Advanced electrode materials and tailored design of the electrified interface are essential for electrochemical processes that rely on electrode/electrolyte interfaces. In particular, electrochemical capacitors (supercapacitors) and electrocatalysts depend on surface confined reactions and thus high surface area nanomaterials are preferred. In this review, key advances in the development of conducting oxide nanosheets towards aqueous pseudocapacitors and fuel-cell related electrocatalysts will be highlighted, emphasizing results primarily from the authors’ laboratory. The synthesis of conductive nanosheets and its application towards pseudocapacitors and hybrid capacitors will be reviewed. The use of nanosheets as co-catalysts for Pt-based electrocatalysts as well as catalysts will be described. The morphology-property relation will be established for nanosheet electrochemistry, hopefully encouraging researchers in materials chemistry and electrochemistry to communicate and move forward together to stimulate enhancement in the important and expanding field of electrochemical energy storage and conversion.
Group I-III-VI2 semiconductor-based quantum dots, such as AgInS2, CuInS2 and their solid solution with ZnS, have recently been reported to show intense photoluminescence, the wavelength of which is tunable in a wide range from visible to near-infrared (NIR) light regions by controlling their chemical composition and/or size. Due to their low toxicity and tunable optical properties, these multinary semiconductor quantum dots (QDs) have been intensively developed as alternative materials to conventional Cd- and Pb-based QDs for applications to photoluminescent devices, photocatalysts, quantum dot solar cells, and biological imaging materials. In this review, the recent progress in the photofunctionality of I-III-VI2-based semiconductor QDs prepared by the colloidal method is outlined with foucus on two advances: (1) extension of the photoluminescence wavelength to NIR light for in vivo biological imaging and (2) improvement of photoenergy conversion properties by nanostructure control of QDs.
Reactive species generated by the oxidation and reduction of organic compounds are generally unstable. To utilize the reactive species as intermediates for organic synthesis and functional materials, it is crucial how to treat them. In this headline, electrochemical reactions utilizing stabilized reactive cations, which enabled benzylic C–H/aromatic C–H cross-coupling, aromatic C–H/C–H cross-coupling, and aromatic C–H amination are demonstrated. Furthermore, energy storage materials utilizing stabilized anions, which enabled to develop organic materials for lithium-ion batteries with high voltage of ca. 3 V and solvent-free redox flow batteries with high energy density, are demonstrated. These studies show the usefulness of stabilized reactive species.
Conversion-type active materials show promise for use in large-scale lithium-ion batteries by virtue of their low cost and large specific capacities. However, there are some challenges in the application of these materials to practical Li-ion batteries. To adapt the conversion-type active materials to the next-generation Li-ion batteries, it is necessary that we understand the conversion reaction in detail. In this review, the electrochemical properties of the iron-based conversion cathode are introduced, and their reaction mechanisms are described based mainly on our own experiments. Finally, we introduce a composite of LiF as an Li source and FeO as an anion accepter as a novel cathode system for the next-generation Li-ion batteries.
The crystal structure, morphology, and galvanostatic cycling and rate performances of cobalt-substituted Li2MnSiO4/C compounds, Li2Mn1−xCoxSiO4/C (x = 0.25, 0.5, and 0.75), were evaluated and compared with those of Li2MnSiO4/C and Li2CoSiO4/C. Li2Mn1−xCoxSiO4/C (x = 0.25, 0.5, and 0.75) compositions comprising uniform nanosized primary particles and no impurities were successfully synthesized using a hydrothermal method, followed by carbon coating. In addition, Li2MnSiO4/C and Li2CoSiO4/C were synthesized for comparison. The synthesized Li2Mn1−xCoxSiO4/C (x = 0.25, 0.5, and 0.75) were solid solutions and were identified using an orthorhombic unit cell with Pmn21 space group symmetry. Although the capacity fades for Li2Mn1−xCoxSiO4/C were similar to those for Li2MnSiO4/C, the discharge capacity, average discharge voltage and rate capability of Li2MnSiO4/C improved when Co was substituted for Mn. Li2Mn0.25Co0.75SiO4/C exhibited the best electrochemical performance with first energy density of 659.7 Wh kg−1 which was greater than that of LiMn2O4 (500 Wh kg−1) and LiNi1/3Co1/3Mn1/3O2 (600 Wh kg−1). The good electrochemical performance of Li2Mn0.25Co0.75SiO4/C is attributed to its lower charge transfer resistance relative to that of Li2MnSiO4/C.
