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 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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transportation sector with electric vehicles. [1] The potential of renewable energy to power electric vehicles can contribute to a future world with cleaner skies, cheaper energy, and healthier air. Energy distribution can also be simplified by sending electrons over the grid, or even by locally generating energy using solar panels, instead of shipping chemical fuels through pipelines or via road transport. One of the core technologies required to realize the viability of renewable energy sources is to develop improved electrochemical energy storage systems. [2] Electric doublelayer capacitors (EDLCs) are more appropriate for high-power applications, while secondary batteries are well suited for high-energy applications. EDLCs are thus sometimes used in tandem with batteries so that the former provide power and the latter provide energy for the integrated system. Current research in the field of energy storage is converging to target single devices that have EDLClevel power density as well as cycling stability and battery-level energy density. [3] Supercapacitors are an important technology for the future of energy storage. Supercapacitors are especially designed for applications that require a high rate capability, where a sudden burst of energy in a very short time interval is needed. However, supercapacitors have a rather limited energy density. Thus, different charge storage mechanisms, in addition to and/or in place of EDLCs, have been developed to boost the energy content of supercapacitors. [4] The most intriguing approach is the incorporation of nanostructured solid-state electrode materials, mainly transition metal oxides/sulfides, [5] layered double hydroxides, [2b] or conductive polymers, [6] that utilize fast Faradaic redox reactions for energy storage. Another intriguing approach is the development of hybrid ion capacitors, which are intermediate in energy between batteries and supercapacitors, while demonstrating supercapacitor-like power performance and cycling stability. [7] Inspired by the solid-state pseudocapacitive charge storage mechanism, the concept of liquid-state redox electrolytes has also been developed to supply extra energy. [8] Via this fascinating approach, the dead weight of the formerly inert electrolytes is utilized as an active component to augment the energy storage performance, and the wasted Discovering efficient pseudocapacitive charge storage materials has become one of the grand challenges to reduce the gap between high energy density batteries and high power density and durable electrical double-layer capacitors.This research direction is facilitated by the introduction of redox-active species that add Faradaic charge storage to the system. However, the astonishing abilities of organic redox species to increase energy density are insufficient to compensate for their poor electrical conductivity and inferior cyclability. Herein, it is proposed that these challenges can be simultaneously met by thoughtful selection of a redox species, thionine, that can be conjugate...