Cathode Catalyst Loading Research Articles

System Design Rules for Intensifying the Electrochemical Reduction of CO2 to CO on Ag Nanoparticles

AbstractElectroreduction of CO2 (eCO2RR) is a potentially sustainable approach for carbon‐based chemical production. Despite significant progress, performing eCO2RR economically at scale is challenging. Here we report meeting key technoeconomic benchmarks simultaneously through electrolyte engineering and process optimization. A systematic flow electrolysis study ‐ performing eCO2RR to CO on Ag nanoparticles as a function of electrolyte composition (cations, anions), electrolyte concentration, electrolyte flow rate, cathode catalyst loading, and CO2 flow rate ‐ resulted in partial current densities of 417 and 866 mA/cm2 with faradaic efficiencies of 100 and 98 % at cell potentials of −2.5 and −3.0 V with full cell energy efficiencies of 53 and 43 %, and a conversion per pass of 17 and 36 %, respectively, when using a CsOH‐based electrolyte. The cumulative insights of this study led to the formulation of system design rules for high rate, highly selective, and highly energy efficient eCO2RR to CO.

PGM-Free Fe/N/C and Ultralow Loading Pt/C Hybrid Cathode Catalysts with Enhanced Stability and Activity in PEM Fuel Cells

In this work, the stability behaviors of the state-of-the-art Fe/N/C and Pt/C catalysts (as well as the activation time of the latter) were firstly systematically investigated, under different cathode catalyst loadings, in the membrane electrode assemblies (MEA) in PEM fuel cells. Based on that, two types of cathode electrodes with the combination of Fe/N/C and Pt/C catalysts were developed (type I: layered hybrid catalysts with Pt/C next to the membrane, and type II: uniformly mixed catalysts). In this way, the shortcomings of the Fe/N/C catalyst (the fast decay) and the Pt/C catalyst (the long activation time) can be compensated at the same time. The hybrid catalysts also showed a very short activation time (a few hours vs. over 10 hours for Pt/C with the same Pt loading). Comparing the two types of hybrid catalysts, type I shows a much higher current density. The loadings of the Fe/N/C and Pt/C catalysts in the hybrid electrode were systematically studied, with optimal values of 1.0 mg cm-2 for Fe/N/C and 0.035 mgPt cm-2 for Pt/C. The Pt loading of this hybrid catalyst (type I) at the cathode only takes ca. 30% of the U.S. Department of Energy (DOE) target of Pt usage (0.100 mgPt cm-2), while its mass activity of Pt (in H2/O2 PEMFC) is 0.22 A mgPt-1 at 0.9iR-free V, reaching half of the DOE activity target (0.44 A mgPt-1), which is among the best performances reported so far. Via both half-cell and single-cell electrochemical evaluations together with other characterizations, the origin of the improved activity and stability is believed to be the synergistic effect between Pt/C and Fe/N/C catalysts to ORR. This work provides an effective strategy for engineering highly performing MEA for the industrialization of PEM fuel cells.

Impact of the Cathode Pt Loading on PEMFC Contamination by Several Airborne Contaminants.

Proton exchange membrane fuel cells (PEMFCs) with 0.1 and 0.4 mg Pt cm−2 cathode catalyst loadings were separately contaminated with seven organic species: Acetonitrile, acetylene, bromomethane, iso-propanol, methyl methacrylate, naphthalene, and propene. The lower catalyst loading led to larger cell voltage losses at the steady state. Three closely related electrical equivalent circuits were used to fit impedance spectra obtained before, during, and after contamination, which revealed that the cell voltage loss was due to higher kinetic and mass transfer resistances. A significant correlation was not found between the steady-state cell voltage loss and the sum of the kinetic and mass transfer resistance changes. Major increases in research program costs and efforts would be required to find a predictive correlation, which suggests a focus on contamination prevention and recovery measures rather than contamination mechanisms.

