De or het thermo-element?

The correct Dutch article is:

het thermo-element

Rule Words ending in -ment: usually het. See the rule
Meaning (Dutch) (natuurkunde, elektrotechniek) element waarin d.m.v. een temperatuurverschil een elektrisch spanningsverschil ontstaat

How to use thermo-element

the thermo-elementhet thermo-element
this thermo-elementdit thermo-element
that thermo-elementdat thermo-element
our thermo-elementons thermo-element
your thermo-elementjouw thermo-element
every thermo-elementelk thermo-element
which thermo-element?welk thermo-element?
a big thermo-element / the big thermo-elementeen groot thermo-element, het grote thermo-element

Meaning, plural, diminutive, pronunciation and translations: WikiWoordenboek (Dutch Wiktionary) (CC BY-SA 4.0). Example sentences: Tatoeba (CC BY 2.0 FR).