No, there is not really anything you should apply. "Wound sealers" and the like just impair the tree's natural process of compartmentalizing wounds. You should remove the broken branch, leaving as clean an edge as possible and healthy bark around the edges. The biggest risk is rot, and possibly disease - a wound that large could eventually kill the tree. But willows are resilient and fast-growing, so it has a good chance of being fine.
Here is some more information from the Morton Arboretum https://mortonarb.org/plant-and-protect/tree-plant-care/plant-care-resources/trunk-wounds-and-decay/