It has been thought about, and the US Supreme Court concluded that electrocution is not a humane method. Electrocution has not been used in the US for many years based on that decision. Firing squad and Guillotine are not bad. Forensic studies have also shown that hanging is pretty quick and painless, but it is more subject to operator error than the other two methods just mentioned. When messed up, hanging can be pretty gruesome and death results from strangulation rather than a quick snapping of the neck and severing of the spinal cord.Glue traps and spring traps are cruel and take a long time to kill. If you think about it, electrocution is fast and merciful without pain. That's how we humans prefer to kill each other when sentenced in court to die... why not apply the same principle to unwanted rodents.
John