I tested a thermocouple made of pure iron. This one works with one metal instead of two different metals.
The thermoelectric voltage is in the range 1...10µV / °K. A solid plate of pure iron contacted with two thin wires made of pure iron. Heating one end oft the plate generates a thermoelectric voltage. It doesn't seem that two different metals are needed to build a thermocouple!
I think such an exotic thermocouple is useful as temperature sensor. A finger pressure heats the iron plate. The thermoelectric voltage triggers a switch (perhaps to open a secret door).
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