New CCL|MPL Architecture Reducing Interfacial Gaps and Enhancing PEM Fuel Cell Performance

AbstractWe demonstrate an enhanced new architecture for fuel cell membrane electrode assemblies (MEAs), by deposition of the microporous layer (MPL) directly on the catalyst coated membrane (CCM), in order to reduce any gaps at the cathode catalyst layer (CCL) surface. A low bonding temperature Teflon was used to allow low temperature sintering of the CCM with the MPL. This modified structure enhances PEMFC performance by improving the electronic contact and minimizing water pooling at the CCL|MPL interface. The improvement in water management at the CCL|MPL is beneficial especially for thinner CCLs to fulfill the performance demand with low cathode catalyst loading MEAs (≤0.125 mgPt cm−2 as targeted by the US Department of Energy).

Smart Control of Composition for Double Perovskite Electrocatalysts toward Enhanced Oxygen Evolution Reaction.

Double perovskites have emerged as efficient candidates for catalyzing the electrochemical oxygen evolution reaction (OER). Smart control of the composition of a B-site ordered double perovskite can lead to improved catalytic performance. By adopting a facile co-doping strategy, the OER-active elements are simultaneously introduced into the B-site and B'-site of a B-site-ordered double perovskite (A2 BB'O6 ), leading to an enhancement of the exposed reactive sites and an optimum surface chemical state. As a result, a model system built from the substitution of Co for Mo and Fe in the Sr2 FeMoO6-δ double perovskite (with a composition of Sr2 Fe0.8 Co0.2 Mo0.6 Co0.4 O6-δ ) shows significantly enhanced OER activity in alkaline media compared with the host material, requiring an overpotential of 345 mV to reach a 10 mA cm-2 current density (catalyst loading≈0.232 mgcat cm-2 GEO ) and a cell voltage of 1.57 V to afford the same current density for the overall water splitting when coupled with a Pt/C cathode (catalyst loading≈2 mg cm-2 ). It also demonstrates excellent electrochemical stability. The generalizability of the compositional control methodology has also been demonstrated in double perovskites incorporating transition metals other than Co (e.g., Ni).

Multi-cathode photocatalytic fuel cell with rotating bamboo charcoal electrodes for electricity production and simultaneous organic pollutants removal

Carbonaceous materials have considerable potential as effective cathode catalysts due to their low cost and high oxygen reduced reaction (ORR) activity. However, current approaches face significant challenges, such as the fall-off of the catalyst and mass transfer inhibition as the catalyst loading increases. In this study, a multi-cathode-based photocatalytic fuel cell (PFC) was developed for maintaining a high cathode catalyst loading and simultaneously enhancing the mass transfer to improve the catalytic activity. Under identical high loading, the cathode configuration would significantly influence the power production of the PFC. The maximum power of the multi-cathode PFC was 50% and 53% higher than those of the Pt cathode and single-cathode PFCs, respectively. Meanwhile, the removal efficiency of methyl orange (MO) in the multi-cathode PFC was also higher than that in the single-cathode PFC. These results were attributed to the relatively large effective area and reduced transfer resistance of electrons and oxygen, owing to the multi-cathode system. In addition, a batch of experiments involving different parameters (such as pH, rotating speed, and initial MO concentration) was performed to obtain the optimal parameter conditions. Considering the high cost of Pt, all the tests indicated that the PFC with the multi-cathode configuration efficiently enhanced the power generation and simultaneously facilitated the removal of organic pollutants.

