Rhodium(III) oxide

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Rhodium(III) oxide
Rhodium(III) oxide
3D model (JSmol)
ECHA InfoCard 100.031.666
EC Number 234-846-9
Molar mass 253.8092 g/mol
Appearance dark grey odorless powder
Density 8.20 g/cm3
Melting point 1,100 °C (2,010 °F; 1,370 K) (decomposes)
Solubility insoluble in aqua regia
+104.0·10−6 cm3/mol
hexagonal (corundum)
not listed
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Rhodium(III) oxide (or Rhodium sesquioxide) is the inorganic compound with the formula Rh2O3. It is a gray solid that is insoluble in ordinary solvents.


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:

Physical properties[edit]

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.[6]

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.[4]


The major application of rhodium oxides is in catalysts (e.g. hydroformylation reactions,[7] N2O production from NO,[8] or the hydrogenation of CO).[9]

See also[edit]


  1. ^ J. M. D. Coey "The crystal structure of Rh2O3" Acta Crystallogr. (1970). B26, 1876
  2. ^ H. L. Grube (1963). "The Platinum Metals". In G. Brauer (ed.). Handbook of Preparative Inorganic Chemistry, 2nd Ed. NY: Academic Press. p. 1588.
  3. ^ A. Wold et al. "The Reaction of Rare Earth Oxides with a High Temperature Form of Rhodium(III) Oxide" Inorg. Chem. 2 (1963) 972
  4. ^ a b S. Y. Kim et al. "Rhodium-oxide-coated indium tin oxide for enhancement of hole injection in organic light emitting diodes" Appl. Phys. Lett. 87 (2005) 072105
  5. ^ R. S. Mulukutla "Synthesis and characterization of rhodium oxide nanoparticles in mesoporous MCM-41" Phys. Chem. Chem. Phys. 1 (1999) 2027
  6. ^ S. Gottesfeld "The Anodic Rhodium Oxide Film: A Two-Color Electrochromic System" J. Electrochem. Soc. 127 (1980) 272
  7. ^ Pino, P.; Botteghi, C. (1977). "Aldehydes from olefins: cyclohexanecarboxaldehyde". Organic Syntheses. 57: 11. doi:10.15227/orgsyn.057.0011.
  8. ^ R. S. Mulukutla "Characterization of rhodium oxide nanoparticles in MCM-41 and their catalytic performances for NO–CO reactions in excess O2" Applied Catalysis A: 228 (2002) 305
  9. ^ P. R. Watson and G. A. Somorjai "The hydrogenation of carbon monoxide over rhodium oxide surfaces" Journal of Catalysis 72 (1981) 347