Easy conversion of protein-rich enoki mushroom biomass to a nitrogen-doped carbon nanomaterial as a promising metal-free catalyst for oxygen reduction reaction

Abstract

The search for low-cost, highly active, and stable catalysts to replace the Pt-based catalysts for oxygen reduction reaction (ORR) has recently become a topic of interest. Herein, we report a new strategy to design a nitrogen-doped carbon nanomaterial for use as a metal-free ORR catalyst based on facile pyrolysis of protein-rich enoki mushroom (Flammulina velutipes) biomass at 900 °C with carbon nanotubes as a conductive agent and inserting matrix. We found that various forms of nitrogen (nitrile, pyrrolic and graphitic) were incorporated into the carbon molecular skeleton of the product, which exhibited more excellent ORR electrocatalytic activity and better durability in alkaline medium than those in acidic medium. Remarkably, the ORR half-wave potential measured on our material was around 0.81 V in alkaline medium, slightly lower than that on the commercial 20 wt% Pt/C catalyst (0.86 V). Meanwhile, the ORR followed the desired 4-electron transfer mechanism involving the direct reduction pathway. The ORR performance was also markedly better than or at least comparable to the leading results in the literature based on biomass-derived carbon-based catalysts. Besides, we significantly proposed that the graphitic-nitrogen species that is most responsible for the ORR activity can function as the electrocatalytically active center for ORR, and the pyrrolic-nitrogen species can act as an effective promoter for ORR only. The results suggested a promising route based on economical and sustainable fungi biomass towards the large-scale production of valuable carbon nanomaterials as highly active and stable metal-free catalysts for ORR under alkaline conditions.

Coprinus comatus-derived nitrogen-containing biocarbon electrocatalyst with the addition of self-generating graphene-like support for superior oxygen reduction reaction

“…For further study, we compared the ORR catalytic property of N-BC@G-900 with other catalysts [13,14,17,21,35,36,38], as displayed in Table S1 (online). Our results are comparable with those of the best N-doped carbon catalysts reported to date in terms of E ORR , half-wave potential, average electron transfer number (n) and limited current density, but the BET surface area of the N-BC@G-900 catalyst is much lower than that of numerous nitrogen-doped carbon catalysts [16,33,34]. In fact, the major reason for the electrocatalytic activity enhancement is the density of surface active sites rather than the total surface area, although the significance of the BET specific surface area cannot be ruled out totally [31].…”

“…Nie et al [45] proposed that The ORR polarization curves of N-BC@G-900 and Pt/C-ETK (inset) before and after undergoing N 2 cycling tests in O 2 -saturated 0.1 mol/L KOH at a rotation rate of 1,600 r/min the planar N on the surface of carbon-based catalysts is closely contacted with an efficient electron transfer pathway and further assured the rapid free-flowing electron transport to the ORR process. The results of our group [21,33] also showed that the pyrrolic N might be a key configuration of catalytic active sites and function as an effective promoter to the ORR. In addition, Rao et al [42] significantly found that the electrocatalytic activity of N-doped carbon-based catalysts might be usually related to the pyridinic N. Guo et al [46] further clarified the ORR active site by using newly designed graphite model catalysts with well-defined p conjugation and well-controlled doping of N species, and found that the active sites in N-doped carbon materials are carbon atoms with Lewis basicity next to pyridinic N. Therefore, we can reasonably conclude that the planar N (pyridinic-N and pyrrolic-N) may be the N functionality that is most responsible for maintaining the ORR catalytic activity, and the graphitic-N functionality can play an essential role in the improvement of the catalytic activity in alkaline medium.…”

“…4b). The XPS spectra for N 1s region of N-BC-900 and N-BC@G-900 can be deconvoluted into four peaks, which are assigned to pyridinic N (*398.3 eV), nitrile N (*399.5 eV), pyrrolic N (*400.3 eV) and graphitic N (*401.5 eV) respectively, in the carbon lattice [31,33]. The schematic illustration for N atoms placed in carbon skeleton plane is also shown in Fig.…”

Surface Modification of Multi-Walled Carbon Nanotubes via Hemoglobin-Derived Iron and Nitrogen-Rich Carbon Nanolayers for the Electrocatalysis of Oxygen Reduction

“…As seen from Figure 1b, all Raman spectra are deconvoluted into two components, and the characteristic “D” and “G” peaks can be found, respectively. According to the previously reported results [13,17], the intensity ratio of D/G ( I D / I G ) is closely related to the amount of structural defects on the catalyst surface. Hence, in the present work, the I D / I G ratios are obtained in N-C@CNT and N-C@CNT-Fe, i.e., 0.78 vs. 0.83, suggesting a lower graphitization degree and more defected structures on the surface of N-C@CNT-Fe, implying the surface doping of more nitrogen atoms on the nitrogen-doped carbon layers.…”

“…For N-C@CNT, two amorphous-carbon peaks with 2θ values of ~25° and ~44° can be identified, which are attributed to the (002) and (101) of graphitic planes, respectively [13]. In addition, a finding is that the width of two diffraction peaks increases largely, compared with the XRD pattern of CNT (inset in Figure 1a), which may be explained by the influence of lower graphitization degree [17,18]. However, the XRD pattern of N-C@CNT-Fe exhibits more complex phase composition, and a series of sharp peaks are displayed at 30.2°, 35.6°, 43.2°, 53.6°, 57.1° and 62.7°, which can be ascribed to crystalline Fe 3 O 4 phases according to the XRD card (No.…”