Pt-free Cathode Catalyst Research Articles

Elucidating the Formation Mechanisms of Fe-N-C Electrocatalysts Using High-Temperature in Situ Characterisation Techniques

Pt-free cathode catalysts are attracting increased interest to replace platinum in polymer electrolyte membrane fuel cells (PEFCs). Heat-treated nitrogen-doped carbons decorated with iron have been the most widely studied alternative. However, lack of understanding of the formation of active sites and degradation mechanisms in such catalysts is hindering their progress. Here, we use a nitrogen-doped carbon foam support with optimised porosity, surface area, and conductivity which is then infiltrated with three different iron precursors: iron (II) acetate (FeAc); iron (III) chloride (FeCl3); and iron phthalocyanine (FePc). These are then pyrolyzed to form Fe-N-C-based ORR electrocatalysts. This approach takes advantage of an already optimized conductive, porous, high surface area and temperature-stable support. The stability of the support helps to separate the role of the different iron precursors from other factors in the generation of catalytic active sites. High temperature X-ray absorption fine structure (HT-XAFS) and high temperature X-ray photoelectron spectroscopy (HT-XPS) were employed to study changes in the iron precursors during the synthesis of Fe-N-C electrocatalysts. Furthermore, near ambient pressure XPS (NAP-XPS) and in-situ electrochemical XAFS were performed to study the interaction between the synthesized catalysts and oxygen. These results are then related to the electrochemical activity.

Integration of a Pd-CeO2/C Anode with Pt and Pt-Free Cathode Catalysts in High Power Density Anion Exchange Membrane Fuel Cells

Recent advances in developing high-performance anion exchange membranes (AEMs) for fuel cell (AEMFC) applications enable catalyst developers to investigate and test cheaper and/or more sustainable ...

Electrocatalytic Activities and Stabilities of Selenium Based Cobalt-Nickel Binary and Ternary Chalcogenides

The requirement of precious platinum (Pt) based materials as electrocatalysts and the sluggish kinetics of oxygen reduction reaction (ORR) in a cathode have significantly impeded the commercialization of proton exchange membrane fuel cells. Much effort has been directly made to search for high performance Pt-free cathode catalysts. Chalcogenides are promising alternatives because of their moderate electrocatalytic activities and good selectivity toward ORR in acidic and basic media. The carbon supported binary cobalt selenide (CoSe2/C), nickel selenide (NiSe2/C) and ternary cobalt-nickel selenide (Co-Ni-Se/C) nanoparticles were prepared by a simple microwave synthesis route without or with heat treatment. The microstructure, electrocatalytic activities and stabilities of CoSe2/C, NiSe2/C and Co-Ni-Se/C catalysts were studied in 0.1 mol/L HClO4 or KOH solutions. The single cell performances of the as-prepared catalysts were further investigated and compared.

Poly(vinyl alcohol)/Poly(diallyldimethylammonium chloride) anion-exchange membrane modified with multiwalled carbon nanotubes for alkaline fuel cells

Hydroxyl anion conducting membrane composed of poly(vinyl alcohol) (PVA), poly(diallyldimethylammonium chloride) (PDDA), and hydroxylated multiwalled carbon nanotubes (MWCNTs-OH) have been synthesized via a facile blending-casting method assisted by a hot-chemical cross-linking process. Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) showed that PDDA and MWCNTs-OH were successfully introduced into the PVA matrix and MWCNTs-OH could effectively improve the network structure of the membrane. With the addition of MWCNTs-OH, many properties of the membranes such as thermal, chemical, mechanical stability and swelling property were improved significantly. Most prominent is the improvement of mechanical property, where the PVA/PDDA/MWCNTs-OH(1:0.5/3 wt.%) membrane showed high tensile strength of 40.3 MPa, tensile elongation of 12.3% and high Young's modulus of 782.8 MPa. Moreover, MWCNTs-OH bound the polymer chains in the membranes more compactly, resulting in decreased water uptake. By tuning the mass fraction of PVA, PDDA, and MWCNTs-OH in the membrane, the maximum OH− conductivity (0.030 S cm−1 at room temperature) was achieved for the composition of 0.5 wt.% MWCNTs-OH doped with the PVA: PDDA (1:0.5 by mass) blend. The membranes showed excellent oxidative stability when treated with both a solution of H2O2 (30 wt.%) at room temperature and in a hot KOH solution (8 M) at 80 °C. Based on the full aliphatic structure membrane (PVA/PDDA-OH/1 wt.%MWCNTs-OH), membrane electrode assemblies (MEAs) fabricated with Pt/C cathode catalyst can achieve power densities of 41.3 mW cm−2 and 66.4 mW cm−2 in a H2/O2 system at room temperature and 40 °C, respectively. Using CoPc as the Pt-free cathode catalyst, power densities of 9.1 mW cm−2 and 14.0 mW cm−2 at room temperature and 40 °C were obtained, respectively.

