Shoichiro Ikeda

Solid-State Ionics: A New High Ionic Conductivity Solid Electrolyte Ag[sub 6]I[sub 4]WO[sub 4] and Use of This Compound in a Solid-Electrolyte Cell

A new high ionic conductivity solid Ag/sub 6/I/sub 4/WO/sub 4/ has been found in the system AgI-Ag/sub 2/WO/sub 4/ at ambient temperature. This compound has a silver ion conductivity of 0.047 (ohm.cm)/sup -1/ at 25/sup 0/C and an activation energy for conduction of 3.6 KCaL/mole between 20/sup 0/ and 293/sup 0/C. The transport number measurement using Tubandts method shows that the transport number of silver ions in this compound is 1.00 within the experiment error. An Ag/Ag/sub 6/I/sub 4/WO/sub 4//I/sub 2/ solid-electrolyte cell shows an open-circuit voltage of 637 MV which agrees well with the value of 686.7 MV calculated from deltag degrees of the cell reaction at 21/sup 0/C. Characteristics of the solid-state cells using Ag/sup 6/I/sub 4/WO/sub 4/ as the electrolyte have been investigated. The phase diagram of the system AgI-Ag/sub 2/WO/sub 4/ has been determined also. 14 references.

Electric and thermoelectric properties of electrodeposited bismuth telluride (Bi2Te3) films

We investigated the relationships among the deposition potential, the electric properties, and the thermoelectric properties of Bi2Te3 films electrodeposited from a solution containing 1.00mM TeO2 and 0.86mM Bi-EDTA complex. From the results of the Hall-effect measurements, the films formed at >−0.27V vs Ag∕AgCl were Te-rich n-Bi2Te3, and the carrier concentration increased with more negative deposition potential. The films formed at <−0.35V were Bi-rich p-Bi2Te3, and the carrier concentration showed a constant value. A depth profile showed that all the electrodeposited films were composed of two layers, and that an n-type layer containing a large excess of Te existed near the substrate surface. From the Seebeck coefficient measurements, the electrical type of all the films was n type, and the maximum Seebeck coefficient (−70±10μVK−1) was observed for the film deposited at −0.20V. The electrical type obtained by the Seebeck coefficient measurements was completely different from the electrical type determi...

Photoelectrochemical reduction products of carbon dioxide at metal coated p-GaP photocathodes in non-aqueous electrolytes

Photoelectrochemical reduction of CO2 was carried out using metal-coated p-GaP photocathodes in non-aqueous electrolytes prepared from tetraalkylammonium salts and propylene carbonate as an aprotic solvent. In non-aqueous electrolytes, the coating of Au, In and Pb increased the cathodic photocurrents and the stability of the electrodes, while Zn coating did not show such significant effects. Photoelectrochemical reduction products at a bare p-GaP in non-aqueous electrolytes were (COOH)2, HCOOH, CO and H2, and the faradaic efficiency for CO formation became 50%, in contrast to that in the aqueous electrolytes where it was only a few %. The Photoelectrochemical reduction products at metal-coated p-GaP photocathodes depended greatly on the catalytic properties of the coated metal, i.e. the catalytic effect on the electrochemical reduction of CO2. By Pb coating, the faradaic efficiency for (COOH)2 formation became ca. 50%, and by Au, In or Zn coating, that for CO became almost 100%. The water content in non-aqueous electrolytes affected the faradaic efficiency of each product significantly.

Solid electrolytes with multivalent cation conduction. 1. Conducting species in MgZrPO4 system

Abstract Magnesium ion conducting materials have been found in the system MgZrPO4, and the composition of the material with maximum conductivity has been estimated to be MgZr4(PO4)6 having the same crystal structure as that of NaZr2(PO4)3. The conductivities are2.9 × 10−5 and 6.1 × 10−3Scm−1 at 400 and 800 °C, respectively and the activation energy for conduction is 79.5 kJ/mol. The charge carrier of this material has been confirmed to be magnesium ions by the Tubandts method and the electron probe micro analysis.

Preparation of CdS thin films by electrodeposition: Effect of colloidal sulfur particle stability on film composition

CdS thin films of about 1 μm thickness were deposited from an aqueous solution containing Cd2+, Na2S2O3 and gelatin as the protective colloid to stabilize the size of colloidal sulfur at from 30 to 40 nm and keep the concentration to an appropriate value during electrolysis. The effects of concentrations of Cd2+ and S2O32− ions and the deposition potential on the composition of CdS films were studied. The reaction mechanism of CdS film formation on the electrode is discussed. CdS film, whose composition is uniform across the film and which does not contain excess metallic cadmium, can be deposited from a solution containing 0.50 to 2.00 mM Cd(NO3)2, 1.00 to 5.00 mM Na2S2O3 and 1.0 × 10−7 to 1.0 × 10−3 wt % gelatin.

