In the production of thermo emf the thermocouple produce the current without a cell so to know the
direction of current Seebeck made an arrangement of metals in series called thermoelectric series.
Antimony, Iron, Zinc, Silver, Lead, Copper, Platinum, Nickel, Bismuth
The direction of current is from earlier metal to the later one of thermoelectric series in cold junction
and as the separation between any two metals of the series increases the thermo emf also increases.
Eg. Iron-Copper provides high emf than Iron-Zinc.