1 research outputs found
Synergistic Effect of Sn and Fe in Fe–N<sub><i>x</i></sub> Site Formation and Activity in Fe–N–C Catalyst for ORR
Iron–nitrogen–carbon (Fe–N–C)
materials
emerged as one of the best non-platinum group material (non-PGM) alternatives
to Pt/C catalysts for the electrochemical reduction of O2 in fuel cells. Co-doping with a secondary metal center is a possible
choice to further enhance the activity toward oxygen reduction reaction
(ORR). Here, classical Fe–N–C materials were co-doped
with Sn as a secondary metal center. Sn–N–C according
to the literature shows excellent activity, in particular in the fuel
cell setup; here, the same catalyst shows a non-negligible activity
in 0.5 M H2SO4 electrolyte but not as high as
expected, meaning the different and uncertain nature of active sites.
On the other hand, in mixed Fe, Sn–N–C catalysts, the
presence of Sn improves the catalytic activity that is linked to a
higher Fe–N4 site density, whereas the possible
synergistic interaction of Fe–N4 and Sn–Nx found no confirmation. The presence of Fe–N4 and Sn–Nx was thoroughly
determined by extended X-ray absorption fine structure and NO stripping
technique; furthermore, besides the typical voltammetric technique,
the catalytic activity of Fe–N–C catalyst was determined
and also compared with that of the gas diffusion electrode (GDE),
which allows a fast and reliable screening for possible implementation
in a full cell. This paper therefore explores the effect of Sn on
the formation, activity, and selectivity of Fe–N–C catalysts
in both acid and alkaline media by tuning the Sn/Fe ratio in the synthetic
procedure, with the ratio 1/2 showing the best activity, even higher
than that of the iron-only containing sample (jk = 2.11 vs 1.83 A g–1). Pt-free materials
are also tested for ORR in GDE setup in both performance and durability
tests