The recent developments of nanostructured WO3 thin films synthesized through the electrochemical route of electrochemical anodization and cathodic electrodeposition for the application in photoelectrochemical (PEC) water splitting are reviewed. The key fundamental reaction mechanisms of electrochemical anodization and cathodic electrodeposition methods for synthesizing nanostructured WO3 thin films are explained. In addition, the effects of metal oxide precursors, electrode substrates, applied potentials and current densities, and annealing temperatures on size, composition, and thickness of the electrochemically synthesized nanostructured WO3 thin films are elucidated in detail. Finally, a summary is given for the general evaluation practices used to calculate the energy conversion efficiency of nanostructured WO3 thin films and a recommendation is provided to standardize the presentation of research results in the field to allow for easy comparison of reported PEC efficiencies in the near future.
Solid polymer blend electrolyte membranes (SPBEM) composed of chitosan and dextran with the incorporation of various amounts of lithium perchlorate (LiClO4) were synthesized. The complexation of the polymer blend electrolytes with the salt was examined using FTIR spectroscopy and X-ray diffraction (XRD). The morphology of the SPBEs was also investigated using field emission scanning electron microscopy (FESEM). The ion transport behavior of the membrane films was measured using impedance spectroscopy. The membrane with highest LiClO4 content was found to exhibit the highest conductivity of 5.16 × 10-3 S/cm. Ionic (ti) and electronic (te) transference numbers for the highest conducting electrolyte were found to be 0.98 and 0.02, respectively. Electrochemical stability was estimated from linear sweep voltammetry and found to be up to ~2.3V for the Li+ ion conducting electrolyte. The only existence of electrical double charging at the surface of electrodes was evidenced from the absence of peaks in cyclic voltammetry (CV) plot. The discharge slope was observed to be almost linear, confirming the capacitive behavior of the EDLC. The performance of synthesized EDLC was studied using CV and charge-discharge techniques. The highest specific capacitance was achieved to be 8.7 F·g-1 at 20th cycle. The efficiency (η) was observed to be at 92.8% and remained constant at 92.0% up to 100 cycles. The EDLC was considered to have a reasonable electrode-electrolyte contact, in which η exceeds 90.0%. It was determined that equivalent series resistance (Resr) is quite low and varies from 150 to 180 Ω over the 100 cycles. Energy density (Ed) was found to be 1.21 Wh·kg-1 at the 1st cycle and then remained stable at 0.86 Wh·kg-1 up to 100 cycles. The interesting observation is that the value of Pd increases back to 685 W·kg-1 up to 80 cycles.
Additive manufacturing also known as 3D printing is being utilised in electrochemistry to reproducibly develop complex geometries with conductive properties. In this study, we explored if the electrochemical behavior of 3D printed acrylonitrile butadiene styrene (ABS)/carbon black electrodes was influenced by printing direction. The electrodes were printed in both horizontal and vertical directions. The horizsontal direction resulted in a smooth surface (HPSS electrode) and a comparatively rougher surface (HPRS electrode) surface. Electrodes were characterized using cyclic voltammetry, electrochemical impedance spectroscopy and chronoamperometry. For various redox couples, the vertical printed (VP) electrode showed enhanced current response when compared the two electrode surfaces generated by horizontal print direction. No differences in the capacitive response was observed, indicating that the conductive surface area of all types of electrodes were identical. The VP electrode had reduced charge transfer resistance and uncompensated solution resistance when compared to the HPSS and HPRS electrodes. Overall, electrodes printed in a vertical direction provide enhanced electrochemical performance and our study indicates that print orientation is a key factor that can be used to enhance sensor performance.
A systematic study of the electrochemical oxidation of 1,2-diarylalkenes was carried out with the focus on detailed product studies and variation of product type as a function of aromatic substitution. A reinvestigation of the electrochemical oxidation of 4,4'-dimethoxystilbene under various conditions was first carried out, and all products formed were fully characterized and quantitated. This was followed by a systematic investigation of the effect of aromatic substitution on the nature and distribution of the products. The aromatic substituents were found to fall into three main categories, viz., substrates in which the nature and position of the aromatic substituents gave rise to essentially the same products as 4,4'-dimethoxystilbene, for example, tetraaryltetrahydrofurans, dehydrotetralins, and aldehydes (p-MeO or p-NMe2 on one ring and X on the other ring, where X = o-MeO or p-alkyl, or m- or p-EWG; e.g., 4-methoxy-4'-trifluoromethylstilbene); those that gave rise to a mixture of indanyl (or tetralinyl) acetamides and dehydrotetralins (or pallidols) (both or one ring substituted by alkyl groups, e.g., 4,4'-dimethylstilbene); and those where strategic placement of donor groups, such as OMe and OH, led to the formation of ampelopsin F and pallidol-type carbon skeletons (e.g., 4,3',4'-trimethoxystilbene). Reaction pathways to rationalize the formation of the different products are presented.
