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Abstract Developing Earth-abundant, highly efficient, and anti-corrosion electrocatalysts to boost the oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and hydrogen evolution reaction (HER) for the Zn–air battery (ZAB) and for overall water splitting is imperative. In this study, a novel process starting with Cu2O cubes was developed to fabricate hollow Ni x Co1−x Se nanocages as trifunctional electrocatalysts for the OER, ORR, and HER and a reasonable formation mechanism was proposed. The Ni0.2Co0.8Se nanocages exhibited higher OER activity than its counterparts with the low overpotential of 280 mV at 10 mA cm−2. It also outperformed the other samples in the HER test with a low overpotential of 73 mV at 10 mA cm−2. As an air–cathode of a self-assembled rechargeable ZAB, it exhibited good performance, such as an ultralong cycling lifetime of > 50 h, a high round-trip efficiency of 60.86%, and a high power density of 223.5 mW cm−2. For the application in self-made all-solid-state ZAB, it also demonstrated excellent performance with a power density of 41.03 mW cm−2 and an open-circuit voltage of 1.428 V. In addition, Ni0.2Co0.8Se nanocages had superior performance in a practical overall water splitting, in which only 1.592 V was needed to achieve a current density of 10 mA cm−2. These results show that hollow Ni x Co1−x Se nanocages with an optimized Ni-to-Co ratio are a promising cost-effective and high-efficiency electrocatalyst for ZABs and overall water splitting in alkaline solutions.