Fe/N/C Cathode Catalyst Prepared from a Low Content of Fe Precursor to Obtain Atomically Dispersed Metal Center

The development of Pt-free catalysts is strongly desired for globalization of proton exchange membrane fuel cells. Our research group has been developing Pt-free cathode catalysts obtained by pyrolyzing Fe containing polyimide nano-particles. While this sort of polyimide derived cathode catalysts shows very good performance, the structure of the Fe center was obscure. Furthermore, the previous synthesis of the catalysts started from a relatively large amount of Fe additives (2 wt%); therefore, extraordinary Fe species require to be washed out using HCl, the process of which was redundant. In the present study, we tried to avoid the acid washing process by starting from a lower amount of Fe additives to simplify the synthetic procedure and increase the fraction of atomically dispersed Fe centers. Polyimide nano-particles were synthesized by the precipitation polymerization of pyromellitic acid dianhydride and 1,3,5-tris(4-aminophenyl)benzene with 0.3-0.5 wt% of Fe(acac)3 (acac = acetylacetonate). The Fe-containing polyimide precursor was heated at 600 °C for 5 h in a nitrogen atmosphere, and then heated again to 800 and 1000 °C for 1 h each in an ammonia atmosphere (50% balanced by nitrogen). Any acid washing was not performed during the whole synthetic procedure. The chemical composition of the resultant carbon was determined using a CHN elemental analyzer (PerkinElmer 2400-II) and an electron probe micro analyzer (Jeol JXA-8100): C 88.3 wt%, H trace, N 2.6 wt% and Fe 1.7 wt%. The Brunauer, Emmett and Teller (BET) surface area was determined to be 1360 m2 g-1 (Bel Japan Belsorp mini II). Thus obtained Pt-free cathode catalyst was tested under H2-O2 fuel cell conditions. Figure 1 shows the I-V performance curves for the membrane electrode assembly (MEA) with the obtained catalyst. The measured and IR-free voltages at 2 A cm-2 reached 0.45 and 0.65 V, respectively; and the maximum power density was 0.89 W cm-2, suggesting the newly synthesized catalyst exhibits an extremely high performance as a Pt-free cathode catalyst. Figure 1

Direct synthesis of Pt-free catalyst on gas diffusion layer of fuel cell and usage of high boiling point fuels for efficient utilization of waste heat

Gas diffusion layers (GDL) and electrocatalysts are integral parts of fuel cells. It is, however, a challenging task to grow Pt-free robust electrocatalyst directly on GDL for oxygen reduction reaction (ORR) – a key reaction in fuel cells. Here, we demonstrate that boron-doped carbon nanotubes (BCNTs) grown directly on gas-diffusion layer (which avoid the need of ionomer solution used for catalyst loading) can be used as efficient Pt-free catalyst in alcohol fuel cells. Increase in boron concentration improves the electrochemical ORR activity in terms of onset and ORR peak positions, half-wave potentials and diffusion-limited current density that ensure the optimization of the device performance. The preferential 4e− pathway, excellent cell performance, superior tolerance to fuel crossover and long-term stability makes directly grown BCNTs as an efficient Pt-free cathode catalyst for cost-effective fuel cells. The maximum power density of the fuel cell is found to increase monotonically with boron concentration. In addition to the application of BCNTs in fuel cell, we have introduced the concept of hot fuels so that waste heat can effectively be used and external power sources can be avoided. The fuel is passed through a hot bath for the realization of hot fuel which eventually increases the operating temperature of the cell (for example: 60°C for methanol and 80°C for ethyleneglycol, avoids the requirement of heating arrangement) and hence, the performance. Overall, different strategies to design ultimate fuel cells for their commercial adoption and effective utilization of waste heat have been outlined.

