Oxygen Reduction Reaction In Proton Exchange Membrane Fuel Cells Research Articles

Sulfur doped iron-nitrogen-hard carbon nanosheets as efficient and robust noble metal-free catalysts for oxygen reduction reaction in PEMFC

Transition metal-nitrogen-carbon (M-N-C) as a promising substitute for the conventional noble metal-based catalyst still suffers from low activity and durability for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). To tackle the issue, herein, a new type of sulfur-doped iron-nitrogen-hard carbon (S-Fe-N-HC) nanosheets with high activity and durability in acid media were developed by using a newly synthesized precursor of amide-based polymer with Fe ions based on copolymerizing two monomers of 2, 5-thiophene dicarboxylic acid (TDA) as S source and 1, 8-diaminonaphthalene (DAN) as N source via an amination reaction. The as-synthesized S-Fe-N-HC features highly dispersed atomic FeNx moieties embedded into rich thiophene-S doped hard carbon nanosheets filled with highly twisted graphite-like microcrystals, which is distinguished from the majority of M-N-C with soft or graphitic carbon structures. These unique characteristics endow S-Fe-N-HC with high ORR activity and outstanding durability in 0.5 M H2SO4. Its initial half-wave potential is 0.80 V and the corresponding loss is only 21 mV after 30,000 cycles. Meanwhile, its practical PEMFC performance is a maximum power output of 628.0 mW cm−2 and a slight power density loss is 83.0 mW cm−2 after 200-cycle practical operation. Additionally, theoretical calculation shows that the activity of FeNx moieties on ORR can be further enhanced by sulfur doping at meta-site near FeN4C. These results evidently demonstrate that the dual effect of hard carbon substrate and S doping derived from the precursor platform of amid-polymers can effectively enhance the activity and durability of Fe-N-C catalysts, providing a new guidance for developing advanced M-N-C catalysts for ORR.

Fe Single‐Atom Catalysts on MOF‐5 Derived Carbon for Efficient Oxygen Reduction Reaction in Proton Exchange Membrane Fuel Cells

AbstractThe development of Fe single‐atom catalysts (Fe SACs) with abundant, accessible Fe sites is a key step toward enhancing the efficiency of the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). In this study, Zn4O(1,4‐benzenedicarboxylate)3 (MOF‐5), which has a 3D microporous cubic structure, is used as the precursor to prepare highly‐porous carbon (denoted as C‐MOF‐5) with an ultrahigh specific surface area (2751 m2 g–1) and high external surface area (1651 m2 g–1). C‐MOF‐5 is demonstrated as an effective carbon support to yield Fe SAC‐MOF‐5 with a large amount of accessible FeNx sites (2.35 wt%). Fe SAC‐MOF‐5 delivers a half‐wave potential of 0.83 V (vs RHE) in a 0.5 m H2SO4 electrolyte, and achieves a peak power density of 0.84 W cm–2 in a 0.2 MPa H2‐O2 PEMFC. This excellent performance originates from the ultrahigh specific surface area of C‐MOF‐5 for the formation of a high density of single Fe atoms, and high external surface area for the increased exposure of active sites. This work may inspire the rational design of metal single‐atom catalysts derived from a wider range of MOF precursors with ultrahigh specific area to improve the performance of the oxygen reduction reaction in PEMFCs.

Improved oxygen reduction reaction in PEMFCs by functionalized CNTs supported Pt–M (M = Fe, Ni, Fe–Ni) bi- and tri-metallic nanoparticles as efficient electrocatalyst

In this work, Functionalized Carbon nanotubes (FCNTs) supported hybrid catalysts including Pt, Fe and Ni nanoparticles were prepared and further used as an electrocatalytic electrode for Proton Exchange Membrane Fuel Cell (PEMFC) cathode. In this regard, various ratios of nitric acid/sulfuric acid were tested for functionalization of CNTs. The ethylene glycol reduction method was applied to deposit the hybrid electrocatalyst nanoparticles on FCNTs. It was revealed that the combination of FCNTs, as the support catalyst, with hybrid platinum and transition metals, accelerated the oxygen reduction reaction (ORR) by passing through the four-electron pathway which was due to the high crystallinity and aspect ratio, low defect density and unique electrical conductivity of CNTs and Pt-transition metals alloys. As a result, the power density profoundly enhanced (up to 237%) while the charge transfer resistance reduced, compared to Pt–C 10%wt commercial catalyst. This study demonstrated the excellent performance of FCNTs decorated Pt–Ni–Fe electrocatalyst can be considered as a good candidate for the future of the catalyst layer in PEMFC.

