Rhodium (Rh): Element 45, Properties, Uses and Facts

Rhodium is a chemical element with the symbol Rh, atomic number 45 and CAS number 7440-16-6, one of the six platinum group metals. Its primary (mined) supply was only 21.8 tonnes (701,000 troy ounces) in 2025, and 84.6% of the rhodium used that year went into exhaust catalysts, according to Johnson Matthey's PGM Market Report of May 2026.

What Is Rhodium?#

Rhodium is a hard, silvery, highly reflective transition metal and the most car-dependent of the six platinum group metals. Autocatalysts took 84.6% of rhodium demand in 2025, against 81.1% for palladium and 41.5% for platinum (Johnson Matthey). It belongs to the platinum group metals, which occur in the same ores and are refined together.

Rhodium Quick Facts#

Rhodium's atomic number is 45, its standard atomic weight is 102.90549 and its CAS number is 7440-16-6. The table lists its identity data.

Rhodium Among the Platinum Group Metals#

Rhodium is one of six platinum group metals, alongside platinum, palladium, iridium, ruthenium and osmium. It sits between ruthenium and palladium in period 5, above iridium in group 9, and forms with its two period-5 neighbors the light triad at 12.0 to 12.4 g/cm³.

Rhodium Properties#

Rhodium has a density of 12.423 g/cm³ at 20 °C and melts at 1,964 °C (2,237 K, 3,567 °F), among the three lightest of the six PGMs. It boils at 3,695 °C (3,968 K) and turns superconducting only at 325 µK, the lowest transition temperature of any element. Each value is expanded on rhodium properties.

Physical Properties: Density, Melting Point and Conductivity#

Rhodium is the best thermal conductor of the platinum group metals at 150 W/(m·K), with iridium a close second at 147. Liquid rhodium falls to 10.7 g/cm³ at its melting point, as detailed on rhodium density. The table compares rhodium with iridium and platinum.

Resistivity needs its temperature. Rhodium's 43.3 nΩ·m is a 0 °C value; at 20 °C it is about 47.3 nΩ·m, level with iridium, so "best electrical conductor of the PGMs" is not established at a common temperature.

Rhodium's melting point sits between iridium's and platinum's; boiling point and latent heat are on rhodium melting point.

Electron Configuration and Oxidation States#

Rhodium's ground-state electron configuration is [Kr] 4d⁸ 5s¹, and its common oxidation state is +3, with a full observed range of −3 to +7. Simple filling order would predict 4d⁷ 5s². Rhodium(I), square-planar, and rhodium(III), octahedral, carry essentially all rhodium catalysis. The shell diagram is on rhodium electron configuration.

Is Rhodium Magnetic?#

Rhodium is paramagnetic, with a molar magnetic susceptibility of +111.0 × 10⁻⁶ cm³/mol at 298 K, weaker than platinum's (+201.9) or palladium's (+567.4) but stronger than ruthenium's, iridium's or osmium's. No pure platinum group metal is ferromagnetic. Measurement detail is on is rhodium magnetic.

Where Rhodium Comes From#

Nearly all rhodium comes from the UG2 Chromitite layer of South Africa's Bushveld Complex, as a co-product of platinum and palladium mining; no mine produces rhodium on its own. South Africa supplied 566,000 of the 701,000 oz of 2025 primary supply, or 80.7% (Johnson Matthey data). Ores are covered on rhodium occurrence.

Rhodium Occurrence and Ores#

Northam Platinum's Mineral Resources statement (30 June 2025) puts rhodium at 7.9-11.4% of the 4E metal content (platinum, palladium, rhodium and gold) in UG2 ore, against 2.4-7.4% in Merensky Reef ore. In the United States, Montana's Stillwater J-M Reef reports platinum and palladium only, and rhodium is essentially absent from its primary reporting. Johnson Matthey's North America line, which includes Canada, shows 15,000 oz of rhodium in 2025.

World Rhodium Production#

World rhodium primary supply was 21.8 tonnes (701,000 oz) in 2025, or 31.5 tonnes (1,013,000 oz) including recycled metal, according to Johnson Matthey's PGM Market Report of May 2026. The "about 30 tonnes a year" often quoted is the combined figure, not mine output. The table sets rhodium beside platinum, each figure with its source.

On the Johnson Matthey basis, platinum primary supply was 7.9 times rhodium's. Rhodium demand exceeded combined supply by 50,000 oz, a third consecutive deficit.

Rhodium Discovery and History#

Rhodium was isolated in 1803 and its discovery published in 1804 by William Hyde Wollaston, who found it in South American platinum ore alongside palladium. After dissolving the ore in aqua regia and precipitating the platinum, he recovered palladium and rhodium from the rose-tinted solution with zinc; a hot-ethanol wash left a rose-red sodium chlororhodate salt, which zinc reduced to metal. The paper appeared in the Philosophical Transactions of the Royal Society in 1804.

The name comes from the Greek rhodon, "rose", after the rose-red color of the sodium hexachlororhodate salt. The full account is on rhodium discovery.

Rhodium Uses#

Rhodium's main uses are three-way autocatalysts, electroplating and high-temperature thermocouples, joined by chemical and glassmaking catalysts. Johnson Matthey splits 2025 rhodium demand into the five end uses listed below.

• Automotive catalysts: 899,000 oz
• Chemical catalysts: 91,000 oz
• Glass manufacturing: 38,000 oz
• Other uses: 26,000 oz
• Electrical and electronics: 9,000 oz

Each application is described on rhodium uses.

