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.

Transition-metal oxides show genuine potential in replacing state-of-the-art carbonaceous anode materials in lithium-or sodium-ion batteries because of their much higher theoretical capacity. However, they usually undergo massive volume change, which leads to numerous problems in both material and electrode levels, such as material pulverization, instable solid-electrolyte interphase, and electrode failure. Here, it is demonstrated that lithium-ion breathable hybrid electrodes with 3D architecture tackle all these problems, using a typical conversion-type transition-metal oxide, Fe 3 O 4 , of which nanoparticles are anchored onto 3D current collectors of Ni nanotube arrays (NTAs) and encapsulated by δ-MnO 2 layers (Ni/Fe 3 O 4 @MnO 2 ). The δ-MnO 2 layers reversibly switch lithium insertion/extraction of internal Fe 3 O 4 nanoparticles and protect them against pulverizing and detaching from NTA current collectors, securing exceptional integrity retention and efficient ion/electron transport. The Ni/Fe 3 O 4 @ MnO 2 electrodes exhibit superior cyclability and high-capacity lithium storage (retaining ≈1450 mAh g −1 , ≈96% of initial value at 1 C rate after 1000 cycles).

Picric acid (PA) is a severe environmental and security risk due to its unstable, toxic, and explosive properties. It is also challenging to detect in trace amounts and in situ because of its highly acidic and anionic character. Here, we assess sensing of PA under nonlaboratory conditions using surface-enhanced Raman scattering (SERS) silver nanopillar substrates and hand-held Raman spectroscopy equipment. The advancing elasto-capillarity effects are explained by molecular dynamics simulations. We obtain a SERS PA detection limit on the order of 20 ppt, corresponding attomole amounts, which together with the simple analysis methodology demonstrates that the presented approach is highly competitive for ultrasensitive analysis in the field.

Nanoarchitectured electroactive materials can boost rates of Li insertion/extraction, showing genuine potential to increase power output of Li-ion batteries. However, electrodes assembled with low-dimensional nanostructured transition metal oxides by conventional approach suffer from dramatic reductions in energy capacities owing to sluggish ion and electron transport kinetics. Here we report that flexible bulk electrodes, made of three-dimensional bicontinuous nanoporous Cu/MnO2 hybrid and seamlessly integrated with Cu solid current collector, substantially optimizes Li storage behavior of the constituent MnO2. As a result of the unique integration of solid/nanoporous hybrid architecture that simultaneously enhances the electron transport of MnO2, facilitates fast ion diffusion and accommodates large volume changes on Li insertion/extraction of MnO2, the supported MnO2 exhibits a stable capacity of as high as ~1100 mA h g−1 for 1000 cycles, and ultrahigh charge/discharge rates. It makes the environmentally friendly and low-cost electrode as a promising anode for high-performance Li-ion battery applications.