Atomically dispersed transition metal active sites have emerged as one of the most important fields of study because they display promising performance in catalysis and have the potential to serve as ideal models for fundamental understanding. However, both the preparation and determination of such active sites remain a challenge. The structural engineering of carbon-and nitrogencoordinated metal sites (M−N−C, M = Fe, Co, Ni, Mn, Cu, etc.) via employing new heteroatoms, e.g., P and S, remains challenging. In this study, carbon nanosheets embedded with nitrogen and phosphorus dual-coordinated iron active sites (denoted as Fe-N/P-C) were developed and determined using cutting edge techniques. Both experimental and theoretical results suggested that the N and P dual-coordinated iron sites were favorable for oxygen intermediate adsorption/desorption, resulting in accelerated reaction kinetics and promising catalytic oxygen reduction activity. This work not only provides efficient way to prepare well-defined single-atom active sites to boost catalytic performance but also paves the way to identify the dual-coordinated single metal atom sites.

The development of rechargeable metal–air batteries and water electrolyzers are highly constrained by electrocatalysts for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). However, the construction of efficient trifunctional electrocatalysts for ORR/OER/HER are highly desirable yet challenging. Herein, hollow carbon nanotubes integrated single cobalt atoms with Co9S8 nanoparticles (CoSA + Co9S8/HCNT) are fabricated by a straightforward in situ self‐sacrificing strategy. The structure of the CoSA + Co9S8/HCNT are verified by X‐ray absorption spectroscopy and aberration‐corrected scanning transmission electron microscopy. Theoretical calculations and experimental results embrace the synergistic effects between Co9S8 nanoparticles and single cobalt atoms through optimizing the electronic configuration of the CoN4 active sites to lower the reaction barrier and facilitating the ORR, OER, and HER simultaneously. Consequently, rechargeable liquid and all‐solid‐state flexible Zn–air batteries based on CoSA + Co9S8/HCNT exhibit remarkable stability and excellent power density of 177.33 and 51.85 mW cm−2, respectively, better than Pt/C + RuO2 counterparts. Moreover, the as‐fabricated Zn–air batteries can drive an overall water splitting device assembled with CoSA + Co9S8/HCNT and achieve a current density of 10 mA cm−2 at a low voltage of 1.59 V, also superior to Pt/C + RuO2. Therefore, this work presents a promising approach to an efficient trifunctional electrocatalyst toward practical applications.

surface of MXene. It is generally obtained by etching the MAX phase (Ti 3 AlC 2) in a HF solution or a solution that generates HF in situ. Similar to other 2D materials (such as graphene, MoS 2 , and black phosphorus, etc.), however, MXene flakes are susceptible to stacking and agglomeration due to the strong interlayer van der Waals force. This problem greatly hindered the dispersion of MXene and significantly reduce their specific surface area, thus limiting the efficient use of interface and seriously affects its performance. [6] To address this issue, a series of strategies have been adopted. For example, Gogotsi and co-workers reported that Ti 3 C 2 T x layer intercalated with cation to suppress the restacking of MXene nanosheets, thus offers high volumetric capacitance. [7] Yu and co-workers reported an MXene@polystyrene nanocomposites constructed by electrostatic assembly MXene flakes on polystyrene microspheres then compressing molding for highly efficient EMI. [8] A 3D MXene hydrogel was fabricated by using metal ions to break electrostatic repulsion force between the MXene nanosheets and serving as connectors to link the nanosheets together, which make the restacking problem of MXene be restrained and effectively increases the surface utilization of MXene. [9] These strategies can effectively inhibit the stacking of MXene and increase the layer spacing. Nevertheless, most of above methods are suffering from complex and harsh manufacturing process limitations. The poor oxidation stability is another major drawback for MXene. Due to the interaction of water and oxygen under ambient surroundings, MXene flakes are unstable and apt to oxidize. [10] It has been reported that the introduction of polyanionic salts [11] or antioxidants sodium l-ascorbate [12] in the MXene solution enables the anions to encapsulate the positively charged MXene flake edges and prevent MXene from interacting with water molecules, thereby achieving the purpose of inhibiting MXene oxidation. A stable MXene organic dispersion was reported based on simultaneous interfacial chemical grafting and phase transfer method, which has strong antioxidant properties. [13] Although the above methods can effectively suppress the oxidation of MXene, on the other hand, MXene is "contaminated" due to the introduction of other substances. Conjugated microporous polymers (CMPs) are a unique class of organic porous materials constructed by rigid conjugated 2D MXenes have attracted wide attention due to their unique chemical and physical properties. However, MXene nanosheets suffer from restacking and are susceptible to oxidation and consequently lose their functional properties which limits their applications. Thus, it is desirable to explore strategies to preserve MXene nanosheets and avoid oxidation. Herein, an effective strategy to produce MXene-based conjugated microporous polymers (M-CMPs) by covalently sandwiching MXene between CMPs using p-iodophenyl functionalized MXene as templates is demonstrated. The as-prepared M-CMPs inherit the 2D architec...

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Two-dimensional molybdenum disulfide (MoS2) is a promising electrode material for supercapacitors, attributing to attractive physical properties, outstanding electrical properties, and ultrahigh exposed surface area. However, MoS2 bulk suffers from low capacity due to the overlaying of the layers and the poor electric conductivity. Covalent functionalization of MoS2 is a promising, yet challenging, approach to overcome the drawbacks and boost electrochemical performance. Here, we report a series of sandwich-like 4-aminophenyl functionalized MoS2/polyaniline (MoS2–NH2/PANI) nanosheets by in situ growth of PANI on MoS2–NH2 templates. The optimized MoS2–NH2/PANI nanosheets express a high capacitance of 326.4 F g–1 at 0.5 A g–1 and a superior rate retention of 63.1% when the current density increased from 0.5 A g–1 to 1000 A g–1 in a three-electrode system. Impressively, the corresponding symmetric supercapacitors deliver an electrochemical cycling stability with 96.5% retention after 10000 cycles at 5 A g–1. Our strategy of covalent linking PANI onto functional MoS2 provides a feasible approach to improve the electrochemical performance of MoS2-based materials for energy storage.