Magnetoelectrocatalysis: enhanced heterogeneous electron transfer reactions at modified electrodes, Grätzel cells, and manganese dioxide electrodes

Magnetoelectrocatalysis is a physical, catalytic process. When magnetic microparticles are incorporated at an electrode surface, increases in current and system efficiency are observed. These enhancements have been observed in both homogeneous and heterogeneous systems. Here, the effects of magnetic fields on three separate, yet related, systems are analyzed: fundamental heterogeneous rate constants at modified electrodes, dye sensitized solar cells (DSSC), and manganese dioxide electrodes for supercapacitor applications.

Previous studies of magnetic field effects on homogeneous systems utilized the cation exchange polymer Nafion and transition metal redox probes, such as tris(bipyridine)ruthenium(II) chloride. At electrodes modified with Nafion films, redox probes experience current enhancement in the presence of a magnetic field. This effect is attributed to increased self exchange, known as Dahms Ruff conduction or hopping between redox species. Here, the impacts of magnetic fields on heterogeneous electron transfer, the electron transfer between the redox probe and solid-state electrode, are demonstrated. A derivative of Nafion, TMODA Nafion is used to study the effect. For transition metal complex redox probes, peak splitting in cyclic voltammagrams are lower for magnetically modified electrodes as compared to analogous nonmagnetic films.

The effects of magnetic modification of DSSCs are analyzed. DSSCs are photoelectrochemical cells (PECs) that convert incident light (photons) to electrical power (electrons). DSSCs, or Grätzel cells, are heterogeneous, excitonic devices which undergo multiple electron transfer reactions to complete this process. For studies here, magnetic modification of the electrodes occurs in the semiconductor layer. Enhancements in current density, fill factor, and power output are observed in variety of systems, both n-type and p-type, on glass and PET substrates, utilizing different magnetic microparticles.

Lastly, the effects of magnetic fields on the electrochemistry of electrolytic manganese dioxide (EMD) electrodes are examined. Manganese dioxide is an abundant, naturally occurring oxide of manganese that is used ubiquitously in alkaline batteries. manganese dioxide; is a complex material, existing, as many transition metal oxides do, in several polymorphs, each with unique properties. For the studies here, the use of manganese dioxide as a capacitor material in mild aqueous systems is considered. In comparison to traditional electrochemical capacitors, manganese dioxide undergoes both non-faradaic and faradaic charge storage. Magnetic field effects look to exploit this faradaic, pseudocapacitant behavior as a mechanism for increasing this power source's energy and power density.