Interfacial Charge Transfer Resistance Research Articles

The Detrimental Effects of Carbon Additives in Li10GeP2S12-Based Solid-State Batteries.

All-solid-state batteries (SSBs) have recently attracted much attention due to their potential application in electric vehicles. One key issue that is central to improve the function of SSBs is to gain a better understanding of the interfaces between the material components toward enhancing the electrochemical performance. In this work, the interfacial properties of a carbon-containing cathode composite, employing Li10GeP2S12 as the solid electrolyte, are investigated. A large interfacial charge-transfer resistance builds up upon the inclusion of carbon in the composite, which is detrimental to the resulting cycle life. Analysis by X-ray photoelectron spectroscopy reveals that carbon facilitates faster electrochemical decomposition of the thiophosphate solid electrolyte at the cathode/solid electrolyte interface-by transferring the low chemical potential of lithium in the charged state deeper into the solid electrolyte and extending the decomposition region. The occurring accumulation of highly oxidized sulfur species at the interface is likely responsible for the large interfacial resistances and aggravated capacity fading observed.

Inhibition Performance of Cetyltrimethylammonium Bromide Against Reinforcing Steel Corrosion in Simulated Concrete Pore Solutions

Reinforcing steel corrosion in concrete is a main reason for the deterioration of durability of reinforced concrete structures. The widespread corrosion of reinforcing steel caused by chloride ions is a common and serious problem all over the world. Obviously, corrosion protection of reinforcing steel in concrete has become an urgent and important task. The use of corrosion inhibitors is one of the promising protection methods for controlling steel corrosion in concrete because of their low cost and easy application. The development and application of surfactant corrosion inhibitors have drawn special attention. Many surfactants have inviting application prospects for the corrosion protection of metals. Cetyltrimethylammonium bromide (CTMAB), a cationic surface active agent, has been studied for metal corrosion protection due to its main advantages of non-toxicity and a popular price. Nevertheless, there is little information on CTMAB as a corrosion inhibitor for steel in concrete. In this work, the surfactant CTMAB was employed as a corrosion inhibitor and its inhibition performance against reinforcing steel corrosion in the simulated concrete pore solutions was studied by electrochemical measurements and surface analyses. The cylindrical specimens with Ø11.2 mm × 4 mm were cut from a Q235 reinforcing steel bar. The specimen mounted in epoxy resin was used as the working electrode with an exposed area of 1.00 cm2during electrochemical measurements, and a platinum sheet and a saturated calomel electrode (SEC) served as the auxiliary electrode and the reference electrode, respectively. The compositions of the specimens were analyzed by X-ray energy dispersive spectroscopy (EDS), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS), and their morphologies were observed by scanning electron microscopy (SEM). A saturated Ca(OH)2 solution with pH about 12.50 was selected as a simulated concrete pore solution. After the solution was adjusted to pH 11.00 with a 0.8 mol/L NaHCO3solution and 0.5 M NaCl was added, it served as a simulated polluted concrete pore (SPCP) solution, namely a test solution. Then different concentrations of CTMAB were added to the SPCP solution to investigate the corrosion inhibition effect of CTMAB on the reinforcing steel. The EIS analysis of the steel in the SPCP solution showed the capacitive reactance arc size increased gradually while the CTMAB concentration was increased from 0 to 0.005 M, then decreased with the increasing of the CTMAB concentration from 0.005 to 0.1 M. When the CTMAB concentration was 0.005 M, the interfacial charge transfer resistance (R ct) of the steel reached a maximum of 41.17 kΩ cm2, and the inhibition efficiency of CTMAB was 79.9%. The inhibition efficiency of CTMAB determined from the polarization curve of the steel in the SPCP solution with 0.005 M CTMAB reached 87.6%, indicating that the CTMAB could inhibit corrosion of reinforcing steel effectively. For the SPCP solution without CTMAB there was not a passive region on the potentiodynamic anodic polarization curve of the steel, indicating that the steel corrosion took place. However, the steel was in a passive state for the solution with 0.005 M CTMAB. The SEM results also indicated that CTMAB could protect the steel from corrosion. XPS and Raman results proved that CTMAB was an adsorption type corrosion inhibitor. The adsorbed CTMAB resulted in the formation of a protective film on the steel surface to protect the steel from corrosion.

