Magnetic field-induced capacitance change in aqueous carbon-based supercapacitors

Summary Carbon-based supercapacitors (SCs) are important electrochemical energy storage devices and are often used in electronic equipment that generates a magnetic field. However, whether the magnetic field affects the charge storage of SCs is unknown. Here, we discover that applying an external magnetic field to carbon-based SCs can induce capacitance change in both aqueous acidic and alkaline electrolytes but not in neutral electrolytes. We further show that, in KOH electrolytes, the competition between the driving force caused by the Lorentz force and the damping force related to the electrolyte conductivity plays a crucial role in affecting the OH− transport under the magnetic field. In H2SO4 electrolytes, the third paramagnetic force generated by the paramagnetic H+ under the magnetic field hinders the H+ transport in addition to the above forces. A quantitative relationship among the limiting current density at the electrode-electrolyte interface, the intensity of the magnetic field, and the concentration and viscosity of electrolytes can therefore be established.