Potassium‐ion batteries (PIBs) are one of the emerging energy‐storage technologies due to the low cost of potassium and theoretically high energy density. However, the development of PIBs is hindered by the poor K+ transport kinetics and the structural instability of the cathode materials during K+ intercalation/deintercalation. In this work, birnessite nanosheet arrays with high K content (K0.77MnO2⋅0.23H2O) are prepared by “hydrothermal potassiation” as a potential cathode for PIBs, demonstrating ultrahigh reversible specific capacity of about 134 mAh g−1 at a current density of 100 mA g−1, as well as great rate capability (77 mAh g−1 at 1000 mA g−1) and superior cycling stability (80.5% capacity retention after 1000 cycles at 1000 mA g−1). With the introduction of adequate K+ ions in the interlayer, the K‐birnessite exhibits highly stabilized layered structure with highly reversible structure variation upon K+ intercalation/deintercalation. The practical feasibility of the K‐birnessite cathode in PIBs is further demonstrated by constructing full cells with a hard–soft composite carbon anode. This study highlights effective K+‐intercalation for birnessite to achieve superior K‐storage performance for PIBs, making it a general strategy for developing high‐performance cathodes in rechargeable batteries beyond lithium‐ion batteries.

Anodes involving conversion and alloying reaction mechanisms are attractive for potassium‐ion batteries (PIBs) due to their high theoretical capacities. However, serious volume change and metal aggregation upon potassiation/depotassiation usually cause poor electrochemical performance. Herein, few‐layered SnS2 nanosheets supported on reduced graphene oxide (SnS2@rGO) are fabricated and investigated as anode material for PIBs, showing high specific capacity (448 mAh g−1 at 0.05 A g−1), high rate capability (247 mAh g−1 at 1 A g−1), and improved cycle performance (73% capacity retention after 300 cycles). In this composite electrode, SnS2 nanosheets undergo sequential conversion (SnS2 to Sn) and alloying (Sn to K4Sn23, KSn) reactions during potassiation/depotassiation, giving rise to a high specific capacity. Meanwhile, the hybrid ultrathin nanosheets enable fast K storage kinetics and excellent structure integrity because of fast electron/ionic transportation, surface capacitive‐dominated charge storage mechanism, and effective accommodation for volume variation. This work demonstrates that K storage performance of alloy and conversion‐based anodes can be remarkably promoted by subtle structure engineering.

Hosting atomically dispersed nitrogen-coordinated iron sites (Fe–N4) on graphene offers unique opportunities for driving electrochemical CO2 reduction reaction (CO2RR) to CO. However, the strong adsorption of *CO on the Fe–N4 site embedded in intact graphene limits current density due to slow CO desorption process. Herein, we report how the manipulation of pore edges on graphene alters the local electronic structure of isolated Fe–N4 sites and improves their intrinsic reactivity for prompting CO generation. We demonstrate that constructing holes on graphene basal plane to support Fe–N4 can significantly enhance its CO2RR compared to the pore-deficient graphene-supported counterpart, exhibiting a CO Faradaic efficiency of 94% and a turnover frequency of 1630 h–1 at 0.58 V vs RHE. Mechanistic studies reveal that the incorporation of pore edges results in the downshifting of the d-band center of Fe sites, which weakens the strength of the Fe–C bond when the *CO intermediate adsorbs on edge-hosted Fe–N4, thus boosting the CO desorption and evolution rates. These findings suggest that engineering local support structure renders a way to design high-performance single-atom catalysts.

The development of sodium-ion batteries is hindered by the poor Na + transport kinetics and structural instability of electrode materials during Na + intercalation/deintercalation. In this work, surface-dominated Na storage is demonstrated on the oxygen-functionalized graphene nanosheets (FGS) with fast surface redox reaction and robust structural stability. The FGS samples with tunable oxygen contents and species are fabricated via a two-step thermal exfoliation method from graphite oxides. The surface-induced oxygen functional groups can serve as the surface-redox sites for the FGS electrode, attaining a high specific capacity of 603 mAh g −1 at a current density of 0.05 A g −1 , excellent rate capability (214 mAh g −1 at 10 A g −1 ), and ultrastable cycling stability (capacity retention close to 100% after 10 000 cycles at 5 A g −1 ). Even at a slow scan rate of 0.1 mV s −1 for cyclic voltammetry, about 67.7% capacity is contributed from the surface adsorption/desorption and surface-redox reaction, suggesting surface-dominated Na storage for the FGS-700 (FGS sample obtained at 700 °C) electrode. The present work demonstrates that the surface oxygen functionalization is an effective strategy to develop high-performance graphene-based anodes due to the surface-dominated Na storage with improved reaction kinetics and suppressed structural variation.

