I’m no scientist, but I’d like to learn the definition of the word “reduce” as used in this quote:
“. . . is capable of reducing protons into hydrogen,” Katarzyna Sokól, first author of the study, said in a statement.
Need electrons? Hydrogen is one proton, one electron.
Reduce means adding electrons. Protons are hydrogen atoms without the electron. Adding the electron gives you hydrogen. The electron comes from oxygen in water being converted to oxygen. Overall it is a redox reaction of water being converted to hydrogen and oxygen by reduction of the hydrogen and oxidation of the oxygen.
Thermodynamically that is going uphill so you need to input energy. That is where the light comes in.
In chemistry, the word “reduce” refers to the change in the charge state of an ion, atom or molecule trough the gain or loss of one or more electrons. In the case of a naked proton, it has a charge of +1. Pairing it with an electron creates a hydrogen atom, with a charge of zero.
Since the charge of the particle the proton is part of went from +1 to zero, it is considered to have been reduced. The chemical term for the opposite of reduction is oxidation.
https://simple.wikipedia.org/wiki/Reduction_(chemistry)
Reduced, as in splitting away the one element combined with another element which together form a chemical compound. The reduction is the process of separating the different chemical elements into individual camps, while at the same time neutralizing electrical charge of those atoms.