Thermally induced top-down nanostructuring for the synthesis of a core/shell-structured CoO/CoSx electrocatalyst

Abstract

Many bottom-up nanostructuring approaches have benefitted the research field of electrocatalysis by significantly increasing the catalytic activity of electrocatalysts. In general, however, they require tedious wet chemistry steps and delicate control while managing considerable surface energies. In addition, they often suffer from scalability issues. As part of an effort to address these issues, we developed a simple two-step thermal route to produce a nanostructured electrocatalyst with high catalytic activity from its bulk form. In this work, we demonstrate the preparation of core/shell CoO/CoS_x from bulk Co₃O₄ as a case study. Our novel approach uses a low-temperature thermal treatment under NH₃ and a subsequent treatment in a H₂S atmosphere, judiciously exploiting the unique features of each reaction atmosphere. Hot NH₃ treatment reduces Co₃O₄ to CoO, during which a significant lattice mismatch between the Co₃O₄ and CoO fractures crystallites, and the coalescence of oxygen vacancies introduces porosity. Subsequent H₂S treatment specifically forms electrocatalytically active CoS_x species on the surface of CoO. We explore the use of the resulting nanostructured CoO/CoS_x as an alternative to state-of-the-art noble metal catalysts in the triiodide reduction and oxygen evolution reactions, finding that its activity is comparable to those of standard catalysts. Given the simplicity and scalability of this innovative low-temperature reaction concept, we anticipate that the present demonstration will open new avenues for the synthesis of highly active electrocatalysts.