Pure hydrogen peroxide was once used as a rocket fuel. 3% is cheap enough, but not the steralant found with 7-1/2% (available through hospital supplies), and that likely to get costly. Hydrogen peroxide is also used to aid in seed germination. I suspect that that may be related to why not used in brewing. I think there is a reason beyond just cost, but nowhere seems to be utilized in relation to brewing. I refer to the taste as soapy, but that is due to the bubbling action mainly. Makes a great mouth wash, only have had two cavities in 62 years.