Transition metal sulfides with a multi‐elemental nature represent a class of promising catalysts for oxygen evolution reaction (OER) owing to their good catalytic activity. However, their synthesis remains a challenge due to the thermodynamic immiscibility of the constituent multimetallic elements in a sulfide structure. Herein, for the first time the synthesis of high‐entropy metal sulfide (HEMS, i.e., (CrMnFeCoNi)Sx) solid solution nanoparticles is reported. Computational and X‐ray photoelectron spectroscopy analysis suggest that the (CrMnFeCoNi)Sx exhibits a synergistic effect among metal atoms that leads to desired electronic states to enhance OER activity. The (CrMnFeCoNi)Sx nanoparticles show one of the best activities (low overpotential 295 mV at 100 mA cm−2 in 1 m KOH solution) and good durability (only slight polarization after 10 h by chronopotentiometry) compared with their unary, binary, ternary, and quaternary sulfide counterparts. This work opens up a new synthesis paradigm for high‐entropy compound nanoparticles for highly efficient electrocatalysis applications.

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Incorporating the intriguing covalent organic framework (COF) into devices and performing their advanced electronic nature are still challenging. Herein, we demonstrate the direct growth of 2D full-conjugated COF ultrathin films on dielectric hexagonal boron nitride (hBN) for the first time and study the carrier transporting characteristics of π-conjugated COF films. Under the optimized solvothermal conditions, few-layered COF-366 films with the covalent connection of tetra(p-aminophenyl)porphyrin and terephthaladehyde are selectively fabricated on mechanically exfoliated hBN flakes. COF-366 films on hBN substrate present red-shift absorption edge and decreased band gap compared to the bulk COF powders.The organic field-effect transistor device based on COF-366 ultrathin films demonstrates p-type current modulation with an On/Off ratio of 10 5 and mobility of 0.015 cm 2 V -1 s -1 . The present work represents a universal method for COF film growth on dielectric surface, and also provides important insight to the carrier transport of 2D π-conjugated system and potential applications of 2D COFs in electronics.