Illustrating the Role of Quaternary-N of BINOL Covalent Triazine-Based Frameworks in Oxygen Reduction and Hydrogen Evolution Reactions

Abstract

Defective nitrogen-doped carbon materials have shown a promising application as metal-free electrocatalysts in the oxygen reduction reaction (ORR) and the hydrogen evolution reaction (HER). However, there are still some challenges in the tuning of metal-free electrocatalysts and in understanding the roles of various nitrogen species in their electrocatalytic performance. Herein, we design a covalent triazine framework (CTF)-based material as an effective metal-free bifunctional electrocatalyst. We chose BINOL-CN (2,2′dihydroxy-[1,1′-binaphthalene]-6,6′-dicarbonitrile) as both a carbon and a nitrogen source for the fabrication of N-containing CTF-based materials. Four BINOL-CTFs with varying Nfunctionalities (pyridinic-N/triazine-N, pyrrolic-N, quaternary-N, and pyridine-N-oxide) were successfully obtained. These materials were evaluated in the ORR and the HER in basic and acidic conditions, respectively. The best material has an onset potential of 0.793 V and a halfwave potential of 0.737 V, and it follows first-order kinetics in a 4e − pathway in the ORR reaction. The same material shows an impressive HER activity with an overpotential of 0.31 V to achieve 10 mA/cm 2 and a small Tafel slope of 41 mV/dec, which is comparable to 31 mV/dec for Pt/C, making it a potential bifunctional electrocatalyst. We showed that the ORR and HER reactivity of CTF-based materials depends exclusively on the amount of quaternary-N species and on the available surface area and pore volume. This work highlights the engineering of CTF materials with varying amounts of N species as high-performance bifunctional electrocatalysts.

Mechanochemically Synthetized PAN-Based Co-N-Doped Carbon Materials as Electrocatalyst for Oxygen Evolution Reaction

“…Moreover, deconvolution of the N1s XPS region of PAN-A, PAN-N, PAN-N/3%Co, and PAN-A/3%Co samples revealed the presence of five signals located around 397.0 ± 0.5, 399.0 ± 0.5, 400.0 ± 0.5, 402.0 ± 0.5, and 403 ± 0.5 eV, which could be associated with pyridinic-N, pyrrolic-N, amine-N, graphitic-N, and pyridone-N groups [43]. Moreover, as reported by Thomas Wagberg and recently described by Van Der Voort et al, two different types of graphitic nitrogen entities could be contributing to the signal located at 401.0 ± 0.5 eV, namely, the quaternary N atoms at the center (at lower binding energy) and at the valley (at higher binding energy) [35,48].…”

“…For instance, nanocarbons such as carbon nanotubes, graphene, borocarbonitride, and covalent triazine framework have been modified with non-metallic atoms, such as N, to support metal nanoparticles, giving rise to ultrahigh catalytic active sites [32][33][34]. The addition of N into the carbon network creates a myriad of structural defects, which decrease the uphill energy states of the catalytic intermediates' species, thus benefiting the overall ORR activity [35]. Among all the aforementioned approaches, self-doping material represents a good alternative for simplifying synthesis and reducing carbon footprint [36].…”

Hierarchical Porous, N-Containing Carbon Supports for High Loading Sulfur Cathodes

“…Identifying those species is important because of their characteristics, which affect the chemical and electronic properties of carbon materials, where the pyridinic N and graphitic N enable to increase affinity to the polysulfide and the electrical conductivity of the carbon-based material, respectively [18]. The high-resolution N 1s spectrum of MGC could be deconvoluted into four peaks at 398.3, 399.5, 400.5, and 402.6 eV corresponding to pyridinic, pyrrolic, graphitic, and oxidized N atoms, respectively (Figure 3c) [19,20]. MGC contains substantial amounts of graphitic N (38.82%), which is responsible for the increased I G /I D ratio in Raman spectra [15].…”

Dimethylglyoxime Clathrate as Ligand Derived Nitrogen-Doped Carbon-Supported Nano-Metal Particles as Catalysts for Oxygen Reduction Reaction

“…Graphitic-N and pyridinic-N are beneficial to the occurrence of ORR. The pyridinic-N has a significant effect on electron delocalization in the carbon framework and, hence, have a profound effect on the ORR performance [ 34 ]. The morphology and corresponding elemental mapping of the synthesized materials are displayed in Figure 2 .…”