Application of Water-Based Ferrofluid for Water Electrolysis

Abstract

A combination of renewable energies and water electrolysis has been attracting much attention as an environmentally-friendly method to produce hydrogen, which has been expected as promising future energy storage and carrier media. And micro-gravity induces the adsorption of gas-bubbles on the surface of electrodes and this leads the declination of water electrolysis. In the present study, a new method which has the potential to dramatically enhance the water electrolysis efficiency was proposed by utilizing the magnetic buoyancy. Using water-based ferrofluids as an electrolyte and directly electrolyzing them in the presence of inhomogeneous magnetic fields enhance the desorption of gas-bubbles adsorbed on electrodes.When non-magnetic bodies are placed in the ferrofluid and are exposed to an inhomogeneous magnetic field, the magnetic buoyancy force acts on the non-magnetic bodies. Because the gradient of the magnetic field gives the magnetic buoyancy force, the non-magnetic body moves as the non-magnetic body is ejected from the magnetic field. When the water-based ferrofluid is used as an electrolyte and magnets are placed nearby electrodes, the magnetic buoyancy force acts on the bubbles (H2 and O2) generated from the surface of the electrodes, resulting in the water electrolysis enhancement.However, the effect of the magnetic fields on the water electrolysis using the ferrofluid is not well understood. In the present study, to understand the effect of the magnetic field on the water electrolysis, the chronoamperometry measurements in the presence of the magnetic field was carried out. The results showed that the water electrolysis is found to be enhanced by increasing the magnetic field intensity due to the magnetic buoyancy force. The present study showed that our proposed method has a great potential to enhance the water electrolysis substantially.In addition, we investigated the effect of magnetic field strength on the water electrolysis process by a dynamic impedance method. The Nyquist plot was obtained by the dynamic impedance method. The tested electrolyte was a water-based ferrofluid adding Na2SO4 with 0.1 mol/L. When the magnetic field intensity increases, Z Re decreases, which represents that the resistance in the water electrolysis becomes smaller. The equivalent circuit fits the experimental data well, resulting in that it is possible to divide the whole resistance into the charge-transfer and solution resistances. The charge-transfer resistance dramatically decreases with the magnetic field strength, while the solution resistance doesn't change. This phenomenon explains that the magnetic buoyancy sufficiently enhances the bubble desorption, resulting in the water electrolysis enhancement.