The Mo as electron trapper and donor to modulate the electron of CoP2 in phosphating process

To prepare bifunctional electrocatalyst towards HER and OER is extremely important for promoting the development of electrochemical water splitting technology. Herein, the element doping method is employed to tune the electron environment of cobalt phosphide (CoP). The Mo-doped CoP supported on carbon cloth (CC) is constructed by solvothermal and annealing method. The effect of Mo on the electron modulation of CoP during different phosphating time was studied carefully. It is noted that the Mo play an important role in tuning the electron state of Co and P elements which can trap the electron and was reduced to low valence, then transfer the electron to Co and P. With increasing the phosphating time, the electron transfer phenomenon between Mo and CoP is obvious. Benefiting from the electron engineering of Mo, Co and P as well as thin and wrinkle sheets structure, the optimal electrocatalyst only requires 39 mV and 251 mV to deliver 10 mA cm⁻² for HER and OER, respectively. Also, as for the whole water splitting performance, it delivers 10 mA cm⁻² at cell voltage of 1.56 V. Importantly, Faraday efficiency of the optimal catalyst achieves 99.9% for HER due to the tuned electron state of Co and P, high ECSA and low R_ct.     

Methylene blue as electron promoters in microbial fuel cell

Microbes and enzymes deliver electrons from carbon sources under anaerobic condition. Electrons are generated as the microorganisms are actively catabolized organic substances. The liberated electrons travel to anode surface. Saccharomyces cerevisiae (PTCC 5269) was implemented as biocatalyst in the anaerobic anode compartment. Glucose was used as carbon source. Also mediator as electron promoter was incorporated in the anode. Among several mediators, methylene blue (MB) as electron promoter with concentration of 50, 100, 200, 300 and 400 μM was selected to shuttle the liberated electron to anode surface. Maximum power and current with MB concentration of 300 μM were obtained. Resistances were applied to control the electron flow from anode to cathode chambers. Data were recorded through an online data-logger. Polarization curves with and without mediator were analyzed in the fabricated cell. MB had good ability to enhance power generation. Maximum open circuit voltage of 250 mV was achieved; the voltage was stabled for the duration of 36 h.     

Electrogenic activity and electron losses under increasing organic load of recalcitrant pharmaceutical wastewater

Relative change in the electrogenic activity and potential losses during electron transfer in microbial fuel cell (MFC) was elucidated using real-field recalcitrant pharmaceutical wastewater as anolyte by varying substrate/organic load (OL1, 1.98; OL2, 3.96; OL3, 5.93, OL4, 7.98 kg COD/m³). Increase in organic load showed improvement in electrogenic activity (OL4: 346 mV, 205.61 mW/m²; OL3: 320 mV, 158.58 mW/m²; OL2: 290 mV, 112.87 mW/m²; OL1: 256 mV, 72.60 mW/m²). Both activation and ohmic losses showed decrement with increase in organic load while concentration losses depicted increment. Improvement in power output was non-linear with increase in organic load due to the anodic over potentials, described as electron transfer resistances and potential losses. Bio-electrochemical analysis also depicted the electron losses in terms of electron discharge and energy generation with the function of varying organic load.     

OPV devices based on functionalized lanthanide complexes for application in UV–light detection

Organic photovoltaic (OPV) devices with the general structure of ITO/PEDOT: PSS (60 nm)/m-MTDATA (40 nm)/(OXD-Pybm)Ln(DBM)₃ (20 nm)/LiF (1 nm)/Al (120 nm) are demonstrated by utilizing (OXD–Pybm)Ln(DBM)₃ (Ln=Pr, Sm, Eu, Gd, and Tb) as electron acceptors and 4,4′,4″-tris(N-(3-methylphenyl)-N-phenylamino) triphenylamine (m-MTDATA) as an electron donor. The performances of these devices are experimentally improved by the introduction of 2,5-diphenyl-1,3,4-oxadiazole (OXD) group into the electron acceptors. Besides, it is found that (OXD–Pybm)Pr(DBM)₃ based device holds the potential application in UV-light detection due to the absence of dark current with the compensatory voltage lower than 1.65 V. The highest power conversion efficiency (η) and the maximum fill factor (FF) among these OPV devices are 2.60% and 0.33, respectively.     

