Direct Chemical Synthesis of Lithium Sub-Stochiometric Olivine Li0.7Co0.75Fe0.25PO4 Coated with Reduced Graphene Oxide as Oxygen Evolution Reaction Electrocatalyst

Abstract

The oxygen evolution reaction (OER) is of fundamental importance for the development of renewable energies. Research on earth-abundant, efficient, and stable OER electrocatalysts is a key factor for the technological improvement of water-splitting systems. In this article, we demonstrate OER performance of olivine-type lithium earth-abundant transition-metal phosphates coated with reduced graphene oxide (rGO). We report on LiCoPO4/rGO and the solid solutions Li1–xCoyFe1–yPO4/rGO synthesized by a nonaqueous sol–gel microwave reaction. Interestingly, such conditions allow for the direct synthesis of substochiometric Li0.7Co0.75Fe0.25PO4/rGO compound with improved OER activity. The materials crystallize in the olivine orthorhombic phase with nanoplatelet-like shape with nanometer-size thickness and micrometer-size width. The substochiometric phase Li0.7Co0.75Fe0.25PO4/rGO exhibits the best OER activity in alkaline medium, generating a current density of 5 mA cm–2 at an overpotential of 0.39 V and a Tafel slo...