In this paper, the electrochemical behavior of myricetin on a gold nanoparticle/ethylenediamine/multi-walled carbon-nanotube modified glassy carbon electrode (AuNPs/en/MWCNTs/GCE) has been investigated. Myricetin effectively accumulated on the AuNPs/en/MWCNTs/GCE and caused a pair of irreversible redox peaks at around 0.408 V and 0.191 V (vs. Ag/AgCl) in 0.1 mol L-1 phosphate buffer solution (pH 3.5) for oxidation and reduction reactions respectively. The heights of the redox peaks were significantly higher on AuNPs/en/MWNTs/GCE compare with MWCNTs/GC and there was no peak on bare GC. The electron-transfer reaction for myricetin on the surface of electrochemical sensor was controlled by adsorption. Some parameters including pH, accumulation potential, accumulation time and scan rate have been optimized. Under the optimum conditions, anodic peak current was proportional to myricetin concentration in the dynamic range of 5.0×10-8 to 4.0×10-5 mol L-1 with the detection limit of 1.2×10-8 mol L-1. The proposed method was successfully used for the determination of myricetin content in tea and fruit juices.
A gas sensor array was developed in a 10 × 10 mm(2) space using Screen Printing and Pulse Laser Ablation Deposition (PLAD) techniques. Heater, electrode, and an insulator interlayer were printed using the screen printing method on an alumina substrate, while tin oxide and platinum films, as sensing and catalyst layers, were deposited on the electrode at room temperature using the PLAD method, respectively. To ablate SnO(2) and Pt targets, depositions were achieved by using a 1,064 nm Nd-YAG laser, with a power of 0.7 J/s, at different deposition times of 2, 5 and 10 min, in an atmosphere containing 0.04 mbar (4 kPa) of O(2). A range of spectroscopic diffraction and real space imaging techniques, SEM, EDX, XRD, and AFM were used in order to characterize the surface morphology, structure, and composition of the films. Measurement on the array shows sensitivity to some solvent and wood smoke can be achieved with short response and recovery times.
Advanced oxidation processes (AOPs) such as Fenton, electro-Fenton and photo-Fenton have been applied effectively to remove refractory organics from landfill leachate. The Fenton reaction is based on the addition of hydrogen peroxide to the wastewater or leachate in the presence of ferrous salt as a catalyst. The use of this technique has proved to be one of the best compromises for landfill leachate treatment because of its environmental and economical advantages. Fenton process has been used successfully to mineralize wide range of organic constituents present in landfill leachate particularly those recalcitrant to biological degradation. The present study reviews the use of Fenton and related processes in terms of their increased application to landfill leachate. The effects of various operating parameters and their optimum ranges for maximum COD and color removal are reviewed with the conclusion that the Fenton and related processes are effective and competitive with other technologies for degradation of both raw and pre-treated landfill leachate.
In this study, the kinetics of adsorption of Pb(II) from aqueous solution onto palm shell-based activated carbon (PSAC) were investigated by employing ion selective electrode (ISE) for real-time Pb(II) and pH monitoring. Usage of ISE was very appropriate for real-time adsorption kinetics data collection as it facilitated recording of adsorption data at very specific and short time intervals as well as provided consistent kinetics data. Parameters studied were initial Pb(II) concentration and agitation speed. It was found that increases in initial Pb(II) concentration and agitation speed resulted in higher initial rate of adsorption. Pseudo first-order, pseudo second-order, Elovich, intraparticle diffusion and liquid film diffusion models were used to fit the adsorption kinetics data. It was suggested that chemisorption was the rate-controlling step for adsorption of Pb(II) onto PSAC since the adsorption kinetics data fitted both the pseudo second-order and Elovich models well.
