Axial Phosphate Coordination in Co Single Atoms Boosts Electrochemical Oxygen Evolution.

Cobalt single atoms coordinated with planar four nitrogen atoms (Co 1 N 4 ) represent an efficient electrocatalyst for oxygen evolution reaction (OER), whereas the large energy barrier of CoOH dehydrogenation limits the OER activity. Herein, axial phosphate (PO 4 ) coordination is incorporated in Co 1 N 4 single atoms of cobalt phthalocyanine@carbon nanotubes (P-CoPc@CNT), so as to boost the intrinsic OER performance through manipulating the reaction pathway. With a relative low mass loading of Co (2.7%), the P-CoPc@CNT shows remarkable alkaline OER activity with the overpotential of 300 mV and Tafel slope of 41.7 mV dec -1 , which dramatically outperforms the CoPc@CNT without axial PO 4 coordination. Based on mechanistic analysis, the axial PO 4 coordination directly participates in the OER cycle by the transformation of axial ligand. Specially, the CoOH dehydrogenation process is replaced by the dehydrogenation of HPO 4 -Co 1 N 4 intermediate, which largely decreases the energy barrier and thus benefits the whole OER process.