It is difficult to perform the electrodeposition of aluminum alloys from aqueous solutions. In this study, aluminum–nickel was electrodeposited from an electrolyte containing dimethyl sulfone, AlCl3, and 0.0 mol%–1.0 mol% NiCl2 at deposition potentials ranging from −1.0 to −5.0 V (Al/Al3+). The surface morphologies of the Al–Ni alloys depended on the NiCl2 concentration and the deposition potential. The crystalline structure of the Al–Ni alloys also depended on the NiCl2-concentration. Furthermore, the content of Ni in the Al–Ni alloys increased with increase in the NiCl2 concentration.
The lifetime of a nickel-metal hydride battery power system (BPS) used in railway systems is investigated. Frequent acceleration and deceleration are performed in normal railway operation, so the narrow range of SOC of the corresponding BPS is discussed. Since the lifetime of the battery used in that BPS should be estimated in accordance with the operation pattern, the operation pattern was analyzed by Fourier transform, and battery lifetime is evaluated in the frequent discharge/charge with a current change every 6 seconds within a 3% depth of discharge (DOD) as the main pattern and the float charging at a constant voltage. Major factors of the battery lifetime are operation voltage and the internal cell temperature caused by an internal resistance. The lifetime of the battery do not depend on the operation pattern such as frequent discharge/charge and float charging. Furthermore, it was almost the same as the lifetime at rest potential in the open circuit state. Applying electrochemical reaction kinetics equations to this system, calculation results indicate a good correlation with the experimental data.
A novel method of Ni recovery from the acid leaching solution of electroplating sludge through preparing Ni-Fe alloy with high Fe2+ content (i.e., 0.5 g/L) is proposed in this paper, and the corresponding electrodeposition process was studied using conventional electrochemical techniques and scanning electron microscopy. The obtained results showed that adding saccharin Na at concentrations from 0 to 14 g/L to the deposition bath increased the cathodic polarization potential of Ni-Fe co-deposition, with sensible grain refinement and disappearance of surface cracks observed after the addition of 14 g/L saccharin Na. Two different mathematical models of metal nucleation were tested, and the different morphologies of the deposits formed with and without saccharin Na suggested disparate nucleation mechanisms. The Ni-Fe deposition potential shifted positively in the presence of thiourea, and it should not be added together with saccharin Na during the nucleation stage for the grain refinement of the deposits. The iron contents in the deposits decreased with the increase of thiourea concentration ascribed to the thiourea complex which adsorbed on the cathodic surface preventing Fe2+electrodeposition from the electrolytes.
This paper reports the occurrence of electrochemical oscillations (EOs) in Cu electro-oxidation of phosphoric acid solution, and systematically investigated the effect of potential, electrolyte composition and concentration, temperature, stirring rate, and scanning speed on EOs. The mechanism of EOs occurred as a result of deposition and dissolution effects of CuH2PO4 through electro-oxidation of the Cu anode. The experimental result for amplitude and frequency can be explained by this simplified qualitative analysis, and further verified the previously speculated EO mechanism. This study provides insights into the relevance of micro-chemical mechanisms for the macroscopic non-equilibrium phenomenon and presents novel concepts for highly efficient electrodissolution in metallurgy.
Mechanical attrition (MA) is applied to assist the electroplating Ni-P coating on a magnesium alloy substrate. The influence of MA on the microstructure and electrochemical performance of the coating was studied with SEM, XRD, electrochemical impedance spectroscopy (EIS) and polarization curves. The results show that under MA, the Ni-P electroplating becomes compact and free of cracks and pores, leading to significant improvement in the coating corrosion resistance. MA promote transformation the coating from amorphous state to crystalline one and produce an obvious transition layer at the coating-substrate interface, which is beneficial to enhancing the coating adhesion strength and other mechanical properties.