Iron sulphide rice grain nanostructures as potential electrocatalysts for an improved oxygen evolution reaction

Iron based chalcogenides are considered a promising group of electro-active materials for various electrochemical technologies. Herein we demonstrate a facile fabrication of various iron sulphide (FeS) nanostructures, including rice grains (RGS)-, nanoflowers (NFS)- and nanoparticles (NPS)-like surface morphologies via electrochemical, solvothermal and chemical strategies, respectively. The as-developed FeS nanostructures have been employed as electrocatalysts for the oxygen evolution reaction (OER) in an alkaline electrolyte. Among other FeS nanostructures, FeS rice grains (FeS-RGS) exhibited an outstanding OER activity with a low onset potential (∼1.37 V), low overpotential (∼0.20 V), small Tafel slope (∼54.2 mV dec^-1), high mass activity (∼5.4 A g^-1), and high durability, outperforming the commercial state-of-the-art RuO₂ catalyst. The high-performance OER activity of the FeS-RGS is associated not only to the synergistic effect of Fe and S, but also to the direct growth (binder-free) and edges of rice grain structures, offering a large number of electrochemical active sites and ensuring fast-diffusion of OH^- ions of the nanostructures. The present one-step, low-cost and highly scalable preparation of FeS-RGS nanostructures provides new possibilities of morphology and synthetic methodology dependence of OER electrocatalysts for effective hydrogen production.