You would need a lot of catalyst because the water infrastructure to supply several hundred million people in the US is massive, let alone the rest of the world.

The problem with those catalysts is that the latter two are minor components of platinum and copper/nickel ores and despite how expensive they are, the extraction is only economically viable as part of other mining. Their supply can only grow as much as platinum extraction allows and demand is already pretty significant with environmental regulations often necessitating their use. Any more demand for them will cause their prices to rise dramatically and its a long way before they become profitable enough to mine on their own (flooding the platinum market in the process which has much higher yields from the ores).

it depends on the scale and the required amounts. If having a limited amount of catalyst wasn't such a big problem I suspect hydrogen power would have been much more economically viable.