Characteristics of triphenylamine-based dyes with multiple acceptors in application of dye-sensitized solar cells

We report the synthesis and photophysical/electrochemical properties of triphenylamine (TPA)-based multiple electron acceptor dyes (TPAR1, TPAR2, and TPAR3) as well as their applications in dye-sensitized solar cells (DSSCs). In these dyes, the TPA group and the rhodanine-3-acetic acid play the role of the basic electron donor unit and the electron acceptor, respectively. It was found that introduction of two rhodanine-3-acetic acid groups into the TPA unit (TPAR2) exhibited better photovoltaic performance due to the increase with a red shift and broadening of the absorption spectrum. The monolayer of these TPA-based dyes was adsorbed on the surface of nanocrystalline TiO₂ mesoporous electrode with the thickness of ∼6 μm, polyethylene oxide (PEO) used as the matrix of gel electrolyte, and 4-nm thick Pt used as a counter-electrode. Photovoltaic device can be realized in a single quasi-solid-state DSSC. TPAR2-based gel DSSC had an open circuit voltage and short circuit current density of about 541 and 10.7 mA cm⁻², respectively, at 1-sun.     

A study on the electron transport properties of TiO2 electrodes in dye-sensitized solar cells

The influences of annealing temperature and different poly (ethylene glycol) (PEG) contents in nano-crystalline TiO₂ electrodes with and without N3 dye on the electron transfer in a dye-sensitized solar cell (DSSC) were investigated. It is found that the power conversion efficiency increases with the increase in annealing temperature and becomes saturated at 400–500 °C, and further increase lowers the performance which is consistent with the enhancement of the crystalline TiO₂ particles observed in X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images. Electrochemical impedance spectroscopy (EIS) also confirms this behavior. These results have been further verified by studying the electron lifetimes (τ_e) and electron diffusion coefficients (D_e) of a bare TiO₂ and a dye-sensitized TiO₂ film using a pulsed laser spectrometer. It is noted that both the electron lifetime and the electron diffusion coefficient increase with the increase in annealing temperature. However, the evolution of rutile TiO₂ begins beyond 600 °C and this lowers the dye absorbance and the electron diffusion coefficients of TiO₂ electrodes. A similar study was made by varying the content of the PEG in the TiO₂ films. It is found that with the increase in the PEG content, a decrease in the electron lifetimes and a little hike in the electron diffusion coefficients are noted, where the cell performance remains almost the same. In addition, the dye adsorption decreases the electron lifetime and increases the electron diffusion coefficient of the TiO₂ films regardless of the PEG content and the annealing temperature.     

Photocatalytic overall water splitting with dual-bed system under visible light irradiation

Photocatalytic overall water splitting has been demonstrated with WO₃ for oxygen producing photocatalyst (OPC), and Rh-doped SrTiO₃ for hydrogen producing photocatalyst (HPC) in a simulated dual-bed system under visible light irradiation (λ ≥ 400 nm). The Fe³⁺/Fe²⁺ redox couple was chosen as the most effective electron mediator between OPC and HPC. The overall performance of the dual-bed system was limited by the low activity of HPC, and thus the activity of HPC should be increased to improve the overall performance. For overall water splitting reaction in a dual-bed system, the conduction band of OPC must be more negative than the redox potential of the electron acceptors and the valence band of HPC must be more positive than the redox potential of the electron donors.     

High performance of low electrocatalysts loading on CNT directly grown on carbon cloth for DMFC

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)₆^3−/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.     

Organic ultraviolet photovoltaic diodes based on copper phthalocyanine as an electron acceptor

Organic ultraviolet (UV) light-sensitive photovoltaic (PV) diodes, based on 4, 4′, 4″-tris-(2-methylphenyl phenylamino) triphenylamine (m-MTDATA) as an electron donor and copper phthalocyanine (CuPc) as acceptor, have been fabricated. The PV diode exhibits high open-circuit voltage (V_OC) of 1.05 V under illumination of 365 nm UV light with 1.7 mW/cm², although the CuPc was generally used as electron donor in other PV diodes. And the short-circuit current (I_SC) of 54.6 μA/cm², fill factor (FF) of 0.304 and power conversion efficiency (η_e) of 1.03% are respectively achieved. This diode can accurately detect the UV radiation according to photo-generated voltage signal.     

