Naoji Furukawa

The possible use of polymer gel electrolytes in nickel/metal hydride battery

Abstract Alkaline polymer gel electrolyte was prepared from potassium salt of cross-linked poly(acrylic acid) and KOH aqueous solution in order to investigate the applicability of the polymer gel electrolyte to alkaline secondary batteries such as nickel/metal hydride (Ni/MH) battery. The polymer gel electrolyte was found to have high ionic conductivity and wide potential window almost comparable to the KOH aqueous solution over the wide ranges of KOH concentration and temperature. An experimental Ni/MH cell was assembled using polymer gel electrolyte and its charge–discharge and capacity retention characteristics were tested. The cell using the polymer gel electrolyte exhibited somewhat better charge–discharge and capacity retention characteristics at 25 °C compared with a similar type of cell assembled using KOH aqueous solution.

Electrochemical characterization of new electric double layer capacitor with polymer hydrogel electrolyte

Abstract A new electric double layer capacitor (EDLC) was constructed by using polymer hydrogel electrolyte prepared from crosslinked potassium poly(acrylate) and KOH aqueous solution, and its electrochemical characteristics were investigated by cyclic voltammetry and charge–discharge cycle tests, compared with a case of the cell using only a KOH aqueous solution as an electrolyte. As a result, the cell with the polymer hydrogel electrolyte was found to exhibit higher capacitance than that with the KOH aqueous solution and excellent high-rate dischargeability. The impedance spectroscopic measurements suggested that the higher capacitance could be ascribed to the pseudocapacitance. These results indicate the potential applicability of the polymer hydrogel electrolyte to EDLCs as an electrolyte with good performance.

All solid-state nickel/metal hydride battery with a proton-conductive phosphoric acid-doped silica gel electrolyte

Abstract All solid-state nickel/metal hydride (Ni/MH) battery was fabricated by using a proton-conductive phosphoric acid-doped silica gel as an electrolyte. The H3PO4-doped silica gel was dried in vacuum at various temperatures for 1 h before fabricating the battery in order to reduce the possibility of corrosion by water on the surface and in the micropores of the gel. The influence of drying temperature on the crystallinity, water content and conductivity of the gel was investigated. The conductivity depended on the drying temperature of the gel. The fabricated all solid-state Ni/MH battery was able to operate several tens of charge–discharge cycles at relatively high current density although the utilization of the battery was low.

Electrochemical preparation and characterization of Ni/(Ni + RuO2) composite coatings as an active cathode for hydrogen evolution

Abstract Ni/(Ni + RuO2) electrodes were prepared by simultaneous electrodeposition of Ni and RuO2 on a Ni substrate from a suspension electrolyte (Watts bath) of RuO2 particles under vigorous stirring condition and they were found to have excellent characteristics as an active cathoe for hydrogen evolution in hot concentrated alkaline solution.

Electrochemical properties of Ni/(Ni+RuO2) active cathodes for hydrogen evolution in chlor-alkali electrolysis

Ni(Ni + RuO2) active cathodes were prepared by simultaneous electrodeposition of Ni and RuO2 on a Ni substrate from an electrolyte solution (Watts bath) in which RuO2 particles were suspended by vigorous stirring. The resulting cathodes were electrochemically characterized and it was found that the enhanced electrocatalytic activity of the cathodes was mainly ascribable to the increase of active sites or the content of RuO2 particles. Furthermore, the performance of the Ni(Ni + RuO2) active cathodes was evaluated for the use in chlor-alkali electrolysis in a laboratory scale. The hydrogen overvoltage of the cathodes was confirmed to be very low and the high durability was observed under the industrial chlor-alkali electrolysis conditions. In addition, the cathodes had excellent tolerance to repeated short-circuiting.

