Mosaic-Structured Cobalt Nickel Thiophosphate Nanosheets Incorporated N-doped Carbon for Efficient and Stable Electrocatalytic Water Splitting

Engineering the nanostructures and compositions of 2D layered metal thiophosphates (MTPs) is significant for extending their applications. Here, a scalable and flexible strategy is presented to prepare single crystalline CoNiPS₃ incorporated with N-doped carbon (CoNiPS₃/C) nanosheets (≈16 nm thickness), which can be further processed into the mosaic-structured CoNiPS₃/C nanosheets (≈6 nm thickness) composed of randomly distributed crystalline nanodomains (≈15 nm diameter) and disordered boundaries (denoted as mosaic CoNiPS₃/C nanosheets), and further into separated CoNiPS₃/C nanodots (≈4 nm diameter). The initial CoNiPS₃/C nanosheeets are prepared by using Co–Ni Prussian-blue analogue nanoplates as templating precursors. As compared to the initial CoNiPS₃/C nanosheets and nanodots, the mosaic CoNiPS₃/C nanosheets exhibit plenty of active edge sites, retained crystallinity, and good structural stability. Synergistically, density functional theory calculations reveal that the bimetallic composition results in higher intrinsic activity, better conductivity, and lower kinetic energy barriers for bifunctional oxygen/hydrogen evolution reactions. More importantly, a water-splitting electrolyzer constructed using the mosaic CoNiPS₃/C nanosheets as both cathode and anode achieves 30 mA cm⁻² at 1.62 V, which is better than the initial CoNiPS₃/C nanosheets (1.69 V) and is comparable to the discreted nanodots (1.58 V). Besides, the mosaic CoNiPS₃/C nanosheets show much better electrocatalytic stability than nanodots.