Enhanced performance of microbial fuel cell with in situ preparing dual graphene modified bioelectrode

This study proposed a three-step method to prepare dual graphene modified bioelectrode (D-GM-BE) by in situ microbial-induced reduction of GO and polarity reversion in microbial fuel cell (MFC). Both graphene modified bioanode (GM-BA) and biocathode (GM-BC) were of 3D graphene/biofilm architectures; the viability and thickness of microbial biofilm decreased compared with control bioelectrode (C-BE). The coulombic efficiency (CE) of GM-BA was 2.1 times of the control bioanode (C-BA), which demonstrated higher rate of substrates oxidation; the relationship between peak current and scan rates data meant that GM-BC was of higher efficiency of catalyzing oxygen reduction than the control biocathode (C-BC). The maximum power density obtained in D-GM-BE MFC was 122.4±6.9mWm−2, the interfacial charge transfer resistance of GM-BA and GM-BC were decreased by 79% and 75.7%. The excellent electrochemical performance of D-GM-BE MFC was attributed to the enhanced extracellular electron transfer (EET) process and catalyzing oxygen reduction.

Improving the electrochemistry performance of layer LiNi0.5Mn0.3Co0.2O2 material at 4.5 V cutoff potential using lithium metaborate

LiNi0.5Mn0.3Co0.2O2 (NMC) cathode material is surface treated by Li active boron oxide (LBO) via a two-step process. The surface morphology, crystal structure, surface composition, and electrochemical properties were characterized based on SEM, XRD, XPS, charge–discharge tests, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) measurements. XPS results showed that the coating layer was composed of LiBO2. The 2 wt% LBO-coated NMC exhibited the best electrochemical performance at high voltage (4.5V). It was achieved a high capacity retention of 91.23% after 50 cycle which was 53.19% for the uncoated one. The rate capability of the coated electrode was improved obviously, exhibiting 114.71 mAh·g-1 discharge capacity at 10C. The interfacial resistance and charge transfer resistance was also decreased owning to the fact that the coating layer played a “firewall” between the electrolyte and the NMC electrode.

Electrochemical characterization of non-stoichiometric Cu2S x cathode for lithium batteries

Electrochemical performances of non-stoichiometric Cu2Sx (1.25 ≤ x ≤ 0.625) cathodes prepared by spray pyrolysis and followed annealing were investigated after coating on carbon fiber paper (CFP) and Cu foil current collectors. The chemical composition influence on the electrochemical properties of Cu2Sx was noticeably observed on a Cu foil current collector, especially at higher charge-discharge rates. Electrochemical impedance spectroscopy revealed that Cu/S ≈ 3.2 M ratio electrode shows lower interfacial charge transfer resistance (Rct) after 5 cycles at 0.1 C compared with Cu/S ≈ 1.6 M ratio electrode on both current collectors. Accordingly, the electrode with Cu/S ≈ 3.2 M ratio showed the highest discharge capacity of 350 mAh g−1 at 5 C on a Cu foil current collector. The excess of Cu in Cu2Sx enhanced electrode utilization with the cycle number and facilitated fast charge transfer.

Enhancing Extracellular Electron Transfer of Shewanella oneidensis MR-1 through Coupling Improved Flavin Synthesis and Metal-Reducing Conduit for Pollutant Degradation.

