Freestanding paper-like electrode materials have trigged significant research interest for their practical application in flexible and lightweight energy storage devices. In this work, we reported a new type of flexible nanohybrid paper electrode based on full inkjet printing synthesis of a freestanding graphene paper (GP) supported three-dimensional (3D) porous graphene hydrogel (GH)-polyaniline (PANI) nanocomposite, and explored its practical application in flexible all-solid-state supercapacitor (SC). The utilization of 3D porous GH scaffold to load nanostructured PANI dramatically enhances the electrical conductivity, the specific capacitance and the cycle stability of the GH-PANI nanocomposite. Additionally, GP can intimately interact with GH-PANI through π-π stacking to form a unique freestanding GP supported GH-PANI nanocomposite (GH-PANI/GP) with distinguishing mechanical, electrochemical and capacitive properties. These exceptional attributes, coupled with the merits of full inkjet printing strategy, lead to the formation of a high-performance binder-free paper electrode for flexible and lightweight SC application. The flexible all-solid-state symmetric SC based on GH-PANI/GP electrode and gel electrolyte exhibits remarkable mechanical flexibility, high cycling performance and acceptable energy density of 24.02 Wh kg(-1) at a power density of 400.33 W kg(-1). More importantly, the proposed simple and scale-up full inkjet printing procedure for the preparation of freestanding GP supported 3D porous GH-PANI nanocomposite is a modular approach to fabricate other graphene-based nanohybrid papers with tailorable properties and optimal components.

The recent dramatic increase in research on isolated metal atoms has received extensive scientific interest in the new frontier of single‐atom catalysis. As newly advanced materials in catalysis, single‐atom catalysts (SACs) have received enormous interest from the perspectives of both scientific research and industrial applications due to their remarkable activity. In addition, other catalytic properties of single metal atoms, including stability and selectivity, can be further improved by tuning their electronic/geometric structures and modulating the metal–support interactions. SACs usually consist of dispersed atoms and appropriate support materials, which are employed to anchor, confine, and/or coordinate with isolated metal atoms. Therefore, the nature of single metal sites allows acquiring a maximum atom utilization approaching 100%, which is of significance, particularly for the development of noble‐metal‐based catalysts. In order to systematically understand the structure–property relationships and the underlying catalytic mechanisms relationship of SACs, the representative scientific research efforts in their synthesis strategies, catalytic applications, and performance regulation are discussed here. Typical single‐atom catalysis processes and the corresponding mechanisms in electrochemistry, photochemistry, organic synthesis, and biomedicine are also summarized. Finally, the challenges and prospects for the development of single‐atom catalysis and SACs are highlighted.

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