Nitrogen-doped graphene with enhanced oxygen reduction activity produced by pyrolysis of graphene functionalized with imidazole derivatives

Abstract

Direct methanol fuel cells (DMFC) are great candidates for portable power source applications. However, the sluggish reaction kinetics are key challenges in DMFC technology. The state-of-the-art electrocatalysts are Pt-based catalysts supported on carbon black. However, the high price of Pt, corrosion of carbon support and Pt degradation are the main problems.In this thesis, carbon nanomaterials, namely few-walled carbon nanotubes (FWCNTs) and graphitized nanofibers (GNFs) were used as catalyst supports in the search for stable and durable catalysts. PtRu nanocatalysts with similar particle size and composition were synthesized and deposited on FWCNTs and GNFs. The electrochemical activities for methanol oxidation were compared with that of PtRu-carbon black in acidic conditions. The half-cell electrochemical measurements revealed higher activity with PtRu-GNFs and PtRu-FWCNTs. Later, the electrocatalysts were tested in macro-and micro-DMFC. The results revealed the significant influence of the catalyst support, inomer contect, electrode structure, preparation method, as well as the fuel cell architecture on the performance of a specific electrode material. The results also highlighted the necessity of electrode composition optimization when applying new materials at the electrodes, in order to achieve the best activity and durability for a certain electrocatalyst.A special effort was also done to achieve Pt-free electrocatalysts with high activity for the oxygen reduction reaction (ORR) by introducing nitrogen heteroatoms in carbon nanomaterials, namely FWCNTs and graphite nanoplatelets (GNPs). N-FWCNTs exhibited remarkable electrocatalytic activity for ORR in alkaline media, despite their very low nitrogen content (~0.5 at.%). N-FWCNTs performed on par or better than a commercial Pt-C at the cathode of an alkaline DMFC. The N-GNPs exhibited enhanced electrocatalytic activity for ORR compared to pristine GNPs in alkaline media. The results indicated that N-doped carbon nanomaterials could be promising alternatives to their Pt counterparts to reduce fuel cell costs. However, further investigations are necessary to ascertain the real active sites in order to design more efficient and durable ORR electrocatalysts.Keywords Carbon nanomaterials, PtRu catalysts, nitrogen-doping, direct methanol fuel cell ISBN (printed) 978-952-60-6140-5 ISBN (pdf) 978-952-60-6141-2

The effect of varying N/C ratios of nitrogen precursors during non-metal graphene catalyst synthesis

“…Compared with CVD, thermal annealing is a simple, low-cost method with high graphene yield [8]. In addition, NG with specific N configurations can be produced by controlling the annealing temperature [9,10].…”

“…This electron pair increases the electron-donor property of the catalyst, weakening the OeO bond via bonding between oxygen and nitrogen and/or an adjacent carbon atom and facilitating the reduction of O 2 [17,18]. Other studies have claimed that pyridinic-N and graphitic-N play equally important roles in ORR performance [3,9,13,19]. Lai et al [13] observed that graphitic-N greatly increased the limiting current density of NG samples, whereas pyridinic-N species converted the ORR reaction mechanism from a 2-electron dominated process to a 4-electron dominated process.…”

Влияние Механического Растяжения На Адсорбционные Свойства Легированного Азотом Графена

“…Впервые N-легированный графен был синтезирован путем химического парофазного осаждения (CVD) в 2009 году [13]. Позднее были предложены и другие способы его получения, например, дуговой разряд [14] или пиролиз графена, функционализированного азотосодержащими группами [15]. Было показано, что азот может встраиваться в решетку графена, связываясь с тремя соседними атомами углерода, или образовывать более сложные дефекты (пиридинового или пирролического типа), приводящие к формированию " отверстий" в графеновом листе [13].…”

Nitrogen and fluorine dual-doped carbon black as an efficient cathode catalyst for oxygen reduction reaction in neutral medium

“…Since Jasinski first reported that non-precious metal catalysts (NPMC) were obtained by pyrolysis of transition metals, carbon and nitrogen precursors at high temperature [5], massive efforts are aimed at developing NPMC to rival Pt-based catalysts. Recently, non-metal heteroatom (B, N, F, P or S)-doped carbon materials such as graphene [6][7][8][9][10][11][12], carbon nanotubes [13,14], carbon spheres [15], graphene array [16], mesoporous carbon [17] have been considered high activity for ORR. In particular, compared to other hetero atoms (B, N, P, S), F atom with high electro-negativity can easily embed in carbon blacks and form new active sites.…”