Electrochemical method for dissolved oxygen consumption on-line in tubular photobioreactor

A new electrochemical tubular photobioreactor is designed for the efficient cultivation of chlorella, alongside eliminating the inhibition of the growth of microalgae caused by the high dissolved oxygen content. With the aid of anion-exchange membrane alkaline fuel cell, the dissolved oxygen in the photobioreactor which is produced by the photosynthesis of microalgae can be consumed and the energy consumption of photobioreactor can be reduced. Besides, the effects of different components and operating parameters on the efficiency of dissolved oxygen removal and the cell performance have been detailed investigated. The experiment results are shown as follows. First, by applying the double-cylinder alkaline direct glucose fuel cell to consume the dissolved oxygen of the microalgae suspension in the tubular photobioreactor on-line, the dissolved oxygen content rapidly decreases from over 20.0 mg L−1 to 10.72 mg L−1 below within 45 min. Second, the efficiency of dissolved oxygen consumption and cell performance increase significantly by using the bimetallic catalyst Pt-Ru as the cathode catalyst in the double-cylinder alkaline direct glucose fuel cell compared with the mono-metallic cathode catalyst by adopting Pd and Pt. Third, it exists an optimal cathode catalyst loading (1.5 mgPtRu·cm−2) to consume the dissolved oxygen with the fuel cell yielding the best performance.

A non-noble V2O5 nanorods as an alternative cathode catalyst for microbial fuel cell applications

This study assessed the feasibility of vanadium pentoxide (V2O5) as a novel cathode catalyst material in air-cathode single chamber microbial fuel cells (SCMFCs). The V2O5 nanorod catalyst was synthesized using a hydrothermal method. MFCs with different cathode catalyst loadings were studied. Cyclic voltammetry (CV) was used to examine the electrochemical behavior of the catalysts in the MFCs. The V2O5 cathode catalyst constructed with a double loading MFC exhibited the highest maximum power density of 1073 ± 18 mW m−2 (OCP; 691±4 mV) compared with 447 ± 12 mW m−2 (OCP; 594 ± 5 mV) and 936 ± 15 mW m−2 (OCP; 647±5 mV) for the single loading MFC and triple loading MFC, respectively. The power density of MFC with double loaded V2O5 is comparable to the traditional Pt/C cathode (2067 ± 25 mW m−2, OCP; 821 ± 4 mV), which covers up to 55% of the performance of Pt/C. This finding highlights the potential of the V2O5 cathode as an inexpensive catalyst material for MFCs that may have commercial applications.

Cathode Loading Impact on Voltage Cycling Induced PEMFC Degradation – a Voltage Loss Analysis

Proton exchange membrane fuel cell (PEMFC) based vehicles are on the verge of commercialization. However, significant hurdles for further market penetration of PEMFC vehicles are cost reductions by decreasing the amount of platinum catalysts while meeting long term durability targets. The durability of catalysts is usually estimated by accelerated stress tests (ASTs) using voltage cycling.[1] Generally, the electrochemically active surface area (ECSA) and mass activity of the cathode catalyst is analyzed over the course of 30000 voltage cycles, while effects of O2 mass transport related losses, especially for varying cathode catalyst loadings have not yet been systematically studied. To better understand the influence of voltage cycling based ASTs on the development of mass transport resistances and on the extent to which they can be captured by currently available in situ diagnostics (ORR kinetics in H2/O2, cathode proton conduction resistance by impedance, oxygen transport resistance via limiting current measurements), we conducted a comprehensive voltage loss analysis on MEAs with high- and low-loaded cathodes (0.4 and 0.1 mgPt/cm2) over the course of ASTs conducted in H2/N2 (anode/cathode) at ambient pressure, 80 °C, and 100% RH, using different voltage cycling profiles: i) triangular wave (TW) and square wave (SW) cycles between 0.6 and 1.0 VRHE; ii) TW cycles between 0.6 and a lowered upper potential limit of 0.85 VRHE (TW-LUPL); and, iii) a combination of a triangular sweep between 0.6 and 1.0 VRHE with potential hold periods at the upper and lower potential (TW-H). For all ASTs, the O2 transport resistance scaled inversely to the cathode electrode roughness factor (rf). Since the ECSA decreases in the course of potential cycling and two different loadings were used, a wide range of rf values with their corresponding pressure-independent O2 transport resistance was analyzed, proving its dependence on the available Pt surface area (Figure 1) as shown also by other researchers.[2] The pressure dependent transport resistance remained essentially constant. Furthermore, ex situ thickness measurements of catalyst layers showed no cathode thinning, indicating the absence of significant carbon corrosion. While 30000 TW or SW cycles dramatically decreased the H2/air performance for low- and high-loaded MEAs, only a negligible degradation in performance was observed when a lower upper potential limit of 0.85 VRHE was applied, providing a guideline to limit MEA degradation under automotive conditions. Figure 1: Pressure independent O2 transport resistance vs the electrode’s roughness factor, rf, for high-loaded (0.4 mgPt/cm2, blue) and low-loaded (0.1 mgPt/cm2, orange) catalyst layers over the course of different voltage cycling ASTs. Figure 1

