Separating the covalent bond between hydrogen and O2 requires more energy than can be utilized by the hydrogen. Nobody has demonstrated an economical method yet.
I remember hearing something about that a while back. Some guy I think from Florida had come up with a way to do it using solar cells and some kind of catalyst. But then I heard that the military scooped up that idea. As soon as it came out. He was doing some kind of welding using a hydrogen Arc. Then again this was maybe 20 years ago or so. That’s all I know. I do know the Russians are working on it recently.