Concentrated (70%) hydrogen peroxide is very difficult to handle and chemically unstable under many conditions. Once it starts to decompose, the whole lot goes up very quickly, so storing large amounts is extra dangerous. Attempts to use hydrogen peroxide as a submarine drive failed for two reasons, the drive could never be made reliable and the amounts required (up to 200 tons) were too dangerous to store in a submarine. The Kriegsmarine somehow never appreciated that the storage issue alone made large hydrogen peroxide drive (Walter drive) U-boats unfeasible.

Torpedoes are another story. The amounts of hydrogen peroxide are much smaller and the torpedo is a one way device, so the drive machinery does not have to last long. The Germans had a Walter drive torpedo (G 7 a Klippfisch) ready for production in 1942, but it never went into production because the follow on model (G 7 ut Steinbutt) was better and supposed to be available soon afterwards, but, of course, it was severely delayed so in the end they never produced any Walter drive torpedo.

Regards,
SuperKraut