An Investigation of Iron-Induced Reconstruction of a Molecular Cobalt Precatalyst for Efficient Oxygen Evolution

Alkaline solutions are widely applied for molecular cobalt (Co)-based electrocatalysis of the oxygen evolution reaction (OER) for achieving steady and high performance. Trace iron (Fe) impurity is commonly contained in alkaline solutions, and its potential impact on affecting the coordination spheres of Co sites with the relevant OER performance remains unclear. Herein, sulfur-doped graphene was applied as a solid matrix to immobilize a molecular Co-2,2'-bipyridine complex, thereby constructing a straightforward Co-based heterogeneous molecular catalyst. It revealed that the Co sites can couple with the Fe impurity of alkaline solutions to decrease the OER overpotential by 70 mV@10 mA cm^-2. <i>In situ</i> Raman spectral analysis identified the coupling configuration as Co-O-Fe coordination. Systematic control experiments suggested that Fe coupling on the molecular Co sites is more efficient for enhancing the OER activity than on traditional Co(OH)₂ solids. Furthermore, the coupled Fe species exist in a dynamic equilibrium between the solid catalyst and the aqueous solution, which is critical for maintaining the Co-Fe coupling and sustaining high OER performance. This work for the first time mechanistically reveals how to improve Co-based OER activity at the molecular level and sheds light on developing novel heterogeneous molecular electrocatalysts.