First of all, hydrogen peroxide is a good teeth whitening element, you can even use it as a mouthwash, but you must never use more that a 3% solution, otherwise your oral health is in trouble . Anything equals to 3% or less is good.
Baking Soda is an abrasive substance, so you should brush with it only one or 2 time a week and even less frequently if you have sensitive teeth.
You can mix both of them, but you should do it correctly,
Check this baking soda teeth whitening full report well explained.
You will understand the whole subject in absolute details.
Search keyword for post:
baking soda teeth whitening safe
is it safe to use baking soda to whiten teeth
bicarbonate of soda teeth whitening safe
bicarbonate soda teeth whitening safe
baking soda and peroxide to whiten teeth safe