Magnetic supercapacitors: Charge storage mechanisms, magnetocapacitance, and magnetoelectric phenomena

Pseudocapacitive (PC) materials are under investigation for energy storage in supercapacitors, which exhibit exceptionally high capacitance, good cyclic stability, and high power density. The ability to combine high electrical capacitance with advanced ferrimagnetic or ferromagnetic properties in a single material at room temperature opens an avenue for the development of advanced magnetically ordered pseudocapacitive (MOPC) materials. This review covers materials science aspects, charge storage mechanisms, magnetocapacitance, and magnetoelectric (ME) phenomena in MOPC materials. Recent studies demonstrate high PC properties of advanced ferrimagnetic materials, such as spinel ferrites and hexagonal ferrites. Of particular importance is the discovery of PC properties of perovskite-type manganites, which exhibit room temperature ferromagnetism and giant negative magnetoresistance. The coupling of high capacitance and magnetization in MOPC provides a platform for strong ME interactions. Various strategies are used for manipulation of electrical capacitance/magnetization of MOPC by a magnetic field/electrode potential. Magnetocapacitance studies show significant increase in capacitance of MOPC under the influence of a magnetic field. Moreover, the application of a magnetic field results in enhanced energy density and power density, reduction of resistance, and improvement of cyclic stability. Such findings offer a potential of a breakthrough in the development of advanced supercapacitors. High magnetocapacitance and ME phenomena are linked to the influence of magnetic fields on electrolyte diffusion, structure of electrical double layer, charge transfer resistance, and variation of conductivity and magnetization of MOPC materials, which facilitate charge/discharge behavior. Various applications of ME effect in MOPC are discussed. Moreover, advantages of magnetocapacitive MOPC are described for applications in electronic and spintronic devices, supercapacitors, and devices for magnetically enhanced capacitive deionization of water.