These are by far the oldest bi metallic coins I know of.
The model penny and halfpenny, Great Britain.
Desgined, struck and issued by Joseph Moore as a suggested improvement on the heavy copper coins in circulation at the time. These were produced in large numbers and were so much favoured by the public
The Royal Mint found it nessesary to disclaim any hand in their manufacture. The centres were to be made of silver to compensate for the small intrinsic copper value. The raised circle of beads around the centre was to enable them to be distinguished from other coins by touch.
The Model Penny, undated.
Generally believed to have been struck in 1848.
BMC2092

The Model Halfpenny, undated.
Generally believed to have been struck in 1848.
BMC2097

Coins referenced and information taken from English Copper, Tin and Bronze Coins in the British Museum 1558-1958, C W Peck.