Dissimilatory metal reducing bacteria (DMRB) are capable of extracellular electron transfer (EET) to insoluble metal oxides, which are used as external electron acceptors by DMRB for their anaerobic respiration. The EET process has important contribution to environmental remediation mineral cycling, and bioelectrochemical systems. However, the low EET efficiency remains to be one of the major bottlenecks for its practical applications for pollutant degradation. In this work, Shewanella oneidensis MR-1, a model DMRB, was used to examine the feasibility of enhancing the EET and its biodegradation capacity through genetic engineering. A flavin biosynthesis gene cluster ribD-ribC-ribBA-ribE and metal-reducing conduit biosynthesis gene cluster mtrC-mtrA-mtrB were coexpressed in S. oneidensis MR-1. Compared to the control strain, the engineered strain was found to exhibit an improved EET capacity in microbial fuel cells and potentiostat-controlled electrochemical cells, with an increase in maximum current density by approximate 110% and 87%, respectively. The electrochemical impedance spectroscopy (EIS) analysis showed that the current increase correlated with the lower interfacial charge-transfer resistance of the engineered strain. Meanwhile, a three times more rapid removal rate of methyl orange by the engineered strain confirmed the improvement of its EET and biodegradation ability. Our results demonstrate that coupling of improved synthesis of mediators and metal-reducing conduits could be an efficient strategy to enhance EET in S. oneidensis MR-1, which is essential to the applications of DMRB for environmental remediation, wastewater treatment, and bioenergy recovery from wastes.

Applications of Electro-Fenton for Sustainable Water Treatment and Reuse: A Case Study in the Electronics Industry

Electrochemistry has an important role to play in increasing the sustainability and energy efficiency of water treatment and reuse systems. In Singapore for example, the water demand has been projected to more than double by 2060, with non-domestic water demand expected to account for 70% (560 millions of gallons per day). In this context, industrial water reuse is becoming a necessity and the electronics sector has been identified as one of the priority targets due to the extra-pure water requirements. The main issue with industrial water reuse is the removal of “hard-to-treat” contaminants and current interest is focusing on advanced oxidation processes (AOPs), because they produce highly oxidizing species like •OH radicals that can non-selectively mineralize all sorts of organic pollutants. Among them, electro-Fenton has emerged because of its many advantages, including ease of operation and high degradation rates of numerous organic pollutants, thanks to the recent development of improved electrode materials (e.g., carbon nanotubes, graphene, etc.) (1-3). In this work, we showcase the performance at lab-scale and pre-pilot scale of an electro-Fenton prototype to treat a real waste stream from a semi-conductor factory using a novel carbon-fiber brush cathode. First, the brush was fully characterized in terms of its electrical conductivity and surface area. Its interfacial charge-transfer resistance (R ct) – as determined by electrochemical impedance spectroscopy – equaled 1.40 Ω. Cyclic voltammetry was used to determine the electroactive surface area of the electrode, which was found equal to 416 cm2, by using the Randles-Sevcik equation (Eq. 1): Ip = 2.69 × 105 × AD 1/2 n 1/2 γ 1/2 C (Eq. 1) where Ip is the peak current (A), n is the number of electrons participating in the redox reaction (n = 1), A is the area of the electrode (cm2), D is the diffusion coefficient of the molecule in solution (7.60 × 10-6 cm2 s-1), C is the concentration of the probe molecule in the bulk solution (1 × 10-5 mol cm-3), and γ is the scan rate of the potential perturbation (0.01 V s-1). The catalytic activity of the novel electrode was then assessed by its capacity to electrogenerate H2O2. Since H2O2 is an intermediate required to produce •OH in the electro-Fenton reaction (Eq. 2) and is easier to detect, due to its longer half-life, its production arguably constitutes a better indicator of the cathode efficiency than the generation of •OH (4, 5): H2O2 + Fe2+ → Fe3+ + •OH + HO- (Eq. 2) The influence of the current density (normalized to the cathode projected surface area) on H2O2 production through cathodic reduction of O2 was thus evaluated and the best results were obtained at 1.25 mA cm-2, yielding a specific maximum H2O2 concentration of 3.00 ± 0.12 mg-H2O2 L-1 cm-2. Upon addition of Fe2+ to trigger the electro-Fenton reaction following Eq. 2, a mineralization efficiency of 80% was attained within 3 hours using real wastewater from the microelectronics industry in a lab-scale batch setup (Fig. 1) and the energy requirement was as low as 0.14 kWh g-1of total organic carbon (TOC). Following these promising results, a continuous-flow pre-pilot scale prototype was designed and a computational flow simulation allowed optimizing various parameters, from electrode spacing to flowrate and mass transfer rates towards the electrodes (Fig. 2). The performance of this pre-pilot prototype was evaluated in the same conditions as the lab-scale reactor, confirming and even improving the results obtained at lab-scale with over 90% TOC removal reached within 3 hours (Fig. 1). However, the energy consumption increased with the intensity of the treatment from 0.8 KWh g-1 of TOC in the first hour to 1.34 kWh/g-1of TOC, after 3 hours, showing that electro-Fenton would be better used as a pre-treatment technology, over a limited period of time. Overall, these results demonstrate the potential of electro-Fenton as a water treatment and reuse technology and constitute an important step towards full-scale applications. A detailed technical economic assessment of the technology for industrial water reuse will be presented at the conference.

