I've read that the trimmed peels and ends of vegetables like onion, carrots and celery can be tossed in a bag in the freezer and kept until you want to make chicken, vegetable or beef broth. Could this include the brown papery peels from onions? I would probably have to add some actual chopped carrots, onions and celery Everything would be strained out when the broth is finished.
Never tried it but I can't imagine the brown papery part of the onion would add much flavor to your stock. Beware of dirt trapped in the nooks and crannies that may work its way into the final product.
Also, be careful of freezing your trimmings; some veggies may need to be blanched prior to freezing to avoid turning mushy when defrosted.