Bulk Charge Research Articles

Maximum Power Point Tracking Charge Controller Using Modified Perturb and Observe Algorithm for Lead Acid Battery

A study was undertaken on development of a modified perturb and observe algorithm for maximum power point tracking (MPPT) charge controller. This MPPT algorithm was developed in Matlab/Simulink environment, using three-state charging method for improved battery charging with higher efficiency. A buck topology was utilised as a DC-DC converter for charge controller implementation. The maximum power of the photovoltaic panel was tracked by a modified perturb and observe algorithm. The battery charge controller charged a lead-acid battery using a three- stage charging strategy including the bulk charge, constant voltage (absorption charge), and float charge stage. The performance analysis of Simulink model was carried out by maximum power point tracking performance, battery charging performance, and overall charge controller efficiency performance. The performance results indicated that the maximum power point tracking was capable to track to the maximum power of PV panel at any solar irradiance variation with power tracking efficiency up to 98 per cent. The efficiency of overall charge controller was up to 98.3%, which matched many high-end commercial charge controller product specifications.

Kinetic study of the enhanced photoelectrochemical properties of microwave-assisted Al and Si co-doped Zr-Fe2O3 photoanodes

Unintended metal oxide layer development during co-doping has been suggested as being highly effective in intensifying the oxygen evolution reaction. Herein, we studied the influence of microwave-assisted co-doping of trivalent Al3+ and tetravalent Si4+ into Zr-Fe2O3 photoanode for effective photoelectrochemical (PEC) performance. The Si co-doping showed effective diffusion into the hematite bulk during high-temperature quenching. Relative to SiOx, an Al2O3 layer notably passivated the surface defects, whilst Si4+ co-doping markedly improved the bulk charge transfer features, compared to Al3+ co-doping. Because of the active passivation effect of the Al2O3 layer, the photocurrent density of Al/Zr-Fe2O3 photoanode was considerably increased at lower potentials. In specific, the Al/Zr-Fe2O3 photoanode displayed an almost 100% enhancement in surface charge transfer rate constant than that of the bare Zr-Fe2O3 at 1.23 VRHE. The comprehensive experimental results provided evidence of the consequence of tri/tetravalent co-dopants on charge transfer in the bulk of the hematite and at the photoanode-electrolyte interface. A probable charge transfer mechanism was proposed under illumination to demonstrate how the Si and Al microwave-assisted attachment impacted the photogenerated charge recombination reduction in the photoanode and subsequently advanced its PEC water splitting performance.

NbO2 a Highly Stable, Ultrafast Anode Material for Li- and Na-Ion Batteries.

Anode materials with fast charging capabilities and stability are critical for realizing next-generation Li-ion batteries (LIBs) and Na-ion batteries (SIBs). The present work employs a simple synthetic strategy to obtain NbO2 and studies its applications as an anode for LIB and SIB. In the case of the LIB, it exhibited a specific capacity of 344 mAh g-1 at 100 mA g-1. It also demonstrated remarkable stability over 1000 cycles, with 92% capacity retention. Additionally, it showed a unique fast charging capability, which takes 30 s to reach a specific capacity of 83 mAh g-1. For the SIB, NbO2 exhibited a specific capacity of 244 mAh g-1 at 50 mA g-1 and showed 70% capacity retention after 500 cycles. Furthermore, detailed density functional theory reveals that various factors like bulk and surface charging processes, lower ion diffusion energy barriers, and superior electronic conductivity of NbO2 are responsible for the observed battery performances.

Flash Joule heating to enhance water oxidation of hematite photoanode via mediating with an oxidized carbon overlayer

Flash Joule heating technique as an innovative and promising strategy has been extensively utilized to synthesize various functionalized nanomaterials within a very short time. This work describes a facile synthesis of an oxidized carbon overlayer-mediated hematite photoanode through a simple NaH2PO2-immersion followed by a flash Joule heating treatment. It discloses that on account of the high conductivity and abundant oxygen-functionalized carbon groups of carbon overlayer, the surface charge transfer of as-resulted photoanode is greatly facilitated and meanwhile the adsorption strength of water oxidation intermediates on Fe sites is improved. Moreover, the oxidized carbon overlayer could confine sufficient P atoms into the hematite nanostructure to realize P-doping to dramatically promote the bulk charge behaviors. Consequently, benefiting from these multiple effects, an enhanced photocurrent density of 2.07 mA cm−2 at 1.23 V vs. RHE is achieved for the as-resulted photoanode. Further, a comparable photocurrent density of 2.37 mA cm−2 at 1.23 V vs. RHE is yielded after the loading of FeNiOOH cocatalyst. This study, for the first time, demonstrates the flash Joule heating strategy for the post-treatment of hematite photoanode, which opens up a novel and facile avenue for the development of efficient photoelectrodes.

