Photoelectrochemical hydrogen evolution on macroscopic electrodes of exfoliated SnSe flakes

Tin(II) selenide (SnSe) is an attractive photocathode candidate for performing photoelectrochemical (PEC) hydrogen evolution reaction (HER), because of its negative conduction band position relative to the HER redox level and a high absorption coefficient for efficiently harvesting solar energy. To prepare thinner layered SnSe flakes from larger size commercial SnSe crystals, liquid phase exfoliation (LPEx) was employed in isopropanol/water mixtures (IPA/H2O) and pure IPA. Macroscopic (1 cm2) electrodes were prepared from the exfoliated SnSe flakes by immobilizing them on glassy carbon electrodes. These flakes obtained by exfoliating the as-received commercial SnSe in pure IPA exhibited 10 times higher PEC activity than those prepared in IPA/H2O. An additional size separation to make three different size fractions of SnSe crystals served to further optimize the LPEx process. Electrodes prepared from the largest flakes showed the highest photocurrent density of 2.44 ± 0.65 mA cm–2 at −0.74 V versus RHE under 1 Sun, and ∼ 30% incident-photon-to-electron conversion efficiency at 900 nm. Decoration of the SnSe surface with Pt catalyst islands further improved the PEC activity to 4.39 ± 0.15 mA cm–2. This photocurrent density represents the highest value reported to date on macroscopic electrodes assembled from SnSe.