The design of cost-effective and highly efficient catalysts for a wide range of electrochemical energy storage applications remains a key element in the societal pursuit of sustainable energy. [1-3] In particular, the electrocatalytic splitting of water to generate hydrogen and oxygen enables the storage of a large amount of energy. [4-6] However, the oxygen evolution reaction (OER) at the anode of a water electrolyzer is kinetically hampered by a complex four-electron oxidation process and therefore requires a considerable overpotential () that could cause significant losses to the overall efficiency of water splitting. To afford fast kinetics and low overpotential in practical applications, noble metal oxide catalysts (e.g., IrO 2 and RuO 2) are often involved, [7,8] but the high cost and scarcity of precious metals hinder their large-scale use. Furthermore, these precious-metal catalysts suffer from poor durability over long-term operations. [9-11] Therefore, it is of prime importance to develop low-cost and earth-abundant alternatives with comparable or even better catalytic activity and improved stability than stateof-the-art precious metal catalysts to achieve energy production on a large scale.