Grain boundaries dominate the property of polycrystalline graphene. We report first-principles calculations and classical molecular dynamics simulations that reveal enhanced defect reactivity induced by an inhomogeneous strain field at grain boundaries. Strained carbon bonds located at heptagons and pentagons can accumulate interstitials and single vacancies, respectively. We find that recombination of vacancies and interstitials can occur locally at grain boundaries, which serve as effective sinks, resulting in efficient annealing of defects. The enhanced defect reactivity indicates that grain boundaries may be manipulated by point defects.
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