A Sulfide Solid Electrolyte Surface Layer Formed Via Electrolyte Additives Enables Stable Plating of Li Metal

Li metal batteries promise the next-generation rechargeable batteries for electric vehicles applications due to the highest specific capacity (3840 mA h g-1) and lowest reduction potential (−3.04 V vs. S.H.E.) of Li among all alkali and alkaline earth metals. However, a non-uniform solid electrolyte interphase (SEI) layer formed via parasite reactions of Li with the electrolytes leads to locally site-specific Li deposition, i.e., dendritic plating.1 Dynamic breaking and forming of this layer, in turn, leads to the accumulative loss of Li, build-up of the SEI and consumption of the electrolyte causing cell failure. Upon prolonged cycling, penetration of dendrites through the separator causes hazardous cell short-circuits. Modified electrolytes including concentrated electrolytes,2 LiF additive3 and artificial SEI layer4 have shown promise in suppressing dendrites. In this presentation, we will demonstrate an in-vivo formed sulfide-based ionic conductive layer — realized by using a low concentration complexed electrolyte additive — that not only generates a kinetically favorable interface, but also reduces the corrosive reactions of the electrolyte with Li. Upon Li plating, the high ionic conductivity of the solid electrolyte layer allows the Li+flux to be evenly distributed over the conductive surface. Furthermore, even at extremely high current densities when incipient dendritic Li start to form, the reservoir additives in the electrolyte facilitate local formation of the conductive layer. Upon resting at OCV, the Li|Li symmetric cell in the presence of the electrolyte additive shows much lower interfacial charge transfer resistance than a cell with a “blank” electrolyte (20 vs. 320 Ω cm-2). Furthermore, the impedance is stable over 2 days of rest, in contrast with significantly increasing impedance exhibited by the blank cell. Greatly improved long-term cycling of the symmetric cells is observed. The cell with additive exhibits extremely stable voltage evolution over 400 hours, whereas the blank electrolyte cell experiences voltage fluctuation followed by short-circuit after 270 hours (Figure 1a). Notably, stable cycling of Li|Li symmetric cells over 2500 hours at 1 mA cm-2 with 1 mA h cm-2 capacity was achieved using 100 mM additive (Figure 1b), and a significant decrease in polymerized solvent is observed compared to a cell with no additive. In a full Li metal cell using Li4Ti5O12 as the positive electrode, the cell with the electrolyte additive exhibits very stable capacity retention (88%) over 400 cycles. Reference 1. Y. S. Cohen, Y. Cohen, D. Aurbach, J. Phys. Chem. B, 2000, 104, 12282-12291. 2. J. Qian, W. A. Henderson, W. Xu, P. Bhattacharya, M. Engelhard, O. Borodin, J.-G. Zhang, Nat. Commun., 2015, 6, 6362. 3. Y. Lu, Z. Tu, L. A. Archer, Nat. Mater., 2014, 13, 961–969. 4. G. Zheng, S. W. Lee, Z. Liang, H.-W. Lee, K. Yan, H. Yao, H. Wang, W. Li, S. Chu, Y. Cui, Nat. Nanotech., 2014, 9, 618–623. Figure 1

