過レニウム酸イオンの電気化学的還元

水溶液からの金属レニウムの電解析出に関する研究 (第1報)

抄録

Deposits were obtained on the platinum cathode from the perrhenate solution under potentiostatic conditions and electroreduction process of perrhenate ion was studied. Polarization study, thermal and X-ray diffraction analysis of the deposits showed the stepwise reduction of perrhenate ion in two stage: the formation of the partly-reduced rhenium oxide film on the cathode, and the reduction of this film to rhenium metal.
Within the cathode potential range more positive than -0.40V vs S. C. E., rhenium oxides of a lower valence state were formed on the cathode and their compositions depended on the cathode potential. With increasing the cathode potential more positive than -0.40 V vs S. C. E., the black deposits containing rhenium of higher oxidation state were obtained, and the composition of the deposits varied to rhenium dioxide with increasing the overpotential. Further, pH of the solution considerably affected the cathode current efficiency of oxide deposition. The optimum pH value for rhenium oxide deposition was found to be 1.65 and the current efficiency decreased with decreasing the pH of the solution.
In the potential range more negative than -0.40 V vs S. C. E., metallic rhenium containing the appreciable amount of lower oxide deposited, which was accompanied by simultaneous hydrogen evolution. Comparison of the conditions which determined the cathode current efficiencies of rhenium metal and lower oxide depositions indicated that metallic rhenium deposition appeared to proceed with preceding lower oxide formation.