Structural and Reactivity Effects of Secondary Metal Doping into Iron-Nitrogen-Carbon Catalysts for Oxygen Electroreduction

Abstract

While improved activity was recently reported for bimetallic iron-metal-nitrogen-carbon (FeMNC) catalysts for the oxygen reduction reaction (ORR) in acid medium, the nature of active sites and interactions between the two metals are poorly understood. Here, FeSnNC and FeCoNC catalysts were structurally and catalytically compared to their parent FeNC and SnNC catalysts. While CO cryo-chemisorption revealed a twice lower site density of M-Nx sites for FeSnNC and FeCoNC relative to FeNC and SnNC, the mass activity of both bimetallic catalysts is 50–100% higher than that of FeNC due to a larger turnover frequency in the bimetallic catalysts. Electron microscopy and X-ray absorption spectroscopy identified the coexistence of Fe-Nx and Sn-Nx or Co-Nx sites, while no evidence was found for binuclear Fe-M-Nx sites. 57Fe Mössbauer spectroscopy revealed that the bimetallic catalysts feature a higher D1/D2 ratio of the spectral signatures assigned to two distinct Fe-Nx sites, relative to the FeNC parent catalyst. Thus, the addition of the secondary metal favored the formation of D1 sites, associated with the higher turnover frequency.

Chemical Kinetic Method for Active-Site Quantification in Fe-N-C Catalysts and Correlation with Molecular Probe and Spectroscopic Site-Counting Methods

“…Mössbauer spectroscopy shows limited generality due to the nature of the Mössbauer effect, whereas the probe molecule and kinetic methods show promise (Table ). It is worth noting, however, that the specificity of Mössbauer spectroscopy can be an advantage when Fe is present in bimetallic or multimetallic catalysts . Some limitations have been encountered with CO pulse chemisorption.…”

Tailoring the Electronic Metal‐Support Interactions in Supported Silver Catalysts through Al modification for Efficient Ethylene Epoxidation

“…Enhanced structural properties and outstanding catalytic performance of metal-modified oxide catalysts have raised tremendous research interest. [1][2][3][4] In particular, the modification by non-noble metals has been extensively utilized in heterogeneous catalytic reactions. [5][6][7][8] By loading a decorating metal onto catalyst support and supported metal particles, the support might induce significant electronic perturbations of the supported metal particles, denoted as electronic metal-support interactions (EMSIs), which can modulate the d-band centers of the metal, leading to excellent catalytic performance.…”

“…Enhanced structural properties and outstanding catalytic performance of metal‐modified oxide catalysts have raised tremendous research interest [1–4] . In particular, the modification by non‐noble metals has been extensively utilized in heterogeneous catalytic reactions [5–8] .…”

Breaking Sabatier's vertex via switching the oxygen adsorption configuration and reaction pathway on dual active sites for acidic oxygen reduction

“…Recently, various dual-atom catalysts have been exploited for the ORR, [27][28][29][30][31][32][33] but the O 2 adsorption behaviour and the mechanism of O-O breakage on diatomic catalysts are still ambiguous. It has been reported that the direct O-O breakage in the dissociative pathway requires overcoming a much higher energy barrier than protonated *O-OH cleavage in the associative path.…”