Facile synthesis of yolk-shell structured ZnFe ₂ O ₄ microspheres for enhanced electrocatalytic oxygen evolution reaction

In this paper, yolk-shell structured ZnFe ₂ O ₄ microspheres assembled using nanoparticles are prepared using a facile solvothermal method and annealing treatment. Through a series of time-dependent experiments, the formation mechanism of the yolk-shell structured ZnFe ₂ O ₄ microspheres is attributed to the Ostwald ripening process. It is worth noting that the yolk-shell structured ZnFe ₂ O ₄ microspheres show a high surface area of 69.94 m ² g ^-1 with a total pore volume of 5.54 cm ³ g ^-1 . The as-prepared yolk-shell structured ZnFe ₂ O ₄ microspheres exhibit an overpotential of 280 mV at a current density of 10 mA cm ^-2 and the Tafel slope is 70 mV dec ^-1 which results in excellent electrocatalytic oxygen evolution capability. Compared with ZnFe ₂ O ₄ particles (without yolk-shell structure), the superior oxygen evolution reaction property can be attributed to one of the most important factors: namely the mesopore/macropore structure with a high surface area and the unique yolk-shell morphology assembled by nanoparticles, which can provide more active sites and enhance the contact of the reactant and active sites to help the transfer of electrons, thereby improving the catalytic activity.