Ionic conduction behavior in zirconium phosphate framework

Abstract A series of M I Zr 2 (PO 4 ) 3 (M I ZP;M=Li, Na, K, Rb, Cs and Ag) solid electrolytes have been investigated. The crystallographic and electrochemical properties of M I ZP are compared with those of M II Zr 4 (PO 4 ) 6 (M II ZP). M I ZP and M II ZP crystallized in the NASICON- and β-Fe 2 (SO 4 ) 3 -structures: The crystal structure was determined by the size of the guest cation. The ionic conductivity of the NASICON-type compound was highly sensitive to the size of the guest (i.e., mobile) cation, whereas that of the β- Fe 2 (SO 4 ) 3 -type one was slightly size-dependent. This difference is expected to arise from the difference in the nature of site in which mobile cation is accommodated; a six coordination site of the NASICON-type structure and a four coordination one of the β-Fe 2 (SO 4 ) 3 -type structure. M I ZP showed ca. two or three orders higher conductivity than M II ZP, when they have almost the same ionic radius of mobile cation. AgZP, CdZP, and BaZP, in which mobile cations have high polarizability, showed high conductivities for the size of the mobile cations.

Multivalent cation conductive solid polymer electrolytes using photo-cross-linked polymers: II. Magnesium and zinc trifluoromethanesulfonate systems

Abstract Solid polymer electrolytes have been prepared consisting of magnesium or zinc trifluoromethanesulfonates [Mg(CF 3 SO 3 ) 2 or Zn(CF 3 SO 3 ) 2 ], ethylene carbonate, and propylene carbonate included in a photo-crosslinked polymer of poly-(ethylene glycol) diacrylate and reinforced by a porous polypropylene membrane. Their conductivities are 1.7×10 −4 S cm −1 at 1 mol% for Mg(CF 3 SO 3 ) 2 , 2.1×10 −4 S cm −1 at 4 mol% for Zn(CF 3 SO 3 ) 2 , and 4.3×10 −4 S cm −1 at 12 mol% for LiCF 3 SO 3 systems at 25°C. Their Arrhenius plots are almost linear between −5 and 55°C with 15–25 kJ mol −1 activation energy for conduction.

Carbon dioxide sensor using solid electrolytes with zirconium phosphate framework

Abstract We adopted divalent cationic conductor, MgZr4(PO4)6(MgZP), for the first time as the electrolyte of EMF type CO2 gas sensors, having the following cell construction: Pt|CO2, O2| metal carbonate | solid electrolyte |O2, Pt. In the case of sodium carbonate (Na2Co3), the sensor showed the Nernstian response to CO2 in pressure range between 1 and 100 KPa at temperatures from 400 to 500°C within a few minutes.

Reduction of carbon dioxide on partially-immersed Au plate electrode and Au-SPE electrode

Abstract The electrocatalytic reduction of carbon dioxide was carried out on two types of Au plate electrode; one was partially immersed in electrolyte solution containing CO2 and the other was completely immersed. Their surface areas in contact with the solution were kept equal, so that the difference in Faradaic efficiency for the reduction of CO2 to CO between the two types of electrodes was examined. The effects of surface treatments of the electrodes and electrolytes on the Faradaic efficiency were also investigated for each type of electrode. When the electrode surface was treated by electroplating Au on the Au plate, the partially-immersed electrode brought about a higher Faradaic efficiency for CO2 reduction than the completely immersed one both in 1 mol dm−3 KHCO3 and in 0.1 mol dm−3 (C2H5)4NClO4 aqueous solution at room temperature. The Au-SPE (SPE: solid polymer electrolyte) electrode was applied as a gas diffusion electrode to the reduction of CO2, and the Faradaic efficiency for CO production was compared with that obtained by the partially-immersed Au plate electrode. The Au-SPE electrode gave rise to a higher Faradaic efficiency than the partially-immersed electrode.

Carbon dioxide sensor using solid electrolytes with zirconium phosphate framework (2). Properties of the CO2 gas sensor using Mg1.15Zr4P5.7Si0.3O24 as electrolyte

Abstract We report EMF type, all solid-state CO 2 gas sensors using Mg 2+ ion conductor in Mg 1.15 Zr 4 P 5.7 Si 0.3 O 24 [MgZrPSiO], having a cell construction of Pt¦CO 2 , O 2 ¦metal carbonate (Na 2 CO 3 or K 2 CO 3 )∥solid electrolyte ¦O 2 , Pt. The sensors showed Nernstian response to CO 2 in pressure range between 0.5 and 60 kPa, at temperatures from 300 to 500 °C. A change in solid electrolyte from MgZr 4 (PO 4 ) 6 to MgZrPSiO brought about a considerable reduction in response time.