: Overcoming Charge-Transport Limitation by Sputtered Ultra-Thin Al <sub/>2</sub> O <sub/>3</sub> Isolating Layer
摘要： The electrically insulating space layer takes a fundamental role in monolithic carbon-graphite based perovskite solar cells (PSCs) and it has been established to prevent the charge recombination of electrons at the mp-TiO2/carbon-graphite (CG) interface. Thick 1 μm printed layers are commonly used for this purpose in the established triple-mesoscopic structures to avoid ohmic shunts and to achieve a high open circuit voltage. In this work, we have developed a reproducible large-area procedure to replace this thick space layer with an ultra-thin dense 40 nm sputtered Al2O3 which acts as highly electrically insulating layer preventing ohmic shunts. Herewith, transport limitations related so far to the hole diffusion path length inside the thick mesoporous space layer have been omitted by concept. This will pave the way towards the development of next generation double-mesoscopic carbon-graphite based PSCs with highest efficiencies. Scanning electron microscope (SEM), energy dispersive x-ray analysis (EDX) and atomic force microscopy (AFM) measurements show the presence of fully oxidized sputtered Al2O3 layer forming a pseudo-porous covering of the underlying mesoporous layer. The thickness has been finely tuned for the achievement of both electrical isolation and optimal infiltration of the perovskite solution allowing full percolation and crystallization. Photo voltage decay, light-dependent and time-dependent photoluminescence measurements showed that the optimal 40 nm thick Al2O3 not only prevents ohmic shunts but also efficiently reduces the charge recombination at the mp-TiO2/CG interface and, at the same time, allows efficient hole diffusion through the perovskite crystals embedded in its pseudo-pores. Thus, stable VOC of 1 V using CH3NH3PbI3 perovskite has been achieved under full sun AM 1.5 G with stabilized device performance of 12.1%.
关键词： Perovskite solar cells,Al2O3 Space layer,Double-mesoscopic,Carbon-graphite,HTM-free,Sputtering,Interface recombination
更新于2025-09-19 17:13:59
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Quantitative spatially resolved <i>post-mortem</i> analysis of lithium distribution and transition metal depositions on cycled electrodes <i>via</i> a laser ablation-inductively coupled plasma-optical emission spectrometry method
摘要： Diminishing the loss of performance of lithium ion batteries (LIBs) is a challenge that is yet to be ful?lled. Understanding of deterioration processes and mechanisms (i.e., so-called aging) requires analytically accurate examination of aged cells. Changes in the distribution of lithium or transition metals in the LIB cells can in?uence their cycle and calendar life signi?cantly. As electrochemically treated cells and especially their electrodes do not age homogeneously and the local electrochemistry (e.g. deposition patterns) is strongly dependent on surface properties, bulk analysis is not a satisfactory investigation method. Therefore, a surface sensitive method, namely laser ablation-inductively coupled plasma-optical emission spectrometry (LA-ICP-OES) is presented. LIB cells with lithium metal oxide LiNi1/3Co1/3Mn1/3O2 (NCM111) as cathode material and graphite as anode material are investigated using a 213 nm Nd:YAG laser.
关键词： graphite,aging,laser ablation-inductively coupled plasma-optical emission spectrometry,NCM111,LA-ICP-OES,LIBs,Nd:YAG laser,lithium ion batteries
更新于2025-09-19 17:13:59