Low-Vacuum Catalyst-Free Physical Vapor Deposition and Magnetotransport Properties of Ultrathin Bi2Se3 Nanoribbons.

In this work, a simple catalyst-free physical vapor deposition method is optimized by adjusting source material pressure and evaporation time for the reliable obtaining of freestanding nanoribbons with thicknesses below 15 nm. The optimum synthesis temperature, time and pressure were determined for an increased yield of ultrathin Bi2Se3 nanoribbons with thicknesses of 8-15 nm. Physical and electrical characterization of the synthesized Bi2Se3 nanoribbons with thicknesses below 15 nm revealed no degradation of properties of the nanoribbons, as well as the absence of the contribution of trivial bulk charge carriers to the total conductance of the nanoribbons.

Bifunctional Co-TiO2 co-promoted bulk and interfacial charge transfer of BiVO4 photoanodes for solar water oxidation

The primary causes of photogenerated carrier recombination in BiVO4 photoanodes are the formation of bulk polarons and sluggish water oxidation kinetics. To address these issues effectively, we designed a bifunctional Co-TiO2 to modify the BiVO4 photoanodes. UV–vis DRS and Mott-Schottky results indicate that Co adjusts the band gap of TiO2, and there forms a type-II heterojunction between BiVO4 and Co-TiO2. The experimental tests and theoretical calculations for OER as well as EIS results demonstrate that Co sites in Co-TiO2 provide more reaction sites for the interfacial oxidation reaction, reducing the overpotential. Under the dual action of Co-TiO2, the co-promotion for the migration ability of photogenerated carriers in the bulk and on the surface of BiVO4 photoanode has been realized. This conclusion is supported by analysis of photogenerated charge transfer behavior through transient photocurrent and IMPS. As a result, the photogenerated current density of BiVO4/Co7 %-TiO2 photoanode reaches 4.38 mA cm−2 at 1.23 V vs. RHE under AM 1.5 G illumination, which is four times that of pure BiVO4 photoanodes.

Determining the Transformation Kinetics of Water Oxidation Intermediates on Hematite Photoanode.

The oxygen evolution reaction (OER) from water is a sequential oxidation reaction process, involved in transformation of multiple reaction intermediates. For photo(electro)catalytic OER, revealing the intermediates transformation kinetics is quite challenging due to its coupling with photogenerated charge dynamics. Herein, we specifically study the transformation kinetics of the OER intermediates in rationally thin hematite photoanodes through increasing the ratio between surface intermediates and photogenerated charges in bulk. We directly identify the formation and consumption kinetics of one-hole OER intermediate (FeIV═O) in photoelectrochemical water oxidation using operando transient absorption (TA) spectroscopy. The microsecond formation kinetics of the FeIV═O species are sensitively changed by the excitation mode of Fe2O3. The subsecond consumption kinetics are closely dependent on surface FeIV═O species density, demonstrating that the cooperation of FeIV═O intermediates is the key to accelerating water oxidation kinetics on the Fe2O3 surface. This work provides insight into understanding and controlling water oxidation reaction kinetics on Fe2O3 surface.

Electrokinetic Thin-Film Model for Electrowetting: The Role of Bulk Charges.

