A porous, hollow, microspherical composite of Li2MnO3 and LiMn1/3Co1/3Ni1/3O2 (composition: Li1.2Mn0.53Ni0.13Co0.13O2) was prepared using hollow MnO2 as the sacrificial template. The resulting composite was found to be mesoporous; its pores were about 20 nm in diameter. It also delivered a reversible discharge capacity value of 220 mAh g?1 at a specific current of 25 mA g?1 with excellent cycling stability and a high rate capability. A discharge capacity of 100 mAh g?1 was obtained for this composite at a specific current of 1000 mA g?1. The high rate capability of this hollow microspherical composite can be attributed to its porous nature.
The three-dimensional porous Li3V2(PO4)3/nitrogen-doped reduced graphene oxide (LVP/N-RGO) composite was prepared by a facile one-pot hydrothermal method and evaluated as cathode material for lithium-ion batteries. It is clearly seen that the novel porous structure of the as-prepared LVP/N-RGO significantly facilitates electron transfer and lithium-ion diffusion, as well as markedly restrains the agglomeration of Li3V2(PO4)3 (LVP) nanoparticles. The introduction of N atom also has positive influence on the conductivity of RGO, which improves the kinetics of electrochemical reaction during the charge and discharge cycles. It can be found that the resultant LVP/N-RGO composite exhibits superior rate properties (92 mA h g?1 at 30 C) and outstanding cycle performance (122 mA h g?1 after 300 cycles at 5 C), indicating that nitrogen-doped RGO could be used to improve the electrochemical properties of LVP cathodes for high-power lithium-ion battery application.
Graphical abstract The three-dimensional porous Li3V2(PO4)3/nitrogen-doped reduced graphene oxide composite with significantly accelerating electron transfer and lithium-ion diffusion exhibits superior rate property and outstanding cycle performance.
In this work, Bi3.64Mo0.36O6.55 nanoparticles (NPs) were successfully prepared by a facile hydrothermal method and utilized in pseudocapacitor for the first time. Within a redox potential range from ?1.0 to 0 V vs. Hg/HgO in a 1 M aqueous KOH solution by cyclic voltammetry (CV), chronopotentiometry (CP) and AC impendence, the specific capacitance could reach 998 F g?1 at 1 A g?1, which is possibly ascribed to the higher Bi content of Bi3.64Mo0.36O6.55 NPs. Furthermore, the Bi3.64Mo0.36O6.55 NP electrode exhibited good cycle stability maintaining over 85 % after 5000 cycles. These results demonstrated Bi3.64Mo0.36O6.55 NPs might be a promising electrode material for pseudocapacitor.
Graphical abstract The fabrication of uniform Bi3.64Mo0.36O6.55 nanoparticles with a diameter of 100 nm were succefully reported by a facial hydrothermal method, which exhibits a extraordinary electronic performance with 998 F g-1 at 1 A g-1 and cycling stability
The electron transport layer (ETL) plays a crucial role in the rapidly developed perovskite solar cells (PSCs). SnO2 has become one of the most promising alternatives to the TiO2 ETL due to its superior characteristics, such as the wider bandgap and hysteresis-free. However, at this stage, a lot of preparation methods of SnO2 ETL exist in high temperature and long time, those undoubtedly increase the cost and time of preparation. Herein, we report a low-temperature solution-processed SnO2 ETL without high annealing temperature, and a special bromine salt is used to modify SnO2, which leads to a higher transmittance and improved carrier transport ability. Due to the excellent optical and electrical properties, the photoelectric conversion efficiency of the prepared PSC reaches up to 18.8%. Moreover, it can be fabricated using facile solution processing at low temperature, making it particularly attractive for flexible development and low-cost commercialization.
Nanoporous gold (NPG) prepared via chemical de-alloying has been recently shown to dramatically improve the reversibility and kinetics of Li-O2 batteries, but high cost makes its use as practical electrode material difficult. Recently developed electrochemical routines for synthesis of very thin NPG layers (<100 nm) on various low-cost substrates could potentially provide a feasible economic alternative. In this work, NPG on both gold and glassy carbon (GC) substrates was successfully synthesized via electrochemical de-alloying method and tested as cathode material in Li-O2 batteries. The results show that electrochemically synthesized NPG cathode cycles repeatedly with LiFePO4 anode. The voltage hysteresis is also significantly reduced when NPG is used in comparison with plain GC. Along with these results, challenges that need to be addressed for future implementation of NPG cathode in practical Li-O2 batteries are also discussed.
