Non-noble
metal catalysts for the oxygen reduction reaction (ORR)
showing catalytic activity comparable or even superior to that of
the benchmark Pt/C are highly attractive systems for the development
of a mature fuel cell technology. Fe–N–C moieties exhibit
an optimal performance in the ORR although a synthetic strategy for
their production still remains a challenging matter of catalysis and
materials science. Herein, an original and general protocol for the
preparation of high-density and discrete Fe–N–C-based
single-atom catalysts has been proposed starting from cheap and food-grade
raw components. The rational combination of chelating citrate ions
with the ancillary monodentate thiocyanate (SCN–) ligand has established an “open gate” for water-soluble
iron ions to be accommodated in the form of Fe–N–C moieties
within the final C–N networks. Although recent findings in
the field of electrocatalysis have pointed out the often beneficial
synergistic action between isolated and metallic iron species or iron
carbides and their protecting C–N shells, the poor selectivity
on the nature of the final Fe species in N-doped C-networks remains
a matter of debate and does not shed light on the effective nature
of the active species in the process. The highly metal-loaded catalysts
in the form of highly dispersed Fe–N–C moieties prepared
with the synthetic protocol described in the paper have been tested
as electrocatalysts in the ORR, showing electrocatalytic performance
under an alkaline environment that ranks among the highest reported
so far for related Fe single-atom catalysts (Fe-SACs) of the state-of-the-art.