High-Yield Electrochemical Production of Large-Sized and Thinly Layered NiPS₃ 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 µm²) and thinly layered (≈70% monolayer) NiPS₃ 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 NiPS₃ crystals, as revealed by in situ and ex situ characterizations. Atomically thin NiPS₃ 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 NiPS₃ 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 NiPS₃ exhibits outstanding performance for overall water splitting.