New Electric Double Layer Capacitor with Polymer Hydrogel Electrolyte

A new electric double layer capacitor (EDLC) was constructed by using polymer hydrogel electrolyte prepared from cross-linked potassium poly(acrylate) and a KOH aqueous solution. The electrochemical characteristics of theEDLC cell were investigated by cyclic voltammetry and charge/discharge cycle testing compared with those of the cell using only a KOH aqueous solution as an electrolyte. As a result, it was found that the cell with the polymer hydrogel electrolyte exhibited higher capacitance and better cycle performance than that with the KOH aqueous solution. It was suggested by impedance spectroscopy that the higher capacitance could be ascribed to pseudocapacitance. These results indicate that the polymer hydrogel electrolyte has potential applicability to the EDLCs as an electrolyte with good performance.

Theoretical evaluation for thermodynamic stability of constituents of hydrogen storage alloy in concentrated alkaline solution at higher temperature

Abstract In order to evaluate thermodynamic stability of constituents of LaNi 5 in 6 M KOH solution at various temperatures less than 70°C, potential–pOH diagrams in La– and Ni–H 2 O systems were drawn at various temperatures based on the thermodynamic data of La and Ni species and the reaction equations. Solubilities of La and Ni species were calculated using the evaluated pOH values at various temperatures. As a result, it was found that La(OH) 3 was extremely stable at any temperature and Ni was easily oxidized to Ni(OH) 2 and HNiO 2 − at higher temperature. The deterioration in the charge–discharge performance of LaNi 5 at high temperature was considered to be attributed to the oxidation of not only La but also Ni.

Charge-Discharge and Capacity Retention Characteristics of New Type Ni/MH Batteries Using Polymer Hydrogel Electrolyte

Positive electrode capacity-controlled nickel/metal hydride (Ni/MH) batteries were assembled using the polymer hydrogel electrolyte and their charge/discharge and capacity retention characteristics were investigated compared to those using a 7.3 M KOH aqueous solution. The interface between the polymer hydrogel electrolyte and nickel positive electrode worked very well and the experimental cell with the polymer hydrogel electrolyte exhibited charge/discharge characteristics such as discharge capacity, cycle performance and high rate capability almost comparable to the cell with a 7.3 M KOH aqueous solution. Moreover, the capacity retention characteristics were markedly improved by using the polymer hydrogel electrolyte. The effects of the polymer hydrogel electrolyte on the capacity retention characteristics were more remarkable at relatively high temperature. These results strongly suggest that the polymer hydrogel electrolyte has a potential applicability to the commercial Ni/MH batteries.

Theoretical evaluation for thermodynamic stability of constituents of Mm-based hydrogen storage alloy in 6 M KOH solution at relatively high temperatures

Abstract Potential-pOH diagrams of some components constituting AB 5 -type Mm-based (Mm: misch metal) hydrogen storage alloy were drawn at various temperatures to predict the deterioration behaviors of the alloy in an alkaline solution at relatively high temperatures. Based on these diagrams, the thermodynamic stability of each constituent of the alloy in 6 M KOH solution at various temperatures was evaluated. As A components, in the charge–discharge potential range, Nd(OH) 3 was extremely stable at temperatures lower than 70°C, while Ce(OH) 3 was oxidized to CeO 2 at the end of discharge above −0.496 V versus NHE at 70°C. On the other hand, as B components, Mn, Al and Co dissolved easily as HMnO 2 − , AlO 2 − and HCoO 2 − ions in 6 M KOH solution and their solubility increased with increasing temperature. However, HCoO 2 − ion was reduced to metallic Co at the charge process. All oxidation reactions, particularly the dissolution of Mn and Al, proceeded at relatively high temperatures.

Self-discharge characteristics of an electric double-layer capacitor with polymer hydrogel electrolyte

An electric double-layer capacitor (EDLC) was assembled with the polymer hydrogel electrolyte prepared from cross-linked potassium poly(acrylate) (PAAK) and KOH aqueous solution, and the self-discharge characteristics were investigated. The EDLC cell with the polymer hydrogel electrolyte showed lower voltage decay on open circuit than that with a KOH aqueous solution. Moreover, it was found that the leakage current of the EDLC cell was markedly suppressed by using the polymer hydrogel electrolyte. The suppression was enhanced with increasing PAAK content in the electrolyte. These results strongly suggest that the PAAK plays an important role in the suppression of self-discharge.