A Molecular Assembly Promotes Reactivity of Cobalt Redox Intermediates in Electrochemical Oxygen Evolution

To optimize the intrinsic activities of catalytic sites at high surface density is crucial for advancing heterogeneous molecular electrocatalysis. However, it remains elusive due to a lack of an appropriate heterogenization strategy in the catalyst design using ubiquitous graphitic supports. Herein, oxidized molybdenum disulfide nanodots (MoSO_x-d) with abundant sulfates edges are identified as efficient linkers to molecular Co-2, 2′-bipyridine (Co(py)₂) complexes, enabling a relatively high surface density of heterogenous Co sites. The sulfates tuned the Co sites from first to second spheres by forming a CoO₂S coordination linkage, which resulted in a moderately reactive HO-Co³⁺-OH intermediate in a Co²⁺, Co³⁺ to Co⁴⁺ redox-mediated pathway for oxygen evolution. This improved the intrinsic turnover frequencies (TOFs) of Co sites compared to ones grafted on common graphitic supports, as well as pristine molybdenum disulfide. A relatively low overpotential (η) of 314 mV is achieved at a current density of 10 mV cm⁻². These results establish a straightforward bottom-up strategy for constructing molecularly well-defined and surface-dense active sites for high-performance electrocatalysis.