Engineering Atomically Dispersed FeN₄ Active Sites for CO₂ Electroreduction

Abstract

Atomically dispersed FeN4 active sites have exhibited exceptional catalytic activity and selectivity for the electrochemical CO2 reduction reaction (CO2RR) to CO. However, the understanding behind the intrinsic and morphological factors contributing to the catalytic properties of FeN4 sites is still lacking. By using a Fe‐N‐C model catalyst derived from the ZIF‐8, we deconvoluted three key morphological and structural elements of FeN4 sites, including particle sizes of catalysts, Fe content, and Fe−N bond structures. Their respective impacts on the CO2RR were comprehensively elucidated. Engineering the particle size and Fe doping is critical to control extrinsic morphological factors of FeN4 sites for optimal porosity, electrochemically active surface areas, and the graphitization of the carbon support. In contrast, the intrinsic activity of FeN4 sites was only tunable by varying thermal activation temperatures during the formation of FeN4 sites, which impacted the length of the Fe−N bonds and the local strains. The structural evolution of Fe−N bonds was examined at the atomic level. First‐principles calculations further elucidated the origin of intrinsic activity improvement associated with the optimal local strain of the Fe−N bond.

Boosting Electroreduction Kinetics of Nitrogen to Ammonia via Tuning Electron Distribution of Single‐Atomic Iron Sites

“…[10] TheE XAFS spectrum of Fe SA -N-C-900 ( Figure 3e) shows as trong peak centered at 1.48 ,w hich is mainly attributed to the scattering of Fe-N or Fe-O coordination. [11] Moreover,i nc omparison with Fe foil and Fe 2 O 3 ,t he scattering peaks derived from Fe-Fec oordination is not observed in the Fe SA -N-C-900, demonstrating the atomic dispersion of Fe species in the N,O-codoped carbon matrix. Thecoordination configuration of the Fe atom in Fe SA -NO-C-900 was further investigated by quantitative EXAFS curve fitting analyses (Figure 3f), which clearly reveal that the Fe center is coordinated with two Natoms and four Oatoms.T o gain further insights into the chemical configuration of the Fe atom, FT EXAFS fittings in R, q, and ks paces were also carried out to give the structural parameters and evaluate the fitting quality ( Figures S11,12).…”

Carbon‐Supported Single Metal Site Catalysts for Electrochemical CO2 Reduction to CO and Beyond

“…To address this issue, we developed a controllable synthesis method to obtain a series of FeN 4 model catalysts, as shown in Figure , and comprehensively studied the effect of particle size (Figure 7a), Fe content (Figure 7b), and FeN bond structure on CO 2 RR performance. [ 83 ] This method involves the synthesis of N‐doped carbon frameworks through the carbonization of ZIF‐8 and followed by subsequent thermal activation to form FeN 4 sites. It separates the FeN bond formation from complex carbonization and N doping process, which facilitates the control of FeN 4 formation and enables the exclusive investigation of the impact of the thermal activation conditions on the structural evolution of FeN 4 sites.…”

Dynamically Unveiling Metal–Nitrogen Coordination during Thermal Activation to Design High‐Efficient Atomically Dispersed CoN4 Active Sites

“…In our previous study on strained FeN 4 active site, [2] we found that some degrees of compressive strain in the FeN 4 moiety would facilitate the *OOH dissociation process and hence kinetically enhance the ORR. Here, we calculated two possible sites: a CoN 4 site embedded in a graphene layer (Figure 5 a) [2, 6, 47–49] and a CoN 2+2 active site bridging two graphene edges (Figure 5 b). [48, 50] The 2 % compressively strained CoN 4 site has a nonplanar configuration with shortened Co−N bonds, while the 1.5 % compressively strained CoN 2+2 active site still maintains the planar configuration.…”