I got some black mucous expelled from my throat this morning. what could it be? can it lead to bad breath? what can be done to cure it?

Anything: Can be almost anything from postnasal drip to tonsiliths to pneumonia. Try Mucinex (guaifenesin) to see if it improves. If not it may need to be cultured.

Smoker?: If you are a smoker, it cold be that, otherwise it's difficult to say. Could be blood or some other dark material. You may want to see your dentist to examine it.

Do you smoke?: It could be the byproducts of smoke mixing with mucus. It could be clotted blood mixing with the mucus. It might be a good idea to have it checked out.