The electrowetting behavior of a charge-carrying sessile droplet is relevant to applications such as point-of-care diagnostics. Often biomedical assays involve droplets that contain charged molecules such as dissolved ions, proteins, and DNA. In this work, we develop a reduced-order electrokinetic model for electrowetting of such a charge-carrying droplet under a parallel-plate electrode configuration. An inertial-lubrication model based on the weighted residual integral boundary layer (WRIBL) technique is used to obtain evolution equations that describe the spatiotemporal evolution of the fluid-air interface and the depth-integrated flow rate. The solutions to the evolution equations are obtained numerically by using the spectral collocation method. We investigate the role of domain and surface charges, characterized by the Debye length, on droplet wetting. Under low relaxation timescales, both droplet deformation and wetting alteration under an AC field are shown to be equivalent to that under a root-mean-square (RMS) DC field. We show that an electrolytic sessile droplet can exhibit a larger deformation in comparison to the two asymptotic limits of a perfect conductor and a perfect dielectric droplet, corresponding, respectively, to very low and high Debye lengths. The effects of several other parameters such as the inherent equilibrium wettability, permittivity ratio, and electric field strength are also investigated.

Dual Heterojunctions and Nanobowl Morphology Engineered BiVO4 Photoanodes for Enhanced Solar Water Splitting.

Photoelectrochemical (PEC) water splitting represents an attractive strategy to realize the conversion from solar energy to hydrogen energy, but severe charge recombination in photoanodes significantly limits the conversion efficiency. Herein, a unique BiVO4 (BVO) nanobowl (NB) heterojunction photoanode, which consists of [001]-oriented BiOCl underlayer and BVO nanobowls containing embedded BiOCl nanocrystals, is fabricated by nanosphere lithography followed by in situ transformation. Experimental characterizations and theoretical simulation prove that nanobowl morphology can effectively enhance light absorption while reducing carrier diffusion path. Density functional theory (DFT) calculations show the tendency of electron transfer from BVO to BiOCl. The [001]-oriented BiOCl underlayer forms a compact type II heterojunction with the BVO, favoring electron transfer from BVO through BiOCl to the substrate. Furthermore, the embedded BiOCl nanoparticles form a bulk heterojunction to facilitate bulk electron transfer. Consequently, the dual heterojunctions engineered BVO/BiOCl NB photoanode exhibits attractive PEC performance toward water oxidation with an excellent bulk charge separation efficiency of 95.5%, and a remarkable photocurrent density of 3.38mA cm-2 at 1.23 V versus reversible hydrogen electrode, a fourfold enhancement compared to the flat BVO counterpart. This work highlights the great potential of integrating dual heterojunctions engineering and morphology engineering in fabricating high-performance photoelectrodes toward efficient solar conversion.

(Invited) Unification of Bulk Storage and Supercapacitive Storage

In typical insertion electrodes for batteries, the capacity is determined by bulk storage within the electroactive particles, which is comparatively well investigated and understood. In contrast, supercapacitor electrodes are dominated by interfacial storage at interfaces, which is well addressed experimentally. However the charge carrier chemistry (defect chemistry) especially in the latter case is not taken seriously. Consequently a bridge between the two important fields is absent. Following and extending our quantitative concept of job-sharing storage, a generalized description that includes bulk and space charge storage (electrochemical and supercapacitive storage) is possible. In other words the treatment of defect chemistry as a function of the degree of storage as well as of position is key to a unification. The experimental part of our research uses TiO2 and Nb2O5 thin films. The precise measurement of the storage capacity of thin films as a function of thickness allows us to deconvolute bulk and interfacial contributions. We discuss the results in terms of bulk and space charge capacitance. The generalized treatment that comprises both contributions shows also how the ratio of both varies with the degree of storage. Meanwhile exploiting various techniques (bias dependent impedance, TEM and EELS) electric field and charge distributions from bulk to the interface region are investigated. In the same context we study the space charge behavior in a discretized manner rather than by using the analytical Poisson-Boltzmann function. In this way a more precise definition and demarcation of electrode and double layer capacity is achieved. In terms of application we expect this work to provide a better understanding of energy and power densities of storage devices which becomes particularly important for nanoionic systems.

