Traditionally rhodium has been applied to the points of gold fountain pen nibs for aesthetic reasons and to enhance wear resistance: Improvements in or relating to gold pens (1935)).
Today the major use of rhodium is in catalytic converters for cars to oxidise carbon monoxide and unburnt hydrocarbons, and to reduce nitrogen oxides in exhaust gases (Rhodium-Containing Catalysts For Automotive Emissions Treatment (2016)).
Rhodium is also used in catalysis in the chemical industry, for making acetic acid (Reaction Product Of Rhodium-Catalyzed Methanol Carbonylation (2008)), and hydrogenation reactions (Process For Hydrogenation Of Di(4-Aminophenyl)Methane With A Rhodium Catalyst (1974)).
It is used for crucibles (Apparatus For The Preparation Of Alkali Metal Monofluorhosphates (1993)), thermocouple elements (Platinum-Rhodium Vs. Platinum Thermocouple Having Base Metal Compensating Leads (1972)), and high performance lamp reflectors (Electric discharge lamp with phosphorcoated rhodium reflector (1957)). It is used as an electrical contact material (A rhodium electrical contact of a switch particularly a reed switch (1980)) as it has a low electrical resistance and is highly resistant to corrosion.
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All patent information has been obtained from Espacenet (European Patent Office).