Rinse the split peas and place in the Instant Pot. Add the vegetable broth, onion, celery, garlic, thyme and black pepper.
Close and lock the lid. Select high pressure according to manufacturer's instructions; set timer for 15 minutes. Allow 10 to 15 minutes for pressure to build.
Release pressure carefully using the quick-release method according to manufacturer's instructions, about 5 minutes.
Open the pot and stir in additional seasonings if desired. Serve hot.