Showing papers in "Journal of Applied Electrochemistry in 2019"

Electrochemical detection of Cr(VI) with carbon nanotubes decorated with gold nanoparticles

Abstract: A nanocomposite consisting of gold nanoparticles deposited on the side walls of functionalised multi-walled carbon nanotubes, Ox-MWCNT-Aunano, was prepared using a simple chemical reduction. The nanoparticles were well dispersed with a mean diameter of 7.5 nm and had a face-centred cubic structure and a gold loading between 2.0% and 2.6% by weight. These gold decorated nanotubes were cast onto a gold electrode to form a uniform and homogeneous sensor. Using cyclic voltammetry, the reduction of Cr(VI) was observed at a peak potential of 0.52 V versus SCE in an acidified H2SO4 solution, pH 2.0. A linear calibration curve with a sensitivity of 0.28 mA mM− 1 and a LOD of 7.2 × 10− 7 M was obtained using constant potential amperometry coupled with rotating disc voltammetry. The electrochemical detection of Cr(VI) was also observed at a MWCNT-modified gold substrate but with a higher LOD, illustrating the advantage of combining the gold nanoparticles with MWCNTs. The sensor showed good selectivity for the detection of Cr(VI) in the presence of Cu(II), chloride and nitrates and in a real water sample. This was attributed to the electropositive reduction potentials of Cr(VI), the acidic H2SO4 supporting electrolyte that provides a well-known cleaning effect at gold, and the size and good dispersion of the gold nanoparticles that minimise particle agglomeration.

Nitrogen and sulfur co-doped graphene-like carbon sheets derived from coir pith bio-waste for symmetric supercapacitor applications

Abstract: An efficient synthesis of nitrogen and sulfur co-doped graphene-like carbon sheets from coir pith bio-waste through the mechanical activation method is reported in this study. The structural characterization reveals the presence of a graphene-like carbon sheet, which is uniformly doped with nitrogen and sulfur atoms in a carbon network. The nitrogen and sulfur co-doped graphene-like carbon sheets (NSG) has amorphous nature with a defective porous carbon structure and it depicts the maximum specific capacitance of 247.1 F g−1 at 0.2 A g−1 and a capacitance retention of 75.2% at 10 A g−1. The synthesized NSG-10 registered a maximum energy density of 33.6 Wh kg−1 at 0.2 A g−1 and shows the maximum power density of 4220.0 W kg−1 at 10.0 A g−1. Furthermore, a symmetric supercapacitor (SSC) device shows the device capacitance of 33.7 F g−1 at 0.2 A g−1 when operated at 1.0 V. The SSC device gives a capacitance retention of 82.0% at 10 A g−1 and reveals an excellent stability with no losses in capacitance with 100% columbic efficiency over 10,000 cycles. The results suggest that the proposed methodology is a simple and unique way to synthesize heteroatoms-doped graphene-like carbon sheets from biomass materials for a supercapacitor.

Electroreduction of carbon dioxide to formate at high current densities using tin and tin oxide gas diffusion electrodes

Abstract: We investigate tin (Sn) and tin oxide (SnO2) nanoparticle catalysts deposited on gas diffusion layers for the electrochemical reduction of carbon dioxide (CO2) to formate. The performance and durability of these electrodes was evaluated in a gas-fed electrolysis cell with a flowing liquid electrolyte stream and an integrated reference electrode. The SnO2 electrodes achieved peak current densities of 385 ± 19 mA cm−2 while the Sn electrodes achieved peak current densities of 214 ± 6 mA cm−2, both at a formate selectivity > 70%. The associated peak formate production rates of 7.4 ± 0.6 mmol m−2 s−1 (Sn) and 14.9 ± 0.8 mmol m−2 s−1 (SnO2) were demonstrated for a 1-h electrolysis and compare favorably to prior literature. Post-test analyses reveal chemical and physical changes to both cathodes during electrolysis including oxide reduction at applied potentials more negative than − 0.6 V versus RHE, nanoparticle aggregation, and catalyst layer erosion. Understanding and mitigating these decay processes is key to extending electrode lifetime without sacrificing formate generation rates or process efficiency.

