Impact of Pore Structure on Two‐Electron Oxygen Reduction Reaction in Nitrogen‐Doped Carbon Materials: Rotating Ring‐Disk Electrode vs. Flow Cell

Abstract

The impact of pore structure on the two‐electron oxygen reduction reaction (ORR) in nitrogen‐doped carbon materials is currently under debate, and previous studies are mainly limited to the rotating ring‐disk electrode (RRDE) rather than the practical flow cell (FC) system. In this study, assisted by a group of reliable pore models, the impact of two pore structure parameters, that is, Brunauer–Emmett–Teller surface area (SBET) and micropore surface fraction (fmicro), on ORR activity and selectivity are investigated in both RRDE and FC. The ORR mass activity correlates positively to the SBET in the RRDE and FC because a higher SBET can host more active sites. The H2O2 selectivity is independent of fmicro in the RRDE but correlates negatively to fmicro in the FC. The inconsistency results from different states of the electrode in the RRDE and the FC. These insights will guide the design of carbon materials for H2O2 synthesis.

A Pentagonal Defect-Rich Metal-Free Carbon Electrocatalyst for Boosting Acidic O2 Reduction to H2O2 Production

“…From the transmission electron microscopy (TEM) images in Figure c,d, abundant mesopores and micropores can be observed in PD/N–C. The hierarchical porous structure can bring about powerful adsorption capability for the gas molecules and fast mass/ion transfer during the ORR. , Additionally, irregular folds and curved edges are widely discerned in PD/N–C (Figures d and S4), implying the presence of surface curvatures and lattice distortions in the carbon matrix. Note that the topological pentagons are known to be responsible for the curvature or distortion of carbon materials, suggesting that PD/N–C contains abundant pentagons that should originate from the unique C 60 precursor .…”

“…The N 2 sorption isotherms in Figure 2g show that PD/N−C possesses a much higher BET surface area (S BET ) of 2120 m 2 g −1 than N-GNS (470 m 2 g −1 ), as given in Table S6, which can offer more accessible active sites. 52 In addition, the t-plots analysis reveals that PD/N−C possesses a much higher micropore area (360 m 2 g −1 ) and volume (0.18 cm 3 g −1 ), which is conducive to facilitating the electrochemical reaction speed. 52 The pore size distribution in Figure 2h shows that PD/N−C possesses a hierarchical porosity ranging from micro-to macropores.…”

“…52 In addition, the t-plots analysis reveals that PD/N−C possesses a much higher micropore area (360 m 2 g −1 ) and volume (0.18 cm 3 g −1 ), which is conducive to facilitating the electrochemical reaction speed. 52 The pore size distribution in Figure 2h shows that PD/N−C possesses a hierarchical porosity ranging from micro-to macropores. Figure 2i gives a comprehensive comparison of the structural characteristics of PD/N−C and N-GNS.…”

Impact of Pore Structure on Electrochemical Reduction of Carbon Dioxide in Iron- and Nitrogen-Doped Carbon Materials: Solid–Liquid Interface Versus Solid–Gas–Liquid Triple-Phase Boundary

“…Carbon-based materials doped by metals and N (M/N/Cs), especially Fe/N/C, have recently emerged as an attractive catalyst to produce carbon monoxide (CO). − Their catalytic sites are considered as atomically dispersed FeN x structures hosted on the pore surface. , It is expected that the pore structure can greatly impact the interface microenvironment near the active site and then affect the reaction activity and selectivity . For instance, Koper et al proposed that the narrower and longer pores would lead to a higher local pH, consequently inhibiting the HER with improved reaction selectivity .…”

“…20,21 It is expected that the pore structure can greatly impact the interface microenvironment near the active site 22 and then affect the reaction activity and selectivity. 23 For instance, Koper et al proposed that the narrower and longer pores would lead to a higher local pH, consequently inhibiting the HER with improved reaction selectivity. 24 This conclusion was proposed according to the porous gold electrode as models, which may be not applicable to heteroatom-doped carbon materials with different surface properties and complex hierarchical pores.…”