cs9b02594_si_001.pdf (2.37 MB)
Volcano Trend in Electrocatalytic CO2 Reduction Activity over Atomically Dispersed Metal Sites on Nitrogen-Doped Carbon
journal contribution
posted on 2019-10-18, 14:09 authored by Jingkun Li, Paulina Pršlja, Tatsuya Shinagawa, Antonio José Martín Fernández, Frank Krumeich, Kateryna Artyushkova, Plamen Atanassov, Andrea Zitolo, Yecheng Zhou, Rodrigo García-Muelas, Núria López, Javier Pérez-Ramírez, Frédéric JaouenThe development of
catalysts for electrochemical reduction of carbon
dioxide (eCO2RR) with high activity and selectivity remains
a grand challenge to render the technology useable. As promising candidates,
metal–nitrogen–carbon (MNC) catalysts with metal atoms
present as atomically dispersed metal–Nx moieties (MNx, M = Mn, Fe, Co,
Ni, and Cu) were investigated as model catalysts. The distinct activity
for CO formation observed along the series of catalysts is attributed
to the nature of the transition metal in MNx moieties because of otherwise similar composition, structure,
and morphology of the carbon matrix. We identify a volcano trend between
their activity toward CO formation and the nature of the transition
metal in MNx sites, with Fe and/or Co
at the top of the volcano, depending on the electrochemical potential.
Regarding selectivity, FeNC, NiNC, and MnNC had Faradaic efficiency
for CO >80%. To correctly model the active sites in operando conditions,
experimental operando X-ray absorption near edge structure spectroscopy
was performed to follow changes in the metal oxidation state with
electrochemical potential. Co and Mn did not change the oxidation
state with potential, whereas Fe and Ni were partially reduced and
Cu largely reduced to Cu(0). Computational models then led to the
identification of M2+N4–H2O as the most active centers in FeNC and CoNC, whereas Ni1+N4 was predicted as the most active one in NiNC at the
considered potentials of −0.5 and −0.6 V versus the
reversible hydrogen electrode. The experimental activity and selectivity
could be rationalized from our density functional theory results,
identifying in particular the difference between the binding energies
for CO2*– and H* as a descriptor of selectivity
toward CO. This in-depth understanding of the activity and selectivity
based on the speciation of the metals for eCO2RR over atomically
dispersed MNx sites provides guidelines
for the rational design of MNC catalysts toward eCO2RR
for their application in high-performance devices.