Carbon Supported Multi-Branch Nitrogen-Containing Polymers as Oxygen Reduction Catalysts

Abstract

A composite catalyst was obtained by covalently linking G4-NH 2 dendrimers and 1,10-phenanthroline-5-carboxylic acid on the surface of carbon powder, and the composite was named as PMPhen/C. In order to improve the catalytic performance of the composite, copper ions (II) were introduced to PMPhen/C by complex to form the PMPhen-Cu/C catalyst. Scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) were applied to investigate the surface microstructure and elemental compositions of the catalysts. The results from electrochemical analysis show that PMPhen/C reduced oxygen to hydrogen peroxide (H 2 O 2 ) through a two-electron transfer process. PMPhen-Cu/C could reduce oxygen to water through a four-electron pathway. Except the slightly lower initial reduction potential, PMPhen-Cu/C has a comparable oxygen reduction ability (ORR) to that of the commercially available Pt/C catalyst, which makes it a potential candidate as the cathodic catalyst in some fuel cells running in neutral medium, such as a microbial fuel cell. Catalysts 2018, 8, 245 2 of 21in the current study of ORR catalysts [7]. Nitrogen and transition metals introduced in a certain way are considered to be key factors for the function of the ORR catalysts, which usually exist in the form of M-N x (M = Fe, Co, Ni, Mn, Cu, etc.) [13]. Meanwhile, the carbon materials were also frequently used as the supporting materials for the catalysts due to their high conductivity, porous microstructure and high specific surface area. The porous structure of carbon materials can not only increase the contact area between catalyst and oxygen, but also construct more channels for the diffusion of O 2 , H 2 O, H 2 O 2 and other additional intermediates and can be beneficial to improve the ORR activities of the catalysts [14]. Apart from providing supporting carbon material, another effective approach for improving the ORR activities of the catalysts was the pyrolysis of the M-N x -containing materials under inert atmosphere, which is beneficial to the fixation and optimization of the structure of the M-N x unit and then improving the stabilities of the catalysts [1,15]. The pyrolysis process is helpful for the doping of hetero atoms and transitional metal atoms on the surface of carbon materials, but the disadvantage is that the reaction of the doping process is unordered, which brings trouble to the quantitative analysis of the relationship between the ORR activities and the catalyst precursors. At present, the nitrogen-containing precursors include polypyrrole, porphyrins, polyphthalocyanines, polyaniline (PANI), phenanthroline (Phen), etc. [16][17][18][19].Many reports adopt some of the nitrogen-containing heterocyclic ligands as the nitrogen source for the preparation of M-N x -containing catalyst, and the M-N x unit has been considered as the active site of the catalysts, which were in the form of the non-pyrolysis state [20][21][22]. During the pyrolysis process, the complexing metal ions contributed to the improved ORR activity by promoting the...

Heterocyclization Strategy for Construction of Linear Conjugated Polymers: Efficient Metal‐Free Electrocatalysts for Oxygen Reduction

“…When evaluated as an ORR electrocatalyst, the covalently linked pyridine and thiophene molecule ( P‐T ), with reduced graphene oxide (rGO), exhibits a remarkable onset and half‐wave potentials of 0.94 V and 0.79 V (vs. RHE), respectively. These values are among the highest values reported for the ORR with metal‐free polymers as catalysts and without the process of pyrolysis and heteroatom doping . DFT calculations reveal that the combined structure of N‐ and S‐heterocycles is the key to developing novel electrocatalysts with distinct chemical compositions and molecular structures for efficient ORR catalytic activity.…”

Heterocyclization Strategy for Construction of Linear Conjugated Polymers: Efficient Metal‐Free Electrocatalysts for Oxygen Reduction

“…Its performance is also much better than the reported state-of-the-art metal-free conjugated organic polymers (Figure 2d). [10][11][12][13][14][15][16][17] TheL SV curves of all the samples were also recorded in ar otation speed from 400 to 2500 rpm (Figure 2b;s ee Figures S4 and S5 in the Supporting Information). The electron-transfer number (n) of P-T/rGO was calculated from the Koutecky-Levich (K-L) equation to be 3.48 at 0.2 V (Figure 2c).…”

“…These values are among the highest values reported for the ORR with metal-free polymers as catalysts and without the process of pyrolysis and heteroatom doping. [10][11][12][13][14][15][16][17] DFT calculations reveal that the combined structure of N-and Sheterocycles is the key to developing novel electrocatalysts with distinct chemical compositions and molecular structures for efficient ORR catalytic activity.…”

One Simple Strategy towards Nitrogen and Oxygen Codoped Carbon Nanotube for Efficient Electrocatalytic Oxygen Reduction and Evolution

“…The noble metal-based materials including Pt and Ru are the most efficient electrocatalysts for ORR or OER, but their prohibitive cost and scarcity greatly impedes the proliferation of related energy technologies. In comparison, carbon materials possess a series of satisfactory features, including natural abundance, superior electrical conductivity, tailorable structures and components, and strong anticorrosion abilities, and thus have been intensively studied as electrocatalysts during the last decade [5,8,9].…”