Roles of organic and inorganic additives on the surface quality, morphology, and polarization behavior during nickel electrodeposition from various baths: a review

Abstract: During the hydrometallurgical processing of nickel from raw materials, the leach liquors are found to be contaminated with several impurities. These impurities in the electrolytic cell affect the deposition characteristics as well as the kinetics and mechanism of nickel electrodeposition process resulting in lower current efficiency (CE) and poor nickel deposits. In order to improve the quality of the nickel deposits, it is imperative to use organic additives in the nickel plating bath to improve the structural, mechanical, and morphological properties of the deposits. Furthermore, it is usually observed that in spite of various purification techniques like cementation and solvent extraction, metals obtained at the cathode are usually contaminated with inorganic impurities. This review thus presents a comprehensive overview of some important studies and investigations performed on various inorganic and organic additives employed in nickel electrodeposition processes from various baths such as Watts, sulfate, acetate, formamide, lactate, and baths containing ionic liquids. The presence of metallic (inorganic) impurities in industrial electrolytes is very common. Most of these impurities affect the deposit’s characteristics, CE, deposition overvoltage, and cathode purity. Addition of inorganic cations such as Al3+, Mg2+, Mn2+, and Zn2+ did not have a significant effect on the CE; nevertheless, the physical appearance and crystallographic orientation of nickel deposits were significantly affected. Organic additives are usually added to the nickel electrolytic bath to counter the harmful effects of these metallic impurities entrained in the bath, where they also affect the growth and crystal building of the deposits through their adsorption onto the cathode surface. Most of these additives act as hydrogen inhibitors, crystal growth modifiers, brighteners, levelers, wetting agents, and stress reducers, and hence, their appropriate addition was important for the formation of fine-grained, smooth, and compact deposits. This review demonstrates that the quality of the nickel deposit was strongly affected if the concentration of the inorganic impurity in the nickel bath exceeded the tolerance limit. From this review article, the roles of various organic additives as a brightener, leveler, and antipitting agent, etc. in the Ni plating bath could be established, and these additives would play a significant role in the formation of bright, smooth, and coherent nickel deposits obtained during hydrometallurgical processing of laterite and sulfide ores in the metallurgical industry.

Determination of norepinephrine using a glassy carbon electrode modified with graphene quantum dots and gold nanoparticles by square wave stripping voltammetry

Abstract: In this work, a glassy carbon electrode modified with graphene quantum dots and gold nanoparticles (GCE/GQDs/AuNPs) was developed for norepinephrine (NE) determination using squarewave stripping voltammetry. GQDs were synthesized by citric acid pyrolysis and characterized by UV–Vis and fluorescence spectroscopy. The chemically synthesized AuNPs were characterized by transmission electron microscopy and UV–Vis spectroscopy (Plasmon Band). GCE/GQDs surface was characterized by Raman spectroscopy and scanning electron microscopy. The conditions for the determination of NE with GCE/GQDs/AuNPs were optimized. The linear range was observed between 0.5 and 7.5 µmol L−1, with a detection limit (LOD) of 0.15 µmol L−1. The proposed methodology was validated with spiked samples for good precision and accuracy. GCE/GQDs/AuNPs were used in pharmaceutical preparations (NE ampoules) and in rat brain tissue with satisfactory results.

Obstructed flow field designs for improved performance in vanadium redox flow batteries

Abstract: In this study, we have investigated the effects of varying flow channel depths and addition of various channel obstructions on the electrochemical performance and pumping power requirements of vanadium redox flow batteries (VRFBs). Specifically, 3D-printed ramps and prismatic obstructions were inserted into the channels of interdigitated flow field (IDFF) and parallel flow field (PFF) designs to observe the effect of non-uniform channel depth on the mass transport properties of open- and closed-ended flow channels. Results were compared with conventional flow field geometries. Integration of ramps into the closed-ended (i.e., IDFF) flow channels resulted in 15% improvement in peak power density (PPD) at a flow rate of 50 mL min−1. Addition of ramps to IDFF has also resulted in a significant 40% drop in required pumping pressure due to guided and gradual delivery of the electrolyte to the electrode plane. In addition, the effects of varying channel depths in open-ended (i.e., PFF) channels were found to be much more drastic with improvements in PPD up to 150%. Overall, findings of this study highlight the significance of varying channel depths on improving the mass transport characteristics of VRFBs and offer an alternative approach for design of high-performance flow cells.

Electrochemical sensor sensitive detection of chloramphenicol based on ionic-liquid-assisted synthesis of de-layered molybdenum disulfide/graphene oxide nanocomposites

Abstract: A novel hybrid nanocomposite based on de-layered molybdenum disulfide (MoS2) by ionic-liquid (IL, [BMIM]BF4)-assisted exfoliation and graphene oxide (GO) was synthesized via a green, efficient, and high-quality method, which combined liquid-phase stripping method and ion-insertion method. In addition, an electrochemical sensor was developed using the MoS2-IL/GO nanocomposites for the determination of chloramphenicol (CAP). The morphology and structure of these synthetic materials were characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray diffraction and the electrochemical characterization by cyclic voltammetry and electrochemical impedance spectroscopy. Based on this method, the insertion of IL can effectively exfoliate de-layered MoS2, and the MoS2-IL/GO nanocomposite exhibit 3D structure with higher surface area, excellent electrical conductivity, and synergistic catalytic capabilities. Under optimized conditions, the sensor responded linearly to CAP ranging from 0.1 to 400 µmol L−1 and the detection limit of 0.047 µmol L−1. In addition, the sensor showed excellent stability, repeatability, reproducibility, and selectivity, and has been applied to detect CAP in eyedrops, milk, and urine samples. Schematic of proposed electrochemical sensor.