Highly efficient noble-metal-free electrocatalysts for oxygen reduction reaction (ORR) are essential to reduce the costs of fuel cells and metal–air batteries. Herein, a single-atom Ce–N–C catalyst, constructed of atomically dispersed Ce anchored on N-doped porous carbon nanowires, is proposed to boost the ORR. This catalyst has a high Ce content of 8.55 wt % and a high activity with ORR half-wave potentials of 0.88 V in alkaline media and 0.75 V in acidic electrolytes, which are comparable to widely studied Fe–N–C catalysts. A Zn–air battery based on this material shows excellent performance and durability. Density functional theory calculations reveal that atomically dispersed Ce with adsorbed hydroxyl species (OH) can significantly reduce the energy barrier of the rate-determining step resulting in an improved ORR activity.

is a senior scientist at the X-ray Science Division in Argonne National Laboratory. He has developed in situ X-ray techniques to understand the fundamental chemistry of complex disordered solid and solution systems, such as energy storage materials, catalysts, soot, heavy petroleum, oil shale, and carbons. Chemistry is combined with characterization techniques, including mass spectrometry, IR, NMR, and X-ray scattering and spectroscopy. IR and MS are used simultaneously with X-ray techniques. In 2009, he was elected to the inaugural class of the ACS Fellows and was the chair of the 2018 International Conference on Small Angle Scattering.

Heme enzymes, with the pentacoordinate heme iron active sites, possess high catalytic activity and selectivity in biosensing applications. However, they are still subject to limited catalytic stability in the complex environment and high cost for broad applications in electrochemical sensing. It is meaningful to develop a novel substitute that has a similar structure to some heme enzymes and mimics their enzyme activities. One emerging strategy is to design the Fe‐N‐C based single‐atomic site catalysts (SASCs). The obtained atomically dispersed Fe‐Nx active sites can mimic the active sites of heme enzymes effectively. In this work, a SASC (Fe‐SASC/NW) is synthesized by doping single iron atoms in polypyrrole (PPy) derived carbon nanowire via a zinc‐atom‐assisted method. The proposed Fe‐SASC/NW shows high heme enzyme‐like catalytic performance for hydrogen peroxide (H2O2) with a specific activity of 42.8 U mg−1. An electrochemical sensor based on Fe‐SASC/NW is developed for the detection of H2O2. This sensor exhibits a wide detection concentration range from 5.0 × 10−10 m to 0.5 m and an excellent limit of detection (LOD) of 46.35 × 10−9 m. Such excellent catalytic activity and electrochemical sensing sensitivity are attributed to the isolated Fe‐Nx active sites and their structural similarity with natural metalloproteases.

Single‐atom and subnanocluster catalysts (SSCs) represent a highly promising class of low‐cost materials with high catalytic activity and high atom‐utilization efficiency. However, SSCs are susceptible to undergo restructuring during the reactions. Exploring the active sites of catalysts through in situ characterization techniques plays a critical role in studying reaction mechanism and guiding the design of optimum catalysts. In situ X‐ray absorption spectroscopy/small‐angle X‐ray scattering (XAS/SAXS) is promising and widely used for monitoring electronic structure, atomic configuration, and size changes of SSCs during real‐time working conditions. Unfortunately, there is no detailed summary of XAS/SAXS characterization results of SSCs. The recent advances in applying in situ XAS/SAXS to SSCs are thoroughly summarized in this review, including the atomic structure and oxidation state variations under open circuit and realistic reaction conditions. Furthermore, the reversible transformation of single‐atom catalysts (SACs) to subnanoclusters/nanoparticles and the application of in situ XAS/SAXS in subnanoclusters are discussed. Finally, the outlooks in modulating the SSCs and developing operando XAS/SAXS for SSCs are highlighted.