Functional electrode materials play an increasingly important role in the advancement of energy conversion and storage technologies used in batteries, electrolyzers, supercapacitors, fuel cells, and other electrochemical devices. To address the problems related to accelerating demand for the so-called renewable energy, which are simultaneously coupled with environmental concerns, new generations of materials, engineering methodologies, and innovative techniques are necessary. Among many synthetic methods, microwave-assisted synthesis becomes nowadays a very popular approach to efficiently control both the composition and morphology of solids. In this review, we focus on its applications to create new advanced energy electrode materials.
Co2(OH)3Cl xerogel interconnected mesoporous structures have been prepared by a facile one pot sol-gel process and heat treated at 200 and 400 °C. All samples are studied for their morphology, structure, and electrochemical stability upon cycling. The specific capacitance of the as-prepared Co2(OH)3Cl from single electrode study is 450 F/g, when the electrodes are cycled in 3 M KOH at a specific current 2 A/g. Interestingly, capacity retention after 500 and 1000 cycles is about 92 and 75 %, respectively. Sample heated at 200 °C exhibits 308 F/g at 2 A/g and that heated at 400 °C shows only 32 F/g at 0.2 A/g. With an increase in preparation temperature, amorphous Co2(OH)3Cl is converted to crystalline Co3O4 phases with lower electrochemical performance. In full cell study, as-prepared Co2(OH)3Cl showed a capacity of about 49 F/g as asymmetric capacitor and 32 F/g as symmetric capacitor at 2 A/g current density. Co2(OH)3Cl being a novel porous material with merits of homogeneous porosity, high surface area, and an interconnected three dimensional (3D) structure exhibits considerably high capacitance. With a significant specific capacity and electrochemical stability, the synthesized material is a novel potential candidate for supercapacitors.
In this paper, a facile immobilization of copper hexacyanoferrate nanoparticles (CuHCFNP) on a paraffin wax-impregnated graphite electrode (PIGE) was carried out using the room-temperature ionic liquid (RTIL) 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) as an ionic binder. The characteristics of the CuHCFNP/EMIMBF4 gel-modified electrode were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques, and the modified electrode morphology was also characterized using field emission scanning electron microscopy (FESEM). The electrocatalytic behavior of butylated hydroxyl anisole (BHA) at the modified electrode has been investigated in 0.1 M KNO3 in static and dynamic conditions. Under the optimum conditions, the oxidation peak current was proportional to the BHA concentration in the range from 1.5 to 1000 μM with a detection limit of 0.5 μM (S/N = 3). The proposed method was applied to determine BHA content in real samples with satisfactory results.
In the lithium-oxygen (Li-O2) cell, the porous structure of the cathode is an important issue as well as challenge for its task of accommodating discharge products and providing free paths for oxygen. Clogging of pores and degradation of materials at the cathode affect the discharge rates and cycling performance of Li-O2 cell. Based on the study of five synthesized nanostructured porous carbons, namely, 2-D ordered mesoporous carbon C-15, 3-D ordered mesoporous carbons C-16 and C-16B with larger pores, hollow core mesoporous shell carbon (HCMSC), and reduced graphene oxide (rGO), we found that the type and pore structure of the carbon significantly affect the electrochemical performance of the cell. Both C-15 and rGO cathodes demonstrate good cell cycleability, while the HCMSC, with its interesting bimodal pore system, is not favorable for further improving cycling performance. The C-16B has similar morphology and electrolyte wettability of C-16. However, the former possesses larger pores, and such porosity significantly improves the cell cycleability up to 44 cycles, corresponding to an extended operation life of 850 h.
Sulfonated polyvinylchloride (SPVC) cation-exchange membranes were coated using chitosan solutions comprising different amounts of Fe3O4 nanoparticles. Influence of chitosan immobilization as well as nanofiller concentration on the electrochemical performance of the membranes was investigated. Electrochemical properties of the membranes including permselectivity, ionic permeability, and areal resistance were studied using an equipped electrodialysis setup and NaCl solution as model electrolyte. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) were employed for membrane characterization. Electrochemical performance of the SPVC membranes was improved by coating chitosan polymer. In addition, ionic permeability and permselectivity of the membranes were initially raised by increasing nanoparticles concentration from nil to 2 wt% and then decreased by further insertion of the nanofiller. The areal resistance of the plain SPVC membrane was decreased from 9.4 to 2.9 (ohm) by coating of chitosan solution including optimum value of nano-Fe3O4 due to electrical potential field enhancement across the membrane.
