Enhanced oxygen reduction reaction activity of iron-containing nitrogen-doped carbon nanotubes for alkaline direct methanol fuel cell application (original) (raw)
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International Journal of Hydrogen Energy, 2016
In this work, the electroreduction of oxygen on nitrogen-doped graphene and multi-walled carbon nanotube (MWCNT) composite catalysts is investigated. Acid-treated MWCNTs and graphite oxide were doped using biuret, carbohydrazide and semicarbazide hydrochloride as the nitrogen precursors. The reactants were mixed with carbon nanomaterials and pyrolysed in an inert atmosphere at 800 C. Scanning electron microscopy was used to characterise the surface morphology of catalysts and X-ray photoelectron spectroscopy (XPS) was used to determine the surface content of the catalysts. XPS revealed different contents of nitrogen gained by using different nitrogen precursors, which were tied to electrochemical activities observed in this work by using the rotating disk electrode (RDE) method. The catalysts revealed high oxygen reduction reaction (ORR) activity even at low loadings and excellent stability over 1000 potential cycles. This indicates their applicability as cathode materials in alkaline anion exchange membrane fuel cells.
International Journal of Hydrogen Energy, 2016
In this work the electrocatalytic performance of nitrogen-doped graphene (NG)-based nonprecious metal (NPM) catalysts for oxygen reduction reaction (ORR) have been compared with their counterparts while supported on multiwalled carbon nanotubes (MWCNTs). Fe and Co nanoparticles were precipitated on NG (M/NG, M ¼ Fe, Co) and for comparison on MWCNTs (M/MWCNT, M ¼ Fe, Co) using a modified polyol method. The electrocatalytic properties of all catalysts towards oxygen reduction reaction in 0.1 M KOH solution were investigated. In comparison with M/MWCNTs, M/NG catalysts exhibited higher ORR activity, which indicates a better electrocatalytic performance of nitrogen-doped graphene compared to those which were supported by MWCNTs. Chronoamperometric results also demonstrated that the Co/NG catalyst was more stable for ORR in alkaline solution rather than Co/MWCNT and commercial Pt/C.
Electrochimica Acta, 2016
Iron-and cobalt-containing nitrogen-doped carbon catalysts based on multi-walled carbon nanotubes are prepared using pyrolysis of dicyandiamide and CoCl 2 or FeCl 3 at 800 C. The electroreduction of oxygen is studied in 0.5 M H 2 SO 4 solution by the rotating disk electrode method and the surface morphology and composition of the catalysts are characterised by scanning and transmission electron microscopies and X-ray photoelectron spectroscopy. The as-prepared catalysts show mediocre electrocatalytic activity for oxygen reduction reaction (ORR), which increases as a result of acid treatment and second pyrolysis. The electrocatalytic activity of Fe-containing catalyst towards the ORR surpasses that of Co-based material and it supports a 4-electron reduction of O 2. Co-containing catalyst, in turn, shows higher stability. Both catalysts are highly methanol tolerant in acid media. The transition metal-containing N-doped carbon materials are promising cathode catalysts for low-temperature fuel cells.
Carbon, 2014
In this work the electrocatalysis of oxygen reduction on nitrogen-doped few-layer graphene/multi-walled carbon nanotube (FLG/MWCNT) composite catalyst has been investigated. These composite materials were prepared from different nitrogen precursors, acid-treated MWCNTs and graphene oxide (GO), which was synthesised from graphite by the modified Hummers' method. Urea and dicyandiamide were used as nitrogen precursors and the doping was achieved by pyrolysing the mixture of GO and MWCNTs in the presence of these nitrogen-containing compounds at 800°C. The N-doped composite catalyst samples were characterised by scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy, the latter method revealed successful nitrogen doping. The oxygen reduction reaction (ORR) was studied in 0.1 M KOH on glassy carbon electrodes modified with N-doped FLG/MWCNT electrocatalysts employing the rotating disk electrode (RDE) method. The RDE results indicated that these metal-free nitrogen-doped nanocarbon catalysts possess remarkable electrocatalytic activity towards the ORR in alkaline media similar to that of commercial Pt/C catalyst. The results obtained in this work are particularly important for the development of non-Pt cathode catalysts for alkaline membrane fuel cells.
Applied Catalysis B: Environmental, 2014
The performance of a direct methanol alkaline anion-exchange membrane (Fumatech FAA3) fuel cell with Pt-free nitrogen-doped few-walled carbon nanotubes (N-FWCNT) as the cathode catalyst is compared with a commercial supported Pt catalyst. The ionomer content of the N-FWCNT cathode catalyst layer is therefore optimized and it is shown to be 40 wt% of FAA3. Scanning electron microscopy images of the catalyst layer show that the ionomer forms aggregates with N-FWCNTs probably due to their charged nature and that the catalyst layer structure is remarkably open even with high ionomer contents facilitating the mass transfer of reactants and products to the active sites. With oxygen as the oxidant, the maximum power density obtained with our Pt-free N-FWCNTs (0.78 mW cm −2 ) is slightly higher than with the Pt catalyst (0.72 mW cm −2 ). However, when more practical air is used as the oxidant, the N-FWCNTs (0.73 mW cm −2 ) show clearly superior performance compared to the Pt catalyst (0.18 mW cm −2 ). The lower performance with the Pt catalyst is attributed to the denser electrode layer structure resulting in higher mass transport resistance and to the presence of methanol in the cathode, which poisons the Pt but not the N-FWCNTs.
