Is it permissible to pay off debts from zakat money without the husband's knowledge?

It is not permissible for an agent to disobey the principal. Therefore, you are not allowed to spend the entrusted money to pay off your debt. You can, however, review the matter with him and advise him to pay off the debt first.

If your husband's debt is due and he has no money other than this, then his action is incorrect. You should explain the situation to him, and if he does not respond, then inform the creditors.