Steric construction and modulation of Co–Nx single-atom electrocatalysts via polyoxometalate clusters integration

Single-atom catalysts (SACs) with nitrogen-coordinated transition metal sites (M-Nx) hold great promise for electrocatalytic oxygen reduction and oxygen evolution reactions (ORR, OER). Despite substantial achievements based on the confinement pyrolysis and heteroatom-doping methods, the M-Nx SACs still suffer from low yield of atomic sites and less tenability of electronic states of M-Nx center. Here, an innovate synthesis methodology is proposed for surface integrating Co atoms onto polyoxometalate (POM) and its derivative clusters, which promise to regulate the atomic distribution and coordination environments of Co-Nx SACs at the sub-nanometer level. The synthetic procedures exhibit general applicability for a variety of POM clusters to achieve high atomic Co loading up to 9.9 wt%. Steric integration by POM-derived clusters (e.g. MoN) also impart strengthened d-p orbital hybridization of Co-Nx SACs by the formation of Co-N-Mo bonding, which surpass common heteroatoms toward modulating the geometric and electronic structures of M-Nx SACs, leading to pronounced catalytic activity and durability. This work validates the effectiveness of the unique POM-integration strategy toward atomic dispersion of transition metal, further guides the engineering of M-Nx SACs to promote catalytic performance from the sub-nanometer scale.