Zinc negative electrodes are well known in primary batteries based on the classical Leclanché cell but a more recent development is the introduction of a number of rechargeable redox flow batteries for pilot and commercial scale using a zinc/zinc ion redox couple, in acid or alkaline electrolytes, or transformation of surface zinc oxides as a reversible electrode. The benefits and limitations of zinc negative electrodes are outlined with examples to discuss their thermodynamic and kinetic characteristics along with their practical aspects. Four main types of redox flow batteries employing zinc electrodes are considered, the zinc-bromine, zinccerium, zinc-air and zinc-nickel. Problems associated with zinc deposition and dissolution, especially in acid media, are summarised. The main features of each battery are identified and the benefits of a flowing electrolyte are explained. In each case, a summary of their development, including the electrode and cell reactions, their potentials, the performance of the positive and negative electrodes, the benefits of a single flow compartment and cell developments for energy storage are included. Remaining challenges are highlighted and possibilities for future advances in redox flow batteries are suggested.

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Lithium-ion capacitors, which possess excellent power and energy densities, can combine both those advantages from supercapacitors and lithium-ion batteries, leading to the novel generation hybrid devices for storing energy. This study synthesized one three-dimensional (3D) hierarchical structure self-assembled from CoS nanosheets, according to a simple and efficient manner, have been used as anode for lithium ion capacitors. This CoS anode, based on a conversion-type Li + storage mechanism dominated by diffusion controlled, showed a large reversible capacity, together with excellent stability for cycling. The CoS shows a discharge capacity ≈ 434 mA h/g at 0.1 A/g. The hybrid lithium-ion capacitor, which had the CoS anode as well as the biochar cathode, exhibits excellent electrochemical performance with ultra-high energy and power densities of 125.2 Wh/kg and 6400 W/kg, respectively, and an extended cycling life of 81.75% retention after 40000 cycles. The CoS with self-assembled 3D hierarchical structure in combination with a carbon cathode offers a versatile device for future applications in energy storage.

NiOOH and its doped species are widely used as electrocatalysts for the oxygen evolution reaction (OER) in alkaline media. In this work, we carried out comprehensive density functional theory (DFT) simulations of Ni-based electrocatalysts for the OER by applying suitable dopants in β-NiOOH. A range of Fe and Co atoms (%) are employed as doping agents to increase the overall catalytic ability, stability, and feasibility of NiOOH. Our simulations indicate that Ni 88% Fe 6% Co 6% OOH is efficient, stable, and provides more catalytic sites at the surface of resulting catalysts for water adsorption and dissociation, which facilitate the OER. The lower overpotential for the OER is estimated from the higher adsorption energy of water molecule over the surface of Ni 88% Fe 6% Co 6% OOH, followed by other electronic properties such as band structure, electrostatic potential, the density of states, and surface formation energy.

Bromine based redox flow batteries (RFBs) can provide sustainable energy storage due to the abundance of bromine. Such devices pair Br2/Br− at the positive electrode with complementary redox couples at the negative electrode. Due to the highly corrosive nature of bromine, electrode materials need to be corrosion resistant and durable. The positive electrode requires good electrochemical activity and reversibility for the Br2/Br− couple. Carbon materials enjoy the advantages of low cost, excellent electrical conductivity, chemical resistance, wide operational potential ranges, modifiable surface properties, and high surface area. Here carbon based materials for bromine electrodes are reviewed, with a focus on application in zinc‐bromine, hydrogen‐bromine, and polysulphide‐bromine RFB systems, aiming to provide an overview of carbon materials to be used for design and development of bromine electrodes with improved performance. Aspects deserving further R&D are highlighted.