Right, so with the perfect catalyst, you get as much energy out as you put in. With imperfect catalysts (anything real), you have to apply a voltage higher tha

Right, so with the perfect catalyst, you get as much energy out as you put in. With imperfect catalysts (anything real), you have to apply a voltage higher than when thermodynamics says is necessary to get the reaction to happen at an appreciable rate. The excess voltage cannot be recovered. The better the catalyst, the lower the excess voltage necessary, so a cheap and very effective catalyst essentially promises an efficient way to store and transport energy as hydrogen gas, which would be excellent.