Improvement of structural and optoelectrical properties by post-deposition electron beam annealing of ITO thin films

Sn-doped In₂O₃ (ITO) thin films were deposited on a glass substrate with reactive RF magnetron sputtering and then post-deposition electro-annealed. The electron accelerating voltage was varied from 300 to 900 V, and the substrate temperature was increased to 250 °C with an electron accelerating voltage of 900 V for 20 min in a 4 × 10^?1 Pa vacuum. As-deposited and ITO films electro-annealed at low energy (≤600 eV) were found to be in the amorphous phase, while ITO films electro-annealed at 900 eV showed diffraction peaks of the ITO (222) and (400) planes. As the electron accelerating voltage increased, the electrical resistivity decreased to as low as 6 × 10^?4 Ωcm, and the mean optical transmittance also increased from 79 to 82% in the visible wavelengths. The electro-annealed films showed a higher figure of merit (1.8 × 10^?3 Ω^?1) than the as-deposited ITO films (6.7 × 10^?3 Ω^?1), indicating that electro-annealed ITO films have better optoelectrical performance than as-deposited films.     

Theoretical and experimental study on the heat transport in metallic nanofilms heated by ultra-short pulsed laser

In this paper the mechanism of heat transport in metallic nanofilms under ultra-short pulsed laser heating is examined theoretically and experimentally. In order to easily understand the non-equilibrium heat transport in metallic nanofilms the study of heat transport behavior is first carried out in dielectrics. The analyses indicate that there may be two kinds of wave phenomena in dielectrics subjected to a periodic surface temperature. One is the thermal wave governed by the C-V model based hyperbolic equation and the other is the diffusive wave governed by the Fourier model based parabolic equation. According to the hyperbolic two step model for non-equilibrium heat transport, such two kinds of wave phenomena can also occur simultaneously in the metallic nanofilms under pulsed laser heating, where the diffusive wave is induced by the electron temperature oscillation at the surface due to the non-equilibrium between electrons and lattices. Unlike the propagation speed of the thermal wave, the propagation speed of the diffusive wave depends not only on the medium properties but also the period of the temperature oscillation at the boundary. Hence, the propagation speed of the diffusive wave in the electron gas may be of as high as 10⁶ m s⁻¹, when the laser pulse duration is less than 1 ps. A transient thermoreflectance (TTR) system has been built to measure the transient electron temperature responses caused by the femtosecond laser heating and a pump-probe technique is used to ensure the femtosecond temporal resolution in the experiments. Different from the commonly used front heating-front detecting (FF) method for measuring the material properties, a rear heating-front detecting (RF) method is applied, so that measuring the propagation speed of heat becomes available. The non-equilibrium heat diffusion model is used to fit the measured normalized electron temperature profiles of 27.2 nm, 39.9 nm and 55.5 nm Au films. The best-fitted coupling factor G basically agrees with the theoretical value 2.3 × 10¹⁶ W m⁻³ K⁻¹. The propagation speed of the diffusive wave in the electron gas can be obtained by comparing the measured delay time of peak electron temperatures of Au films with different thicknesses. The average propagation speed of the temperature oscillation or diffusive wave in Au films for the range of thickness from 27.2 nm to 55.5 nm is equal to 8.1 × 10⁵ m s⁻¹, which is close to the value predicted by the non-equilibrium heat diffusion model.     

Electricity generation by Shewanella sp. HN-41 in microbial fuel cells

Microbial fuel cells (MFCs) provide new opportunities for energy generation through conversion of organic matter to electricity by electricity-generating bacteria. In this study, Shewanella sp. strain HN-41 was described as an exoelectrogen that had the ability of extracellular electron transfer in MFCs fed with lactate or glucose. The maximum power density produced by the strain HN-41 in lactate- and glucose-fed single-chamber MFCs reached 71.6 and 18.2 mW m⁻², respectively. The strain showed strong capability to reduce Fe(III) with lactate or glucose as electron donor during the initial incubation period, and secreted flavin mononucleotide (FMN), riboflavin, and traces of flavin adenine dinucleotide in MFCs. Addition of riboflavin and FMN as electron mediators contributed to 2–5 folds increase in power density. These findings on the ability of Shewanella sp. HN-41 to couple oxidation of glucose contributed to the expansion of our knowledge on utilization of carbon source by Shewanella sp.     

