Transition‐metal oxides as faradaic charge‐storage intermediates sandwiched between conductor and electrolyte are key components to store/deliver high‐density energy in microsupercapacitors for many applications in miniaturized portable electronics and microelectromechanical systems. While the conductor facilitating their electron transports, they generally suffer from a switch of rate‐determining step to their sluggish redox reactions in pseudocapacitive energy storage, during which poor cation accessibility and diffusion leads to high internal resistances and lowers volumetric capacitance and rate performance. Here it is shown that the faradaic processes in a model system of MnO2 can be radically boosted by tuning crystallographic structures from cryptomelane (α‐MnO2) to birnessite (δ‐MnO2). As a result of greatly enhanced Na+ accessibility and diffusion, 3D layered crystalline δ‐MnO2 microelectrodes exhibit volumetric capacitance as high as ≈922 F cm−3 (≈1.5‐fold higher than α‐MnO2, ≈617 F cm−3) and excellent rate performance. This enlists δ‐MnO2 microsupercapacitor to deliver ultrahigh stack electrical powers (up to ≈295 W cm−3) while maintaining volumetric energy density much higher than that of thin‐film lithium battery.

Pseudocapacitance holds great promise for improving energy densities of electrochemical supercapacitors, but state-of-the-art pseudocapacitive materials show capacitances far below their theoretical values and deliver much lower levels of electrical power than carbon-based materials due to poor cation accessibility and/or long-range electron transferability. Here we show that in situ corundum-to-rutile phase transformation in electron-correlated vanadium sesquioxide can yield nonstoichiometric rutile vanadium dioxide layers that are composed of highly sodium ion accessible oxygen-deficiency quasi-hexagonal tunnels sandwiched between conductive rutile slabs. This unique structure serves to boost redox and intercalation kinetics for extraordinary pseudocapacitive energy storage in hierarchical isomeric vanadium oxides, leading to a high specific capacitance of ~1856 F g–1 (almost sixfold that of the pristine vanadium sesquioxide and dioxide) and a bipolar charge/discharge capability at ultrafast rates in aqueous electrolyte. Symmetric wide voltage window pseudocapacitors of vanadium oxides deliver a power density of ~280 W cm–3 together with an exceptionally high volumetric energy density of ~110 mWh cm–3 as well as long-term cycling stability.

Kinetic formation of the peroxo-like O22− dimer is identified as the origin of a voltage hysteresis in oxygen-redox battery electrodes.

Developing high‐power battery chemistry is an urgent task to buffer fluctuating renewable energies and achieve a sustainable and flexible power supply. Owing to the small size of the proton and its ultrahigh mobility in water via the Grotthuss mechanism, aqueous proton batteries are an attractive candidate for high‐power energy storage devices. Grotthuss proton transfer is ultrafast owing to the hydrogen‐bonded networks of water molecules. In this work, similar continuous hydrogen bond networks in a dense oxide‐ion array of solid α‐MoO3 are discovered, which facilitate the anhydrous proton transport even without structural water. The fast proton transfer and accumulation that occurs during (de)intercalation in α‐MoO3 is unveiled using both experiments and first‐principles calculations. Coupled with a zinc anode and a superconcentrated Zn2+/H+ electrolyte, the proton‐transport mechanism in anhydrous hydrogen‐bonded networks realizes an aqueous MoO3–Zn battery with large capacity, long life, and fast charge–discharge abilities.

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The direct conversion of biorenewable alcohols into value‐added graphene and pure hydrogen (H2) at benign conditions is an important challenge, especially, considering the open carbon‐reduced cycle. In this study, it is demonstrated that inexpensive calcium oxide (CaO, from eggshells) can transform alcohols into bulky nanoporous graphene and pure hydrogen (≈99%) with robust selectivity at the temperature as low as 500 °C. Consequently, the growth of graphene can follow the direction of alcohol flow and uniformly penetrate into bulky nanoporous CaO platelets longer than 1 m without clogging. The experimental results and density functional theory calculations demonstrate that alcohol molecules can be catalytically carbonized on the surface of CaO at low temperature. The concept of the comprehensive utilization of biomass‐derived alcohols offers a carbon‐negative cycle for mitigating global warming and the energy demand.

Nanostructured transition‐metal oxides can store high‐density energy in fast surface redox reactions, but their poor conductivity causes remarkable reductions in the energy storage of most pseudocapacitors at high power delivery (fast charge/discharge rates). Here it is shown that electron‐correlated oxide hybrid electrodes made of nanocrystalline vanadium sesquioxide and manganese dioxide with 3D and bicontinuous nanoporous architecture (NP V2O3/MnO2) have enhanced conductivity because of metallization of electron‐correlated V2O3 skeleton via insulator‐to‐metal transition. The conductive V2O3 skeleton at ambient temperature enables fast electron and ion transports in the entire electrode and facilitates charge transfer at abundant V2O3/MnO2 interface. These merits significantly improve the pseudocapacitive behavior and rate capability of the constituent MnO2. Symmetric pseudocapacitors assembled with binder‐free NP V2O3/MnO2 electrodes deliver ultrahigh electrical powers (up to ≈422 W cm23) while maintaining the high volumetric energy of thin‐film lithium battery with excellent stability.

The precise identification of metal-metal bonds is critical to fully understanding the nature of metalmetal bonding but remains a fundamental challenge. Herein, we show the essence of Sc-Sc bonds with a metal-metal distance of 3.36 Å in a C 3v (8)-C 82 fullerene cage using crystallography. To elucidate the metal-metal bond formation, a metallofullerene Sc 2 C 2 @C 3v (8)-C 82 with a Sc 2 C 2 endo-unit encapsulated inside the same fullerene[82] cage was studied as a unique control molecule. Theoretical calculations reveal that each Sc atom donates one electron to the Sc-Sc bond. The existence of the Sc-Sc bond in Sc 2 @C 3v (8)-C 82 versus Sc 2 C 2 @C 3v (8)-C 82 is thoroughly investigated.