Influence of binder content in silver-based gas diffusion electrodes on pore system and electrochemical performance

Abstract: The influences of the polytetrafluoroethylene (PTFE) content in silver-based gas diffusion electrodes on the resulting physical properties and the electrochemical performance during oxygen reduction in concentrated sodium hydroxide electrolyte were investigated through half-cell measurements. A systematic variation of the pore system was achieved by application of different silver/PTFE ratios during the production of the gas diffusion electrodes (GDE). In all electrodes, a silver skeleton structure with relatively constant properties was formed, while the PTFE fills up part of the open pore space. The resulting structures were characterized with a variety of methods for the physical properties supported by focused ion beam milling and scanning electron microscope (FIB/SEM) tomography. It could be shown that variations in the obtained pore system strongly influence the electrochemical performance of the electrodes. Determination of the Tafel slopes revealed that this is not due to changes in the electrocatalytic activity but rather caused by variations in the electrolyte uptake. While too small amounts of PTFE (1 wt%) lead to decreased performance through electrolyte flooding, higher PTFE contents above about 5 wt% also deteriorate the electrode performance because the extent of the three-phase boundary diminishes. The decisive role of the electrolyte intrusion was confirmed by measurements at higher electrolyte pressure. While the best electrochemical performance was achieved with an electrode containing 98 wt% silver, a slightly higher PTFE content is advisable to prevent breakthrough of the electrolyte.

Electrodeposited zinc phosphate hydrate electrodes for electrocatalytic applications

Abstract: Zinc phosphate hydrate Zn3(PO4)2·4H2O thin films were deposited making use of chronoamperometric mode, on three types of substrates: fluorine-doped tin oxide (FTO) on glass, stainless steel, and titanium. The precursors were solutions in aqueous medium of Zn(NO3)2·6H2O and NH4H2PO4. The effects of various parameters (concentrations of starting precursors, nature of substrates) on the properties of electrodeposited films were analyzed. The films were characterized by X-ray diffraction, scanning electron microscopy, Raman spectroscopy, and electrochemical cyclic voltammetry. The material Zn3(PO4)2·4H2O, electrodeposited on the three different substrates to form three types of anodes, crystallized in the orthorhombic structure of hopeite β. The first determinations of the electrocatalytic degradation of rhodamine B (RhB) were performed using the three types of anodes. The RhB degradation was followed by UV–Visible spectrophotometry and also by chemical oxygen demand: it was found that the best degradation was obtained on FTO substrate.

Decoration of cobalt/iron oxide nanoparticles on N-doped carbon nanosheets: Electrochemical performances for lithium-ion batteries

Abstract: Cobalt/iron oxide nanoparticles (CFO/NPs) were fabricated with a facile solid combustion method and decorated on polyaniline-derived porous N-doped carbon nanosheets. The N-doped carbon nanosheets provide a pathway for charge transfer and act as defensive layers to avoid the agglomeration of nanoparticles. The decoration of CFO nanoparticles on porous N-doped carbon nanosheets (CFO/NC) typically leads to hybrid material that displays an exceptionally high electrochemical performance for Li-ion batteries (LIBs) with excellent diffusion of electrolyte ions and ensures fast Li+/e− transport. The initial discharge capacity reaches up to 1270 mAh g−1 (1.65 mAh cm−2) at a current density of 500 mA g−1 (0.65 mA cm− 2). Furthermore, it also exhibits an exceptionally high specific capacity of 635 mAh g−1 at a high current density of 500 mA g−1 (500 mA g−1) after long cycling (250 cycles) and a remarkable rate capability with 93% capacity retention. These excellent electrochemical characteristics demonstrate that CFO/NC is a promising anode material for LIBs.

