Hierarchical Nanostructured Electrocatalysts for Oxygen Reduction Reaction

Hierarchical nanostructured materials, which possess the porous structure of multiscale porosities on different pore diameters from micro-, meso- to macropores based on International Union of Pure and Applied Chemistry, are much desired to present the synergistic attractive advantages of each scale of hierarchical pores in the development of catalysis, adsorption, separation, energy, and biochemistry. The use of hierarchical nanostructured materials as oxygen reduction reaction (ORR) electrocatalysts is advanced to increase specific surface area for active sites dispersion and exposure as well as enhance reactants/products transfer. However, complex and costly templateincorporated methods and relatively uncontrollable template-free methods motive us to develop novel and efficient preparation methods. Herein, recent developments and synthesis strategies that have been made in the field of hierarchical nanostructured materials as well as their application for ORR electrocatalysts are reviewed.