Abstract
Efficient solar to hydrogen conversion using photoelectrochemical (PEC) process requires semiconducting photoelectrodes with advanced functionalities, while exhibiting high optical absorption and charge transport properties. Herein, we demonstrate magneto-tunable photocurrent in CoFe2O4 nanostructure film under low applied magnetic fields for efficient PEC properties. Photocurrent is enhanced from ~1.55 mA/cm2 to ~3.47 mA/cm2 upon the application of external magnetic field of 600 Oe leading to ~123% enhancement. This enhancement in the photocurrent is attributed to the reduction of optical bandgap and increase in the depletion width at CoFe2O4/electrolyte interface resulting in an enhanced generation and separation of the photoexcited charge carriers. The reduction of optical bandgap in the presence of magnetic field is correlated to the shifting of Co2+ ions from octahedral to tetrahedral sites which is supported by the Raman spectroscopy results. Electrochemical impedance spectroscopy results confirm a decrease in the charge transfer resistance at the CoFe2O4/electrolyte interface in the presence of magnetic field. This work evidences a coupling of photoexcitation properties with magnetic properties of a ferromagnetic-semiconductor and the effect can be termed as magnetophototronic effect.
Highlights
In recent years, the effect of external magnetic field on conventional semiconductors for applications such as spin pumping[1], Seebeck spin tunneling[2], spin Hall effect[3] and spin transfer torque oscillators[4] has been widely investigated
In the XRD data, in addition to the peaks originating from the fluorine doped tin oxide (FTO) conducting substrate, all observed diffraction peaks matches well with the standard diffraction data (JCPDS-1086) corresponding to cubic crystal phase of CoFe2O4 nanostructure film
To confirm the enhanced separation of the photogenerated charge carriers leading to the enhancement in the photocurrent, we carried out electrochemical impedance spectroscopy (EIS) measurements with and without magnetic field under light irradiation
Summary
The effect of external magnetic field on conventional semiconductors for applications such as spin pumping[1], Seebeck spin tunneling[2], spin Hall effect[3] and spin transfer torque oscillators[4] has been widely investigated. Photoelectrochemical measurements were performed using a three electrode cell assembly with the CoFe2O4 nanostructure film coated onto FTO substrate as the photoanode, Ag/AgCl and platinum wire as the reference and counter electrodes, respectively and 0.1 M Na2S solution as an electrolyte (Fig. 2a).
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