Single-atom catalysts (SACs) supported on two-dimensional (2D) materials are highly attractive for maximizing their catalytic activity.However,graphene based SACs are primarily bonded with nitrogen and carbon sites,resulting in poor performance for the oxygen evolution reaction (OER).Herein,we develop a general bimetal-ion adsorption strategy for the synthesis of individually dispersed Ni SACs anchored on the oxygenated sites of ultrathin reduced graphene oxide as efficient OER electmcatalysts.The resultant Ni SACs for OER in alkaline electrolyte exhibit a highly stable overpotential of 328 mV at the current density of 10 mA cm-2,and Tafel slope of 84 mV dec-1 together with long-term durability and negligible degradation for 50 h,which is greatly outperform its counterparts of nitrogen bonded Ni SACs (564 mV,364 mV dec-1) and Ni(OH)2 nanoparticles anchored on graphene (450 mY,142 mV dec-1),and most reported Ni based OER electrocatalysts.Furthermore,the extended X-ray absorption fine structure at the Ni K-edge and theoretical simulation reveal that the nickel-oxygen coordination significantly boost OER performance.Therefore,this work will open numerous opportunities for creating novel-type 2D SACs via oxygen-metal bonding as highly robust OER catalysts.