Dopant-Induced Electronic Structure Modification of HOPG Surfaces: Implications for High Activity Fuel Cell Catalysts

Abstract

N-doped graphite has been reported to provide enhanced catalytic properties as a support material for Pt catalysts in fuel cell applications. With use of a combined experimental and modeling approach, this work identifies the potential fundamental mechanisms for this enhancement effect. To ensure a well-defined experimental system, this work employs highly oriented pyrolitic graphite (HOPG) as a model analogue of the graphite support commonly used in fuel cell applications. Undoped, Ar-doped, and N-doped HOPG substrates have been investigated via electrochemical capacitance and X-ray photoelectron spectroscopy (XPS) measurements. The results indicate that doping, especially N-doping, induces significant modification to the electronic structure of the HOPG surface. A simplified model of the doping effects and band structures for the doped graphite surfaces are proposed to explain these results. When Pt nanoparticles are grown on top of these dopant-modified HOPG surfaces, the resulting Pt/surface-defect interactions significantly impact the Pt nanoparticle nucleation, growth, and catalytic activity.

One step synthesis of chlorine-free Pt/Nitrogen-doped graphene composite for oxygen reduction reaction

“…S6 indicate that the ratio of the oxidized species was higher in case of Pt/NG than in case of Pt/CB. This finding strongly supports our assumption about the interaction between platinum nanoparticles and the nitrogen doped support [49].…”

Pt nanoparticles interacting with graphitic nitrogen of N-doped carbon nanotubes: Effect of electronic properties on activity for aerobic oxidation of glycerol and electro-oxidation of CO

“…As shown in Table S4 in the Supporting Information, the representative literature using liquid-phase reduction methods, with EG and NaBH 4 as reductants [16], reported negative BE shifting of metal or the increase of zerovalent metallic species on N-doped carbon materials, suggesting the role of N-doped carbons as electron donors. On the other hand, positive shifting of metal BE is usually observed when metal NPs are formed through ex situ reduction after adsorption of metal precursors [17,49]. In these cases, vacancies containing N P favor the adsorption of charged metal ions, e.g., [PtCl 6 ] 2À ; therefore the electron acceptance of N P dominates the electronic properties.…”

Nitrogen‐Doped Pt/C Electrocatalysts with Enhanced Activity and Stability toward the Oxygen Reduction Reaction

“…[7] The enhancement of the electrocatalytic activity of the Pt/N-CNT could be due to the nitrogen-induced modification of the electronic structure of Pt: as determined by X-ray photoelectron spectroscopy (XPS), the Pt 4f core-level peaks of Pt nanoparticles deposited on the N-CNT surface shifted to the higher binding energy side, thus indicating the weakening of interactions between Pt and hydroxyl adsorbates, thereby resulting in enhanced ORR activity. [14,15] In addition, the increased specific capacitance of nitrogen-doped carbon materials could provide surface sites for additional charged species that are involved in the destruction of reaction intermediates such as OH and OOH. [5] Therefore, nitrogen-doped surfaces could participate in the ORR mechanism, thus the oxygen reduction is well proceeded on Pt as well as on "NÀC" sites.…”

“…The chemical vapor deposition method has been widely applied to prepare nitrogen-doped carbon materials, where gaseous nitrogen sources are used with metal catalysts under high reaction temperature (> 600 8C). [1-3, 7-12, 15-23] Other methods, including the graphitization of nitrogen-containing polymer [24] and ionic liquid, [25] and implantation with a nitrogen ion beam, [6,14] also provide nitrogen-doped carbon frameworks. However, the low-temperature and water-based synthesis of nitrogen-doped carbon materials has rarely been explored because of the formidable difficulties in carrying out nitrogen-doping under such mild conditions.…”