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.{{cite journal | last=Coey | first=J. M. D. | title=The crystal structure of Rh₂O₃ | journal=Acta Crystallographica Section B: Structural Crystallography and Crystal Chemistry | publisher=International Union of Crystallography (IUCr) | volume=26 | issue=11 | date=1970-11-01 | issn=0567-7408 | doi=10.1107/s0567740870005022 | pages=1876–1877}}

Rhodium oxide can be produced via several routes:

• Treating RhCl₃ with oxygen at high temperatures.{{cite book|editor=G. Brauer|author=H. L. Grube|chapter=The Platinum Metals|title=Handbook of Preparative Inorganic Chemistry, 2nd Ed.|publisher=Academic Press|year=1963|place=NY|page=1588}}
• Rh metal powder is fused with potassium hydrogen sulfate. Adding sodium hydroxide results in hydrated rhodium oxide, which upon heating converts to Rh₂O₃.{{cite journal | last=Wold | first=Aaron | last2=Arnott | first2=Ronald J. | last3=Croft | first3=William J. | title=The Reaction of Rare Earth Oxides with a High Temperature Form of Rhodium(III) Oxide | journal=Inorganic Chemistry | publisher=American Chemical Society (ACS) | volume=2 | issue=5 | year=1963 | issn=0020-1669 | doi=10.1021/ic50009a023 | pages=972–974}}
• Rhodium oxide thin films can be produced by exposing Rh layer to oxygen plasma.
• Nanoparticles can be produced by the hydrothermal synthesis.{{cite journal | last=Mulukutla | first=Ravichandra S. | last2=Asakura | first2=Kiyotaka | last3=Kogure | first3=Toshihiro | last4=Namba | first4=Seitaro | last5=Iwasawa | first5=Yasuhiro | title=Synthesis and characterization of rhodium oxide nanoparticles in mesoporous MCM-41 | journal=Physical Chemistry Chemical Physics | publisher=Royal Society of Chemistry (RSC) | volume=1 | issue=8 | year=1999 | issn=1463-9076 | doi=10.1039/a900588i | pages=2027–2032| bibcode=1999PCCP....1.2027M}}

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.{{cite journal | last=Gottesfeld | first=S. | title=The Anodic Rhodium Oxide Film: A Two-Color Electrochromic System | journal=Journal of the Electrochemical Society | publisher=The Electrochemical Society | volume=127 | issue=2 | year=1980 | issn=0013-4651 | doi=10.1149/1.2129654 | page=272}}

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.{{cite journal | last=Kim | first=Soo Young | last2=Baik | first2=Jeong Min | last3=Yu | first3=Hak Ki | last4=Kim | first4=Kwang Young | last5=Tak | first5=Yoon-Heung | last6=Lee | first6=Jong-Lam | title=Rhodium-oxide-coated indium tin oxide for enhancement of hole injection in organic light emitting diodes | journal=Applied Physics Letters | publisher=AIP Publishing | volume=87 | issue=7 | date=2005-08-15 | issn=0003-6951 | doi=10.1063/1.2012534 | page=072105| bibcode=2005ApPhL..87g2105K | url=https://scholarworks.unist.ac.kr/handle/201301/7384}}

Rhodium oxides are catalysts for hydroformylation of alkenes,{{cite journal|last1=Pino|first1=P.|last2=Botteghi|first2=C.|title=Aldehydes from olefins: cyclohexanecarboxaldehyde|journal=Organic Syntheses|date=1977|volume=57|page=11|doi=10.15227/orgsyn.057.0011}} N₂O production from NO,{{cite journal | last=Mulukutla | first=Ravichandra S | last2=Shido | first2=Takafumi | last3=Asakura | first3=Kiyotaka | last4=Kogure | first4=Toshihiro | last5=Iwasawa | first5=Yasuhiro | title=Characterization of rhodium oxide nanoparticles in MCM-41 and their catalytic performances for NO–CO reactions in excess O₂ | journal=Applied Catalysis A: General | publisher=Elsevier BV | volume=228 | issue=1–2 | year=2002 | issn=0926-860X | doi=10.1016/s0926-860x(01)00992-9 | pages=305–314}} and the hydrogenation of CO.{{cite journal | last=Watson| first=P |first2=G. A. |last2=Somorjai| title=The hydrogenation of carbon monoxide over rhodium oxide surfaces | journal=Journal of Catalysis | publisher=Elsevier BV | volume=72 | issue=2 | year=1981 | issn=0021-9517 | doi=10.1016/0021-9517(81)90018-x | pages=347–363| url=https://escholarship.org/uc/item/861193km| url-access=subscription }}

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

{{reflist}}

{{Rhodium compounds}}

{{Oxides}}

Category:Transition metal oxides

Category:Rhodium(III) compounds

Category:Sesquioxides

Category:Chromism