Poly(aniline-co-o-anisidine)/graphene oxide Au nanocomposites for dopamine electrochemical sensing application

Abstract: We describe here the manufacture of poly(aniline-co-o-anisidine)/graphene oxide nanocomposites, with the common abbreviation [PANI-co-PoAN/GO1−5], by the well-known in situ oxidative polymerization method with ultrasonic assistance. FE-SEM and TEM micrographs were utilized to examine the morphological characteristics of the composite materials. Moreover, FT-IR, XRD, TGA, and electrical conductivity measurements were used to investigate their complete performance. All the composites had almost equal final copolymer decomposition temperatures, which were in the range of 609.3–663.8 °C. Our essential objective is to study the electro selective application using gold nanoparticles (AuNPs) as a coating. Dopamine (DA) electrochemical sensor based on [AuNPs/PANI-co-PoAN/GO] nanocomposite covalently modified gold electrode was modified by an electroabsorption technique. The electrochemical behavior of the modified electrode towards the oxidation of DA was studied by square wave voltammetry (SWV) and cyclic voltammetry (CV) in pH 5.0 phosphate buffer solution. The sensor developed a current response to the oxidation of DA. Using SWV, the electrochemical sensor gave a linear relationship to DA in the concentration range of 5–100 µM with a limit of detection of 0.0334 µM. The modified electrode was highly stable, sensitive, and selective.

Platinum decorated polythiophene modified stainless steel for electrocatalytic oxidation of benzyl alcohol

Abstract: Platinum nanoparticles were electrochemically deposited on conducting polymer polythiophene (PTh)-coated stainless steel (SS) substrate. A thin layer of PTh on the steel substrate facilitates uniform deposition of Pt nanoparticles on the substrate, thereby improving the surface area to a great extent. The electrochemical properties of the modified electrodes were analyzed by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The physicochemical properties of the modified electrodes were investigated by Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray diffraction spectroscopy (XRD), Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR). The proposed method has been applied for the electrocatalytic oxidation of benzyl alcohol in the presence of a mediator, 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO). Cyclic voltammetric studies reveal that the electrocatalytic activity of Pt–PTh/SS electrode is higher than that of PTh/SS electrode toward the conversion of benzyl alcohol to benzaldehyde.

New Si–Cu and Si–Ni anode materials for lithium-ion batteries

Abstract: The functioning of the new anode materials in the form of silicene on copper and nickel substrates was tested by the method of molecular dynamics. It is shown that, two-layer silicene, both ideal and with vacancy defects, on Cu (111) and Ni (111) substrates is more preferable for intercalation of lithium than the corresponding material on Ag (111) substrate. In turn, a higher capacity was found for a lithium-filled silicene channel on a nickel substrate than for a corresponding anode on a copper substrate. In addition, local shear stresses in a functioning silicene anode on a Ni (111) substrate are lower than those on a Cu (111) substrate.

A novel MnO2/rGO composite prepared by electrodeposition as a non-noble metal electrocatalyst for ORR

Abstract: A MnO2/rGO composite with a novel yarn-rod shape was fabricated by a simple, economic and environmentally friendly electrodeposition method. The as-prepared MnO2/rGO composite was systematically characterized via X-ray Diffraction, X-ray Photoelectron Spectroscopy, Raman Spectra, Scanning Electron Microscope, Transmission Electron Microscope, and Specific Surface Area measurement. The experimental results indicate that the MnO2 nanoparticles with rod-like morphology scatter over the yarn-shaped rGO sheet through the electrodeposition procedure. The current density of O2 reduction on the MnO2/rGO composite modified electrode is higher than those on MnO2 and rGO. The initial oxygen-reduction peak potential and half-wave potential of the MnO2/rGO composite are more positive than those of MnO2 and rGO. The MnO2/rGO composite, as a non-noble metal oxide catalyst, not only exhibits superior electrocatalytic activity for oxygen-reduction reaction (ORR) in an alkaline medium compared with MnO2 and rGO but also shows better ORR stability, higher electron transfer numbers, and stronger methanol-tolerant ability than the commercial Pt/C catalyst. These considerable results enable the development of a cheap and efficient non-noble metal electrocatalyst for ORR in fuel cells. The MnO2/RGO composite prepared by the facile electrodeposition method shows the comparable electrocatalytic ORR performance with Pt/C

A high-performance, disposable screen-printed carbon electrode modified with multi-walled carbon nanotubes/graphene for ultratrace level electrochemical sensors

Abstract: In this work, a screen-printed carbon paste electrode (SPCE) combined with multi-walled carbon nanotubes (MCNT) and graphene (GP) in different mixing ratios was fabricated. Electrode materials were characterized by scanning electron microscopy as well as Raman spectroscopy and their performance as electrochemical sensors was evaluated by cyclic voltammetry. Results showed that SPCEs composited with 1 w% MCNT and 1 w% graphene achieved the most promising sensing performance for K4FeCN6 with a sensitivity of 0.0054 µA µM−1 and limit of detection (LOD) (3S/N) at 3.1 µM. The so-prepared electrode was then employed to detect H2O2 and nicotinamide adenine dinucleotide (NAD+/NADH) achieving sensitivity and LOD of 0.0027 µA µM−1 and 7.1 µM for H2O2, and 0.0075 µA µM−1 and 3.6 µM for NADH, respectively. Therefore, it was found that the addition of MCNT and graphene to commercial carbon paste for screen printable electrochemical sensor is feasible for fabrication of sensing electrodes for electrochemical detection.

