An Investigation of the Electrochemistry of a Series of Metal Dioxides with Rutile‐Type Structure: MoO2, WO 2, ReO2, RuO2, OsO2, and IrO2

Six transition metal dioxides, MoO/sub 2/, WO/sub 2/, ReO/sub 2/, RuO/sub 2/, OsO/sub 2/, and IrO/sub 2/, have been examined as electrodes in H/sub 2/SO/sub 4/ solution. The oxides MoO/sub 2/, WO/sub 2/, ReO/sub 2/, and RuO/sub 2/ have broad current-potential profiles, indicating the formation of a surface layer which can exist over a range of compositions. Steady-state measurements of O/sub 2/ reduction showed catalytic activities which were low compared to common O/sub 2/ catalysts such as Pt, but of the same order as other oxide catalysts. Activities were lowest for WO/sub 2/ and ReO/sub 2/, which form resistive surface layers of a higher oxide. The only material studied which was sufficiently stable to allow measurement of both O/sub 2/ evolution and O/sub 2/ reduction was RuO/sub 2/. The current-potential profiles of OsO/sub 2/ and IrO/sub 2/ are characterized by distinct changes of oxidation state. These two oxides were not sufficiently stable to allow the measurement of O/sub 2/ reduction.