Contamination of Low Platinum Catalyst Loading Cathodes for Proton Exchange Membrane Fuel Cells

Fuel cell vehicles have recently entered the market place (1). Future increases in technology adoption are dependent on concurrent cost reduction and improved durability (2). This is a major challenge because membrane/electrode assemblies based on low platinum catalyst loadings have shown inferior durability (3). Many processes limit the proton exchange membrane fuel cell (PEMFC) durability including the presence of contaminants in ambient air. Although a filter is added at the air intake to remove particulates and undesirable gaseous species, contaminant slippage, missed replacements after the filter has reached its end of life and other failures increase fuel cell exposure risks. A strategy relying on the understanding of contamination mechanisms is expected to result in a more robust system with the development of mitigation, recovery and maintenance procedures that supplement the air filter. Such a strategy is necessary because the impact of many contaminants is still unknown (4). Furthermore, relatively little contaminant related information is available for low platinum catalyst loadings (5-7). In this tutorial, focus will be given to recent contamination results and fundamental understanding obtained with a low cathode platinum loading of 0.1 mg cm-2, a value consistent with the United States Department of Energy 2020 target of 0.125 mg cm-2 for the sum of anode and cathode catalyst loadings. All tested contaminants are organic and representative of alcohols (iso-propanol), alkenes (propene), alkynes (acetylene), esters (methyl methacrylate), halocarbons (bromomethane), nitriles (acetonitrile), and polycyclic aromatics (naphthalene). The impact of catalyst loading and contaminant on cell performance, contaminant hydrophobicity on liquid water transport, a long duration contaminant exposure on degradation, a fuel cell stack compatible recovery procedure on cell voltage losses sustained during contamination, and a contaminant mixture on the synergy between species and cell performance will be discussed and contextualized with the relevant literature. All these contamination aspects have either not been explored or been insufficiently documented. Acknowledgments Authors are grateful to the Office of Naval Research (award N00014-13-1-0463), the Department of Energy (award DE-EE0000467), the National Institute of Standards and Technology (neutron imaging beam time), and the Hawaiian Electric Company for their ongoing support to the operations of the Hawaii Sustainable Energy Research Facility.

Performance of an Active Micro Direct Methanol Fuel Cell Using Reduced Catalyst Loading MEAs

The micro direct methanol fuel cell (MicroDMFC) is an emergent technology due to its special interest for portable applications. This work presents the results of a set of experiments conducted at room temperature using an active metallic MicroDMFC with an active area of 2.25 cm2. The MicroDMFC uses available commercial materials with low platinum content in order to reduce the overall fuel cell cost. The main goal of this work is to provide useful information to easily design an active MicroDMFC with a good performance recurring to cheaper commercial Membrane Electrode Assemblies MEAs. A performance/cost analysis for each MEA tested is provided. The maximum power output obtained was 18.1 mW/cm2 for a hot-pressed MEA with materials purchased from Quintech with very low catalyst loading (3 mg/cm2 Pt–Ru at anode side and 0.5 mg/cm2 PtB at the cathode side) costing around 15 euros. Similar power values are reported in literature for the same type of micro fuel cells working at higher operating temperatures and substantially higher cathode catalyst loadings. Experimental studies using metallic active micro direct methanol fuel cells operating at room temperature are very scarce. The results presented in this work are, therefore, very useful for the scientific community.

