Copper is really soft theres not too much to do your coins are most likely "toasted" . I've never been able to clean them without adverse effects. Now I just soak them in water for a few hours, gently rinse them, let them dry thoroughly and once any loose grit is off them I apply a light coating of Vaseline to keep them from further oxidization. I don't see how H202 would help. Oxidization is the enemy and the free oxygen molecules from the h202 from a chemical standpoint further damage your coin. I'll try it on some old coins as it sounds like its working for people but chemistry tells me otherwise.
I've been working on a water cleaning system. I place the coin on a pedestal in a bucket. Get a two liter and put a pin hole in the cap until it drips very slowly. Hang the two liter bottle from your shower or somewhere high where you won't make a mess accidentally (basement, garage). Aim the drip so it hits the coin consistently. The drips falling from a few feet will clean loose grit from the coin without damage from rubbing. In theory one would use distilled water as tap water has chlorine and other free radicals that interact with the coin but we are not talking valuable coins here. I am more environmental so I just pour the water back in the 2 liter and reuse it. Flip the coin and repeat. This is just me reinventing the wheel. Its slow so you set it up while you are out running errands or working.
