Green synthesis of cobalt ferrite from rotten passion fruit juice and application as an electrocatalyst for the hydrogen evolution reaction

Abstract

Green synthesis of an efficient and low-cost electrocatalyst for the hydrogen evolution reaction (HER) in a basic medium is highly desirable for renewable energy conversion. Herein, cobalt-ferrite (CoFe₂O₄) was prepared by green coprecipitation synthesis using a precipitating agent (citrate) extracted from rotten passion fruit. The preparation followed two steps, in which the cobalt–iron citrate precursor was first obtained by coprecipitation, followed by pyrolysis in the air at 850 °C. While Fourier transform infrared (FTIR) and thermogravimetry (TG) confirmed the successful preparation of the precursor, X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM) revealed without any doubt the formation of polyhedron-like shape CoFe₂O₄. The electrocatalytic properties of the as-prepared material for the HER in 1 M KOH have been investigated. CoFe₂O₄ demonstrated good electrochemical performance with an overpotential of 440 mV at a current density of 10 mA cm⁻², a Tafel slope of 98 mV dec⁻¹, an electrical double layer capacitance (C_dl) of 0.43 mF cm⁻² and very high stability with an overpotential loss of only 13.07 mV after 12 hours. This paper provides a simple, easy method for HER catalyst preparation by recycling waste fruit.