A hybrid Pt/NbO/CNTs catalyst with high activity and durability for oxygen reduction reaction in PEMFC

To improve the kinetics and durability of Pt-based electrodes toward the oxygen reduction reaction (ORR), high electroactive and stable catalysts were synthesized by depositing Pt over niobium oxide (NbO) supported on commercial multi-wall carbon nanotubes (CNTs). The Pt/NbO/CNTs, exhibits excellent electroactivity and stability toward ORR, reaching a high electroactivity of 57 mA mgPt−1, higher than the Pt/CNTs and commercial Pt/C (20% Pt/C HiSPEC™). Moreover, the developed Pt/NbO/CNTs demonstrated outstanding durability under accelerated stress testing (AST) according to load cycling and startup/shutdown stability protocols. Proton exchange membrane fuel cells (PEMFC) tests with an MEA fabricated using Pt/NbO/CNTs showed excellent performance, with a low Pt loading down to 0.15 mg cm−2, achieving a maximum power density of 772 mW cm−2. Furthermore, a short-term durability test in PEMFC demonstrated only a 4% loss on the maximum power density at 80 °C. The superior electrocatalytic activity and durability of Pt/NbO/CNTs can be ascribed to the anchoring effect of Pt nanoparticles over the NbO/CNTs hybrid support, showing that the developed Pt/NbO/CNTs is a promising durable electrocatalyst for PEMFC applications.

Fully Ordered Pt3Co Intermetallic Nanoparticles Derived from MOFs for Oxygen Reduction in PEMFCS

Proton exchange membrane fuel cells (PEMFCs) are considered to be a promising power source for electric vehicles and stationary residential applications. However, current PEMFCs have several problems that need to be overcome including high cost, insufficient power density, and poor performance durability. Current Pt-based cathodes for the oxygen reduction reaction (ORR) are primarily responsible for these issues. Development of advanced Pt-based catalysts are crucial for solving these problems in order for large-scale application of PEMFCs to be feasible. Recently, highly ordered PtM alloy catalysts have exhibited significantly enhanced activity and stability for the ORR in PEMFCs, which have attracted substantial attention. Based on our ongoing research projects [1-3], in this presentation, we introduced our recent progress to develop low-PGM catalysts with emphasis on the innovative synthesis methods of using pre-doped transition metals such as Co or Ni into metal–organic-framework (MOF)-derived carbon as the sources to prepare highly ordered PtM catalysts. As an example, ordered Pt3Co intermetallic nanoparticles through a facile thermal treatment of Pt nanoparticles supported on Co-doped MOF-derived carbon. Atomically dispersed Co sites are originally embedded into MOF-derived carbon. Then we can accurately control the diffusion of Co into Pt crystals and form ordered Pt3Co structures. It is very crucial for the formation of the ordered Pt3Co to carefully control the doping content of Co into the MOFs and the heating temperatures for Co diffusion. The optimal Pt3Co nanoparticle catalyst has achieved significantly enhanced activity and stability. The highly ordered intermetallic structure was retained after the accelerated stress tests made evident by atomic-scale elemental mapping. Fuel cell tests further verified the high intrinsic activity of the ordered Pt3Co catalysts. The new synthesis approach provides an effective strategy to develop active and stable Pt alloy catalysts by leveraging the unique properties of MOFs such as 3D structures, high surface areas, and controlled nitrogen and transition metal dopings. This concept also provides a solution to take advantages of current atomically dispersed PGM-free catalyst to develop high-performance low-PGM cathode catalysts.

Highly active and durable Pt–Co nanowire networks catalyst for the oxygen reduction reaction in PEMFCs

Well-defined Pt–Co nanowire networks (NWNs) were successfully prepared as oxygen reduction reaction (ORR) electrocatalysts by a surfactant-assisted soft template (cetyltrimethylammonium bromide, CTAB) synthesis procedure for proton exchange membrane fuel cells (PEMFCs). We systematically investigate the impact of synthesis conditions, including the amount of reducing agent used, reaction stirring rates and CTAB concentrations, to determine the conditions for synthesizing Pt–Co NWNs with optimal ORR activity. Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) results reveal that Pt–Co NWNs exhibit superior ORR activity in comparison to commercial Pt/C used as a benchmark. The mass and specific activities of Pt–Co NWNs are 0.179 AmgPt−1 and 357.5 μAcmPt−2, respectively. This represents improvements of about 210% and 220%, respectively, in comparison to Pt/C. In addition, accelerated degradation testing (ADT) shows that the Pt–Co NWNs catalysts demonstrate evidently improved durability than commercial Pt/C in terms of electrochemical surface area and ORR activity retention. This renders Pt–Co NWNs as a highly promising, emerging class of ORR catalysts for PEMFCs application.