A cobalt polypyrrole composite catalyzed cathode for the direct borohydride fuel cell

A cobalt polypyrrole carbon (Co-PPY-C) composite has been attempted for use as a cathode catalyst in a direct borohydride fuel cell (DBFC). A Co-PPY-C composite has been fabricated in laboratory and characterized by the field emission scanning electron microscopy, transmission electron microscopy, as well as X-ray photoemission spectroscopy. Fabricated Co-PPY-C catalyst demonstrates good short-term durability and activity which are comparable to those obtained from the Pt/C catalyst. A maximum power density of 65 mW cm⁻² has been achieved at ambient conditions. This research concludes that metallo-organic coordination compounds would be potential candidates for use as cathode catalysts in the DBFC.     

A new organic dye bearing aldehyde electron-withdrawing group for dye-sensitized solar cell

A new metal-free dye (I) with a diketopyrrolopyrrole (DPP) core was synthesized, in which triphenylamine was used as electron donor, thiophene units as the π-conjugated bridge, aldehyde units as electron acceptor. The corresponding dye II containing carboxy group as the electron-withdrawing acceptor for the purpose of comparison was also synthesized. The absorption spectra, electrochemical and photovoltaic properties of I and II were extensively investigated. Electrochemical measurements data indicate that the tuning of HOMO and LUMO energy levels can be conveniently accomplished by alternating electron acceptor. The short-circuit photocurrent density and conversion efficiency of solar cell based on aldehyde-containing dye is more dominant than that bear a carboxy group as the electron withdrawing anchoring group. The new sensitizer I exhibited a photovoltaic performance: a short-circuit photocurrent density (J_sc) of 6.07 mA cm^?2, an open-circuit photovoltage (V_oc) of 568 mV, and a fill factor (FF) of 0.66, corresponding to an overall conversion efficiency of 2.27% under standard global AM 1.5 solar light condition. This work suggests that aldehyde units as new type of electron withdrawing anchoring group are promising candidates for improvement of the performance of DSSCs.     

Visible light induced dye-sensitized photocatalytic hydrogen production over platinized TiO2 derived from decomposition of platinum complex precursor

Pt/TiO₂ derived from complete decomposition of the surface-anchored Pt(dcbpy)Cl₂ (dcbpy = 4,4′-dicarboxy-2,2′-bipyridine) precursor (denoted as C-Pt/TiO₂) was prepared to serve as photocatalyst in visible light region. For dye-sensitized hydrogen production experiments, the photocatalyst was sensitized by Ru(2,2′-bipyridine-4,4′-dicarboxylic)₂(NCS)₂ (the N3 dye) and Ru(2,2′bipyridyl-4,4′-dicarboxylic) (4,4′- dinonyl-2,2′bipyridine) (NCS)₂ (the Z907 dye) to induce hydrogen evolution in the presence of sacrificial electron donor, triethanolamine (TEA). The hydrogen generation results showed that C-Pt/TiO₂ was found to be a much more active photocatalyst when compared to P-Pt/TiO₂, prepared by conventional method of photochemical deposition of H₂PtCl₆ (denoted as P-Pt/TiO₂). For further investigation, the photodegradation experiments in visible region were also confirmed the better photocatalytic activity of C-Pt/TiO₂. The enhanced catalytic activity is due to efficient interparticle electron transfer with the small-size and high-disperse platinum particles generated from photodeposition of Pt(dcbpy)Cl₂, which was verified by the transmission electron microscopy (TEM) measurement.     

8 MeV electron irradiation studies on electrical characteristics of Cu(In,Ga)Se2 solar cells

Cu(In,Ga)Se₂ (CIGS) solar cells are gaining considerable interest due to their high optical absorption coefficient and adjustable band gap, which enables them to achieve high conversion efficiency and also present many promising applications in space power systems. In this paper we report the results of the effect of temperature and 8 MeV electron irradiation on the electrical characteristics of ZnO/CdS/Cu(In,Ga)Se₂/Mo polycrystalline thin-film solar cells under forward and reverse bias studied in the temperature range 270-315 K. The solar cells were subjected to 8 MeV electron irradiation from the Microtron accelerator and were exposed to graded doses of electrons up to 75 kGy. I-V characteristics of the cells under dark and AM 1.5 illumination condition were studied before and after the irradiation. Capacitance measurements were also carried out at various frequencies before and after irradiation. In the measured temperature range, the dark current contribution is due to the generation-recombination of the minority carriers in the depletion region. The ideality factor is found to decrease with increase in temperature. It seems that electron irradiation has not altered the dark current conduction mechanism significantly. The effect of electron irradiation on the solar cell parameters such as fill factor (FF), conversion efficiency (η), saturation current (I_o), short circuit current (I_sc), open circuit voltage (V_oc), and ideality factor (n) was studied. They were found to be stable up to 75 kGy of electron dose as only small changes were observed in the solar cell parameters.     

