High-Yield Electrochemical Production of Large-Sized and Thinly Layered NiPS Flakes for Overall Water Splitting.

Achieving large-sized and thinly layered 2D metal phosphorus trichalcogenides with high quality and yield has been an urgent quest due to extraordinary physical/chemical characteristics for multiple applications. Nevertheless, current preparation methodologies suffer from uncontrolled thicknesses, uneven morphologies and area distributions, long processing times, and inferior quality. Here, a sonication-free and fast (in minutes) electrochemical cathodic exfoliation approach is reported that can prepare large-sized (typically ≈150 µm ) and thinly layered (≈70% monolayer) NiPS flakes with high crystallinity and pure phase structure with a yield ≈80%. During the electrochemical exfoliation process, the tetra-n-butylammonium salt with a large ionic diameter is decomposed into gaseous species after the intercalation and efficiently expands the tightly stratified bulk NiPS crystals, as revealed by in situ and ex situ characterizations. Atomically thin NiPS flakes can be obtained by slight manual shaking rather than sonication, which largely preserves in-plane structural integrity with large size and minimum damage. The obtained high quality NiPS offers a new and ideal model for overall water splitting due to its inherent fully exposed S and P atoms that are often the active sites for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Consequently, the bifunctional NiPS exhibits outstanding performance for overall water splitting.