Correction to “Estimation of the Inherent Kinetic Parameters for Oxygen Reduction over a Pt-Free Cathode Catalyst by Resolving the Quasi-Four-Electron Reduction”

Understanding the kinetics of the oxygen reduction reaction (ORR) for fuel cell applications is quite important but difficult because the four-electron pathway is often overestimated by including a quasi-four-electron pathway that consists of the formation and reduction of H2O2. To solve this problem, here we demonstrate a novel analysis method with experimental data over a Pt-free Fe/N/C cathode catalyst. In this study, H2O2 voltammetry was conducted separately to evaluate the rate constant of the H2O2 reduction more accurately, and the obtained data were combinatorally analyzed with those from the ORR experiments. First, mathematical modification of the conventional Damjanovic approach was performed, and then the effect of the catalyst loading density was carefully studied by utilizing a novel reaction model with consideration of the quasi-four-electron pathway to avoid overestimation of the four-electron pathway kinetic parameters. In the most overestimated case, the percentages contribution of four-el...

Ethanol - Tolerant Pt-free Cathode Catalysts for the Alkaline Direct Ethanol Fuel Cell

The structure and electrochemical activity of carbon supported Pt-free cathode catalysts (Ag/C, Mn3O4/C and AgMnO2/C) are investigated by means of transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and cyclic voltammetry (CV). The catalysts display ethanol-tolerance for the oxygen reduction reaction (ORR) in 0.1 M KOH electrolyte containing ethanol at different temperatures. Because crossover of ethanol from anode to cathode through the membrane can occur in alkaline direct ethanol fuel cells (ADEFCs), selectivity of the cathode catalyst is of high importance. AgMnO2/C catalyst exhibits the highest catalytic activity toward ORR in presence of alkaline electrolytes containing ethanol.

Estimation of the Inherent Kinetic Parameters for Oxygen Reduction over a Pt-Free Cathode Catalyst by Resolving the Quasi-Four-Electron Reduction

Estimation of the Inherent Kinetic Parameters for Oxygen Reduction over a Pt-Free Cathode Catalyst by Resolving the Quasi-Four-Electron Reduction

Selective CoSe2/C cathode catalyst for passive air-breathing alkaline anion exchange membrane μ-direct methanol fuel cell (AEM-μDMFC)

In this work, carbon-supported CoSe2 is used as a Pt-free cathode catalyst in a passive, air-breathing, alkaline anion exchange membrane μ-direct methanol fuel cell (AEM-μDMFC). The obtained results demonstrate the improvement in the performance, when the device is operated at high fuel concentrations, if the proposed cathode catalyst is used instead of the standard Pt/C catalyst, due to the better tolerance to methanol crossover even in alkaline medium. This result reinforces the suitability of AEM-DMFC's as a promising option for mobile devices powering.

Enhanced Oxygen Reduction Activity of N-Doped Multiwalled Carbon Nanotubes in Alkaline Media

A great deal of work has been made to develop new electrocatalysts for oxygen reduction reaction (ORR) in acid and alkaline media. In order to replace expensive and scarce Pt-based catalysts that have been primarily employed as cathode catalysts in low-temperature fuel cells, different carbon-based materials that possess lower price, better availability and improved chemical stability have been studied. Nitrogen-doped nanocarbons can be used as alternatives to Pt-based cathode catalysts. Previously, we have investigated the reduction of O2 on CVD grown nitrogen-doped carbon nanotubes,1 on CNTs heat-treated in the presence of urea2 and on N-doped graphene3 and few-layer graphene/multiwalled carbon nanotube (FLG/MWCNT) composites.4 In this work the electrocatalysis of oxygen reduction on nitrogen-doped carbon nanotube (NCNT) catalysts has been investigated. These NCNT materials were prepared from two different nitrogen precursors and acid-treated MWCNTs. Cyanamide (CM) and dicyandiamide (DCDA) were used as nitrogen precursors and the doping was achieved by pyrolysing MWCNTs in the presence of these nitrogen-containing compounds at 800 °C. The MWCNT-to-nitrogen precursor mass ratio was 1:20. The N-doped carbon nanotube catalyst samples were characterized by scanning electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy, the latter method revealed successful nitrogen doping. The electrocatalysis of the ORR was studied in 0.1 M KOH on glassy carbon (GC) electrodes modified with N-doped CNT electrocatalysts employing the rotating disk electrode (RDE) method. The NCNT-DCDA material showed a better ORR performance than the NCNT-CM catalyst. Fig. 1 presents the ORR polarization curves on NCNT-DCDA at various rotation rates and Fig. 2 shows the Koutecky-Levich plots for this catalyst. As can be seen, the number of electrons transferred (n) is close to 4, which is advantageous from the point of view of fuel cell application. A comparison of the RDE results indicated that these metal-free NCNT catalysts possess remarkable electrocatalytic activity toward the ORR in alkaline media similar to that of commercial Pt/C catalyst (Fig. 3). The results obtained in this work are important for the development of Pt-free cathode catalysts for alkaline membrane fuel cells (AMFC). In the next stage of work these materials will be tested in AMFC conditions.

