The theory of excess energy is nonsense. Especially when it comes to solar, which you would optimize to use peak capacity at peak production times. Pumped hydro is vastly more efficient than electrolysis to produce hydrogen, and it doesn’t require us mining. Any precious metals.
Since the point of this research is to reduce the impact of mining, you would think that mining for the catalyst material would have been considered. Those metals are not readily found and bodies of water, for example.