Autocatalysts#

Rhodium became commercially important through the three-way automotive catalytic converter, commercialized by Volvo on 1977 California-specification models, where rhodium reduces NOx to nitrogen. Its 84.6% autocatalyst share in 2025 fell just below the 85-95% band Johnson Matthey quotes for it.

Rhodium Plating#

Rhodium electroplating has been a standard corrosion-resistant, reflective finish on white gold and sterling silver jewelry since the 1940s, a plating fact rather than purchase advice. Umicore's RHODUNA 271 sulfate electrolyte runs at 2 g/L rhodium and deposits a bright, crack-free layer of 99.9 wt% rhodium at about 800 HV.

Other Industrial Uses#

Platinum-rhodium thermocouples measure temperatures up to 1,800 °C, with especially good stability between 1,300 and 1,800 °C; the IEC 60584 types are S (platinum-10% rhodium), R (13% rhodium) and B (30% against 6% rhodium). Rhodium-platinum gauze has replaced pure platinum gauze in Ostwald-process nitric acid plants since the early 1900s.

Rhodium Compounds#

Rhodium's commercial chemistry starts from rhodium(III) chloride trihydrate (CAS 13569-65-8, per the Wikipedia compound record), the soluble form used to make plating baths and catalysts; the anhydrous salt (CAS 10049-07-7, PubChem CID 24872) is insoluble. More are covered on rhodium compounds.

Is Rhodium Toxic?#

Soluble rhodium compounds carry an occupational exposure limit of 0.001 mg/m³ as rhodium (OSHA PEL and NIOSH REL), half the 0.002 mg/m³ limit for soluble platinum salts and the strictest PGM limit on that basis. ACGIH sets its own value at 0.01 mg/m³. Metal fume and insoluble compounds, the class of metallic rhodium, carry 0.1 mg/m³. Rhodium(III) chloride is flagged "suspected of causing genetic defects" (H341) in 56.5% of ECHA C&L Inventory notifications. Health data are collected on rhodium toxicity.

Rhodium Isotopes#

Rhodium is the only platinum group metal with a single natural isotope, rhodium-103, at 100% abundance; among the precious metals only gold shares this. Its atomic weight, 102.90549(2), is therefore known to eight significant figures and carries no CIAAW variability flag. Artificial isotopes are listed on rhodium isotopes.

Rhodium Price, Investing and Scrap#

Rhodium's price, investment options and scrap value each have a dedicated page. Dealers and producers quote rhodium without a futures contract, and its supply, demand and volatility are analyzed under the rhodium market.

Rhodium Price Today#

DailyPlatinum publishes a live rhodium price page in troy ounces, grams and kilograms, with the quoting dealer named. The live value sits on rhodium price today.

Dated past moves are plotted on the rhodium price chart.

Investing in Rhodium#

Rhodium investment is limited to bars, powder and specialist dealers, with risks that differ from platinum and palladium. Products and risks are compared under rhodium investment, rhodium powder specifications are listed separately, and weights convert on the troy ounce converter.

Selling Rhodium Scrap#

Rhodium scrap value is driven mainly by spent autocatalysts, the only recycling stream in Johnson Matthey's balance (312,000 oz in 2025). Refiners pay on assayed content, explained under rhodium scrap value.

Rhodium vs the Other Platinum Group Metals#

Rhodium sits between ruthenium and palladium in the periodic table and in most physical properties. The table compares the six metals.

Head-to-head pages cover the metals rhodium is most often weighed against: rhodium vs platinum, rhodium vs gold and rhodium vs sterling silver.

Rhodium FAQ#

Is rhodium rarer than platinum?#

Yes. Rhodium primary supply was 701,000 oz in 2025, against 5,557,000 oz for platinum, 7.9 times more, on Johnson Matthey's May 2026 figures. Gold is compared on rhodium vs gold.

Is rhodium toxic in jewelry?#

Rhodium plating is metallic rhodium, in the insoluble class with a 0.1 mg/m³ workplace limit, not the soluble-compound class at 0.001 mg/m³. Those limits cover airborne exposure at work, not skin contact with a plated ring.

What is the cost of 1 gram of rhodium?#

One gram of rhodium costs the troy-ounce quote divided by 31.1034768, the grams in a troy ounce. The live value, from a named dealer, is on rhodium price per gram.

How much is 1 ounce or 1 pound of rhodium worth?#

One pound of rhodium is worth 14.583 times the troy-ounce quote, because an avoirdupois pound (453.59 g) holds 14.583 troy ounces. The ounce quote itself is on rhodium price today.

Why do jewelers put rhodium over sterling silver?#

Jewelers plate sterling silver with rhodium for a hard, bright, corrosion-resistant surface. The two metals are set side by side on rhodium vs sterling silver.

What dissolves rhodium?#

Rhodium metal resists nitric acid completely and dissolves only slightly in aqua regia. Refiners use molten sodium bisulfate, hot concentrated sulfuric acid or high-temperature chlorination.

Is rhodium priced higher than platinum?#

Rhodium averaged above platinum in each year from 2021 to 2024 and in the 2025 estimate of USGS's annual-average series (Engelhard unfabricated metal, February 2026). Current levels are compared on rhodium vs platinum.

What are 5 uses for rhodium?#

The five main uses of rhodium are listed below.

1. Three-way automotive catalysts
2. Chemical catalysts
3. Glassmaking equipment
4. Jewelry and industrial electroplating
5. Platinum-rhodium thermocouples