A Stable Graphitic, Nanocarbon‐Encapsulated, Cobalt‐Rich Core–Shell Electrocatalyst as an Oxygen Electrode in a Water Electrolyzer

The oxygen electrode plays a vital role in the successful commercialization of renewable energy technologies, such as fuel cells and water electrolyzers. In this study, the Prussian blue analogue‐derived nitrogen‐doped nanocarbon (NC) layer‐trapped, cobalt‐rich, core–shell nanostructured electrocatalysts (core–shell Co@NC) are reported. The electrode exhibits an improved oxygen evolution activity and stability compared to that of the commercial noble electrodes. The core–shell Co@NC‐loaded nickel foam exhibits a lower overpotential of 330 mV than that of IrO2 on nickel foam at 10 mA cm−2 and has a durability of over 400 h. The commercial Pt/C cathode‐assisted, core–shell Co@NC–anode water electrolyzer delivers 10 mA cm−2 at a cell voltage of 1.59 V, which is 70 mV lower than that of the IrO2–anode water electrolyzer. Over the long‐term chronopotentiometry durability testing, the IrO2–anode water electrolyzer shows a cell voltage loss of 230 mV (14%) at 95 h, but the loss of the core–shell Co@NC–anode electrolyzer is only 60 mV (4%) even after 350 h cell‐operation. The findings indicate that the Prussian blue analogue is a class of inorganic nanoporous materials that can be used to derive metal‐rich, core–shell electrocatalysts with enriched active centers. Prussian blue analogue‐derived porous nanocarbon‐encapsulated cobalt metal‐rich core–shell electrocatalysts show improved oxygen evolution activity and ultrastability compared to the state‐of‐the‐art catalyst in alkaline water electrolyzer, due to the existence of the coordinatively unsaturated active centers. Porous and thin carbon layers enhance the active site–electrolyte interface and suitable electron pathways during the water electrolysis.