Developing a passive air-breathing tubular direct methanol fuel cell fed with concentrated methanol

ABSTRACTThis study develops and investigates a fully passive air-breathing tubular direct methanol fuel cell (t-DMFC) with a steel-tube anode and a steel-mesh cathode. The effects of methanol concentration, cathode catalyst loading, mesh structure, and forced air convection are experimentally explored. Results indicate that the t-DMFC performs better at a relatively higher methanol concentration of 8 M. It is recommended to use a catalyst loading of 4 mg cm−2. Both the electrochemical impedance spectroscopy (EIS) and performance tests confirm that the 40-mesh setup is preferred at the cathode. The fuel cell yields a poor performance when the cathode works with forced air convection because the air-blowing operation reduces the cell temperature and this effect dominates the cell performance. The dynamic and constant-load behaviors are also inspected.

Optimization of the catalyst loading for the direct borohydride fuel cell

Direct borohydride fuel cells (DBFC) are considered as attractive energy suppliers because of their high electrochemical activity, open circuit potential, energy storage capacity, and power performance at ambient temperature. For the successful commercialization of the DBFCs, cost effective and high performance cells should be produced. In this study, the analysis and optimization of the DBFC operation conditions are carried out with Design Expert software central composite tool. Power density is chosen as a response (dependent) parameter and cell temperature, borohydride concentration, anode and cathode flow rates and catalyst loading are chosen as independent parameters. Based on ANOVA (analysis of variance) analyses, the maximum power density of 108.5 mW cm−2 is obtained at cell temperature of 79.8 °C, borohydride concentration of 1.5 M, anode flow rate of 5 cm3 min−1, cathode flow rate of 0.1 dm3 min−1and PtRu/C catalyst loading of 0.7 mg cm−2.

Nitrogen-doped carbon nanofiber catalyst for ORR in PEM fuel cell stack: Performance, durability and market application aspects

A noble metal-free catalyst based on N-doped carbon nanofibers supported on graphite (N-CNF/Fe) was employed for the oxygen reduction at the cathode of a Nafion PEMFC with a commercial Pt/C anode. Obtained performance in pure H2 and O2 indicated the presence of significant mass-transport limitations when utilizing catalyst loading between 1 and 10 mg cm−2. Strategies to reduce the limitations were explored by optimization of the cathode ionomer content, catalyst loading and application technique. Pore-formers (Li2CO3, (NH4)2CO3 and polystyrene microspheres) were utilized to improve the mass-transport within the layer. A maximum of 72 mW cm−2 and 1400 A g−1 or 300 W g−1 at peak power was demonstrated. The catalyst was then applied to the cathode of a 10-cell fuel cell stack, and a 400-h durability test was conducted. The average cell voltage decay amounted to 162 μV h−1. Finally, a market application analysis was conducted to illustrate the potential and challenges of replacing platinum as cathode catalyst. It was shown that even a near-complete elimination of the cathode catalyst cost by substitution of platinum with a carbon-based catalyst cannot produce a cost competitive product unless both the performance and the durability of the fuel cell with the new catalyst are very close to that of the state-of the art Pt-based system.

Design of a proton exchange membrane (PEM) fuel cell with variable catalyst loading

The performance and durability of proton exchange membrane (PEM) fuel cells is greatly affected by sharp temperature and stress gradients owing to the significant variation in local current density distribution. To improve the uniformity in local current density distribution and enhance the catalyst utilization, this paper proposes use of functionally graded catalyst loading in the cathode catalyst layer along the gas channel. A two-dimensional isothermal numerical model for PEM fuel cells combined with an optimization model was developed to determine the optimum cathode catalyst loadings and the associated local current density distributions for different operating conditions. Experiments were conducted to measure the local current density distribution for graded catalyst loading, using a segmented current collector. The results show that an optimized graded catalyst loading significantly reduces the current density variation along the length of the channel and enhances the catalyst utilization.

