Hierarchical porous single-wall carbon nanohorns with atomic-level designed single-atom Co sites toward oxygen reduction reaction

• Published in: Nano energy 2022-06, Vol.97, p.107206, Article 107206
• Main Authors: Jung, Jae Young, Kim, Sungjun, Kim, Jeong-Gil, Kim, Min Ji, Lee, Kug-Seung, Sung, Yung-Eun, Kim, Pil, Yoo, Sung Jong, Lim, Hyung-Kyu, Kim, Nam Dong
• Format: Article
• Language: English
• Subjects: Anion exchange membrane fuel cells; Hierarchical pore structure; Oxygen reduction reaction; Single atom catalysts; Single-wall carbon nanohorns
• ISSN: 2211-2855
• DOI: 10.1016/j.nanoen.2022.107206

Hierarchical pore structure is crucial for effective mass transfer and utilization of a number of active sites in single-metal atom catalysts. Here, we present a strategy for developing a hierarchical porous structure in single-wall carbon nanohorns with Co-Nx sites (Co/CNH) and maximizing their oxygen reduction activity. Thermal annealing is effective for generating hierarchical pore by removing amorphous carbons and opening internal and interstitial pore channels. Ammonia annealing modifies coordination structure and relieves local strain around cobalt atoms to form more ideal Co-N4-C moieties. DFT calculations reveal that the enhanced intrinsic catalytic activity (ik = 60.16 mA cm−2 for Co/CNH Air NH3 vs. 8.24 mA cm−2 for Pt/C) is attributed to the ligand-push effect of water molecules on the other side of Co-N4 sites. In a single-cell experiment, a power density of 742 mW cm−2 was achieved, which is the remarkably high value among M-N-C catalysts using commercialized membrane electrode assemblies (MEAs). [Display omitted] •We synthesized a hierarchical porous single-wall carbon nanohorns with Co-Nx sites.•Annealing played a critical role in the formation of hierarchical porous structures.•A superior activity was achieved, which is 7.3 times higher than commercial Pt/C.•The high catalytic activity originates from ligand push effect of the water to Co-N4.•A power density of 742 mW cm−2 was achieved, which is remarkable high performance among SACs.