Electrode system for large-scale reverse electrodialysis: water electrolysis, bubble resistance, and inorganic scaling

Abstract: It is generally accepted that the effect of electrode resistance is not predominant in determining the performance of reverse electrodialysis (RED), because the contribution of electrode resistance to total internal resistance decreases as the number of cell pairs increases. However, this is not true under the condition in which gas is continuously produced by water electrolysis owing to the large stack voltage in pilot-scale applications. We verified that the bubble resistance of the electrode spacer in a conventional endplate causes the electric power of a RED system with 1000 cells to decrease by more than 20% under the specific condition in which the outermost feed solution (OFS) at both electrodes and the electrode solution (ES) are river water. This configuration, called OFS(river)/ES(river), is the best for minimizing inorganic scaling and toxic gas evolution. Another problem associated with the conventional endplate is fluid congestion owing to very narrow spaces, which causes sudden pH changes and deteriorates further with inorganic scaling. To address these issues, we removed the electrode spacer from the electrode system and utilized an open-type endplate with interconnected open spaces. This endplate maintained high electric power without the bubble resistance and suppressed the abrupt changes in the pH around the electrodes and the shielding membranes. We believe that our approach will be useful in the search for an optimum electrode design for RED systems on the industrial scale.

A framework for charging strategy optimization using a physics-based battery model

Abstract: This paper uses a physics-based battery model to develop a generic framework to solve optimal charging strategies. The study will also provide insight into the interplay between optimized charging strategies and the battery internal electrochemical kinetics. With a physics-based battery model, a multi-objective optimal control problem is proposed to investigate the charging strategies that optimally trade off the temperature rise, charging time, and loss. First, a fast-charging strategy (minimum time) with the sole purpose of reducing charging time is presented and experimentally validated. The fast-charging strategy can significantly reduce the charging time but causes a high-temperature rise and charging loss. Next, the interplays between temperature rise and charging time, charging loss, and charging time are investigated, respectively. It is found that, in order to reduce the battery temperature during charging, high-current charging at the initial stage should be avoided. Finally, a balanced charging strategy, which considers temperature rise, charging time, and charging loss simultaneously, is developed and analyzed. Experimental results show that the balanced charging strategy has a similar temperature rise as 4C CC/CV charging, but the charging time is reduced by 24.8% and the charging loss is reduced by 56.4%.

Single-step electrodeposition of superhydrophobic black NiO thin films

Abstract: Black finished surfaces have extensive applications in many domains, such as optics, solar cells, and aerospace The single-step electrodeposition of superhydrophobic black NiO films from a dimethyl sulfoxide-based electrolyte is described in this paper The physicochemical properties of the obtained film were characterized using scanning electron microscopy, X-ray diffraction, and electrochemical tests (electrochemical impedance spectroscopy and potentiodynamic polarization) A rough surface with a low reflection of light was formed after the deposition process that increased the contact angle of water from about 87° (for bare Cu) to 163° (in presence of the black coating), which improved the corrosion resistance of the Cu substrate by about 30% The formed black NiO film revealed a notably high stability and kept its appearance even after corrosion tests

Isomorphic MOF-derived porous carbon materials as electrochemical sensor for simultaneous determination of hydroquinone and catechol

Abstract: It is needed to speed up the development of a sensitive detection platform for simultaneous determination of dihydroxybenzene isomers with harmful properties. Here, two isomorphic Metal–organic frameworks (MOFs) [Zn(Trz)(R-BDC)1/2] (FJU-40-R, R = H or NH2; Trz = 1,2,4-Triazole; H-BDC = terephthalic acid) were selected to derive two N-doping porous carbon (NPC) materials. Further, a strategy for constructing electrochemical sensors for simultaneous determination of hydroquinone (HQ) and catechol (CT) was proposed by the MOF-derived NPC modifying glass carbon electrode (GCE). It was found that HQ and CT had good responses on NPC-FJU-40-H/GCE, but had no obvious responses on NPC-FJU-40-NH2/GCE. NPC-FJU-40-H/GCE displayed excellent reproducibility, stability, and anti-interference. Under the optimal conditions, the linear ranges of HQ and CT on NPC-FJU-40-H/GCE were 1 ~ 70 µmol L−1 and 1 ~ 100 µmol L−1 with the detection limits of 0.18 µmol L−1 for HQ and 0.31 µmol L−1 for CT, respectively. Although the porous carbon (PC) derived from MOFs has been applied in electrochemical sensing, the effect of the ligand functional groups of isomorphic MOFs on the electrochemical properties of the derived PC materials is still lack of relevant research. Our research provided an idea that the electrocatalysis properties of MOF-derived porous carbon materials could be tuned by changing the functional groups in ligands of isomorphic MOFs in electrochemical sensing field. A feasible strategy was proposed by changing the ligands of the two isomorphic MOFs (FJU-40-H and FJU-40-NH2) to tune the electrocatalysis properties of MOF-derived N-doped porous carbon materials for the simultaneous determination of dihydroxybenzene isomer.

