| Abstract
| - The structural features and catalytic activities of PtIr electrocatalysts derived from vertical IrO2 nanotubes(IrO2NT) of 1100 nm in height and 80−100 nm in diameter have been studied using scanning electronmicroscopy, transmission electron microscopy, X-ray powder diffraction, and cyclic voltammetry towardCOad and methanol oxidation. Lattice oxygen of IrO2NT is removed under high-vacuum thermal annealingto facilitate nucleation of 3−5 nm Ir grains and subsequent synthesis of PtIr catalyst on the tube walls.Interestingly, the apparent dimensions and orientation of IrO2NT can be preserved via pore generation inthe oxygen removal process. The tubular wall was transformed from a thin dense plate of IrO2(110)single crystal into a porous plate consisting of connected Ir grains that exhibit lattice fringes of the Ir{110} spacing with preferential orientation of Ir[11̄0] parallel to the IrO2NT growth direction. The amountof Ir being reduced, the Ir grain size, and the deposited Pt size strongly influence the surface area and thecatalytic activity. The Pt−Ir−IrO2NT catalyst reduced at 500 °C exhibits a significantly higher activitythan Pt−IrO2NT and Pt−IrNT in methanol oxidation and also a higher current density than that of aJohnson−Matthey PtRu catalyst in the high potential region.
- A PtIr structural electrocatalyst of high activity is synthesized using IrO2 thin-wall nanotubes grown in CVD. The IrO2 single-crystal wall constrains the Ir grains nucleated in lattice oxygen removal to a preferred direction so that the synthesized PtIr catalysts exhibit the structural characteristics of the Ir(110) plane.
|
