Periodically eclipsed π-stacking columns in two-dimensional covalent organic frameworks (2D COFs) could function as direct channel paths for charge carrier transport. Incorporating a well-defined 2D COF into organic electronic devices, however, is still a challenge. Herein, we have reported the solvothermal synthesis of a COFTFPy-PPDA film on single-layer graphene (SLG), which was constructed via covalent imine-type linkage by employing 1,3,6,8-tetrakis(p- formylphenyl)pyrene (TFPy) and p-phenylenediamine (PPDA) as building blocks. A vertical field-effect transistor (VFET) based on the heterostructure of COFTFPy-PPDA film and SLG shows ambipolar charge carrier behavior under lower modulating voltages. Work-function-tunable contact between SLG and COFTFPy-PPDA film and suitable injection barriers of charge carriers lead to the ambipolar transport with high current density on/off ratio (>105) and high on-current density (>4.1 A cm-2). Interfacing 2D COF with graphene for VFET could shed light on the promising application prospect of 2D COFs in organic electronics and optoelectronics.

The development of high energy electrode materials for lithium ion batteries is challenged by their inherent instabilities, which become more aggravated as the energy densities continue to climb, accordingly causing increasing concerns on battery safety and reliability. Here, taking the high voltage cathode of LiNi_0.5Mn_1.5O₄ as an example, we demonstrate a protocol to stabilize this cathode through a systematic phase modulating on its particle surface. We are able to transfer the spinel surface into a 30 nm shell composed of two functional phases including a rock-salt one and a layered one. The former is electrochemically inert for surface stabilization while the latter is designated to provide necessary electrochemical activity. The precise synthesis control enables us to tune the ratio of these two phases, and achieve an optimized balance between improved stability against structural degradation without sacrificing its capacity. This study highlights the critical importance of well-tailored surface phase property for the cathode stabilization of high energy lithium ion batteries.

Although single-atomically dispersed metal-N_x on carbon support (M-NC) has great potential in heterogeneous catalysis, the scalable synthesis of such single-atom catalysts (SACs) with high-loading metal-N_x is greatly challenging since the loading and single-atomic dispersion have to be balanced at high temperature for forming metal-N_x. Herein, we develop a general cascade anchoring strategy for the mass production of a series of M-NC SACs with a metal loading up to 12.1 wt%. Systematic investigation reveals that the chelation of metal ions, physical isolation of chelate complex upon high loading, and the binding with N-species at elevated temperature are essential to achieving high-loading M-NC SACs. As a demonstration, high-loading Fe-NC SAC shows superior electrocatalytic performance for O₂ reduction and Ni-NC SAC exhibits high electrocatalytic activity for CO₂ reduction. The strategy paves a universal way to produce stable M-NC SAC with high-density metal-N_x sites for diverse high-performance applications.