A Controllable Synthesis of Pt-Based Electrocatalyst for the Oxygen Reduction Reaction of PEMFC with High Pt Utilization

Proton exchange membrane fuel cells (PEMFCs) are characterized with many advantages including high power density, low operating temperature (~80 oC), quick start-up and quick match to shifting demands for power, and regarded as a very promising technology for powering transportation and stationary applications1. However, the kinetics of the cathodic oxygen reduction reaction (ORR) in PEMFCs is sluggish and the most efficient material is platinum (Pt) that is rare on the earth and has a prohibitive cost. To make PEMFCs economically available, it is imperative to maximize the utilization of Pt or rather noble metal by improving catalyst layer’s mass transport of reactants and products, and by increasing noble-metal-mass activities toward the ORR in cathode. One of the strategies to improve mass transport in cathode is to thin the catalyst layer through developing high-content and high-dispersion Pt electrocatalysts. However, it is difficult to prepare Pt supported catalysts with a high Pt content because of the agglomeration of Pt nanoparticles. It was reported that the commercial Pt/VC catalysts had a particle size of 2.0 nm in Pt(10 wt%)/VC, 3.2 nm in Pt(30 wt%)/VC, and 8.8 nm in Pt(60 wt%)/VC2. Although great efforts have been made to improve traditional methods, such as impregnation method and colloidal method, it remains very challenging to find an economical and controllable way to synthesize Pt/VC electrocatalysts with a high Pt content for the ORR in PEMFCs. This can be attributed to several facts, including the poor size control, the contaminants from stabilizer residue, tedious procedures and so on. In this work, we propose a simple and controllable approach to deposit highly-dispersed Pt nanoparticles on Vulcan XC-72 carbon black. The as-synthesized Pt/VC possesses a high Pt content as well as high-dispersion Pt NPs via controlling the nucleation and growth process, and was investigated as the cathodic catalyst in PEMFC. Ideally highest Pt utilization with an extraordinary Pt-mass activity has been achieved by the Pt-monolayer-shell electrocatalysts which possess monoatomic thick Pt shells on noble-metal substrates3. However, the noble-metal-mass activities for these Pt-monolayer-shell electrocatalysts were also compromised, since the noble-metal substrates are quite essential for fabricating such electrocatalysts. In this regard, with the highest Pt utilization, improving the non-Pt noble-metal utilization in the substrates is critical for developing the Pt-monolayer-shell electrocatalysts. In this work, a surfactant-based, composition- and size-tunable method has been demonstrated to synthesize the monodispersed Pd-Ni as the substrates for fabricating the carbon-supported Pd-Ni@Pt nanospheres with Pt monolayer shells. And an excellent balance among activity, durability and noble-metal utilization was acquired. Acknowledgements This work was supported in part by National Natural Science Foundation of China (Grant No. 21373135 and 21533005) and Science Foundation of Ministry of Education of China ( Grant No. 413064). Reference 1. M.L. Perry, F.T. Fuller, J Electrochem Soc, 149 S59-S67 (2002). 2. B. L. Gratiet, H. Remita, G. Picq, M. Delcourt, J Catal, 164, 36 (1996). 3. (a) J. Zhang, M. B. Vukmirovic, Y. Xu, M. Mavrikakis, R. R. Adzic, Angewandte Chemie International Edition, 44 2132-2135, (2005); (b) M. Shao, K. Shoemaker, A. Peles, K. Kaneko, L. Protsailo, J Am Chem Soc, 132 9253-9255, (2010). (c) J. X. Wang, H. Inada, L. Wu, Y. Zhu, Y. Choi, P. Liu, W. P. Zhou, R. R. Adzic, J Am Chem Soc, 131,17298( 2009) .