Fibres from oil palm empty fruit bunches, generated in large quantities by palm oil mills, were processed into self-adhesive carbon grains (SACG). Untreated and KOH-treated SACG were converted without binder into green monolith prior to N2-carbonisation and CO2-activation to produce highly porous binderless carbon monolith electrodes for supercapacitor applications. Characterisation of the pore structure of the electrodes revealed a significant advantage from combining the chemical and physical activation processes. The electrochemical measurements of the supercapacitor cells fabricated using these electrodes, using cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge-discharge techniques consistently found that approximately 3h of activation time, achieved via a multi-step heating profile, produced electrodes with a high surface area of 1704m(2)g(-1) and a total pore volume of 0.889cm(3)g(-1), corresponding to high values for the specific capacitance, specific energy and specific power of 150Fg(-1), 4.297Whkg(-1) and 173Wkg(-1), respectively.
The cathode reaction is one of the most important limiting factors in bioelectrochemical systems even with precious metal catalysts. Since aerobic bacteria have a much higher affinity for oxygen than any known abiotic cathode catalysts, the performance of a microbial fuel cell can be improved through the use of electrochemically-active oxygen-reducing bacteria acting as the cathode catalyst. These consume electrons available from the electrode to reduce the electron acceptors present, probably conserving energy for growth. Anaerobic bacteria reduce protons to hydrogen in microbial electrolysis cells (MECs). These aerobic and anaerobic bacterial activities resemble those catalyzing microbially-influenced corrosion (MIC). Sulfate-reducing bacteria and homoacetogens have been identified in MEC biocathodes. For sustainable operation, microbes in a biocathode should conserve energy during such electron-consuming reactions probably by similar mechanisms as those occurring in MIC. A novel hypothesis is proposed here which explains how energy can be conserved by microbes in MEC biocathodes.
Hydroquinone (HQ), a phenolic compound is expansively used in many industrial applications and due to the utilization of HQ, water pollution tragedies frequently found by the improper handling and accidental outflows. When HQ is adsorbed directly through the skin that create toxic effects to human by affecting kidney, liver, lungs, and urinary tract and hence, a highly selective and sensitive technique is required for its quantification. Herein, we have developed the ultrasonic synthesis of copper oxide nanoflakes (CuO-NFs) using ultrasonic bath (20 kHz, 100 W) and successfully employed for the sensitive detection of the environmental hazardous pollutant HQ. The formed CuO-NFs were confirmed by X-ray diffraction, field emission scanning electron microscopy (FE-SEM), FT-IR spectroscopy and UV-visible spectroscopy and fabricated with the screen-printed carbon electrode (SPCE). The SEM images exhibited the uniform CuO-NFs with an average width of 85 nm. The linker-free CuO-NFs fabricated electrode showed the appropriate wide range of concentrations from 0.1 to 1400 µM and the limit of detection was found to be 10.4 nM towards HQ. The fabricated sensor having long term stability and sensitivity was successfully applied for the environmental and commercial real sample analysis and exhibited good recovery percentage, implying that the SPCE/CuO-NFs is an economically viable and benign robust scaffold for the determination of HQ.
Vibrio parahaemolyticus (V. parahaemolyticus) is a common foodborne pathogen that contributes to a large proportion of public health problems globally, significantly affecting the rate of human mortality and morbidity. Conventional methods for the detection of V. parahaemolyticus such as culture-based methods, immunological assays, and molecular-based methods require complicated sample handling and are time-consuming, tedious, and costly. Recently, biosensors have proven to be a promising and comprehensive detection method with the advantages of fast detection, cost-effectiveness, and practicality. This research focuses on developing a rapid method of detecting V. parahaemolyticus with high selectivity and sensitivity using the principles of DNA hybridization. In the work, characterization of synthesized polylactic acid-stabilized gold nanoparticles (PLA-AuNPs) was achieved using X-ray Diffraction (XRD), Ultraviolet-visible Spectroscopy (UV-Vis), Transmission Electron Microscopy (TEM), Field-emission Scanning Electron Microscopy (FESEM), and Cyclic Voltammetry (CV). We also carried out further testing of stability, sensitivity, and reproducibility of the PLA-AuNPs. We found that the PLA-AuNPs formed a sound structure of stabilized nanoparticles in aqueous solution. We also observed that the sensitivity improved as a result of the smaller charge transfer resistance (Rct) value and an increase of active surface area (0.41 cm2). The development of our DNA biosensor was based on modification of a screen-printed carbon electrode (SPCE) with PLA-AuNPs and using methylene blue (MB) as the redox indicator. We assessed the immobilization and hybridization events by differential pulse voltammetry (DPV). We found that complementary, non-complementary, and mismatched oligonucleotides were specifically distinguished by the fabricated biosensor. It also showed reliably sensitive detection in cross-reactivity studies against various food-borne pathogens and in the identification of V. parahaemolyticus in fresh cockles.
