Untangling Cooperative Effects of Pyridinic and Graphitic Nitrogen Sites at Metal‐Free N‐Doped Carbon Electrocatalysts for the Oxygen Reduction Reaction

Abstract

Metal-free carbon electrodes with well-defined composition and smooth topography were prepared via sputter deposition followed by thermal treatment with inert and reactive gases. XPS and Raman spectroscopies show that three carbons of similar N/C content that differ in Nsite composition were thus prepared: an electrode consisting of almost exclusively graphitic-N (NG), an electrode with predominantly pyridinic-N (NP) and one with ca. 1:1 NG:NP composition. These materials were used as model systems to investigate activity of N-doped carbons in the oxygen reduction reaction (ORR) using voltammetry. Results show that selectivity towards 4e-reduction of O2 is strongly influenced by the NG/NP site composition, with the material possessing nearly uniform NG/NP composition being the only one yielding a 4e-reduction. Computational studies on model graphene clusters were carried out to elucidate the effect of N-site homogeneity on the reaction pathway. Calculations show that for pure NGdoping or NP-doping of model graphene clusters, adsorption of hydroperoxide and hydroperoxyl radical intermediates, respectively, is weak thus favoring desorption prior to complete 4e-reduction to hydroxide. Clusters with mixed NG/NP sites display synergistic effects, suggesting that co-presence of these sites improves activity and selectivity by achieving high theoretical reduction potentials while facilitating retention of intermediates.

Metal‐organic framework‐derived Fe/Cu‐substituted Co nanoparticles embedded in CNTs‐grafted carbon polyhedron for Zn‐air batteries

“…[38][39][40] The high-resolution N 1s spectrum ( Figure S5B) could be deconvoluted into five peaks centered at 398.1, 399.1, 399.8, 401.2, and 403.1 eV, respectively, corresponding to pyridinic-N, Co-N x , pyrrolic N, graphitic-N, and oxidized graphitic-N. 41,42 Compared with C-C@NC (without Fe substitution) and C@NC (without Fe and Cu substitution), FC-C@NC exhibited energy shifts in binding energies in Co 2p and N 1s spectra (a positive shift of about 0.6 eV for Co 2p and a negative shift of about 0.6 eV for N 1s, as shown in Figure 3E,F), indicating Fe and Cu substitution into Co sites had a little influence on the chemical states of Co and N. In addition, FC-C@NC contained higher N content (10.8%), and the content of pyridinic N and graphitic-N was 60% of the total N content, which was supposed to be beneficial for ORR process. 43 The electrocatalytic activities of all samples for ORR were first evaluated using a three-electrode configuration cell in alkaline solution (0.1 M KOH) at room temperature. As shown in Figure S6, no redox peak was observed for FC-C@NC in Ar-saturated KOH solution, while a welldefined cathodic peak (0.85 V vs RHE and all the potentials in this study were compared with RHE) was observed in O 2 -saturated KOH solution, predicting its effective ORR catalytic activity.…”

Thermodynamically Stable Mesoporous C3N7 and C3N6 with Ordered Structure and Their Excellent Performance for Oxygen Reduction Reaction

“…Although platinumbased materials offer superior catalytic activity in ORR, scare reserve and low methanol tolerance of platinum prompt development of nonprecious alternatives such as transition metal alloys, metal oxides and metal-free compounds. [20][21][22][23][24][25] The ORR activity of g-C 3 N 4 as a metal-free electrocatalyst was first reported by Lyth et al and at the same time, they suggested to mix the g-C 3 N 4 with carbon to overcome sluggish kinetics of the g-C 3 N 4 . [26] The strategy of compositing the g-C 3 N 4 with carbon materials brought a huge improvement in ORR activity of the g-C 3 N 4.…”

“…Electrochemical oxygen reduction reaction (ORR) is a crucial process for renewable energy applications such as fuel cells, metal‐air batteries and solar cells. Although platinum‐based materials offer superior catalytic activity in ORR, scare reserve and low methanol tolerance of platinum prompt development of nonprecious alternatives such as transition metal alloys, metal oxides and metal‐free compounds . The ORR activity of g‐C 3 N 4 as a metal‐free electrocatalyst was first reported by Lyth et al and at the same time, they suggested to mix the g‐C 3 N 4 with carbon to overcome sluggish kinetics of the g‐C 3 N 4 .…”

Harnessing inherently hierarchical microstructures of plant biomass to construct three-dimensional nanoporous nitrogen-doped carbons as efficient and durable oxygen reduction electrocatalysts

“…18,32 It has been reported that pyridinic and graphitic nitrogens play a vital role in the ORR catalytic activity. [33][34][35][36][37] According to Table 2, the combined amounts of pyridinic N and graphitic N account for 76.36, 62.73 and 56.28% of the total amounts of nitrogen of NEA, NA and NE, respectively. Consequently, NEA possesses both the highest level of total nitrogen and the largest amounts of pyridinic N and graphitic N among the four materials, suggesting its ability to operate as a high-performance ORR catalyst.…”