Highly durable silica-coated Pt/carbon nanotubes for proton-exchange membrane fuel cells application

Platinum nanoparticles supported on carbon nanotubes (Pt/CNTs) have been used as an electrocatalyst in proton-exchange membrane fuel cells (PEMFCs). These catalysts show higher activity in oxygen reduction reaction in PEMFCs than conventional carbon-black-supported Pt nanoparticles. However, their durability is lower than that of other metal-alloy-based or nonmetal-based catalysts. In this study, Pt/CNTs were synthesized by solution plasma followed by coating with silica layer by the sol–gel method using a cationic surfactant [cetyltrimethylammonium bromide (CTAB)]. This material can be used as a cathode in PEMFCs. The silica layer was coated on the surface of Pt/CNTs to prevent agglomeration and detachment of Pt nanoparticles from carbon nanotubes during operation. The formation of silica layers significantly improved the durability of the Pt/CNT catalysts under acidic conditions. After 300 cycles of the cyclic voltammetry test in 0.5#M sulfuric acid (H2SO4), silica-coated Pt/CNTs increased the durability by 43.0 and 24.0% compared with those of noncoated commercial Pt/C and Pt/CNTs, respectively.

Cobalt oxide-based catalysts deposited by cold plasma for proton exchange membrane fuel cells

In proton exchange membrane fuel cells (PEMFC), both the anodic hydrogen oxidation reaction and the cathodic oxygen reduction reaction (ORR) require appropriate catalysts. So far, platinum-based catalysts are still the best option for this purpose. However, because these catalysts are too expensive for making commercially viable fuel cells, extensive research over the past decade has focused on developing noble metal-free alternative catalysts. In this paper, an approach based on cobalt oxide films fabricated by plasma-enhanced metal-organic chemical vapor deposition is presented. Such a material can be used to prepare catalysts for ORR in PEMFC. The films containing CoOX were deposited on a carbon paper thereby forming the electrode. Morphology and atomic composition of the films were investigated by scanning electron microscopy and energy-dispersive X-ray spectroscopy, respectively. The possibility of their application as the electro-catalyst for ORR in PEMFC was investigated and the electro-catalytic activities were evaluated by the electrochemical measurements and single cell tests. It was found that the fuel cell with Pt as the anode catalyst and CoOX deposit as the cathode catalyst was characterized by the open circuit voltage of 635mV, Tafel slope of approx. 130mV/dec and the maximum power density of 5.3W/m2.

Preparation of Buckypaper By Surface Modified Multi-Walled Carbon Nanotubesfor Oxygen Reduction Reaction in PEMFC

As the key material of proton exchange membrane fuel cell (PEMFC), the carbon supported Pt nanoparticles are the most widely used catalyst for cathode and anode of PEMFC. Recently we reported anultra-low Pt loading catalytic layer based on buckypaper for oxygen reduction reaction1. The buckypaper is a double-layer thin film containing a multi-walled carbon nanotubes rich surface and a carbon nanofibers rich surface. And Pt has a gradient distribution in this catalytic layer in order to reduce the Pt content. In this paper, varies of surface modification methods for MWNTs,such as oil-bath acidic reflux, ultrasonic and microwave treatment, were systematically studied,and the oxygen reduction activity of those treated MWNTs were measured. The results showed that surface modified MWNTs have better oxygen reduction reaction activity than the as received MWNTs. Among those treatments, microwave treated MWNTs have better performance than other treatments. Next step buckypaper will be prepared by surface modified MWNTs. As surface modification can also enhance the dispersion of the catalyst2, it has a potential to show good ORR performance in a low Pt loading thus reduce the cost of catalyst. Acknowledgments The authors acknowledge the support from the Shanghai Rising-Star Program (11QA1407200), the National Natural Science Foundation of China (21006073), the Scholarship Council and the Fundamental Research Funds for the Central Universities at Tongji University. Reference J.Zheng, T.Tian,Y. Gao, Q. Wu, J. Ma, J. Zheng. Int. J. Hydrogen.Energ, 39(2014) 13816.Y. Xing, L. Li, C. Chusuei, R. Hull. Langmuir, 21 (2005) 4185. Figure 1