This paper primarily demonstrates the approach to enhance the sensing performance on antigen C-reactive protein (CRP) and anti-CRP antibody binding event. A nanogapped electrode structure with the gap of ~100 nm was modified by the anti-CRP antibody (Probe) to capture the available CRP. In order to increase the amount of antigen to be captured, a gold nanorod with 119 nm in length and 25 nm in width was integrated, to increase the surface area. A comparative study between the existence and non-existence of gold nanorod utilization was evaluated. Analysis of the sensing surface was well-supported by atomic force microscopy, scanning electron microscopy, 3D nano-profilometry, high-power microscopy and UV-Vis spectroscopy. The dielectric voltammetric analysis was carried out from 0 V to 2 V. The sensitivity was calculated based on 3σ and attained as low as 1 pM, which is tremendously low compared to real CRP concentration (119 nM) in human blood serum. The gold nanorod conjugation with antibody has enhanced the sensitivity to 100 folds (10 fM). The specificity of the CRP detection by the proposed strategy was anchored by ELISA and failure in the detection of human blood clotting factor IX by voltammetry. Despite, CRP antigen was further detected in human serum by spiking CRP to run-through the detection with the physiologically relevant samples.
Tungsten trioxide (WO₃) possesses a small band gap energy of 2.4-2.8 eV and is responsive to both ultraviolet and visible light irradiation including strong absorption of the solar spectrum and stable physicochemical properties. Thus, controlled growth of one-dimensional (1D) WO₃ nanotubular structures with desired length, diameter, and wall thickness has gained significant interest. In the present study, 1D WO₃ nanotubes were successfully synthesized via electrochemical anodization of tungsten (W) foil in an electrolyte composed of 1 M of sodium sulphate (Na₂SO₄) and ammonium fluoride (NH₄F). The influence of NH₄F content on the formation mechanism of anodic WO₃ nanotubular structure was investigated in detail. An optimization of fluoride ions played a critical role in controlling the chemical dissolution reaction in the interface of W/WO₃. Based on the results obtained, a minimum of 0.7 wt% of NH₄F content was required for completing transformation from W foil to WO₃ nanotubular structure with an average diameter of 85 nm and length of 250 nm within 15 min of anodization time. In this case, high aspect ratio of WO₃ nanotubular structure is preferred because larger active surface area will be provided for better photocatalytic and photoelectrochemical (PEC) reactions.
The effect of pH and redox potential on the redox equilibria of iron oxides in aqueous-based magnetite dispersions was investigated. The ionic activities of each dissolved iron species in equilibrium with magnetite nanoparticles were determined and contoured within the Eh-pH framework of a composite stability diagram. Both standard redox potentials and equilibrium constants for all major iron oxide redox equilibria in magnetite dispersions were found to differ from values reported for noncolloidal systems. The "triple point" position of redox equilibrium among Fe(II) ions, magnetite, and hematite shifted to a higher standard redox potential and an equilibrium constant which was several orders of magnitude higher. The predominant area of magnetite stability was enlarged to cover a wider range of both pH and redox potentials as compared to that of a noncolloidal magnetite system.
Rechargeable zinc-air batteries are deemed as the most feasible alternative to replace lithium-ion batteries in various applications. Among battery components, separators play a crucial role in the commercial realization of rechargeable zinc-air batteries, especially from the viewpoint of preventing zincate (Zn(OH)42-) ion crossover from the zinc anode to the air cathode. In this study, a new hydroxide exchange membrane for zinc-air batteries was synthesized using poly (2,6-dimethyl-1,4-phenylene oxide) (PPO) as the base polymer. PPO was quaternized using three tertiary amines, including trimethylamine (TMA), 1-methylpyrolidine (MPY), and 1-methylimidazole (MIM), and casted into separator films. The successful synthesis process was confirmed by proton nuclear magnetic resonance and Fourier-transform infrared spectroscopy, while their thermal stability was examined using thermogravimetric analysis. Besides, their water/electrolyte absorption capacity and dimensional change, induced by the electrolyte uptake, were studied. Ionic conductivity of PPO-TMA, PPO-MPY, and PPO-MIM was determined using electrochemical impedance spectroscopy to be 0.17, 0.16, and 0.003 mS/cm, respectively. Zincate crossover evaluation tests revealed very low zincate diffusion coefficient of 1.13 × 10-8, and 0.28 × 10-8 cm2/min for PPO-TMA, and PPO-MPY, respectively. Moreover, galvanostatic discharge performance of the primary batteries assembled using PPO-TMA and PPO-MPY as initial battery tests showed a high specific discharge capacity and specific power of ~800 mAh/gZn and 1000 mWh/gZn, respectively. Low zincate crossover and high discharge capacity of these separator membranes makes them potential materials to be used in zinc-air batteries.