Development and performance analysis of a metallic passive micro-direct methanol fuel cell for portable applications

Due to the growing interest on miniaturization for application on portable devices, the Micro Direct Methanol Fuel Cells (Micro-DMFC) proved to have great benefits. Passive fuel cells have extra advantages leading to less complex and cheaper systems. In the present work, an experimental study on the performance of a passive Micro-DMFC with an active area of 2.25 cm2 working at ambient conditions is described. Several commercially available materials for Membrane Electrode Assembly (MEA) are tested including materials with low platinum content to achieve lower prices. The effect of methanol concentration on the cell performance is evaluated. The performance is compared with the one obtained using an active Micro-DMFC with the same active area. A optimized design is proposed corresponding to a maximum power density, 19.2 mW/cm2, obtained using a Nafion 117 membrane, 3 mg/cm2 Pt–Ru and 0.5 mg/cm2 Pt as, respectively, anode and cathode catalyst loading, carbon paper as anode gas diffusion layer (GDL) and Sigracet carbon paper with micro porous layer (MPL) as cathode GDL at methanol feed concentration of 3 M. This result higher than the optimal power obtained with the active Micro-DMFC clearly demonstrates that membranes with low catalyst content could be used in passive MicroDMFC with success. This is an important result bearing in mind the use of micro-DMFCs in portable applications.

Study of the Variation of Catalyst Loading in Cathode for SPEEK/CSMM Membrane in Direct Methanol Fuel Cell (DMFC)

Variation of anode catalyst loading for modified sulfonated poly (ether ether ketone) (SPEEK) with charged surface modifying macromolecules (cSMM) membrane was studied, in order to get the higher performance in DMFC. The best optimal anode catalyst loading was 4 mgcm-2 for 30% Pt/Ru based on our previous result for this application. The modified SPEEK/CSMM membrane was characterized to ensure of its better performance in term of water uptake and methanol permeability. In cathode side, the effect of 5% and 10% Pd/C in 2,4 and 6 mgcm-2 of catalyst loading has been investigated with a fuel cell assembly. The preparation method of catalyst ink and membrane electrode assembly (MEA) was based on Dr. Blade method and hot pressing by using catalyzed diffusion media (CDM) method. The air flowrates were varied from 25-1000ml min-1, while 1M methanol concentrations, 1 ml min-1 of methanol flowrate and 60°C operating temperature were kept constant. These parameters were tested on the performance of single cell DMFC with 4 cm2 electrodes.The optimization catalyst loading will enhance the DMFC performance. It was found, the best optimal cathode catalyst loading was 4 mgcm-2 for 10% Pd/C with 4 mgcm-2 for 30% Pt/Ru in anode side for this application.