In situ preparation of P, O co-doped carbon spheres for high-energy density supercapacitor

Abstract: Phosphorus and oxygen co-doped carbon spheres with formaldehyde and resorcinol as precursor were successfully prepared by using phosphoric acid solution as phosphorus source and catalyst. When the pH value of applied phosphoric acid solution is set at 1.38, the spherical carbon materials can be obtained. The corresponding specific surface area can reach 739.48 m2 g−1, and the phosphorus amount can be 0.44 at.%. By contrast, bulk carbon materials were produced when the pH value increased to 3.72. The corresponding specific surface area decreased to 444.3 m2 g−1, and the phosphorus amount declined to 0.10 at.%. It is demonstrated that spherical carbon materials exhibit superior electrochemical performance. The specific capacitance can reach 297.5 F g−1 at the scan rate of 1 mV s−1. Symmetric supercapacitors were constructed with KOH and Na2SO4 as electrolytes, respectively. The specific capacitance can reach 186.8 F g−1 at the current density of 0.1 A g−1 when KOH is used as electrolyte and its energy density can reach up to 50.86 Wh kg−1. However, the stability of the device is relatively poor. In contrast, when sodium sulfate is used as the electrolyte, after 5000 cycles of constant current charge and discharge, the capacity is still 84.09% remaining, exhibiting excellent cycle stability. In addition, the energy density of the device can reach 39.4 Wh kg−1. Even when the power density is 4000 W kg−1, the energy density can still reach 10 Wh kg−1. The obtained materials show great potential for practical application.

Facile construction of hierarchically porous carbon nanofiber aerogel for high-performance supercapacitor

Abstract: Nanofibrillated cellulose with the features of nano-scale fibers and self-assembly has attracted significant attention to acquire porous structure for low-cost and high-performance electrode materials. Here, a carbon nanofiber aerogel was prepared by self-assembling the building-blocks of nanofibrillated cellulose into controlled macro and mesoporous structure. A typical activation was further applied to engineer abundant micropores, which led to narrowed carbon walls as well as improved surface area (1726 m2 g−1). Due to the facile-constructed hierarchical pore structure and large ion-accessible surface area, the resultant carbon aerogel exhibited comparable performance to reported electrodes from porous bio-carbons. It displayed a high specific capacitance of 169 F g−1 at a high current of 20 A g−1, retaining 73% of that at 0.2 A g−1 (231 F g−1). Furthermore, the symmetric supercapacitor showed a high capacitance retention during the long-term charge–discharge. This work provides a facile and renewable way to develop hierarchical porous bio-carbons with high charge storage capability.

Synthesis of MOF-74-derived carbon/ZnCo2O4 nanoparticles@CNT-nest hybrid material and its application in lithium ion batteries

Abstract: Carbon/ZnCo2O4 nanoparticles’ hybrid highly dispersed within a carbon nanotube nest were synthesized by the carbonization of in situ formed MOF-74-ZnCo/CNT hybrid materials. Results demonstrated that the synthesized mixed transition metal oxides/carbon/CNT composite provided a stable energy density of 800 mAh g−1 at 100 mA g−1. It could also provide a reversible capacity of 430 mAh g−1 under a high current of 2000 mA g−1 even after 1000 cycles. The outstanding performances of C/ZnCo2O4@CNT can be accredited to the synergistic effects from the porous nanostructured bi-metal oxides, the carbon and the CNT nest. These properties can improve the conductance of the material, alleviate the stress on ZnCo2O4 nanoparticles through accommodating the volume variation during lithium exchange processes, and offer fast diffusion roads for ions and more active sites for lithium storage.

