2D Porous TiO₂ Single-Crystalline Nanostructure Demonstrating High Photo-Electrochemical Water Splitting Performance

Porous single crystals are promising candidates for solar fuel production owing to their long range charge diffusion length, structural coherence, and sufficient reactive sites. Here, a simple template-free method of growing a selectively branched, 2D anatase TiO₂ porous single crystalline nanostructure (PSN) on fluorine-doped tin oxide substrate is demonstrated. An innovative ion exchange-induced pore-forming process is designed to successfully create high porosity in the single-crystalline nanostructure with retention of excellent charge mobility and no detriment to crystal structure. PSN TiO₂ film delivers a photocurrent of 1.02 mA cm^-2 at a very low potential of 0.4 V versus reversible hydrogen electrode (RHE) for photo-electrochemical water splitting, closing to the theoretical value of TiO₂ (1.12 mA cm^-2 ). Moreover, the current-potential curve featuring a small potential window from 0.1 to 0.4 V versus RHE under one-sun illumination has a near-ideal shape predicted by the Gartner Model, revealing that the charge separation and surface reaction on the PSN TiO₂ photoanode are very efficient. The photo-electrochemical water splitting performance of the films indicates that the ion exchange-assisted synthesis strategy is effective in creating large surface area and single-crystalline porous photoelectrodes for efficient solar energy conversion.