Enhanced electricity generation for biocathode microbial fuel cell by in situ microbial-induced reduction of graphene oxide and polarity reversion

A simple effective and environmentally friendly pathway to form graphene modified biocathode was induced by polarity reversion of graphene modified bioanode, which was made by in situ microbial-induced reduction of graphene oxide (GO). Graphene assembled by microbes showed that D/G intensity increased from 0.84 to 0.91 and C/O atomic ratio added from 2.13 to 4.45, indicating GO was reduced largely. The graphene modified biocathode exhibited crumples that grown on the lamellar and glossy surface and was capable of improving catalytic reduction of oxygen. Microbial fuel cell (MFC) fabricated with graphene modified biocathode obtained 1.22 times in maximum power density, 0.21 times in interfacial charge transfer resistance, and recorded an obvious redox peaks at −0.50 V (vs. SCE) than control biocathode MFC. Geobacter, Clostridium, Pseudomonas, Geothrix and Hydrogenophaga belonged to exoelectrogens occupied 17.53% in graphene modified biocathode, 2.07% in control biocathode in genus level. This study provided a new insight into the feasibility to make microbes self-assembled graphene to improve electrochemical performance of biocathode MFC.

Depositing Pt nanoparticles by pulse electrodeposition for DSSCs counter electrode with high electrocatalytic activity

A Pt counter electrode of dye-sensitized solar cells (DSSCs) was prepared by a simple and low-cost pulse electrodeposition method. The catalytic activity and the Pt utilization efficiency of Pt films were investigated. In this study, four Pt counter electrodes were prepared by pulse electrodeposition at high current density on FTO substrates. The catalytic activity of the counter electrode and DSSC performance were optimized by varying the pulse electrodepositing cycles. The relationships between Pt nanostructure, electrochemical properties, interfacial charge transfer resistance and photovoltaic performance are investigated in detail. The Pt film prepared by 25 pulse electrodepositing cycles shows well-distributed Pt nanoparticles on the FTO substrate, which provides not only a larger electrochemical active surface area but also lower charge transfer resistance than others. The photovoltaic performance proves that the Pt counter electrode prepared by 25 pulse electrodepositing cycles at 30 mA/cm2 current density achieves the highest energy conversion efficiency of 8.45% among these samples.

Impedimetric biosensor based on bimetallic AgPt nanoparticle-decorated carbon nanotubes as highly conductive film surface

In the present study, an ultrasensitive impedimetric aptasensor for the quantitative detection of diclofenac (DCF) was fabricated based on a novel signal amplification strategy. As a transducer material, acid-oxidized carbon nanotubes (CNT-COOH) and Pt and Ag nanoparticles (PtAgNPs) were used for promoting electron transfer between the electroactive probe and electrode. It is worth noting that the proposed nanocomposite revealed significant properties through the synergistic effects of the nanocomponent materials. In this strategy, aminated capture probe (ssDNA1) and DCF aptamer (ssDNA2) as a detection probe were attached at the surface of a modified electrode via the formation of covalent amide bond and hybridization, respectively. The proposed nanoaptasensor combined the advantages of the deposition of neatly arranged PtAgNPs and the covalent attachment of the capture probe at the surface of the modified electrode. The change of interfacial charge transfer resistance (R ct ) recorded by [Fe(CN)6]3−/4− as a redox probe was monitored for sensitive quantitative detection of DCF. Addition of DCF resulted in the increase of the value of R ct due to suppression of the electron exchange between [Fe(CN)6]3−/4− in the surface layer. Under optimized conditions, the proposed aptasensor showed good detection range from 10 pM to 800 nM with unprecedented detection limit of 2.8 pM. More importantly, the developed strategy showed highly sensitive responses to DCF, responses that are more sensitive than those of previously reported methods.