The electrochemical oxidation of single-crystal gold surfaces has been well studied, and the exposed crystal planes can be reliably distinguished based on the peak potentials of oxide formation. However, the multiple oxidation peaks of polycrystalline gold have not yet been unambiguously related to crystal planes. In this work, we used cyclic voltammetric responses of activated polycrystalline gold electrodes recorded in sulfuric acid solutions to allow constructing relationships between crystal planes and oxide peaks. The studies of oxide formation were complemented by measuring double-layer non-faradaic currents, lead underpotential deposition (Pb-upd), the oxygen reduction reaction (ORR), and the hydrogen evolution reaction (HER).
Graphical abstract The link between three gold oxide current peaks and exposed low index crystal planes, viz. Au(100), Au(110) and Au(111) on polycrystalline gold electrode
The utility of energy sequencing for extracting an accurate matrix level interface profile using ultra-low energy SIMS (uleSIMS) is reported. Normally incident O2+ over an energy range of 0.25–2.5 keV were used to probe the interface between Si0.73Ge0.27/Si, which was also studied using high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). All the SIMS profiles were linearized by taking the well understood matrix effects on ion yield and erosion rate into account. A method based on simultaneous fitting of the SIMS profiles measured at different energies is presented, which allows the intrinsic sample profile to be determined to sub-nanometer precision. Excellent agreement was found between the directly imaged HAADF-STEM interface and that derived from SIMS.
LiNi1-x-yCoxMnyO2 (NCM) with excessive lithium is known to exhibit high rate capability and charge–discharge cycling durability. However, the practical usage of NCM is difficult, because the positive electrode slurry is unstable and battery cells swell due to the alkaline residual lithium compound generated on the surface of NCM particles. To reduce the residual lithium compound, ammonium metatungstate (AMT) added to NCM is studied, and the effect is investigated by scanning electron microscopy, aberration-corrected scanning transmission electron microscopy, X-ray diffractometry, synchrotron X-ray diffractometry, and several electrochemical measurements. It is found that the AMT modification reduces the amount of alkaline residual lithium compound and improves the rate capability due to the ~1-nm-thick W-rich layer generated on the NCM surface.
Hierarchical CuO nanosheets were synthesized through a facile, eco-friendly reflux deposition approach for supercapacitor electrode material for energy storage. The resultant CuO nanosheets were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and nitrogen adsorption-desorption isotherm techniques. The supercapacitor behavior of CuO nanosheets was investigated by cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy in novel 0.1 M aqueous 1-(1′-methyl-2′-oxo-propyl)-3-dimethylimidazolium chloride [MOPMIM][Cl] ionic liquid as an electrolyte. The result demonstrate that CuO nanosheets exhibit specific capacitance of 180 F g?1 at 10 mV s?1 scan rate which is the highest value in ionic liquid electrolyte and 87% specific capacitance retention after 5000th cycle. The electrochemical performance proves CuO nanosheets as electrode with ionic liquid electrolyte for developing green chemistry approach in supercapacitor.
Graphical abstract As-synthesized, CuO nanosheets demonstrate excellent supercapacitor electrode performance with high specific capacitance of 180 F g?1 at 10 mV s?1 scan rate and 87% specific capacitance retention in 0.1 M aqueous [MOPMIM][Cl] IL electrolyte
A novel molecular model of carbonyl-substituted phthalocyanine compounds used as the cathode material in a lithium-ion battery is demonstrated. Tetra-carboxyl and octa-carboxyl groups are substituted onto a phthalocyanine-conjugated system. The conductivities of phthalocyanine compounds are effectively improved by I2 doping, without affecting the capacity and energy density. Taking lithium as the counter-electrode, the electrochemical properties of the microparticles are investigated, and the electrochemical mechanism of carboxyl groups substituted with phthalocyanines is analyzed. The results indicate that carboxyl-substituted phthalocyanines have high specific capacities. After 20 or 50 cycles, they still retain capacities of about 300 and 500 mA?·?h/g for tetra-carboxyl- and octa-carboxyl-substituted phthalocyanines, respectively. The multiple carbonyl groups and the large numbers of electrons on the phthalocyanine-conjugated system are the two factors contributing to the high specific capacity.
Graphical Abstract A novel molecular model of carbonyl-substituted phthalocyanine compounds used as the cathode in a lithium-ion battery is demonstrated. Multiple carbonyl groups with high electrochemical activity are substituted onto a stable phthalocyanine-conjugated system, resulting in excellent conductivity and high specific capacity after using an iodine-doping technique; this could provide new ideas for electrode materials in lithium-ion batteries.