Improved performance of polyvinylidene fluoride membrane blended with modified multi‐walled carbon nanotubes by electret treatment

AbstractIn this paper, electret treatment was used to enhance the electrostatic repulsion between the membrane and bovine serum albumin, so as to improve the anti‐fouling ability and recycling rate of the membrane. The polarization charge is provided by the dipole orientation of polyvinylidene fluoride (PVDF) materials, and the space charge is composed of the interfacial charge between the filler and the matrix and the bulk charge of the hollow structure of the multi‐walled carbon nanotubes. The results showed that after electret treatment, the surface potential of the membrane increased, the PVDF crystal type changed from α to β, and the crystallinity increased. Grafting of N‐vinylpyrrolidone onto multi‐walled carbon nanotubes (MWCNTs‐g‐PVP), which contain a large number of hydrophilic groups after modification, reduces the contact angle of the composite film from 86.9° to 62.7°. The pure water flux and flux recovery rate of MWCNTs‐g‐PVP/PVDF composite membranes after electret treatment was increased from 189.31 L·m−2·h−1 and 90% to 233.55 L·m−2·h−1 and 94.7%, respectively, and the rejection rate increased about 30%. Through the circulation experiment, it can be seen that the anti‐fouling performance and recycling rate of the membrane is improved, which is caused by electrostatic repulsion.

Mechanistic insight into efficient electrocatalysis for hydrogen evolution by a platinum film prepared on an FTO electrode using a mixed metal-imidazole casting method

A Pt nanoparticle (Pt(w-MI)) film was prepared on a fluorine-doped tin oxide (FTO) conducting substrate from a precursor solution containing H2PtCl6 in a mixed solvent of methanol/1-methyimidasol (MI) (3:1 v/v) by a mixed metal-imidazole casting (MiMIC) method. The Pt(w-MI) film is the uniformly dense morphology composed of compacted and well-connected Pt nanoparticles compared to the hollow morphology for the Pt(w/o-MI) film fabricated without MI. The Pt(w-MI)/FTO cathode showed efficient and durable HER activities, generating a current density of 10 mA cm−2 at an overpotential (η10) of 198 mV, a Tafel slope of 128 mV dec−1, and a Pt mass activity of 0.11 A cm−2 mgPt−1 at 200 mV in the alkaline medium (1.0 M KOH solutions, pH = 14.0), which are substantially higher than the Pt(w/o-MI)/FTO and the commercially available Pt-loaded carbon (Pt/C) on the FTO cathodes. The mechanism of the efficient HER for the Pt(w-MI)/FTO cathode was investigated by an electrochemical impedance spectroscopic (EIS) method. The bulk charge transport in the Pt(w-MI) film is faster than that in the Pt(w/o-MI) film, ascribed to the compacted and well-connected Pt nanoparticles for Pt(w-MI). Furthermore, the surface proton reduction for Pt(w-MI) is also faster than that for Pt(w/o-MI), affording the efficient HER activity for Pt(w-MI) compared to Pt(w/o-MI).

Ultrasensitive Photocathodic Biosensor Based on the Cu2O/PTB7-Th/PDA+ Composite with Enhanced Photoelectrochemical Performance for the Detection of MicroRNA-375-3p.

Herein, an ultrasensitive photocathodic biosensor was fabricated based on Cu2O/PTB7-Th/PDA+ photoactive materials with high photocarrier separation efficiency for the detection of microRNA-375-3p. Impressively, the photocathodic signal of the Cu2O material was significantly enhanced by using PTB7-Th as an energy level-matching photoactive material to enhance the bulk charge separation and N,N-bis (2-(trimethylammoniumiodide) propylene) perylene-3,4,9,10-tetracarboxydiimide (PDA+) as an interfacial charge transfer mediator to efficiently suppress charge recombination at the photoelectrode/electrolyte interface. Compared with the pristine Cu2O as a photocathode, the obtained Cu2O/PTB7-Th/PDA+ exhibited a 17 times higher photocathodic signal. As a proof of concept, a PEC biosensor was fabricated by using Cu2O/PTB7-Th/PDA+ as a photoactive material and a target-triggered 3D DNA walker integrated with the dumbbell hybridization chain reaction (DHCR) as a signal amplifier to achieve the sensitive detection of microRNA-375-3p with a detection limit of 0.3 fM. This work provided a method to increase the photocurrent signal and the sensitivity of PEC-sensing platforms for the detection of biomarkers and disease diagnosis.

Multifunctional Role of Ag-Substitution in Enhancing the Photoelectrochemical Properties of LaFeO3 Photocathodes.

