Solution-processed GaSe nanoflake-based films for photoelectrochemical water splitting and photoelectrochemical-type photodetectors

Gallium selenide (GaSe) is a layered compound, which has been exploited in nonlinear optical applications and photodetectors due to its anisotropic structure and pseudo-direct optical gap. Theoretical studies predicted that its two-dimensional (2D) form is a potential photocatalyst for water splitting reactions. Herein, we first report the photoelectrochemical (PEC) characterization of GaSe nanoflakes (single-/few-layer flakes), produced via liquid phase exfoliation, for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in both acidic and alkaline media. In 0.5 M H2SO4, the GaSe photoelectrodes display the best PEC performance, i.e. a ratiometric power-saved metric for HER ({\Phi}saved,HER) of 0.09% and a ratiometric power-saved metric for OER ({\Phi}saved,OER) of 0.25%. When used as PEC-type photodetectors, GaSe photoelectrodes show a responsivity of ~0.16 A W-1 upon 455 nm illumination at light intensity of 63.5 uW cm-2 and applied potential of -0.3 V vs. reversible hydrogen electrode (RHE). The stability analysis of the GaSe photodetectors evidences a durable operation over tens of cathodic linear sweep voltammetry scans in 0.5 M H2SO4 for HER. Viceversa, degradation effects have been observed in both alkaline and anodic operation due to highly oxidizing environment and O2-induced (photo-)oxidation effects. Our results provide new insight into PEC properties of GaSe nanoflakes for their exploitation in photoelectrocatalysis, PEC-type photodetectors and (bio)sensors.