Palladium

Category: transition metal Atomic number: 46 Colour: silvery white Melting point: 1,555°C (2,831°F) Boiling point: 2,963°C (5,365°F) First identified: 1803

Brazilian miners in the eighteenth century occasionally found lumps of ouro podre, meaning ‘worthless gold’. This was a naturally occurring alloy of gold and palladium – the latter would also occasionally be found on its own, but it was not identified as an element until 1803. At the same time that William Wollaston discovered rhodium, precipitating it from platinum, he also produced a quantity of palladium. His immediate response to this was not to announce it in the usual manner to the scientific community.

Instead, he wrote a pamphlet eulogizing his discovery and put the metal up for sale at a shop in Gerrard Street, Soho. The leaflet was called ‘Palladium; or, New Silver’, and it offered this ‘In Samples of Five Shillings, Half a Guinea & One Guinea each’. It was only when a chemist challenged his claims, suggesting it was merely a platinum alloy, that he published his method.

Like rhodium, palladium is used in catalytic converters in cars; it is good at reducing unburned or partially burned hydrocarbons before they are emitted into the atmosphere. It is also widely used in the electronics industry; for instance, in ceramic capacitors (which are made of thin layers of ceramic and palladium). Ouro podre is prized more highly today than it was in the past – ‘white gold’ is a popular option for jewellery and is most often made from a gold and palladium alloy.

Palladium has more than once been hailed as providing a potential solution to our energy problems. In 1989, the American scientists Martin Fleischmann and Stanley Pons claimed they had electrolysed heavy water using a platinum anode and a palladium cathode and created energy from a nuclear fusion reaction. This would have been an amazing breakthrough, but it proved illusory, as the result could not be replicated.

Second, palladium could theoretically solve the problem of large-scale hydrogen storage (for future fuel cells). It has a weird quality: hydrogen molecules are absorbed into its structure, where they diffuse into the metal and are compressed into a space up to a thousand times smaller. Palladium is currently too expensive for this to be a useful property, but if a way could be found to create a cheaper compound, alloy or palladium product that behaves similarly (as a ‘hydrogen sponge’) it could be extremely useful in future.