Cobalt-Based Noble-Metal-Free Electrocatalysts for Acidic Oxygen Evolution Reaction Toward Practical Proton Exchange Membrane Water Electrolysis

Proton exchange membrane water electrolyzer (PEMWE) is one of the promising techniques to produce high-purity and green hydrogen when powered by sustainable electricity. Its large-scale implementation is currently limited by the limited reserve and high cost of noble metal Ir/Ru-based electrocatalysts for the anodic oxygen evolution reaction (OER) in acidic conditions. It is therefore highly desirable to develop highly active, durable, and nonprecious metals like cobalt-based acidic OER electrocatalysts for practical PEMWE. In this Concept, a recent achievement in developing cobalt-based noble-metal-free electrocatalysts for acidic OER in PEMWE is highlighted and future opportunities are discussed. We begin with a brief introduction of three typical OER mechanisms including the adsorbate evolution mechanism (AEM), lattice-oxygen-mediated mechanism (LOM), and oxide path mechanism (OPM), and then discuss the thermodynamic stability region of cobalt species under different pH and potential conditions by means of the corresponding Pourbaix diagram. Subsequently, several representative cobalt-based nonprecious electrocatalysts are reviewed, with emphasis on their rational design, structure-activity/stability correlation, and performance in practical PEMWE. Remarks on the challenges and perspectives in this field are also provided finally.