Enhanced open-circuit voltage and power for two types of microbial fuel cells in batch experiments using Saccharomyces cerevisiae as biocatalyst

Abstract: The combined influence of iron and calcium salts can increase the voltage and power of MFC systems using Saccharomyces cerevisiae as biocatalyst, but no systematic studies were performed. To explore these incomplete understood interactions, the production of bioelectricity has been studied in two types of dual-chambered MFC systems: in small volume batch system with frit as separator and in a medium volume batch system with nafion. In both MFC experiments, CaCO3 and FeSO4 were added as supplements in a modified medium. In the MFC experiment with frit, the highest OCV (1.143 V) was recorded at about 8 h, while in the MFC experiment with nafion, the highest OCV (1.128 V) was recorded at about 132 h, values which are attributable to the above-mentioned mineral salts and exceeding the OCV value of 0.847 V reported in the literature, thus, to our knowledge, higher than any OCV ever recorded from one single MFC operated in batch mode. The power density in the MFC experiment with frit was 1.031 W m− 2, being in concordance with the best literature values. The power densities in the MFC experiment with nafion were lower but increased over time, while the high OCV values were more stable over longer time periods. Overall, the experimental data showed the potential of Saccharomyces cerevisiae in generation of bioelectricity in different MFC configurations.

Synthesis and characterization of polyaniline nanofibers as cathode active material for sodium-ion battery

Abstract: Conducting electroactive polymers are promising candidates for next-generation sodium-ion batteries due to their environmentally benign properties, high stability, and low cost. In this work, polyaniline (PANI) nanofibers have been successfully prepared by interfacial polymerization and characterized using Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The effect of initiator concentration and interfacial contact area on the yield and surface morphology of PANI nanofibers has been studied. The yield and nanofibrous structure of PANI are found to be directly proportional to the interfacial contact area and the concentration of initiator. PANI nanofibers prepared from 1 M ammonium persulfate (APS) in a container having highest interfacial area of 200 cm2 has the highest yield of 0.9 and uniform nanofibrous structure which is clear from SEM study. Preparation of PANI nanofibers and doping with sodium-ion salt is confirmed by FTIR spectroscopy. Sodium-ion battery prepared with doped PANI delivered a highest discharge capacity value of 112 mAh g−1 at 0.047 mA cm−2 during initial cycling. The rate capability tests indicated that after cycling at different C-rates, the cell regained its initial discharge capacity value of 123 mAh g−1 at 0.047 mA cm−2.

Temperature dependency of activity of nano-catalysts on La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3−δ cathode of solid oxide fuel cells

Abstract: In this study, Ag-ceria, Co-ceria, and Ba0.5Sr0.5Co0.8Fe0.2O3 nano-catalysts were introduced onto the structure of La0.6Sr0.4Co0.2Fe0.8O3−δ cathode of solid oxide fuel cells through infiltration technique and the electrochemical features of the infiltrated cathodes were examined by electrochemical impedance spectroscopy and analysis of distribution of relaxation times in the temperature range of 500–800 °C. The results revealed that Ba0.5Sr0.5Co0.8Fe0.2O3 exhibits considerable promoting behavior in the upper portion of the studied temperature range, while Co-ceria demonstrates significant catalytic activity for the oxygen reduction reaction at lower temperatures probably due to the active valence exchange of cobalt species in the spinel structure of cobalt oxide. Analysis of distribution of relaxation times revealed that low frequency arc of the impedance spectra is effectively hampered as a result of Ag-ceria and Co-ceria infiltration. Cathodic polarization of the infiltrated cells showed stable performance of the infiltrated electrodes over 50 h at 700 °C.

3D nanostructured NiMo catalyst electrodeposited on 316L stainless steel for hydrogen generation in industrial applications

Abstract: Nowadays, massive NiMo alloys are considered highly active catalysts for the hydrogen evolution reaction (HER) in industrial alkaline electrolysers. Thus, it is desirable to study other alternative materials, preserving the specific properties of these alloys. In this study, a NiMo coating on 316L stainless steel with high resistance to the corrosive medium is obtained by electrodeposition process. Properties and structural characteristics of the new synthesized material have been correlated with its efficiency as electrocatalyst. In this study, using a simple plating method, it was possible to obtain a material with a catalytic activity for the HER in alkaline media, which is 37.6 times higher than that of conventional raw Ni catalysts, at a considerably lower cost. The 3D nanostructured NiMo catalyst synthesized presented a highly roughened surface with porous microstructure, which is an essential requirement for obtaining high catalytic activity with this type of systems. The porous microstructure in the coating has been confirmed by X ray diffraction and scanning electron microscopy. Raman spectra of the surface evidenced the formation of superficial species before and after the ageing treatment by prolonged chronoamperometry in alkaline electrolyte. This feature was also confirmed by the analysis of X ray photoelectron spectroscopy measurements.