New Developments in Electrospun Nanofiber Electrodes for Hydrogen/Air Fuel Cells

The hydrogen/air proton-exchange membrane (PEM) fuel cell is a promising candidate for automotive power plants due to its high power output, moderate operating temperature, and quick start-up. The commercialization of such devices is hindered by the high price and inadequate durability of the platinum catalyst electrodes. Recent R&D efforts have been directed at reducing Pt loading and fabricating catalysts with supports that can withstand the harsh automotive operating environment. Work in this area includes the investigation of metal alloys, core-shell nanostructures, and metal oxide supports. Work on non-platinum group metal catalysts for the oxygen reduction cathode in a hydrogen/air fuel cell has also been reported. The creation of particle/polymer nanofiber mat electrodes via electrospinning represents an entirely different strategy for lowering cathode catalyst loading while maintaining high power output in a hydrogen/air fuel cell. A nanofiber electrode morphology with intra and inter-fiber porosity is advantageous because: (i) it increases catalyst contact with reactant gases, (ii) it provides a sufficient number of pathways for effective proton and electron conduction, and (iii) there is sufficient inter-fiber porosity for release of cathode product water. Previously, we have shown that more power was generated from nanofiber electrode MEAs than a conventional MEA with decal electrodes [1,2]. For example, the maximum power density for a H2/air fuel cell with a nanofiber cathode and anode (at loadings of 0.065 mgPt/cm2 and 0.10 mgPt/cm2, respectively) was 437 mW/cm2 vs. 400 mW/cm2 for a decal MEA with a cathode containing 40% more Pt (a loading of 0.104 mgPt/cm2) and an anode loading of 0.10 mg/cm2. In these experiments, the nanofiber catalyst binder was a mixture of Nafion® and poly(acrylic acid), the binder used in decal electrodes was neat Nafion, and the membrane was Nafion 212. The fuel cell operating conditions were: 80oC, 1 atm (ambient) pressure, 125 sccm H2, and 500 sccm air. As another example, an electrospun cathode with a Pt loading of 0.055 mg/cm2 produced a maximum power density of 906 mW/cm2 at 80°C and 3 atm pressure with 2000 sccm fully humidified air and 500 sccm H2. Additionally, the mass activity (0.16 A/mgPt at 0.9 V) and electrochemical surface area (~41 m2/g) of nanofiber cathodes containing Johnson-Matthey HiSpec™ 4000 catalyst were found to be very high and electrospun cathodes exhibited less degradation than a conventional decal cathode in an accelerated voltage cycling durability test.In this presentation, new catalyst/binder electrode formulations will be discussed, in terms of the conditions required to electrospin well-formed fibers and the performance of the fiber mats as cathodes in a hydrogen/air fuel cell operating at 80oC. MEAs are assessed in terms of the initial power density at high and low humidity operation and the changes in power output during voltage cycling Pt dissolution and carbon corrosion durability experiments. All anode and cathodes were prepared with Johnson Matthey HiSpec 4000 catalyst (40% Pt on Vulcan carbon), at a Pt loading of 0.10 mg/cm2. Acknowledgments This work was funded by EMD Millipore and the NSF-funded TN-SCORE program, NSF EPS-1004083, under Thrust 2. References W. Zhang and P. N. Pintauro, ChemSusChem, 4, 1753-1757 (2011).M. Brodt, R. Wycisk, and P. N. Pintauro, Journal of the Electrochemical Society, 160, F744-F749 (2013).

Ultra-low platinum loadings in polymer electrolyte membrane fuel cell electrodes fabricated via simultaneous electrospinning/electrospraying method

In this study, membrane electrode assemblies (MEAs) were fabricated using a simultaneous electrospinning/electrospraying (E/E) technique to produce a unique nanoparticle/nanofiber cathode catalyst layer morphology evidenced by scanning electron microscopy. H2/O2 and H2/air polymer electrolyte membrane fuel cell performance was evaluated for E/E MEAs at ultra-low Pt cathode loadings of 0.052 and 0.022 mgPt cm−2, where maximum power densities of 1.090 and 0.936 W cm−2 (H2/O2) and 0.656 and 0.625 W cm−2 (H2/air) were achieved at these two Pt loadings, respectively. This was compared to a conventional control MEA at a 0.42 mgPt cm−2 cathode catalyst loading with maximum power densities of 1.420 and 0.839 W cm−2 for H2/O2 and H2/air, respectively. These results correspond to a significant reduction in Pt loading (5–12% of control) at only a modest reduction in power density (∼66–78% of control) for the E/E electrodes. Excellent platinum utilization in the cathode of 0.024 gPt kW−1 (∼42 kW gPt−1) was achieved for the E/E electrode at 0.022 mgPt cm−2 cathode loading. Cyclic voltammetry results show an electrochemical surface area higher in the E/E electrodes compared to the control, which provides a rationale for the excellent platinum utilization results, where the E/E morphology results in more triple phase boundaries with more accessible Pt in the electrode.