Enhanced Electronic Communication and Electrochemical Sensitivity Benefiting from the Cooperation of Quadruple Hydrogen Bonding and π–π Interactions in Graphene/Multi-Walled Carbon Nanotube Hybrids

By designing a molecule labeled as UPPY with both ureidopyrimidinone (UP) and pyrene (PY) units, the supramolecular self-assembly of multiwalled carbon nanotube (MWNT) and reduced graphene oxide (rGO) was driven by the UP quadruple hydrogen-bonding and PY-based π-π interactions to form a novel hybrid of rGO-UPPY-MWNT in which the morphology of rGO-wrapped MWNT was found. Bridged by the two kinds of noncovalent bonding, enhanced electronic communication occurred in rGO-UPPY-MWNT. Also, under the cooperation of UP quadruple hydrogen-bonding and PY-based π-π interactions, higher electrical conductivity and better charge transfer were observed for rGO-UPPY-MWNT, compared with the rGO-MWNT composite without such noncovalent bonds, and that with just single PY-based π-π interaction (rGO-PY-MWNT) or UP quadruple hydrogen bond (rGO-UP-MWNT). Specifically, the electrical conductivity of rGO-PY-MWNT hybrids was increased approximately sevenfold, and the interfacial charge transfer resistance was nearly decreased by 1 order of magnitude compared with rGO-MWNT, rGO-UP-MWNT, and rGO-PY-MWNT. Resulting from its excellent electrical conductivity and charge transfer properties, the rGO-UPPY-MWNT modified electrode exhibited enhanced electrochemical activity toward dopamine with detection limit as low as 20 nM.

A Peptide‐Based Electrochemical Biosensor for Facile Measurement of Whole‐Blood Heparin

AbstractThe first peptide‐based electrochemical biosensor for the measurement of the anti‐coagulant heparin using electrochemical impedance spectroscopy is reported. The peptide immobilized on the electrode interface specially captures heparin with high affinity. The composites formed on the electrode can thus effectively repel electrochemical species, leading to an increase in interfacial charge transfer resistance. After analyzing the electrochemical signals, a linear detection range from 0.05 to 10.0 μg/mL is obtained. The detection limit is calculated to be 0.01 μg/mL, which is extremely low with such a simple sensing mechanism. Moreover, the proposed method has potential application for sensitive and separation‐free detection of heparin in whole‐blood samples.

A carbon-quantum-dot-sensitized ZnO:Ga/ZnO multijunction composite photoanode for photoelectrochemical water splitting under visible light irradiation

A carbon quantum dot (CQD)-sensitized ZnO:Ga/ZnO composite photoanode for photoelectrochemical water splitting has been designed and tested. In the composite, a ZnO array is grown on a piece of indium tin oxide glass and facilitates the essential integrity of the photoanode. An overlayer of Ga–doped ZnO (ZnO:Ga) is then hydrothermally grown on the ZnO nanorods. A type I ZnO:Ga/ZnO junction forms with a ZnO:Ga shell possessing visible light activity and a narrow bandgap. However, a highly positive onset potential exists due to the location of the conduction band (CB) of ZnO:Ga at the high end. The deposition of the CQDs on the surface of the overlayer provides a negatively shifted CB with a type II junction between ZnO:Ga and CQDs. The CQDs@ZnO:Ga/ZnO multijunction composite photoanode exhibits a negative shift of the onset potential and a significantly increased photocurrent density, up to 1.5mAcm−2 at 1.6V vs. RHE, with good photostability under AM 1.5 G simulated light. The multijunction composite photoanode also achieves a current density of 0.16mAcm−2 under visible light at a bias of 1.0V, which is comparable to that of ZnO under AM 1.5 G simulated light. Electrochemical impedance spectra reveal that the CQD modification acts to decrease the interfacial charge transfer resistance associated with eliminating the energy barrier in the type I ZnO:Ga/ZnO junction that causes charge transfer resistance.

