Water electrolysis is to split water into hydrogen and oxygen using electricity as the driving force.To obtain low-cost hydrogen in a large scale,it is critical to develop electrocatalysts based on earth abundant elements with a high efficiency.This computational work started with Cobalt on CoTa2O6 surface as the active site,CoTa2O6/Graphene heterojunctions have been explored as potential oxygen evolution reaction (OER) catalysts through density functional theory (DFT).We demonstrated that the electron transfer (δ) from CoTa2O6 to graphene substrate can be utilized to boost the reactivity of Co-site,leading to an OER overpotential as low as 0.30 V when N-doped graphene is employed.Our findings offer novel design of heterojunctions as high performance OER catalysts.