Electrocatalysis of Fuel Cell Relevant Reactions in Protic Ionic Liquids

Protic ionic liquids (PILs) are a sub-class of ionic liquids that have attracted attention recently as effective proton carriers for medium-temperature fuel cells because PILs have favorable properties such as high proton conductivity, low vapour pressure and excellent chemical and thermal stability.1,2 PIL-based fuel cells (PILFCs) can conduct protons without deliberate humidification, unlike the polymer electrolytes used in conventional proton exchange membrane fuel cells (PEMFCs), meaning that water management in PILFCs is simpler than in PEMFCs. Moreover, the rate of the oxygen reduction reaction (ORR) in PILFCs can exceed that of the rate of ORR in PEMFCs as PILFCs are able to operate above 100 °C. Despite recent research in the development of PIL-based fuel cells, electrocatalysis in this media has not yet been studied in any great detail. In particular, detailed study on the effect of electrode-adsorbate interactions during electrocatalysis of the ORR at Pt in PILs has been lacking. This contribution investigates the role of ion adsorption on the electrocatalysis of ORR, CO oxidation and hydrazine oxidation in a series of ammonium-based PILs. Surface oxides that form during trace water oxidation play a key role during electrocatalysis in PILs. Pt surface oxides hinder the ORR, and this reaction only occurs at potentials where the Pt surface is in its reduced state. By contrast, the rate of hydrazine oxidation in PILs increases as the extent of residual Pt oxide increases. Moreover, CO oxidation coincides with oxidation of the Pt surface in each PIL, suggesting that the reaction proceeds via a Langmuir-Hinshewood mechanism involving adsorbed CO and surface oxides. The “CO displacement” technique was used to determine whether the cations or anions of the PILs were adsorbed on the Pt surface, and this insight was used to explain the trends observed during electrocatalysis of the ORR in PILs. For example, the onset potential of the ORR in diethylmethylammonium trifluoromethanesulfonate ([dema][TfO], see Figure 1A for structure) was 0.7 V vs RHE at 45 °C, and in diethylmethylammonium bis (trifluoromethanesulfonyl)imide ([dema][Tf2N]) was -0.2 V vs RHE at 45 °C. It is important to note that the cations of these PILs are the same, and their physicochemical properties such as viscosity and conductivity are similar. Figure 1 shows the i-t curve when CO was dosed at various potentials into [dema][TfO] and [dema][Tf2N]. In [dema][TfO], cation displacement was observed negative of 0.25 V vs RHE and anion ([TfO]-) displacement was seen positive of 0.28 V vs RHE (Figure 1A). In contrast, anion displacement was observed at all potentials studied in [dema][Tf2N] (Figure 1B), indicating the strong interaction between Pt surfaces and the [Tf2N]- anion. This result indicates that the binding of the [Tf2N]- anions to the Pt surface causes the high overpotential of the ORR in [dema][Tf2N]. Extension of the “surface electrocatalysis” approach described here to well-defined surfaces will reveal whether ion adsorption from PILs exhibits structural sensitivity and will yield new insights into electrocatalysis in PILs. Ultimately, this approach may lead to the rational design of electrocatalysts for use in PIL electrolytes

Core–shell Pt modified Pd/C as an active and durable electrocatalyst for the oxygen reduction reaction in PEMFCs

A series of Pt modified Pd/C catalysts (Pt/Pd/C) with different Pt/Pd molar ratio (Pt:Pd=1:4, 1:2 and 1:1) are synthesized by a chemical reduction method for oxygen reduction reaction (ORR). X-ray diffraction (XRD), transmission electron microscope (TEM) and cyclic voltammetry (CV) measurements confirm that Pt is deposited on the Pd nanoparticles and the Pt/Pd/C catalysts have a Pdcore@Ptshell structure. In the half cell testing, the catalytic ORR activity of Pt1/Pd2/C and Pt1/Pd4/C are superior to commercial Pt/C. Moreover, the electrochemical durability to potential cycling of Pt1/Pd2/C and Pt1/Pd1/C catalysts is better than Pt/C catalysts. The improved durability is believed to be associated with the dissolution of Pd and the corresponding structure transformation from core–shell structure to Pt-Pd alloy with Pt rich surface. The structure change is confirmed by TEM, CV, XRD and X-ray photoelectron spectroscopy (XPS). In addition, the electrochemical active surface area (ECSA) loss and polarization behavior in the single cell testing also suggest that the Pt/Pd/C show a much better durability than Pt/C catalysts. Similarly, the dissolution of Pd is observed by CV and scanning electron microscope-energy dispersive X-ray spectra (SEM-EDX). The Pt/Pd/C electrocatalysts have high ORR activity and this high activity can be further improved during potential cycling, that is, the activity and durability can be obtained simultaneously. This Pdcore@Ptshell structure allows for the development of highly active and durable ORR electrocatalysts, with potential for the application in proton exchange membrane fuel cells (PEMFCs).

