Determining the Electrochemical Oxygen Evolution Reaction Kinetics of Fe₃S₄@Ni₃S₂ Using Distribution Function of Relaxation Times

We designed a heterostructure of Fe₃S₄@Ni₃S₂, as a potent oxygen evolution reaction (OER) electrocatalyst in an alkaline medium. Intriguingly, Fe₃S₄@Ni₃S₂ exhibits low onset potential of 290 mV and overpotential of 360 mV at a current density of 10 mA cm⁻². We examined the OER kinetics of Fe₃S₄@Ni₃S₂ using distribution function of relaxation times (DFRT), which are attained with the help of impedance spectroscopy genetic programming (ISGP). ISGP reveals the occurrences of three events of OER, manifested as peaks in the DFRT, such as active material or pores (P2), charge transfer (P1’), and production rate of intermediates (P1) in case of Fe₃S₄@Ni₃S₂ at different faradic overpotentials. The effective resistance of each phenomenon can be easily calculated. It decreases with an increase in conductivity at high overpotentials for all the three, which suggests the high performance of the as-synthesized composite due to faster kinetics. Further, structural investigation of the catalyst employing x-ray photoelectron spectroscopy is elaborated and it is suggested that the catalyst activation takes place by the constant exchange of anions between electrode and electrolyte during electrochemical oxidation.