Developing an Impedimetric Aptasensor for Selective Label–Free Detection of CEA as a Cancer Biomarker Based on Gold Nanoparticles Loaded in Functionalized Mesoporous Silica Films

This study aims at designing a novel impedimetric aptasensor to determine carcinoembryonic antigen (CEA). The CEA aptasensor was developed by covalent immobilization of an amine-modified CEA aptamer on the surface of a glassy carbon electrode (GCE) which was modified by gold nanoparticles (AuNPs) incorporated in amino-functionalized MCM–41 (AMCM). After the aptamer was immobilized, CEA was incubated on the surface of an Ap-GA-AuNPs/AMCM-GCE. The change in the interfacial charge transfer resistance (Rct) of the redox marker served as an excellent signal for the quantitative determination of CEA. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to display the aptamer immobilization on the electrode surface. Through the EIS method, the linear range and the detection limit of CEA were found to be 1.0 × 10−3−100.0 ng mL−1 and 9.8 × 10−4 ng mL−1 respectively. Moreover, the proposed aptasensor was used to determine of CEA in patient and healthy human serum samples and the results indicated that this aptasensor has great potential for practical application which the strength point of this aptasensor.

Effect of PEG as Soft Template in Hydrothermal Synthesis of Porous TiO2 Nanoparticles for DSSC Application

Porous TiO2 nanoparticles were prepared by soft template assisted hydrothermal method. XRD pattern confirms the formation of tetragonal anatase phase of TiO2. HRSEM images show homogeneous spherical shaped porous TiO2 nanoparticles. UV-Visible spectrum ensures broad absorption in ultraviolet regime with absorption maximum at 291 nm. Nyquist plot reveals that decrease in electrical resistance with increasing applied potential results in enhancing the conductivity. The interfacial charge transfer resistance and electron recombination lifetime of the fabricated DSSC was examined using EIS analysis. Photovoltaic performance of the device was studied using standard solar simulator and the power conversion efficiency of ∼2.3% was achieved.

Enhanced photopromoted electron transfer over a bilayer WO3 n–n heterojunction prepared by RF diode sputtering

A bilayer WO3 photoelectrode was obtained by radio frequency (RF) plasma sputtering in a reactive 40%O2/Ar atmosphere by depositing two successive WO3 coatings on a tungsten foil at two different total gas pressures (3 Pa and 1.7 Pa, respectively), followed by calcination at 600 °C. Two monolayer samples deposited at each of the two pressures and a bilayer sample deposited at inverted pressures were also prepared. Their photoelectrocatalytic (PEC) activity was evaluated by both Incident Photon-to-Current Efficiency (IPCE) measurements and separate evolution of H2 and O2 by water splitting in a two-compartment PEC cell. SEM analysis revealed that the photoanodes have a nanostructured porous double layer surmounting a columnar basement (Staffa-like morphology, after the name of the Scottish island). Mott–Schottky analysis showed that the single layer deposited at 3 Pa has a conduction flat band potential 0.1 V more positive than that deposited at 1.7 Pa. The equivalent n–n heterojunction at the interface of the double-layer creates a built-in electric field that facilitates the photopromoted electron transfer toward the lower lying conduction band material, while the columnar innermost layer introduces percolation paths for efficient electron transport toward the conductive tungsten foil. Both phenomena contribute to decrease the interfacial charge transfer resistance (Rct) and lead up to a ca. 30% increase in the PEC performance compared to the monolayer and the inverted bilayer coatings and to a 93% faradaic efficiency, which is among the highest reported so far for WO3 photoanodes. Upon methanol addition an outstanding 4-fold photocurrent density increase up to 6.3 mA cm−2 was attained over the bilayer WO3 photoanode, much larger than the usually observed current doubling effect.