Electrochemical Characteristics and Performance of Platinum Nanoparticles Supported by Vulcan/Polyaniline for Oxygen Reduction in PEMFC

AbstractWe report a Pt/Vulcan carbon–polyaniline (VC–PANI) catalyst for the oxygen reduction reaction (ORR). This electrocatalyst was prepared from Pt nanoparticles supported by a VC–PANI composite substrate. Electrochemical performance was measured using potentiostat/galvanostats technique and a proton exchange membrane fuel cell (PEMFC) test station. The electrochemical properties of the electrodes were characterized using linear sweep voltammetry, AC impedance spectroscopy and chronoamperometry. Electrochemical characterization by hydrogen adsorption/desorption cyclic voltammetry and CO stripping voltammetry indicates that the electrochemical active surface areas of the Pt/VC–PANI are comparable to the commercial catalyst. The performance of the Pt/VC–PANI and Pt/C(E‐TEK) + PANI electrocatalysts were found to be 1.82 and 1.33 times higher than of the Pt/C(E‐TEK) electrode. The surface morphologies of the electrodes were characterized by using scanning electron microscopy (SEM). PANI has a fibrous structure and the improved performance was attributed to the PANI effect and synergistic effects between the carbon Vulcan and the PANI fiber. These results indicate that Pt/VC–PANI is a promising catalyst for the ORR in PEMFCs using an H2/O2 feed.

Analysis of the SO2 Contamination Effect on the Oxygen Reduction Reaction in PEMFCs by Electrochemical Impedance Spectroscopy

Previous tests revealed that SO2 contamination in proton exchange membrane fuel cells (PEMFCs) resulted in a two-stage degradation in cell voltage. Unfortunately, the effect of SO2 on the cell cathode reactions and the corresponding SO2 contamination mechanism are still unknown. In this paper, the effect of SO2 contamination on oxygen reduction reactions (ORR) was analyzed using electrochemical impedance spectroscopy (EIS) through an equivalent electrical circuit model (ECM). The ORR parameters extracted from the ECM suggested that during the first poisoning stage, the SO2 adsorption increased the charge transfer resistance of the ORR, causing the initial cell performance degradation. During the second poisoning stage, SO2 adsorption may assist in shifting the ORR from the “direct four electron pathway” to the “series two electron pathway.” This shift resulted in a decrease in the current efficiency of the ORR, which then resulted in the subsequent degradation of cell performance. The increase in the fluorine emission rate, as detected by ion chromatography, was indirect evidence for the ORR pathway shift during the second poisoning stage and the decrease in current efficiency.

Kinetics and electrocatalytic activity of IrCo/C catalysts for oxygen reduction reaction in PEMFC

The purpose of this study is to develop a novel binary Iridium-Cobalt/C catalyst as a suitable substitute for platinum/C applied in proton exchange membrane fuel cells (PEMFCs). The carbon-supported IrCo catalysts were successfully synthesized using IrCl 3 and C 4H 6CoO 4 as the Ir and Co precursors respectively, in ethylene glycol (EG) refluxing at 120 °C. The nanostructured catalysts were characterized by X-ray diffraction (XRD) and high-resolution transmission electron microscope (TEM). Homogeneous catalyst particles supported on carbon showed a size of proximately 2 nm. Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were conducted for the characterization of the catalyst performances. With a cathodic loading of 0.4 mg Ir cm −2, 20%Ir-30%Co/C achieved a maximum power density of 501.6 mW cm −2 at 0.418 V, with a 50 cm 2 H 2/O 2 single cell. Although such a performance is about 26% lower than commercial Pt/C catalyst, it is still helpful in terms of Pt replacement and cost reduction.

Performance of Proton Exchange Membrane Fuel Cells Using Pt/MWNT–Pt/C Composites as Electrocatalysts for Oxygen Reduction Reaction in Proton Exchange Membrane Fuel Cells

Multiwalled carbon nanotubes (MWNTs) have been synthesized by the pyrolysis of acetylene using hydrogen decrepitated Mischmetal based AB3 alloy hydride catalyst. Structural, morphological, and vibrational characterizations have been carried out using X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy (HRTEM), Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR) spectroscopy. Pt-supported MWNTs (Pt/MWNTs) have been prepared by chemical reduction method using functionalized MWNTs. Composites of Pt/MWNTs and Pt/C in different weight proportions have been used as electrocatalysts for oxygen reduction reaction in proton exchange membrane fuel cell (PEMFC) and the performance on the accessibility of Pt electrocatalysts for the oxygen reduction reaction in PEMFC has been systematically studied. The cyclic voltammetric studies of the electrodes have been performed in order to understand the factors influencing the elecetrocatalytic activity and fuel cell performance and the results have been discussed.

