Porosity-Induced High Selectivity for CO₂ Electroreduction to CO on Fe-Doped ZIF-Derived Carbon Catalysts

Abstract

Metal-doped zeolitic imidazolate framework-8 (ZIF-8)-derived carbon materials are attractive for the electrocatalytic reduction of CO2 into CO. In such carbon materials, due to the fusion and aggregation of ZIF-8 precursors during the high-temperature pyrolysis process, it is desirable yet still challenging to create a high specific surface area with more active sites available for reacting with reactants. Using SiO2 as a protective coating on the ZIF-8 surface, we synthesize Fe, N-co-doped porous carbon nanoparticles (Fe-CNPs) which possess a hierarchical pore structure with a specific surface area as high as 1156.6 m2 g–1, much higher than the counterparts without a SiO2 coating (360.1 m2 g–1). Over these highly porous Fe-CNPs, the total current densities are more than 3 times higher than those of the lowly porous ones for the electrochemical CO2 reduction. More importantly, the maximum CO Faradaic efficiency for Fe-CNPs increases from ca. 75.0 to 98.8% in a concentrated KHCO3 solution (1 mol L–1). The porosity-induced high selectivity for CO production is also revealed on Ni-doped and Co-doped ZIF-derived CNPs, suggesting a new pathway for designing high-performance carbon catalysts through engineering the porosity for the electrochemical CO2 reduction.

Achieving Near‐Unity CO Selectivity for CO2 Electroreduction on an Iron‐Decorated Carbon Material

“…It has to be pointed out that one cannot directly compare the current densities recorded in linear sweep voltammetry and electrolysis experiments as they are recorded under different experimental conditions. Finally, Fe−NC exhibits good long‐term stability over 12 h electrolysis of CO 2 at −0.57 V vs. RHE, with a steady FE CO ≈95 % over the entire period and with a decrease of | j | mainly occurring in the first 2 h (Figure 4d), similar to what is observed for many other carbon‐based materials [19b,21] …”

Engineering Atomically Dispersed FeN4 Active Sites for CO2 Electroreduction

“…Among studied sizes, the 200 nm Fe‐N‐C catalyst has the highest SA BET of approximately 1300 m 2 g −1 . The increases in both micropores and mesopores contribute to the higher BET surface area [39–41] . Such a high SA BET for ZIF‐8‐derived Fe‐N‐C catalysts has not been achieved before, suggesting that proper size control, along with optimal carbonization, can attain favorable morphologies.…”

“…Using N-C hosts derived from ZIF-8s,w ef urther introduced active Fe species to form Fe-N-C model catalysts with tunable particle sizes,Fecontent, and thermally activated FeÀ Nb ond structures.I natypical procedure,w ee mployed asubset of N-C hosts to adsorb active Fe species followed by thermal activation, forming FeN 4 sites embedded in carbon. [18] At first, the N-C hosts with disparate particle sizes (e.g., 40,80,200, and 300 nm) were used to study Fe-N-C catalysts size effect. As for the control of the Fe content, aspecific N-C host (e.g., 200 nm) was used to adsorb Fe nitrate solution (100 mg mL À1 )with various amounts (e.g., 10, 60, and 90 mL).…”

Engineering Atomically Dispersed FeN4 Active Sites for CO2 Electroreduction

“…Chemie N-C catalyst has the highest SA BET of approximately 1300 m 2 g À1 .The increases in both micropores and mesopores contribute to the higher BET surface area. [39][40][41] Such ah igh SA BET for ZIF-8-derived Fe-N-C catalysts has not been achieved before,s uggesting that proper size control, along with optimal carbonization, can attain favorable morphologies.T he graphitization degree is nearly identical for various Fe-N-C catalysts with different sizes (Figure S16). Overall, Fe-N-C catalysts carbon defects became more dominant than N-C,likely due to FeN 4 sites formation.…”