Kenzo Matsuki

Oxygen reduction electrocatalysis on some manganese oxides

Abstract Cathodic oxygen reduction on some manganese oxides in alkaline solution was examined by using a rotating ring−disk electrode ( rrde ) and a Teflon-bonded electrode technique. The activity of γ-MnO 2 for cathodic oxygen reduction was larger than that of γ-MnOOH at the potential below —200 mV vs Hg/HgO ( rrde ). The electrochemical activity of carbon-supported γ-MnOOH Teflon-bonded electrode, on the contrary, was extremely high compared with that of γ-MnO 2 . It was found that the γ-MnOOH in the Teflon-bonded electrode was thermally decomposed mainly to Mn 3 O 4 and Mn 5 O 8 in the course of the electrode preparation. These facts suggest that one of the causes of the high activity of the Teflon-bonded electrode containing γ-MnOOH is manganese oxides with distortion which have been produced in the electrode by the thermal decomposition of γ-MnOOH.

Oxygen reduction catalysis of Mn–Co spinel oxides on agraphite electrode in alkaline solution

Binary Mn–Co spinel oxides have been applied as catalysts for oxygen reduction on graphite electrodes in alkaline solution. Oxides with cation deficiencies were obtained by heating the homogeneous citrate and carbonate precursors with different atomic ratios of Mn/Co (0–1.5) at 400–600 °C in an O 2 atmosphere. The oxygen reduction was studied by a rotating ring-disk electrode method, and these oxides loaded onto graphite showed catalytic activity for the direct four-electron reduction of oxygen. It is considered that cation deficiencies in the oxide catalysts contribute to the appearance of catalytic activity.

Preparation of Superconducting Y?Ba?Cu?O and Bi?Pb?Sr?Ca?Cu?O Compounds by Chelating Method

Superconducting Y?Ba?Cu?O (YBCO) and Bi?Pb?Sr?Ca?Cu?O (BPSCCO) compounds were prepared by a chelating method with various chelating agents, such as nitrilotriacetic acid (NTA), hydroxyethylethylenediaminetriacetic acid (HEDTA) and ethylenediaminetetraacetic acid (EDTA). Above 600?C, the precursors YBCO and BPSCCO turned into a mixture of metal oxides and BaCO3, which finally transformed into the almost single phase of YBCO at 850?930?C and into the high-Tc phase of BPSCCO at 840?C. The critical current densities of YBCO and BPSCCO in blocks of 1*4*15 mm3 were estimated to be as high as 350 and 500 A/cm2 at 77 K, respectively.

SEM studies of electrolytic manganese dioxide

Abstract Manganese dioxide is deposited on the anode from MnSO4 solution (95°C) containing H2SO4 and another acid, such as HCl and HNO3. X-ray diffraction reveals a γ-MnO2 structure. Addition of 0.1 M HCl or HNO3 to the MnSO4 solution containing H2SO4 results in lower cell voltage. Scanning electron micrographs of these surface deposits show that, in the case of a MnSO4 + H2SO4 solution, a so-called fibrous microstructure was observed and crystal size became greater when the hydrochloric acid was added up to about 0.1 M.

Thermal behaviour of dicarboxylic acids. Determination of melting points by DTA

Abstract The melting points of dicarboxylic acids HOOC(CH 2 ) n COOH have been determined using DTA. The melting points obtained, except that for fumaric acid, are in close agreement with the literature values. All the acids are anhydrous; the decomposition of the acids with n = 0–2 in an air atmosphere takes place in two steps and that of the other acids ( n = 3–8 and maleic and fumaric acids) involves a single step.

SEM/EDX analysis of electrolytic manganese dioxide deposits

Abstract The morphology change of electrolytic manganese dioxide deposits and their surface analysis were investigated using SEM and EDX. Manganese dioxide was deposited on the anode from a manganese sulphate solution (95°C) containing H2SO4 or both H2SO4 and HCl at current densities ranging from 1 to 3 A dm−2. In the course of the electrolysis, a rapid increase in the anodic potential was observed after a certain electrolysis time, depending upon current densities and bath composition. Some deposits, rich in sulphur, were observed on the surface of the fine manganese dioxide deposits which were obtained before and after the abrupt potential change. These observations suggest that the participation of the SO2−4 ion in the solution is important in the anodic deposition process of electrolytic manganese dioxide.

In situ measurement of free radicals in manganese dry cells

Abstract In situ ESR spectra of carbon in manganese dry cells were measured by an L-band ESR spectrometer during discharge. A part of a zinc anode sheet was cut in order to make a microwave pass through the cathode. The ESR signal obtained was assigned to the free radical in the carbon. After the beginning of discharge, the signal intensity of the free radical started to decrease and then reached its minimum, followed by a gradual increase. A definitive difference in g -factor was found before and after the minimum intensity, suggesting the generation of a new type of radical. ESR imaging showed that the decrease in the intensity of free radical occurred at zinc anode side.

Oxygen reduction electrocatalysis on some oxide perovskites in alkaline solution.

アルカリ水溶液中での酸素カソード還元の電極触媒として, ペロブスカイト型構造を有するLa0.6Sr0.4MnO3 と CaMnO3-xをとりあげ, カーボンを主体としたポリ (テトラフルオロエチレン) (PTFE) 結着型ガス拡散電極に混合して用いたときの電極触媒特性を, 9mol・dm-3NaOH,85℃中におけるカレントインターラプター法による分極測定と, X線回折, SEMおよびXPSなどによる電極のキャラクタリゼーションにより調べた。これらの複合酸化物はアルカリ水溶液中において, 化学的および電気化学的にも安定であり, ガス拡散電極の酸素還元に対する活性を高めるのに有効であった。La0.6Sr0.4MnO3と比較して, CaMnO3-xの活性の持続性は非常に大であった。用いるカーボンの種類によって, 複合酸化物の酸素還元に対する最適配合比が異なるが, この最適混合比において, カーボン粉とガス拡散電極との比表面積の差から求めたカーボンの比表面積損は, カーボンの種類に関係なく約50%であった。分極前後における電極のX線回折やXPS測定から, 酸素カソード還元のさいに, CaMnO3-xやLa0.6Sr0.4MnO3の電解液と接する表面の格子酸素が, カソード還元を受けて酸素欠損を生ずることが考えられた。