Is vowing to pay the value of usurious interest, which was taken as a loan out of necessity, considered expiation for the sin of dealing in usury?

Borrowing with usurious interest is a grave sin that warrants a curse. The one who commits it must make sincere repentance, and if he is truthful in his repentance, Allah will forgive him. This is if the borrowing was not out of necessity. However, if it was out of necessity, then what is forbidden becomes permissible, as necessity permits the prohibited. Vowing to give the value of the interest for the sake of Allah the Almighty is not initially obligatory, and repentance suffices. However, after the vow, it becomes binding and must be fulfilled.