Earth-abundant LaFeO3 is a promising p-type semiconductor for photoelectrochemical cells due to its stable photoresponses, high photovoltages and appropriate band alignments, but the photoelectrochemical properties of LaFeO3 , especially the incident-photon-to-current conversion efficiency, need to be further improved. Herein, we propose to partially substitute La3+ of LaFeO3 with Ag+ to enhance the photoelectrochemical performance of LaFeO3 . The combined experimental and computational studies show that Ag-substitution improves surface charge transfer kinetics through introducing active electronic states and increasing electrochemically active surface areas. Furthermore, Ag-substitution decreases grain boundary number and increases majority carrier density, which promotes bulk charge transports. Ag-substitution also reduces the bandgap energy, increasing the flux of carriers involved in photoelectrochemical reactions. As a result, after 8 % Ag-substitution, the photocurrent density of LaFeO3 is enhanced by more than 6 times (-0.64 mA cm-2 at 0.5 V vs RHE) in the presence of oxygen, which is the highest photocurrent gain compared with other cation substitution or doping. The corresponding photocurrent onset potential also demonstrates a positive shift of 30 mV. This work highlights the versatile effects of Ag-substitution on the photoelectrochemical properties of LaFeO3 , which can provide useful insights into the mechanism of enhanced photoelectrochemical performance by doping or substitution.

Novel Sb2S3-xSex photocathode decorated NiFe-LDH hole blocking layer with enhanced photoelectrochemical performance

The alloyed Sb2S3-xSex has attracted widespread attention as a promising light absorbing material in recent years because it has the advantages of both Sb2S3 and Sb2Se3, such as adjustable band gap in the range of 1.1–1.8 eV and good stability. However, expensive selenourea enormously increases its manufacturing cost. In this paper, using Se powder as Se source, high-quality and low-cost Sb2S3-xSex film photoelectrode is successfully prepared by one-step hydrothermal method, and applied to photoelectrochemical (PEC) water splitting. Furthermore, with the help of NiFe-layered double hydroxide (LDH) modification, an increase in photocurrent density from −0.22 mA cm−2 to −1.21 mA cm−2 at 0 VRHE is achieved, and the onset potential is positively shifted by 120 mV. NiFe-LDH significantly improve hydrogen evolution reaction (HER) performance. The relevant characterization can confirm that this is mainly due to the blocking effect of NiFe-LDH on photogenerated holes, promoting effect of Ni2+ on the kinetics of hydrogen evolution reactions, and the strengthening of bulk charge separation efficiency. Undoubtedly, this work opens up a simple and effective way for the development of low-cost, high-efficiency antimony chalcogenides photoelectrodes, and provides new ideas for its excellent application in the field of PEC water splitting.

Towards "Green" ANFO: Study of Perchlorates and Inorganic Peroxides as Potential Additives.

Ammonium nitrate-fuel oil (ANFO) explosives are inexpensive and readily produced, but are highly prone to misfires, with the remaining explosive being a significant risk and environmental contaminant. In this work, studies on various additives, such as selected perchlorates and inorganic peroxides, which are intended to lower the susceptibility of ANFO to misfires by increasing its sensitivity to shock, have been conducted. These studies showed the viability of using these additives in ANFO, allowing for conducting shock wave sensitivity tests for bulk charges in the future. We investigated the effects of introducing these additives into ANFO (on its sensitivity), as well as thermal and energetic properties. We observed minor increases in friction and impact sensitivity, as well as a moderate reduction in the decomposition temperature of the additive-supplemented ANFO in comparison to unmodified ANFO.

Tuning the surface states by in-situ Zr/Hf co-doping and MoO3 hole transport layer modification for boosting photoelectrochemical performance of hematite photoanode

Hematite (α-Fe2O3) is a potential photoanode material for photoelectrochemical (PEC) water splitting; nevertheless, its PEC performance is constrained by substantial bulk and surface charge recombination rates. Herein, the effect of in-situ Zr/Hf dual-ion doping and the MoO3 hole transport layer (HTL) on regulating the surface states of α-Fe2O3 photoanodes for effective water oxidation is investigated. The co-doping improves bulk properties by enhancing the electrical conductivity, thereby facilitating hole transfer via intermediate surface states (i-SS). Furthermore, the MoO3 HTL passivates the recombination surface states (r-SS), thus alleviating the Fermi level pinning, resulting in an improved open-circuit photovoltage. As a result, a novel Zr/Hf-HT:MoO3 photoanode attains a photocurrent density of 2.34 mA cm−2 at 1.23 V vs. RHE (1.23 VRHE), which is 123% higher than that of Bare-HT. The Zr/Hf-HT:MoO3 photoanode achieves 86 and 61.3% of surface charge separation and charge transfer efficiencies at 1.23 VRHE, respectively, representing 26 and 100% enhancements over those of Bare-HT. Lastly, the FeNi(OH)x cocatalyst coated Zr/Hf-HT:MoO3 photoanode reaches a photocurrent density of 2.62 mA cm−2 at 1.23 VRHE with 98% stability and generates 47.8 and 22 μmol h−1 of H2 and O2 gases, respectively.