A facile chemical reduction approach is adopted for the synthesis of iron tungstate (FeWO4)/ceria (CeO2)-decorated reduced graphene oxide (rGO) nanocomposite. Surface morphological studies of rGO/FeWO4/CeO2 composite reveal the formation of hierarchical FeWO4 flower-like microstructures on rGO sheets, in which the CeO2 nanoparticles are decorated over the FeWO4 microstructures. The distinct anodic peaks observed for the cyclic voltammograms of studied electrodes under light/dark regimes validate the electroactive proteins present in the microalgae. With the cumulative endeavors of three-dimensional FeWO4 microstructures, phase effect between rGO sheet and FeWO4/CeO2, highly exposed surface area, and light harvesting property of CeO2 nanoparticles, the relevant rGO/FeWO4/CeO2 nanocomposite demonstrates high power and stable biophotovoltaic energy generation compared with those of previous reports. Thus, these findings construct a distinct horizon to tailor a ternary nanocomposite with high electrochemical activity for the construction of cost-efficient and environmentally benign fuel cells.
That water may not be an inert medium was indicated by the presence at water's interfaces a negatively charged solute free zone of several hundred microns in thickness called the exclusion zone (EZ). Further evidence was demonstrated by Ovchinnikova's experiments (2009) showing that water can store and release substantial amount of charge. We demonstrate that the charge storage capacity of water arises from highly stable large-scale ionic structures with measurable charge imbalances and discrete levels of charge density. We also show evidence that the charge zones formation requires ionic solutes, and their formation correlate to large change in conductivity, by as much as 250%. Our experiments indicate that large-scale structuring plays a pivotal role in electrolysis and conductivity in ionic solution. We propose that water is an electrochemically active medium and present a new model of electrolysis and conductivity in ionic solution.
This study aims to investigate the potential of porous Co3O4 nanorods as the cathode catalyst for oxygen reduction reaction (ORR) in aqueous air cathode microbial fuel cells (MFCs). The porous Co3O4 nanorods were synthesized by a facile and cost-effective hydrothermal method. Three different concentrations (0.5mg/cm(2), 1mg/cm(2), and 2mg/cm(2)) of Co3O4 nanorods coated on graphite electrodes were used to test its performance in MFCs. The results showed that the addition of porous Co3O4 nanorods enhanced the electrocatalytic activity and ORR kinetics significantly and the overall resistance of the system was greatly reduced. Moreover, the MFC with a higher concentration of the catalyst achieved a maximum power density of 503±16mW/m(2), which was approximately five times higher than the bare graphite electrode. The improved catalytic activity of the cathodes could be due to the porous properties of Co3O4 nanorods that provided the higher number of active sites for oxygen.
A series of heteroatom-containing porous carbons with high surface area and hierarchical porosity were successfully prepared by hydrothermal, chemical activation, and carbonization processes from soybean residues. The initial concentration of soybean residues has a significant impact on the textural and surface functional properties of the obtained biomass-derived porous carbons (BDPCs). SRAC5 sample with a BET surface area of 1945 m2 g-1 and a wide micro/mesopore size distribution, nitrogen content of 3.8 at %, and oxygen content of 15.8 at % presents the best electrochemical performance, reaching 489 F g-1 at 1 A g-1 in 6 M LiNO3 aqueous solution. A solid-state symmetric supercapacitor (SSC) device delivers a specific capacitance of 123 F g-1 at 1 A g-1 and a high energy density of 68.2 Wh kg-1 at a power density of 1 kW kg-1 with a wide voltage window of 2.0 V and maintains good cycling stability of 89.9% capacitance retention at 2A g-1 (over 5000 cycles). The outstanding electrochemical performances are ascribed to the synergistic effects of the high specific surface area, appropriate pore distribution, favorable heteroatom functional groups, and suitable electrolyte, which facilitates electrical double-layer and pseudocapacitive mechanisms for power and energy storage, respectively.