Water oxidation is the primary reaction of both natural and artificial photosynthesis. Developing active and robust water oxidation catalysts (WOCs) is the key to constructing efficient artificial photosynthesis systems, but it is still facing enormous challenges in both fundamental and applied aspects. Here, the recent developments in molecular catalysts and heterogeneous nanoparticle catalysts are reviewed with special emphasis on biomimetic catalysts and the integration of WOCs into artificial photosystems. The highly efficient artificial photosynthesis depends largely on active WOCs integrated into light harvesting materials via rational interface engineering based on in‐depth understanding of charge dynamics and the reaction mechanism.

The practical deployment of promising NiFe‐based oxygen evolution reaction (OER) electrocatalysts is heavily limited due to the constrain in both stability and activity under industrial conditions. Herein, a 3D free‐standing NiFe(oxy)hydroxide‐based electrode with Schottky junction is constructed, in which NiFe(oxy)hydroxide (NiFe(OH)x) nanosheets are chemically assembled on the top of metal‐like Ni3S2 scaffold that are in situ formed on commercial Ni mesh. Such an assembly enhances the binding strength of each components, promotes the charge transfer across the interfaces, and modulates the electronic and nanostructural features of NiFe(OH)x. Consequently, the electrode delivers current densities of as high as 500 and 1000 mA cm−2 for OER at overpotentials of only 248 and 270 mV with long‐term stability in 1 m KOH. When it was paired with a NiMo hydrogen evolution cathode in a practical two‐electrode system, a current density of 1000 mA cm−2 is achieved at a low cell voltage of ≈1.61 V at 80 °C in 30% KOH without losing performance for at least 1500 h. This is the best performance reported thus far for alkaline water electrolysis under industrial conditions, demonstrating its great potential for practical applications.