Anatase TiO 2 structure has been widely studied as an electrode for Li-ion battery and as electrocatalyst for water splitting. Inserting guest species into TiO 2 has been demonstrated as an effective approach to tune the electronic structure and consequently improves the hydrogen evolution reaction (HER) catalytic activity. In this work, by using mesoporous TiO 2 electrodes, we have demonstrated the interplays between HER and Li-ion insertion in Water-in-Salt Electrolyte (WISE). Low C-rates favor the electro-catalytic reaction (HER), but the latter does also depend on the amount of Li in the electrode. Finally, this study guides the experimental conditions for an optimum functioning either in battery environment or in electro-catalysis.