Photovoltaic performance and long-term stability of quasi-solid-state fluoranthene dyes-sensitized solar cells

Two new fluoranthene-based organic dye sensitizers (I and II), in which 7, 12-diphenylbenzo[k]fluoranthene moiety is acted as electron donor, thiophene and phenylethynyl units as electron spacers and carboxylic acid as electron acceptor were successfully applied in quasi-solid-state dye-sensitized solar cells. The quasi-solid-state DSSCs based on the dye I showed the better photovoltaic performance: a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 66%, a short-circuit photocurrent density (J_sc) of 3.53 mA cm^?2, an open-circuit photovoltage (V_oc) of 542 mV, and a fill factor (ff) of 0.70, corresponding to an overall conversion efficiency of 1.33% under standard global AM 1.5 solar condition. Moreover, the two sensitizers exhibited good stability during a long-term accelerated aging, in which the photovoltaic parameters retained more than 90% of its initial value even after 1000 h under light soaking at 60 °C.     

Optimization of glassy carbon electrode based graphene/ferritin/glucose oxidase bioanode for biofuel cell applications

A glassy carbon (GC)/graphene/ferritin/glucose oxidase (GOx) anode was developed by using graphene/ferritin biocomposite as an electron transfer enhancer and mediator, respectively. The electrode exhibited good electrocatalytic activity towards the oxidation of glucose. The electrocatalytic oxidation of glucose using GOx modified electrode increased with increasing the concentration of glucose upto 45 mM. The results showed that the graphene/ferritin biocomposite mediator provides enhancement in electron transfer generated at the active cites of GOx to the electrode. All electrochemical measurements were carried out by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). A saturation current density of 66.5 ± 2 mA cm⁻² at scan rate 100 mV s⁻¹ for the oxidation of 45 mM glucose was achieved.     

Electrodeposition of mesoporous manganese dioxide supercapacitor electrodes through self-assembled triblock copolymer templates

Mesoporous manganese dioxide supercapcitor electrode materials were electrochemically deposited onto silicon substrates coated with Pt using triblock copolymer species (Pluronic P123 and F127) as the structure-directing agents. Deposited electrodes of manganese dioxide film were physically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and were electrochemically characterized by cyclic voltammetry (CV) in 0.5 M Na₂SO₄ electrolyte. Maximum specific capacitance (SC) values of 449 F g⁻¹ was obtained at a scan rate of 10 mV s⁻¹ from F127 templated mesoporous MnO₂.     

Conversion of heat and light simultaneously using a vacuum photodiode and the thermionic and photoelectric effects

The photoelectric and thermionic effects are combined in an illustrative experiment to demonstrate that solar light and heat can be converted into electrical energy simultaneously. When an electron is ejected from the cathode and is collected by the anode, a difference in chemical potential develops between the anode and cathode Fermi levels. Work can be extracted as the electron returns to the emitter Fermi level via the load. When the electron is not thermalized, it is said to be a “hot” electron. Ross and co-workers have predicted that the AM1.5 efficiency limit for a hot carrier conversion system, 66%, is greater than that for a purely thermal system, 52%, or for a quantum system, 33% (e.g., a photovoltaic cell). The present work was undertaken to provide an easy to reproduce experimental format to explore these concepts. As an example suitable for a student laboratory, a commercial vacuum phototube is used as a quantum and thermal energy converter. An S1 photocathode comprised of Ag₂O:Cs is employed at low temperatures, T<100°C, to demonstrate that the power converted by a heated and illuminated phototube is greater than that obtained either heated in the dark, or under illumination at room temperature. Although the conversion efficiency and power production is small in this example (approx. 10⁻³%), the experiment demonstrates how two forms of solar energy can be simultaneously utilized. It also promotes a thermodynamic approach to the evaluation of solar converters. The use of cesiated III/V materials (e.g. InGaAsP:Cs) as photocathodes is discussed as a possible research pathway for realizing efficient hot electron devices.