Hierarchical Metal-[Carbon Nitride Shell/Carbon Core] Electrocatalysts: A Promising New General Approach to Tackle the ORR Bottleneck in Low-Temperature Fuel Cells

A new family of electrocatalysts (EC) exhibiting a hierarchical (H) core-shell support, wherein the core is covered by a carbon nitride (CN) shell stabilizing the active sites in unique coordination nests, was developed. The synthesis of the resulting HCN-based EC is overviewed, highlighting the role played by each fundamental component and reaction step toward the design of ECs including Pt and exhibiting a well-controlled chemical composition, structure, and morphology to achieve a performance and durability level beyond the state of the art. The features of HCN-based EC are correlated to the trends in performance observed both in ex situ studies via cyclic voltammetry with the thin-film rotating ring disk electrode method and in situ in a single proton-exchange membrane fuel cell tested under operating conditions. The advantages of HCN-based EC in comparison with state-of-the-art EC and with other families of oxygen reduction reaction EC.with finely controlled morphologies are discussed, as well as the unique opportunities created by HCN-based ECs in marketable devices.