Nitrogen-Doped Carbon Nanotube and Graphene Materials for Oxygen Reduction Reactions
Catalysts, 2015
Nitrogen-doped carbon materials, including nitrogen-doped carbon nanotubes (NCNTs) and nitrogen-doped graphene (NG), have attracted increasing attention for oxygen reduction reaction (ORR) in metal-air batteries and fuel cell applications, due to their optimal properties including excellent electronic conductivity, 4e − transfer and superb mechanical properties. Here, the recent progress of NCNTs-and NG-based catalysts for ORR is reviewed. Firstly, the general preparation routes of these two N-doped carbon-allotropes are introduced briefly, and then a special emphasis is placed on the developments of both NCNTs and NG as promising metal-free catalysts and/or catalyst support materials for ORR. All these efficient ORR electrocatalysts feature a low cost, high durability and excellent performance, and are thus the key factors in accelerating the widespread commercialization of metal-air battery and fuel cell technologies.
Electrocatalytic oxygen reduction on nitrogen-doped graphene in alkaline media
Applied Catalysis B: Environmental, 2014
Nitrogen-doped graphene nanosheets were prepared from nitrogen precursor and graphene oxide (GO), which was synthesised from graphite by modified Hummers' method. Melamine, urea and dicyandiamide (DCDA) were used as nitrogen precursors and the doping was achieved by pyrolysing GO in the presence of these nitrogen-containing compounds at 800 • C. The N-doped graphene (NG) samples were characterised by scanning electron microscopy and X-ray photoelectron spectroscopy, the latter method revealed successful nitrogen doping. The oxygen reduction reaction (ORR) was examined on NG-modified glassy carbon (GC) electrodes in alkaline media using the rotating disk electrode (RDE) method. It was found on the basis of the RDE results that nitrogen-containing catalysts possess higher electrocatalytic activity towards the ORR than the annealed GO. Oxygen reduction on this GO material and on NG catalysts prepared by pyrolysis of GO-melamine and GO-urea followed a two-electron pathway at low overpotentials, but at higher cathodic potentials the desirable four-electron pathway occurred. For NG catalyst prepared from GO-DCDA a four-electron O 2 reduction pathway dominated in a wide range of potentials. The half-wave potential of O 2 reduction on this NG catalyst was close to that of Pt/C catalyst in 0.1 M KOH. These results are important for the development of alkaline membrane fuel cells based on non-platinum cathode catalysts.
Applied Catalysis B: Environmental, 2020
Nitrogen-doped carbide-derived carbon/carbon nanotube (CDC/CNT) composites were prepared and employed for the first time as a cathode electrocatalyst for the anion exchange membrane fuel cell (AEMFC). The CDC/CNT composites were doped with nitrogen using high temperature pyrolysis in the presence of different nitrogen precursors. In the rotating disk electrode measurements all N-CDC/CNT catalysts showed good electrocatalytic activity for oxygen reduction reaction (ORR) in alkaline solution with the half-wave potential (E 1/2) around-0.25 V vs SCE. Moreover, the materials showed high tolerance to methanol and excellent stability after 10,000 potential cycles with a negative shift in E 1/2 of 10 and 14 mV, respectively. In AEMFC testing employing hexamethyl-p-terphenyl poly(benzimidazolium) (HMT-PMBI) anion exchange membrane, N-CDC/CNT as a cathode catalyst exhibited very good performance with the peak power density of 310 mW cm-2. It can be concluded that the N-CDC/CNT composites are promising cathode catalysts for AEMFCs and alkaline direct methanol fuel cells.
Activity and active sites of nitrogen-doped carbon nanotubes for oxygen reduction reaction
Journal of Applied Electrochemistry, 2013
Nitrogen-doped carbon (CNx) nanotubes were synthesized by thermal decomposition of ferrocene/ethylenediamine mixture at 600-900°C. The effect of the temperature on the growth and structure of CNx nanotubes was studied by transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. With increasing growth temperature, the total nitrogen content of CNx nanotubes was decreased from 8.93 to 6.01 at.%. The N configurations were changed from pyrrolic-N to quaternary-N when increasing the temperature. Examination of the catalytic activities of the nanotubes for oxygen reduction reaction by rotating disk electrode measurements and single-cell tests shows that the onset potential for oxygen reduction in 0.5 M H 2 SO 4 of the most effective catalyst (CNx nanotubes synthesized at 900°C) was 0.83 V versus the normal hydrogen electrode. A current density of 0.07 A cm-2 at 0.6 V was obtained in an H 2 /O 2 proton-exchange membrane fuel cell at a cathode catalyst loading of 2 mg cm-2. Keywords Nitrogen-doped carbon nanotubes Á Thermal decomposition Á Oxygen reduction reaction Á Non-precious metal catalysts