Oxygen Reduction Reactions on Single‐ or Few‐Atom Discrete Active Sites for Heterogeneous Catalysis

• Published in: Advanced energy materials Vol. 10; no. 11
• Main Authors: Sharifi, Tiva, Gracia‐Espino, Eduardo, Chen, Anran, Hu, Guangzhi, Wågberg, Thomas
• Format: Journal Article
• Language: English
• Published: 01.03.2020
• Subjects: active sites; catalyst motifs; electrocatalysis; oxygen reduction reaction; single active atom catalysts; transition metals; X‐ray adsorption spectroscopy
• ISSN: 1614-6832; 1614-6840
• DOI: 10.1002/aenm.201902084

The oxygen reduction reaction (ORR) is of great importance in energy‐converting processes such as fuel cells and in metal–air batteries and is vital to facilitate the transition toward a nonfossil dependent society. The ORR has been associated with expensive noble metal catalysts that facilitate the O2 adsorption, dissociation, and subsequent electron transfer. Single‐ or few‐atom motifs based on earth‐abundant transition metals, such as Fe, Co, and Mo, combined with nonmetallic elements, such as P, S, and N, embedded in a carbon‐based matrix represent one of the most promising alternatives. Often these are referred to as single atom catalysts; however, the coordination number of the metal atom as well as the type and nearest neighbor configuration has a strong influence on the function of the active sites, and a more adequate term to describe them is metal‐coordinated motifs. Despite intense research, their function and catalytic mechanism still puzzle researchers. They are not molecular systems with discrete energy states; neither can they fully be described by theories that are adapted for heterogeneous bulk catalysts. Here, recent results on single‐ and few‐atom electrocatalyst motifs are reviewed with an emphasis on reports discussing the function and the mechanism of the active sites. The oxygen reduction reaction is of great importance in energy‐converting processes. Here, recent results on single‐ or few‐atom motifs based on earth‐abundant transition metals, such as Fe, Co, and Mo, combined with nonmetallic elements, such as P, S, and N, embedded in a carbon‐based matrix are reviewed with an emphasis on the function and the mechanism of the active sites.