Electrochemical probing into the active sites of graphitic-layer encapsulated iron oxygen reduction reaction electrocatalysts

Lijie Zhong; Jens Oluf Jensen; Lars Nilausen Cleemann; Chao Pan; Qingfeng Li

doi:10.1016/j.scib.2017.11.017

Electrochemical probing into the active sites of graphitic-layer encapsulated iron oxygen reduction reaction electrocatalysts

Sci Bull (Beijing). 2018 Jan 15;63(1):24-30. doi: 10.1016/j.scib.2017.11.017. Epub 2017 Nov 24.

Authors

Lijie Zhong¹, Jens Oluf Jensen², Lars Nilausen Cleemann², Chao Pan², Qingfeng Li³

Affiliations

¹ Department of Energy Conversion and Storage, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark. Electronic address: lzho@dtu.dk.
² Department of Energy Conversion and Storage, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark.
³ Department of Energy Conversion and Storage, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark. Electronic address: qfli@dtu.dk.

PMID: 36658914
DOI: 10.1016/j.scib.2017.11.017

Abstract

The graphitic-layer encapsulated iron-containing nanoparticles (G@Fe) have been proposed as a potential type of active and stable non-precious metal electrocatalysts (NPMCs) for the oxygen reduction reaction (ORR). However, the contribution of the encapsulated components to the ORR activity is still unclear compared with the well-recognized surface coordinated FeN_x/C structure. Using the strong complexing effect of the iron component with anions, cyanide (CN^-) in alkaline and thiocyanate (SCN^-) in acidic media, the metal containing active sites are electrochemically probed. Three representative catalysts are chosen for a comparison including the as-prepared encapsulated G@Fe, commercial Fe/N/C catalyst with iron-nitrogen coordinated surface functionalities and molecular iron phthalocyanine (FePc) containing well-defined structures and compositions. It was found that all samples showed significant shifts of half-wave potentials indicating that surface Fe coordinated sites in all cases. The G@Fe catalyst showed the weakest poisoning effect (the lowest shifts of half-wave potential) compared to the Fe/N/C and FePc catalysts in both electrolytes. These results could be explained that the encapsulated iron components influence the FeN_x/C and/or N_xC surface functionality.

Keywords: Active sites; Encapsulated Fe catalysts; Ion poisoning; NPMCs; Oxygen reduction reaction.