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.

The formation of the soluble polysulfides (Na2Sn, 4 ≤ n ≤ 8) causes poor cycling performance for room temperature sodium–sulfur (RT Na–S) batteries. Moreover, the formation of insoluble polysulfides (Na2Sn, 2 ≤ n < 4) can slow down the reaction kinetics and terminate the discharge reaction before it reaches the final product. In this work, coffee residue derived activated ultramicroporous coffee carbon (ACC) material loading with small sulfur molecules (S2–4) as cathode material for RT Na–S batteries is reported. The first principle calculations indicate the space confinement of the slit ultramicropores can effectively suppress the formation of polysulfides (Na2Sn, 2 ≤ n ≤ 8). Combining with in situ UV/vis spectroscopy measurements, one‐step reaction RT Na–S batteries with Na2S as the only and final discharge product without polysulfides formation are demonstrated. As a result, the ultramicroporous carbon loaded with 40 wt% sulfur delivers a high reversible specific capacity of 1492 mAh g−1 at 0.1 C (1 C = 1675 mA g−1). When cycled at 1 C rate, the carbon–sulfur composite electrode exhibits almost no capacity fading after 2000 cycles with 100% coulombic efficiency, revealing excellent cycling stability and reversibility. The superb cycling stability and rate performance demonstrate ultramicropore confinement can be an effective strategy to develop high performance cathode for RT Na–S batteries.

The rise of micro-supercapacitors is satisfying the demand for power storage in portable devices and wireless gadgets. But the miniaturization of the energy-storage components is significantly limited by their energy density. Electrode materials with adequate electrochemical active surfaces are therefore required for improving performance. 2D materials with ultralarge specific surface areas offer a broad portfolio of the development of high-performance micro-supercapacitors in spite of their several critical drawbacks. An architecture engineering strategy is therefore developed to break these natural limits and maximize the significant advantages of these materials. Based on the approaches of phase transformation, intercalation, surface modification, material hybridization, and hierarchical structuration, 2D architectures with improved conductivity, enlarged specific surface, enhanced redox activity, as well as the unique synergetic effect exhibit great promise in the application of miniaturized supercapacitors with highly enhanced performance. Herein, the architecture engineering of emerging 2D materials beyond graphene toward optimizing the performance of micro-supercapacitors is discussed, in order to promote the application of 2D architectures in miniaturized energy-storage devices.

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Sodium transition metal oxides with layered structures are attractive cathode materials for sodium-ion batteries due to their large theoretical specific capacities. However, these layered oxides suffer from poor cyclability and low rate performance because of structural instability and sluggish electrode kinetics. In the present work, we show the sodiation reaction of Mn3O4 to yield crystal water free NaMnO2−y−δ(OH)2y, a monoclinic polymorph of sodium birnessite bearing Na/Mn(OH)8 hexahedra and Na/MnO6 octahedra. With the new polymorph, NaMnO2−y−δ(OH)2y exhibits an enlarged interlayer distance of about 7 Å, which is in favor of fast sodium ion migration and good structural stability. In combination of the favorable nanosheet morphology, NaMn2−y−δ(OH)2y cathode delivers large specific capacity up to 211.9 mAh g–1, excellent cycle performance (94.6% capacity retention after 1000 cycles), and outstanding rate capability (156.0 mAh g–1 at 50 C). This study demonstrates an effective approach in tailoring the structural and electrochemical properties of birnessite towards superior cathode performance in sodium-ion batteries.

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 photocatalytic hydrogen evolution (PHE) is highly desirable for addressing the global energy crisis and environmental problems. Although much attention has been given to electron-hole separation, ridding photocatalysts of poor efficiency remains challenging. Here, a two-electron catalytic reaction is developed by utilizing the distinct trion behavior of ReS and the efficient reduction of two H (2H + 2e → H ) is realized. Due to the monolayer-like structure of the catalyst, the free electrons in ReS can be captured by the tightly bound excitons to form trions consisting of two electrons and one hole. These trions can migrate to the surface and participate in the two-electron reaction at the abundant active sites. As expected, such a two-electron catalytic reaction endows ReS with a PHE rate of 13 mmol g h under visible light irradiation. Meanwhile, this reaction allows the typically poor PHE efficiency of pure transition metal dichalcogenides to be overcome. The proposed two-electron catalytic reaction provides a new approach to the design of photocatalysts for PHE.

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