The effect of dip time variations on electrochemical performance of polypyrrole (PPy)-copper hydroxide hybrid thin-film electrodes was studied well in depth. Synthesis was carried out using a successive ionic layer adsorption and reaction (SILAR) method via an aqueous route, using 0.1 M pyrrole, 0.1 M Cu(NO3)2, and H2O2. The electrochemical analysis was made by using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) analysis, and electrochemical impedance spectroscopy (EIS). Scanning electron microscopy (SEM) image of optimized electrode shows nanolamellae-like structures. The characteristic peak observed in Fourier transform infrared (FTIR) analysis at 1558 cm?1 validates the existence of PPy in hybrid electrode material, while the peaks observed at 21.5° and 44.5° in X-ray diffraction (XRD) patterns are evidence for triclinic Cu(OH)2. The observed maximum values of specific capacitance (SC), specific power (SP), specific energy (SE), and coulombic efficiency (η) of the optimized electrode are 56.05 F/g, 10.48 Wh/kg, 11.11 kW/kg, and 46.47%, respectively. For originality and value, the SILAR synthesis of PPy-Cu(OH)2 hybrid thin-film electrodes was carried out for the very first time. Synthesized electrodes showed improved surface structures and electrochemical stability than the pristine PPy electrodes which are necessary for the supercapacitive applications.
Free-standing and flexible NiMoO4 nanorods/reduced graphene oxide (rGO) membrane with a 3D hierarchical structure was successfully synthesized by a general approach including vacuum filtration followed by thermal reduction. NiMoO4 nanorods with about 50–100 nm diameter were embedded homogenously into the 3D rGO sheets and assembled with rGO to form a membrane about 10 μm in thickness. The NiMoO4/rGO membrane could be directly evaluated as anode materials for lithium-ion batteries (LIBs) without using binder. The 3D layer stacked graphene hierarchical architecture can not only offers a continuous conducting framework for efficient diffusion and transport of ion/electron but also accommodates the large volume expansion of NiMoO4 nanorod changes during cycling. Moreover, our results show that the NiMoO4/rGO membrane exhibited excellent electrochemical performance with a high reversible capacity of 945 mAh g?1 at a current density of 0.25 A g?1 as anode materials in LIBs.
A gold bare template modified with self-assembled layers (SAMs) composed of gold nanoparticles and organic S-containing compound: cysteamine and dihydrolipoic acid were prepared. The electrode with SAMs endowed with gold nanoparticles gave a high catalytic effect for dopamine electrooxidation alone and in the presence of biogenic interfering compounds: ascorbic acid and uric acid in solution at pH 7. For this novel sensor, a linear relationship between the current response of dopamine at the potential of peak maximum (jp) and the concentration of this compound in solution (cDA) was found over the range 0.1 μM to 0.85 mM with the detection limit of 0.023 μM.
We obtained Tannin-4-azobenzoic acid (azo dye) by the conventional method of diazotization and coupling of aromatic amines. The properties of the azo dye were characterized via ultraviolet-visible (UV–vis), infrared (IR), and nuclear magnetic resonance (NMR) spectroscopy. Nanocrystalline titanium dioxide (TiO2) thin films were deposited by hydrothermal method onto fluorine-doped tin (IV) oxide (FTO)-coated glass substrate at 353 K for 4 h. The as-deposited and annealed films were characterized for structural, morphological, optical, thickness, and wettability properties. The synthesized metal free azo dye was used to sensitize the prepared TiO2 thin film with thickness of 26 μm. The photoelectrochemical (PEC) performance of TiO2 sensitized with the azo dye was evaluated in polyiodide (0.1 M KI + 0.01 M I2 + 0.1 M KCl) electrolyte at 40 mW cm?2 illumination intensity. The cell yielded a short circuit current of 2.82 mA, open circuit voltage of 314.3 mV, a fill factor of 0.30, and a photovoltaic conversion efficiency value of 0.64%.
The activated carbon was modified by the wet method with a solution of ammonium persulfate at room temperature with different times. Kinetics studies showed that the modification took place mostly during the first 60 min of the process. The physicochemical properties of the obtained carbon were evaluated by thermogravimetric studies, Raman and FTIR spectroscopy, elementary and BET analyses. Furthermore, the fabricated material was applied in symmetric capacitors operated on the three aqueous electrolytes (1 M H2SO4, 6 M KOH and 1 M Na2SO4). Mild conditions of the modification process are optimal to obtain electroactive groups on the carbon surface, which make this material useful in a supercapacitor application. In our studies, we noticed that this type of functional groups mainly appears on the surface of the activated carbon, in the first oxidation stage. With prolonged oxidation, they may transform into undesirable groups. The results show that this kind of modification improves the capacity of all the tested supercapacitors. It was connected mainly with an increase of the carbon material’s wettability and in the case of capacitor operated in acid and base electrolytes due to a redox reaction of oxygen functional groups.
