The best solvent to split water is water. Water splitting means 2H2O -> O2 + 2H2 and includes water oxidation. Ionic liquids (organic materials) are much easier to oxidize than water.
Fundamentally, water splitting requires medium with high oxidation and reduction potential of anion and cation, respectively. Quaternary cation especially organic ammonium, imidazolium cation or others has high reduction potential. Complex anion especially BF4-, PF6-, bis(trifluoromethylsulfonyl)imide etc anions have high oxidation potential. The ionic liquids containing these ions would fundamentally be suitable for your purpose. There are also couple of refs available. So you may try..
I do not know if this could help you. My research group is able to design custom-made ionic liquids for a given application. If you need more information about it, don't hesitate to contact me.
So what you generally are looking for is a new IL which will boost your catalyst. I would generally avoid BF4 and PF6 based ILs, since they decompose in water, releasing HF, which might actually be one of the effects the authors of the paper see.
Yes, using a certain IL as medium, the proton reduction step is improved.
the authors textually concluded: '' The use of an ionic liquid/aqueous solution enhances the observed catalytic rate by more than a factor of 50, compared to a similar acid in a traditional organic solvent''.
have you previuosly worked with an IL? can you recommend one ?