Li-ion insertion coupled solar HER

This paper studies how electrochemically inserting or extracting lithium ions in TiO 2 can trigger and orient solar hydrogen evolution reaction. Li x TiO 2 is envisioned as a photo(electro)catalyst, whose rejuvenation can be achieved by in situ potential control. The investigations are conducted in a half-battery cell design where a mesoporous, anatase TiO 2 thin film (negative electrode candidate) is deposited onto a transparent conducting oxide (FTO) substrate, water-in-salt (WiSE) is used as an electrolyte. Changing the state of charge of the working electrode material, will adjust the ratio between the Li-rich phase (Li 0.5 TiO 2 blue) and the Li-poor phase (Li 0.01 TiO 2 uncolored), which will tune the opto-electronic properties of the material, potentially changing the light-matter interaction. The impact of light on the interplay between hydrogen evolution reaction and lithium insertion/extraction in TiO 2 is investigated using classical electrochemical characterizations inspired from both battery and photoelectrode communities. With a minimum of Li-rich phase solar hydrogen is produced at the working or at the counter electrode while lithium in photo-extracted of the Li-rich phase to reform TiO 2 . Graphical Abstract This paper deals with the interplay between hydrogen evolution reaction and lithium insertion/extraction in TiO 2 under light. To investigate this behavior, mesoporous, crystalline TiO 2 thin films, synthesized by the sol-gel chemistry, have been investigated as working electrodes of a Li-ion battery to control in situ its chemical composition by inserting Li + to study the photo(electro)catalytical decomposition of water in WiSE.