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Replacing precious Pt-based catalysts with cheap and earthabundant materials to facilitate the sluggish oxygen reduction reaction(ORR)at the cathode is critical to realize the commercialization of fuel cells.In this work,we explored the potential of utilizing the experimentally available carbon(C)-doped boron nitride(BN)nanosheet as an ORR electrocatalyst by means of comprehensive density functional theory(DFT)computations.Our computations revealed that C-singly doping into h-BN nanosheets can cause high spin density and charge density and reduce the energy gap,resulting in the enhancement of O2 adsorption.In particular,the CN sheet(substituting N by C atom)exhibits appropriate chemical reactivity toward O2 activation and promotes the subsequent ORR steps to take place though a four-electron OOH hydrogenation pathway with the largest activation barrier of 0.61 eV,which is lower than that of the Pt-based catalyst(0.79 eV).Therefore,the CN-based BN sheet is a promising metal-free ORR catalyst for fuel cells.