Electronic Spin Moment As a Catalytic Descriptor for Fe Single-Atom Catalysts Supported on C₂N

Abstract

The electrocatalytic activity of transition-metal-based compounds is strongly related to the spin states. However, the underlying relationship connecting spin to catalytic activity remains unclear. Herein, we carried out density functional theory calculations on oxygen reduction reaction (ORR) catalyzed by Fe single-atom supported on C2N (C2N–Fe) to shed light on this relationship. It is found that the change of electronic spin moments of Fe and O2 due to molecular-catalyst adsorption scales with the amount of electron transfer from Fe to O2, which promotes the catalytic activity of C2N–Fe for driving ORR. The nearly linear relationship between the catalytic activity and spin moment variation suggests electronic spin moment as a promising catalytic descriptor for Fe single-atom based catalysts. Following the revealed relationship, the ORR barrier on C2N–Fe was tuned to be as low as 0.10 eV through judicious manipulation of spin states. These findings thus provide important insights into the relationship between catalytic activity and spin, leading to new strategies for designing transition metal single-atom catalysts.

An Adjacent Atomic Platinum Site Enables Single‐Atom Iron with High Oxygen Reduction Reaction Performance

“…To further investigate the impact of Pt-N 4 site on the Fe-N 4 site for OOH* adsorption, the projected density of states (PDOS) calculations was carried out for the d orbitals of Fe and p orbital of Of or Fe-N 4 and Fe-N 4 /Pt-N 4 after OOH* adsorption, respectively.A sd epicted in Figure 1c,f or OOH bonding on Fe site in pristine Fe-N 4 ,t he frontier orbitals for FeÀObonding are mainly p*anti-bonding orbitals,leading to relatively weak Fe-OOH bonding.I nc ontrast, as shown in Figure 1d,t he introduction of Pt greatly varies the orbital energy levels and spatial distributions of Fe 3d orbitals, making the original p 3 *a nti-bonding orbitals become p bonding orbitals by the rehybridization of Fe d z 2 and O p orbitals.T his thus strengthens the Fe À Ob ond [24] and makes the adsorption free energy of OOH* intermediate increases by 0.37 eV.Intriguingly,the free energy diagrams in Figure 1b also show that the adsorption free energy of O* and OH* are increased by 0.18 and 0.20 eV,r espectively,m aking the potential-limiting step from OOH* adsorption to OH* desorption and lowering down the overpotential from 1.18 to 1.03 Va fter co-embedding Pt-N 4 with Fe-N 4 .S uch overpotential reduction caused by enhancing the adsorption of intermediates has also been reported in many other graphenebased systems,such as FeCoN 5 . [7a] and O p orbitals can form p 1 bond, and the Fe d xy , d x 2 Ày 2 and O p orbitals can form p 2 bond.…”

An Adjacent Atomic Platinum Site Enables Single‐Atom Iron with High Oxygen Reduction Reaction Performance

“…In contrast, as shown in Figure 1 d, the introduction of Pt greatly varies the orbital energy levels and spatial distributions of Fe 3d orbitals, making the original π 3 * anti‐bonding orbitals become π bonding orbitals by the rehybridization of Fe d and O p orbitals. This thus strengthens the Fe−O bond [24] and makes the adsorption free energy of OOH* intermediate increases by 0.37 eV. Intriguingly, the free energy diagrams in Figure 1 b also show that the adsorption free energy of O* and OH* are increased by 0.18 and 0.20 eV, respectively, making the potential‐limiting step from OOH* adsorption to OH* desorption and lowering down the overpotential from 1.18 to 1.03 V after co‐embedding Pt‐N 4 with Fe‐N 4 .…”

Understanding Single-Atom Catalysis in View of Theory

“…Zhong et al reported the oxygen reduction reaction catalyzed by single iron atoms supported on C 2 N, and they found a nearly linear relationship between the catalytic activity and spin moment variation. 103 The spin–activity correlation in a single Co atom supported by TaS 2 -catalyzed oxygen evolution reaction was also reported in a combined experimental and theoretical work. 104 By using ab initio nonadiabatic molecular dynamics simulations, Cheng et al found the spin selection could enhance charge carrier lifetimes and thus boost the reaction in a photocatalytic water-splitting reaction catalyzed by single copper atoms on Anatase TiO 2 .…”