Axial Phosphate Coordination in Co Single Atoms Boosts Electrochemical Oxygen Evolution

Abstract

Cobalt single atoms coordinated with planar four nitrogen atoms (Co1N4) 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 (PO4) coordination is incorporated in Co1N4 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 PO4 coordination. Based on mechanistic analysis, the axial PO4 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 HPO4-Co1N4 intermediate, which largely decreases the energy barrier and thus benefits the whole OER process.