Reduction in energy for electrochemical disinfection of E. coli in urine simulant

Abstract: We report the development of novel modes of operation for electrochemical disinfection of E. coli in human urine simulant with an aim to minimize the energy required for disinfection. The system employs boron-doped diamond electrodes and will be part of an energy neutral, water and additive free outdoor toilet being developed for use in developing countries. Disinfection had been previously demonstrated with voltage being continuously applied to the electrode until disinfection was achieved. In the present study, a new pulsed mode of operation is investigated. This includes a continuous on mode, where oxidants are generated until disinfection is achieved, a single cycle mode, where oxidants are generated for a fixed time and the water is circulated so allow already generated oxidants to disinfect, and a pulsed mode with different duty cycles, which is like the single cycle mode but with multiple cycles. Disinfection was achieved with pulsed mode operation with a 68% energy reduction compared to the continuous on mode. Energy saving was most likely achieved by lengthening the contact time of the disinfectant with the bacteria and increased generation of non-chlorine disinfecting oxidants.

Effect of Co(NO 3 ) 2 ·6H 2 O thermal decomposition temperature on the nano-Co 3 O 4 product morphology and electrocatalysis of water oxidation

Abstract: Herein, we report the electrochemical water oxidation efficiency of nano-Co3O4 catalyst samples obtained by the thermal decomposition of Co(NO3)2·6H2O at various temperatures (320, 420, 520, and 620 °C). The structural and morphological details of the synthesized samples were determined by employing X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. These studies revealed the formation of well-dispersed nano-Co3O4 particles with sizes, shapes, and crystallinity levels that differed for the different decomposition temperatures. The prepared catalysts were immobilized on filter-paper-derived carbon electrodes for checking their electrochemical properties. The electrochemical efficiency levels of the Co3O4 catalyst samples were evaluated by employing each of them as an anode to study the water oxidation reaction. The nano-Co3O4 sample prepared at 420 °C yielded the highest efficiency and good stability towards the water oxidation reaction. The higher efficiency of this sample was attributed to the relatively small average size and low level of agglomeration of its nanoparticles, and to the high electrochemically active surface area of its electrode. Different morphology and crystallinity of nano-Co3O4 were prepared by simple and straightforward thermal decomposition of Co(NO3)2·6H2O for electrochemical water oxidation. The nano-Co3O4 prepared at 420 °C showed the highest efficiency and good stability towards water oxidation.

Investigation of electrochemical reaction mechanism for antimony selenide nanocomposite for sodium-ion battery electrodes

Abstract: Antimony selenide and its carbon composite were synthesized through a mechanochemical process and investigated as anode materials for sodium-ion secondary batteries. X-ray diffraction (XRD) with rietveld refinement and transmission electron microscopy (TEM) analyses confirm that Sb2Se3 were composed of agglomerated highly crystalline nanocrystallites and the Sb2Se3/C composite consisted of nanocrystalline Sb2Se3 dispersed homogeneously throughout an amorphized carbon matrix. The initial Coulombic efficiency, rate capability, and cycle performance of the Sb2Se3/C composite were superior to those of Sb, or Sb2Se3. The Sb2Se3/C composite, in particular, showed excellent cycle stability, with 98.2% of initial capacity at 200 mA g−1 after 200 cycles. Based on the reaction potentials, ex situ XRD patterns and ex situ HR-TEM analysis of the Sb2Se3/C composite electrode revealed the structural changes which occurred reversibly within the Sb2Se3/C composite by conversion and recombination reaction during sodiation and desodiation process. Furthermore, XPS analysis study was carried out for identifying the surface films formed on both the electrodes and their effects on the performances.

Comparative study of monolithic platinum and iridium as oxygen-evolving anodes during the electrolytic reduction of uranium oxide in a molten LiCl–Li2O electrolyte

Abstract: A series of four electrolytic reduction runs was performed in molten salt at bench scale to compare the performance characteristics of monolithic platinum and iridium as oxygen-evolving anodes, while simultaneously reducing uranium oxide to metal. In each run, 25 g of uranium oxide particulate was loaded into a permeable steel basket, which, in turn, was immersed in a pool of LiCl—1 wt% Li2O at 650 °C. Both anodes, each 3 mm in diameter, were suspended vertically in the salt pool, adjacent to the steel cathode basket. The anodes were connected in parallel to separate direct current power supplies with the uranium oxide-loaded basket as the common cathode. A cell voltage (3.1 V) was intermittently applied to the system with both power supplies operating concurrently, effecting the reduction of uranium oxide to uranium metal at the cathode basket and the simultaneous oxidation of oxygen anions in the salt to oxygen gas at each anode. Anode and cathode potentials and currents were recorded to compare the performance of platinum vis-a-vis iridium. After completing the series of runs, both anodes were removed and subjected to dimensional, chemical, and microscopic analyses. Even though the accumulated charges on each anode over the series of four runs were similar, the platinum anode exhibited up to 29% reduction in cross-sectional area compared to < 3% for the iridium anode.