Rhodium(III) oxide

Rh₂O₃ has been found in two major forms. The hexagonal form adopts the corundum structure. It transforms into an orthorhombic structure when heated above 750 °C.^[1]

Rhodium oxide can be produced via several routes:

• Treating RhCl₃ with oxygen at high temperatures.^[3]
• Rh metal powder is fused with potassium hydrogen sulfate. Adding sodium hydroxide results in hydrated rhodium oxide, which upon heating converts to Rh₂O₃.^[4]
• Rhodium oxide thin films can be produced by exposing Rh layer to oxygen plasma.^[5]
• Nanoparticles can be produced by the hydrothermal synthesis.^[6]

Rhodium oxide films behave as a fast two-color electrochromic system: Reversible yellow ↔ dark green or yellow ↔ brown-purple color changes are obtained in KOH solutions by applying voltage ~1 V.^[7]

Rhodium oxide films are transparent and conductive, like indium tin oxide (ITO) - the common transparent electrode, but Rh₂O₃ has 0.2 eV lower work function than ITO. Consequently, deposition of rhodium oxide on ITO improves the carrier injection from ITO thereby improving the electrical properties of organic light-emitting diodes.^[5]

Rhodium oxides are catalysts for hydroformylation of alkenes,^[8] N₂O production from NO,^[9] and the hydrogenation of CO.^[10]

• Rhodium
• Rhodium(IV) oxide
• Rhodium-platinum oxide