Probing the Active Sites of Carbon‐Encapsulated Cobalt Nanoparticles for Oxygen Reduction

Abstract

Great effort has been contributed to exploring efficient and cost‐effective oxygen reduction reaction (ORR) catalysts for fuel cell applications in the past decades. Now various electrocatalysts can be synthesized for high‐performance ORR catalysis. However, the identification of the ORR active sites in many nonprecious metal‐based catalysts is still difficult. This is due to the heterogeneity and complexity of the catalyst structures. For example, the active site of core–shell ORR electrocatalysts has been a continuously debatable issue, hampering the exploration of new ORR catalysts. Herein, a carbonized Co metal organic framework (Co@C) is used to uncover the ORR active sites in core–shell electrocatalysts. The surface Co particles in the Co@C sample are removed by HCl wash, and the Co cores are removed using an electrochemical activation method. The characterizations reveal that both the samples before and after the electrochemical activation show the existence of single Co species. The corresponding electrocatalysis test results indicate that neither the surface Co particles nor the encapsulated Co cores influence the ORR performance of the samples. It is deduced that the single Co species coordinated with the nitrogen in the carbon layers of the core–shell catalysts are the actual ORR active sites.

Bacterium, Fungus, and Virus Microorganisms for Energy Storage and Conversion

“…Carbon‐based materials have stimulated great interest as catalysts in hydrogen evolution reaction (HER), ORR, etc. However, pure carbon materials with little defects and active sites are electrochemically inert and exhibit inferior catalytic abilities.…”

Defective Structures in Metal Compounds for Energy‐Related Electrocatalysis

“…Energy‐related electrocatalysis plays a deciding role in accelerating the electrode reactions such as in hydrogen‐based proton exchange membrane fuel cells (PEMFCs), overall water splitting, electrochemical nitrogen and carbon dioxide fixation, and lithium‐ion batteries (LIBs). [ 1–7 ] Extensive research has been devoted to exploiting low‐cost and efficient materials to replace the expensive noble metal‐based electrocatalysts such as Pt, Pd, RuO 2 , and IrO 2 . Transition metal compounds and metal‐free carbon materials as the alternatives are widely studied.…”

Strategies for Engineering High‐Performance PGM‐Free Catalysts toward Oxygen Reduction and Evolution Reactions

“…[ 40 ] The intrinsic activity of M‐N‐C catalysts still needs further improvement and the understanding of the real active sites is still controversial because of the complicated components in M‐N‐C catalysts (i.e., the active sites may involve core@shell M@C, metals, oxides, heteroatom‐doped carbon, single‐atom MN x moieties, etc.). [ 41 ] For example, the core–shell structure with Fe and Fe 3 C cores encapsulated by (N‐doped) carbon shells were demonstrated as the active sites for ORR due to the unique electronic interaction between guest and host. [ 42 ] The metals and their oxides supported by carbon were also found to be the active sites for ORR.…”