The performance of 3-D graphite doped anodes in microbial electrolysis cells

Abstract This study investigated the use of granular activated carbon (GAC) as high surface area 3-dimensional (3-D) anode in MECs systems. The interfacial anodes' charge transfer resistance of the doped GAC did not impact the overall performance of MECs. Based on our finding, the 3-D anode packed with GAC-doped with nonconductive calcium sulfide (CaS) outperformed the more conductive iron (II) sulfide (FeS), magnetite (Fe 3 O 4 ), or GAC without doping. The results showed higher current densities for 3-D CaS (40.1 A/m 3 ), as compared with 3-D FeS (34.4 A/m 3 ), 3-D Fe 3 O 4 (29.8 A/m 3 ), and 3-D GAC (23.1 A/m 3 ). The higher current density in the 3-D CaS translated to higher coulombic efficiency (96.7%), hydrogen yield (3.6 mol H 2 /mol acetate), and attached biomass per anode mass (54.01 mg COD biomass/g GAC). Although the 3-D MEC achieved similar hydrogen yield, hydrogen recovery efficiency, and COD removal rate to a conventional sandwich type MEC, the current density, coulombic efficiency, and overall energy efficiency were higher.

Electrochemical impedance spectroscopy characterization of LiFePO4 cathode material with carboxymethylcellulose and poly-3,4-ethylendioxythiophene/polystyrene sulfonate

Novel cathode material compositions based on lithium iron phosphate (LFP) were prepared using conducting polymer dispersion poly-3,4-ethylenedioxythiopene/polystyrene sulfonate (PEDOT:PSS) and water-based carboxymethylcellulose (СМС) as a binder solely and in mixture PEDOT:PSS/СМС. The electrochemical properties of materials in lithium-ion batteries were investigated by galvanostatic charge-discharge curves and by electrochemical impedance spectroscopy and the results were compared with conventional PVDF-bound material. Our best materials consisting of 92wt% of C-LiFePO4, 4wt% of carbon black and 4wt% of conducting polymer binder exhibited excellent rate capability with discharge capacity 148mAhg−1 (at 0.2C, normalized by the electrode mass), 143mAhg−1 at 1C and 128mAhg−1 at 5C as well as good cycling stability at 1C (less than 1% decay after 100 cycles).Impedance spectra of batteries with different compositions were measured and analyzed. Comparison of kinetic parameters obtained for different electrodes revealed main factors responsible for significant improvement of electrochemical performance of LFP-based cathode materials modified with conducting polymer in comparison with conventional electrode. The transition from conventional PVDF-bound LFP-based cathode composition to modified by conducting polymer PEDOT:PSS/CMC was found very effective. The electrode with optimal composition showed substantial decrease of interfacial charge transfer resistance for 30 times, and decrease of Warburg diffusion resistance.The mechanism of positive influence of conducting binder on electrochemical properties of cathode material is discussed.

Facile preparation of poly(methylene blue) modified carbon paste electrode for the detection and quantification of catechin

Free radicals are formed as byproducts of metabolism, and are highly unstable due to the presence of unpaired electrons. They readily react with other important cellular components such as DNA causing them damage. Antioxidants such as (+)-catechin (CAT), neutralize free radicals in the blood stream. Hence there is a need for detection and quantification of catechin concentration in various food sources and beverages. Electro-oxidative properties of catechin were investigated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). A carbon paste working electrode modified by electropolymerizing methylene blue (MB) was fabricated. Field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) techniques were used to study the surface morphology of the electrode. Quasi-reversible electron transfer reaction occurred at +0.260V through a diffusion controlled process. In comparison to the bare carbon paste electrode (CPE), there was a significant 5.3 times increment in anodic current sensitivity at the modified electrode at physiological pH. Our findings indicate that for the electro-oxidation of CAT, CPE is a better base material for electropolymerization of MB compared to glassy carbon electrode (GCE). Nyquist plot followed the theoretical shape, indicating low interfacial charge transfer resistance of 0.095kΩ at the modified electrode. Calibration plots obtained by DPV were linear in two ranges of 1.0×10−3 to 1.0×10−6 and 1.0×10−7 to 0.1×10−8M. The limit of detection (LOD) and limit of quantification (LOQ) was 4.9nM and 14nM respectively. Application of the developed electrode was demonstrated by detecting catechin in green tea and spiked fruit juice with satisfactory recoveries. The sensor was stable, sensitive, selective and reproducible.