Zr-substituted maghemite catalyst for water splitting activity

It has been observed that Fe²⁺ has more impact than Fe³⁺ in hydrogen evolution reactions (HER) and oxygen evolution reactions (OER). If we dope one Zr⁴⁺ ion in γ-Fe₂O₃ then it reduces one Fe³⁺ ion into a Fe²⁺ ion and simultaneously replaces another Fe³⁺ ion to maintain the charge neutrality. Thus, to get more Fe²⁺ ions for better effect on electrochemical water splitting reactions, we prepared Zr substituted inverse spinel γ-Zr_xFe_2-xO₃ (where 0.07 ≤ x ≤ 0.27) magnetic nanoparticles of average size 18 nm using a one step solvothermal method. The X-ray diffraction (XRD), Mössbauer spectra, and electron diffraction patterns confirm the formation of single phased material up to x = 0.2. The presence of Zr, Fe, and O in their expected oxidation states was indicated by X-ray photoelectron spectroscopy. The maximum value for saturation magnetization was obtained as 62 emu/g for the γ-Zr_0.13Fe_1.87O₃ sample. The γ-Zr_0.2Fe_1.8O₃ sample after coating over 3D-Nickel foam, in an alkaline media demonstrates exceptional catalytic activity and great electrochemical stability. It offered low overpotentials of 1.48 V and 192 mV, respectively, to reach 10 mA/cm² for catalyzing OER and HER. Furthermore, the as-fabricated bifunctional electrocatalyst needs a cell voltage of 1.80 V to permit a current density of 10 mA/cm² for water electrolysis suggesting it as a very effective electrocatalyst for water splitting.