Highly durable Pt-free fuel cell catalysts prepared by multi-step pyrolysis of Fe phthalocyanine and phenolic resin

A Pt-free cathode catalyst for polymer electrolyte membrane fuel cells has been developed by multi-step pyrolysis of Fe phthalocyanine and phenolic resin and shows a quite promising fuel cell performance.

High performance Pt-free cathode catalysts for polymer electrolyte membrane fuel cells prepared from widely available chemicals

A high performance Pt-free cathode catalyst for polymer electrolyte fuel cells has been synthesized by the multi-step pyrolysis of polyimide fine particles with a diameter of about 100 nm.

Pt-Free Cathode Catalyst Prepared From Polyimide Fine Particles

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Pt-Free Cathode Catalyst Prepared From Polyimide Fine Particles

Pt-free cathode catalyst was prepared by pyrolyzing fine nano particles of polyimide. The catalytic activity for oxygen reduction in acidic media was confirmed with the sample paralyzed at over 600 ˚C. The morphology of the fine particles was retained even after the carbonization. Carbon based cathode catalyst with such morphology is quite promising considering the application in polymer electrolyte membrane fuel cells.

Direct Accessing the Nanostructure of Carbon Supported Ru−Se Based Catalysts by ASAXS

A structural model of selenium-modified ruthenium nanoparticles was derived from anomalous small-angle X-ray scattering (ASAXS) and small-angle neutron scattering (SANS) experiments and further approved and supported by TEM, XRD, and extended X-ray adsorption fine-structure (EXAFS) analysis. Carbon-supported ruthenium nanoparticles modified with selenium (RuSex/C) have been suggested as highly active and Pt-free cathode catalysts for the oxygen reduction reaction in PEM fuel cells. However, so far no definite conclusion regarding the nature of the catalytically active surface could be drawn. ASAXS and SANS experiments now revealed that the surface of Se modified Ru nanoparticles after reductive catalyst activation at elevated temperatures is not completely covered by Se. The Se rather forms patches on the Ru surface while the rest of the surface is covered by oxygen. It could be demonstrated that the different scattering contributions of the carbon black carrier and various metallic constituents of the supported nanoparticles can be well separated by means of ASAXS measurements. The structural model derived from the ASAXS energy dependencies could be confirmed by results of SANS measurements. Thus, the previously assumed core−shell model for the Se modified Ru particles was clearly disapproved.

Retracted article: Pt-free cathode catalysts prepared via multi-step pyrolysis of Fe phthalocyanine and phenolic resin for fuel cells

Pt-free cathode catalysts for polymer electrolyte membrane fuel cells have been prepared by multi-step pyrolysis of FePc and PhRs, in the best of which show extensively high initial cell performance and good durability compared to other present precious-metal-free cathode catalysts to date.

Pt-Free Cathode Catalyst Performance in H2/O2 Anion-Exchange Membrane Fuel Cells (AMFCs)

H2/O2 AMFCs enable the use of Platinum Group Metal (PGM) free Membrane Electrode Assemblies (MEAs), especially for the Oxygen Reduction Reaction (ORR). A promising catalysts for the ORR (Acta's "K14"), has been developed and tested using Rotating Disk Electrode (RDE) analysis, showing promising performance. In this paper we characterize current Anion-Exchange Membranes (AMs), show the fuel cell activity of AM-based MEAs prepared with K14 ORR catalyst, and compare their performance with the kinetic and ohmic limits projected from the membrane and catalyst properties. The data and projections show promising results for this technology.

Pt-free Cathode Catalyst Performance in H2/O2 Anionic Membrane Fuel Cells (AMFCs)

not Available.

Oxygen Reduction Electrocatalysis at Chalcogen-Modified Ruthenium Cathodes

We have recently developed a method for obtaining chalcogenide catalysts, which is based on surface modification of ruthenium black particles rather than the synthesis of a bulk metal-chalcogen compound [1]. Electrochemical, non- electrochemical and fuel cell testing have revealed high ORR activity and very good methanol tolerance of such surface chalcogenide catalysts [2,3]. Uniquely for Pt-free cathode catalysts, such surface chalcogenides also exhibit very good performance durability under fuel cell operating conditions at 70{degree sign}C. In this paper, we focus on hydrogen-air and direct methanol fuel cell performance of chalcogen-modified Ru blacks as well as on the mechanism of oxygen reduction on such catalysts, as determined in rotating ring disk-electrode (RRDE) studies.