Catalyst electrode preparation for PEM fuel cells by electrodeposition

The preparation of catalyst electrodes by electrodeposition for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs) has been studied. This work looks at the potential to apply the electrodeposition technique, in the forms of direct current (DC) and pulse plating electrodepositions, to prepare Pt and Pt–Co alloy catalysts for membrane electrode assemblies (MEAs). The preparation of the non-catalyst layer was found to be important for the electrodeposition of Pt catalysts. The activities of the electrodeposited catalysts, both pure Pt and Pt–Co alloy, produced by pulse plating are substantially higher than that of the Pt catalyst produced by DC electrodeposition. The improvement in electroactivity towards the ORR of the electrodeposited catalysts produced by pulse plating is likely due to the finer structures of electrodeposited catalysts which contain smaller catalyst particles compared to those produced by DC electrodeposition. A maximum performance towards the ORR in PEMFCs was achieved from the catalysts prepared by pulse plating using a charge density of 2 C cm−2, a pulse current density of 200 mA cm−2, a 5% duty cycle and a pulse frequency of 1 Hz.

Preparation of Pt–Co alloy catalysts by electrodeposition for oxygen reduction in PEMFC

Direct current (DC) and pulse current (PC) electrodeposition of Pt–Co alloy onto pretreated electrodes has been conducted to fabricate catalyst electrodes for oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFC). The effect of plating mode and pulse plating parameters on the Pt–Co alloy catalyst structure, composition and electroactivity for the ORR in PEMFC has been investigated. The electrodeposited Pt–Co alloy catalyst indicates higher electrocatalytic activity towards the ORR than the electrodeposited Pt catalyst. The activity of the electrodeposited Pt–Co catalysts is further improved by applying the current in a pulse waveform pattern. The electrodeposition mode and the pulse plating parameters do not have the significant effect on the Pt:Co composition of deposited catalysts, but show the substantial effect on the deposit structures produced. The Pt–Co catalysts prepared by PC electrodeposition have finer structures and contain smaller Pt–Co catalyst particles compared to that produced by DC electrodeposition. By varying the Pt concentration in deposition solution, the Pt:Co composition of the electrodeposited catalyst that exhibits the highest activity is found. The Pt–Co alloy catalyst with the Pt:Co composition of 82:18 obtained at the charge density of 2 C cm−2, the pulse current density of 200 mA cm−2, 5% duty cycle and 1 Hz was found to yield the best electrocatalytic activity towards the ORR in PEMFC.

A novel non-noble electrocatalyst for oxygen reduction in proton exchange membrane fuel cells

Tungsten nitride supported on carbon black was prepared by temperature-programmed reaction (TPR) process and is proposed as a catalyst for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). The as-prepared catalyst was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. The ORR activities of the catalyst were studied by electrochemical measurements and single cell tests, respectively. The results indicated that the tungsten nitride electrocatalyst exhibited attractive catalytic activity and stability for the ORR in PEMFCs. It is expected to be a promising cathode electrocatalyst for PEMFCs, especially for the comparatively high temperature proton exchange membrane fuel cells.

Platinum/multiwalled carbon nanotubes-platinum/carbon composites as electrocatalysts for oxygen reduction reaction in proton exchange membrane fuel cell

Pt-loaded multiwalled carbon nanotubes (Pt/MWCNTs) have been prepared by chemical reduction method using functionalized MWCNT synthesized by pyrolysis of acetylene over MmNi2 (Mm denotes misch metal) hydride catalyst. Composites of Pt/MWCNT and commercial Pt-loaded carbon black (Pt∕C) have been used as electrocatalysts for oxygen reduction reaction in proton exchange membrane fuel cell (PEMFC). Cathode catalyst with 50% Pt/MWCNT and 50% Pt∕C showed best performance due to better dispersion and good accessibility of MWCNT support and Pt electrocatalysts for oxygen reduction reaction in PEMFC. A maximum performance of 540mV at a current density of around 535mAcm−2 has been obtained.