Highly Active and Corrosion-Resistant PtCr / C Catalyst for PEMFC & DMFC Applications

Sluggish kinetics of Pt catalyst for oxygen reduction reaction (ORR) and insufficient corrosion resistance of catalyst/support are major drawbacks that delay PEMFC and DMFC commercialization. Some Pt alloys such as PtCo, PtNi, PtCu, PtCr and PtFe have already shown an improved activity for ORR in phosphoric acid compared to that of pure Pt [1]. Both, electronic (shift of d-band center) and geometric (tensile/compressive strain) effects are supposed to be responsible for the increase in activity of Pt after alloying process. Addition of a second transition metal causes also changes of local bond, active site distribution and reactivity of Pt surface atoms for ORR. However, dissolution or/and segregation to the surface of the non-noble metal in the case of an alloy and core-shell structure, respectively affect the long-term activity of these systems. According to Mukerjee et al. [2], PtCr/C lies at the top of vulcano-type curves in which electrocatalytic activity of different Pt alloys (i900mV) was plotted against either electronic (Pt d-band vacancies per atom) or geometric (Pt-Pt bond distance) parameters. Surprisingly, despite of numerous promising results, little attention has been paid to PtCr alloy in the last decade.In this work, activity and stability of PtCr/C were investigated under half-cell and full-cell conditions. The bi-metal catalyst was synthesized by co-reduction of hexachloroplatinic acid and chromium(III) nitrate hydrate in formaldehyde at 80°C for 1h. The nominal mass ratio of Pt:Cr was fixed to 3:1 and the total metal loading on carbon Vulcan to 40 wt%. The structural characterization of the as-prepared catalysts was performed by means of XRD, TGA, and TEM. Electrochemical activity of Pt-Cr/C catalyst was studied in O2-saturated 0.5 M H2SO4 electrolyte at room temperature by using a rotating disk electrode (RDE) cell. The total catalyst/support loading was about 80 μg cm-2. The electrochemical surface area (ECSA) of the catalyst was calculated by integrating the hydrogen desorption region in the cyclic voltammogramms at 40 mV s-1. Fuel cell experiments were performed in H2/air atmospheres with a 180 µgPt cm-2 anode catalyst and a Nafion HP membrane at 80°C. The cathode catalyst loading was 236 µgPtCr cm-2 for the MEA with the as-prepared PtCr/C and 360 µgPt cm-2 for the MEA with commercial Pt/C (JM). The accelerated degradation tests consisted of 7000 cycles in the half-cell and of 1000 cycles in the full-cell whereas 500 cycles were performed between 0.4 and 1.4 V and the last 500 cycles between 0.05 and 1.4V at dE/dt=1 V s-1. A commercial 40 wt% Pt/C catalyst from Johnson Matthey (JM) was used for comparison.In half-cell experiments, PtCr/C exhibited twice higher ESCA-normalized specific activity (SA) and total catalyst mass-normalized activity (MA) for ORR at 850mV compared to that of the commercial catalyst (see values in Table 1). Some results regarding electrochemical surface area (ECSA) behaviour during accelerated degradation test (ADT) are shown in Figure 1. It can be seen that the initial ECSA of PtCr/C is 33% lower than that of Pt/C (JM) and the degradation rate after 7000 cycles is quite similar. TEM images revealed an increase in PtCr particle size from about 4.5 nm for the as-prepared powder catalyst up to 8-9 nm after 7000 cycles in the half-cell (see Fig. 1).Table 1: Summary of the results Half-CellFull-cell SA @0.85V mA cm-2 MA @0.85V mA mgPtCr -1 Pmax @100c mW cm-2 Pmax @1000c mW cm-2 Pt0.12941368242PtCr0.32780348263 Excellent performances have been obtained in the full-cell with PtCr/C as cathode catalyst since effective Pt loading is 49% lower than that in the MEA with Pt/C (JM) (177 vs. 360 µg cm-2). The stability of MEA with PtCr/C cathode is remarkable as well, if compared to that one of the most performing available commercial catalyst (see Fig. 2).