urgent strategies worldwide. [1] Rechargeable lithium-ion batteries have achieved great success during the last 40 years, while they gradually display certain limitations in further large-scale applications, such as high cost, uneven geological distribution and short supplies of lithium resources (0.0017 wt%) around the world. As alternative energy storage sources, sodium ion batteries (SIBs) and potassium ion batteries (PIBs) have recently attracted tremendous interest owing to their natural abundance, low cost and environmental friendliness. Despite having a similar abundance with sodium (sodium and potassium represent 2.36 and 2.09 wt% in the Earth's crust, respectively), potassium presents some specific advantages. K + /K exhibit a lower standard redox potential of −2.93 V (vs E°) compared with that of Na + /Na (−2.71 V vs E°), implying a higher working voltage and energy density of PIBs. [2] Moreover, potassium ions have much better conductivity and relatively lower desolvation energy in organic solvents. [3] These merits of potassium make it a promising low-cost candidate for high-energy and power density energy storage applications.The progress of PIBs mainly follows the development of electrode materials, especially considering the large-size of Metallic bismuth (Bi) has been widely explored as remarkable anode material in alkali-ion batteries due to its high gravimetric/volumetric capacity. However, the huge volume expansion up to ≈406% from Bi to full potassiation phase K 3 Bi, inducing the slow kinetics and poor cycling stability, hinders its implementation in potassium-ion batteries (PIBs). Here, facile strategy is developed to synthesize hierarchical bismuth nanodots/graphene (BiND/G) composites with ultrahigh-rate and durable potassium ion storage derived from an in situ spontaneous reduction of sodium bismuthate/graphene composites. The in situ formed ultrafine BiND (≈3 nm) confined in graphene layers can not only effectively accommodate the volume change during the alloying/dealloying process but can also provide high-speed channels for ionic transport to the highly active BiND. The BiND/G electrode provides a superior rate capability of 200 mA h g −1 at 10 A g −1 and an impressive reversible capacity of 213 mA h g −1 at 5 A g −1 after 500 cycles with almost no capacity decay. An operando synchrotron radiation-based X-ray diffraction reveals distinctively sharp multiphase transitions, suggesting its underlying operation mechanisms and superiority in potassium ion storage application.

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Oxidative coupling of methane (OCM) catalyzed by MnOx‐Na2WO4/SiO2 has great industrial promise to convert methane directly to C2–3 products, but its high light‐off temperature is the most challenging obstacle to commercialization and its working mechanism is still a mystery. We report the discovery of a low‐temperature active and selective MnOx‐Na2WO4/SiO2 catalyst enriched with Q2 units in the SiO2 carrier, being capable of converting 23 % CH4 with 72 % C2–3 selectivity at 660 °C. From experiments and theoretical calculations, a large number of Q2 units in the MnOx‐Na2WO4/SiO2 catalyst is a trigger for markedly lowering the light‐off temperature of the Mn3+↔Mn2+ redox cycle involved in the OCM reaction because of the easy formation of MnSiO3. Notably, the MnSiO3 formation proceeds merely through the SiO2‐involved reaction in the presence of Na2WO4: Mn7SiO12+6 SiO2↔7 MnSiO3+1.5 O2. The Na2WO4 not only drives the light‐off of this cycle but also gets it working with substantial selectivity toward C2–3 products. Our findings shine a light on the rational design of more advanced MnOx‐Na2WO4 based OCM catalysts through establishing new Mn3+↔Mn2+ redox cycles with lowered light‐off temperature.