Electrochemical energy storage (EES) materials and devices should be evaluated against clear and rigorous metrics to realize the true promises as well as the limitations of these fast-moving technologies.

The increasing demand for energy has triggered tremendous research efforts for the development of lightweight and durable energy storage devices. Herein, we report a simple, yet effective, strategy for high-performance supercapacitors by building three-dimensional pseudocapacitive CuO frameworks with highly ordered and interconnected bimodal nanopores, nanosized walls (∼4 nm) and large specific surface area of 149 m(2) g(-1). This interesting electrode structure plays a key role in providing facilitated ion transport, short ion and electron diffusion pathways and more active sites for electrochemical reactions. This electrode demonstrates excellent electrochemical performance with a specific capacitance of 431 F g(-1) (1.51 F cm(-2)) at 3.5 mA cm(-2) and retains over 70% of this capacitance when operated at an ultrafast rate of 70 mA cm(-2). When this highly ordered CuO electrode is assembled in an asymmetric cell with an activated carbon electrode, the as-fabricated device demonstrates remarkable performance with an energy density of 19.7 W h kg(-1), power density of 7 kW kg(-1), and excellent cycle life. This work presents a new platform for high-performance asymmetric supercapacitors for the next generation of portable electronics and electric vehicles.

The search for faster, safer, and more efficient energy storage systems continues to inspire researchers to develop new energy storage materials with ultrahigh performance. Mesoporous nanostructures are interesting for supercapacitors because of their high surface area, controlled porosity, and large number of active sites, which promise the utilization of the full capacitance of active materials. Herein, highly ordered mesoporous CuCo2O4 nanowires have been synthesized by nanocasting from a silica SBA-15 template. These nanowires exhibit superior pseudocapacitance of 1210 F g–1 in the initial cycles. Electroactivation of the electrode in the subsequent 250 cycles causes a significant increase in capacitance to 3080 F g–1. An asymmetric supercapacitor composed of mesoporous CuCo2O4 nanowires for the positive electrode and activated carbon for the negative electrode demonstrates an ultrahigh energy density of 42.8 Wh kg–1 with a power density of 15 kW kg–1 plus excellent cycle life. We also show that two asymmetric devices in series can efficiently power 5 mm diameter blue, green, and red LED indicators for 60 min. This work could lead to a new generation of hybrid supercapacitors to bridge the energy gap between chemical batteries and double layer supercapacitors.

The need for enhanced energy storage and improved catalysts has led researchers to explore advanced functional materials for sustainable energy production and storage. Herein, we demonstrate a reductive electrosynthesis approach to prepare a layer-by-layer (LbL) assembled trimetallic Fe−Co−Ni metal−organic framework (MOF) in which the metal cations within each layer or at the interface of the two layers are linked to one another by bridging 2-amino-1,4-benzenedicarboxylic acid linkers. Tailoring catalytically active sites in an LbL fashion affords a highly porous material that exhibits excellent trifunctional electrocatalytic activities toward the hydrogen evolution reaction (η j=10 = 116 mV), oxygen evolution reaction (η j=10 = 254 mV), as well as oxygen reduction reaction (half-wave potential = 0.75 V vs reference hydrogen electrode) in alkaline solutions. The dispersion-corrected density functional theory calculations suggest that the prominent catalytic activity of the LbL MOF toward the HER, OER, and ORR is due to the initial negative adsorption energy of water on the metal nodes and the elongated O−H bond length of the H 2 O molecule. The Fe−Co−Ni MOF-based Zn−air battery exhibits a remarkable energy storage performance and excellent cycling stability of over 700 cycles that outperform the commercial noble metal benchmarks. When assembled in an asymmetric device configuration, the activated carbon||Fe−Co−Ni MOF supercapacitor provides a superb specific energy and a power of up to 56.2 W h kg −1 and 42.2 kW kg −1 , respectively. This work offers not only a novel approach to prepare an LbL assembled multimetallic MOF but also provides a benchmark for a multifunctional electrocatalyst for water splitting and Zn−air batteries.

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