Synergistic mechanism of B doping and NiO loading on the excellent PEC performance and high stability of TiO2 nanotube photoanodes

The severe photogenerated charge recombination rate, poor visible light utilization and slow oxygen precipitation kinetics are the technical bottlenecks limiting the photo-electrolysis of TiO2 nanotube array (TNAs) photoanode for hydrogen production from water. To solve these problems, NiO nanoparticles were uniformly loaded into B-doped TNAs by the CV method. It is found that B-doping improves the energy band structure of TNAs, and doping-induced surface defects could become traps for photogenerated carriers to substantially improve the charge separation efficiency of the bulk phase. The P-N junctions formed between TiO2 anatase and NiO nanoparticles not only promoted the OER kinetics at the interface but also greatly improved the surface carrier separation efficiency of the catalyst, as well as ensured the stability and activity of the B-doping-induced surface defects. Moreover, the carrier concentration and visible light absorption properties of TNAs were enhanced and improved. Due to the synergistic effect of B doping and NiO loading, the bulk charge separation efficiency and surface charge separation efficiency of NiO/BT (B doping and NiO loading TNAs) were as high as 88.9 and 82.4%, respectively, at 1.23 V vs. RHE, and the photocurrent density reached 2.05 mA/cm2, which was 10 times higher than that of pure TNAs.

Surface conductivity in SmB6

We present a study of low temperature electron transport (resistivity, magnetoresistance and Hall coefficient) in SmB6 single crystals having different polar (100) and nonpolar (110) and (111) surfaces after mechanical polishing and chemical etching. The estimation of effective parameters for surface and bulk charge carriers allows us to conclude that surface conductivity is very sensitive to the method of surface treatment. The most pronounced change is observed for the polar (100) surface, for which the related Hall concentration of charge carriers at 2 K decreases more than by 2 orders of magnitude and the Hall mobility increases by a factor of 15 after etching these faces in diluted nitric acid. We suggest that the strong dependence of surface properties on the type of treatment may result from both topological protection, which is influenced by intrinsic defects or surface reconstruction, and band bending effects, which modulate the properties of the surface conduction layer in case of polar faces.

2D TiO2/Ti3C2 conductive substrate enhanced the photoelectrochemical performance of hematite for water splitting

Since the photoelectrochemical properties of hematite are affected by its bulk and surface charge recombination, the introduction of a conductive substrate is a feasible way to improve its properties. In this paper, the Ti3C2 and TiO2/Ti3C2 conductive substrates were prepared by electrophoretic depositing multilayered Ti3C2 and TiO2/Ti3C2 nanosheet powders onto F-doped SnO2 glass (FTO), respectively. Then, the TiO2/Ti3C2-hematite and Ti3C2-hematite photoanodes were obtained by in-situ growth of hematite on Ti3C2 and TiO2/Ti3C2 conductive substrates by hydrothermal method. The photoanodes were characterized by scanning electron microscopy (SEM), UV–vis spectroscopy, X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS) and photoelectrical measurements. The photocurrent density of TiO2/Ti3C2-hematite reaches 1.29 mA cm−2 at 1.23 V (vs. RHE), which is 3.7 times than that of the FTO-hematite as 0.35 mA cm−2. The enhancement of the photocurrent response of TiO2/Ti3C2-hematite is mainly due to the great improvement of the bulk charge separation efficiency and the surface charge injection efficiency. This is attributed to the fact that the layered TiO2/Ti3C2 conductive substrate can improve the interface property of FTO/hematite, provide Ti source and a larger specific surface area for the growth of hematite.