High performance polymer electrolyte fuel cells with ultra-low Pt loading electrodes prepared by dual ion-beam assisted deposition

Ultra-low pure Pt-based electrodes (0.04-0.12 mg_Pt/cm²) were prepared by dual ion-beam assisted deposition (dual IBAD) method on the surface of a non-catalyzed gas diffusion layer (GDL) substrate. Film thicknesses ranged between 250 and 750 Å, these are compared with a control, a conventional Pt/C (1.0 mg_Pt(MEA)/cm², E-TEK). The IBAD electrode constituted a significantly different morphology, where low density Pt deposits (largely amorphous) were formed with varying depths of penetration into the gas diffusion layer, exhibiting a gradual change towards increasing crystalline character (from 250 to 750 Å). Mass specific power density of 0.297 g_Pt/kW is reported with 250 Å IBAD deposit (0.04 mg_Pt/cm² for a total MEA loading of 0.08 mg_Pt/cm²) at 0.65 V. This is contrasted with the commercial MEA with a loading of 1 mg_Pt(MEA)/cm² where mass specific power density obtained was 1.18 g_Pt/kW (at 0.65 V), a value typical of current state of the art commercial electrodes containing Pt/C. The principal shortcoming in this effort is the area specific power density which was in the range of 0.27-0.43 W/cm² (for 250-750 Å IBAD) at 0.65 V, hence much below the automotive target value of 0.8-0.9 W/cm² (at 0.65 V). An attempt to mitigate these losses is reported with the use of patterning. In this context a series of patterns ranging from 45 to 80% Pt coverage were used in conjunction with a hexagonal hole geometry. Up to 30% lowering of mass transport losses were realized.     

Enhanced activity and interfacial durability study of ultra low Pt based electrocatalysts prepared by ion beam assisted deposition (IBAD) method

Ultra low loading noble metal (0.04–0.12 mg_Pt/cm²) based electrodes were obtained by direct metallization of non-catalyzed gas diffusion layers via dual ion beam assisted deposition (IBAD) method. Fuel cell performance results reported earlier indicate significant improvements in terms of mass specific power density of 0.297 g_Pt/kW with 250 Å thick IBAD deposit (0.04 mg_Pt/cm² for a total MEA loading of 0.08 mg_Pt/cm²) at 0.65 V in contrast to the state of the art power density of 1.18 g_Pt/kW using 1 mg_Pt(MEA)/cm² at 0.65 V. In this article we report the peroxide radical initiated attack of the membrane electrode assembly utilizing IBAD electrodes in comparison to commercially available E-TEK (now BASF Fuel Cell GmbH) electrodes and find the pathway of membrane degradation as well. A novel segmented fuel cell is used for this purpose to relate membrane degradation to peroxide generation at the electrode/electrolyte interface by means of systematic pre and post analyses of the membrane are presented. Also, we present the results of in situ X-ray absorption spectroscopy (XAS) experiments to elucidate the structure/property relationships of these electrodes that lead to superior performance in terms of gravimetric power density obtained during fuel cell operation.     

3D Visualisation of PEMFC Electrode Structures Using FIB Nanotomography

It is well known that the electrode structure of a PEMFC has a huge influence on the water management and thereby on the cell performance. In this work, two MEAs – one prepared by an airbrushing technique and the other by a novel fast spray coating technique (multilayered MEA) – were analysed with respect to porosity, pore size distribution, tortuosity and their electrochemical performance. FIB nanotomography with following 3D reconstruction, SEM investigation on ultramicrotomic thin‐sections, and single cell tests were performed on these MEAs. The results show a higher porosity and lower pore size for the multilayered MEA. The multilayered MEA reaches a Pt utilisation of 1,962 mW mg^–1 and a peak power density of 210 mW cm^–2, whereas the airbrushed MEA only provides a Pt utilisation of 879 mW mg^–1 and a peak power density of 218 mW cm^–2. The Pt utilisation calculations showed in combination with the structural characterisations that a homogeneous pore structure and Pt distribution provide an advantage with regard to performance and efficiency of the PEMFC. Furthermore, the multilayered MEA may offer an advantage over the airbrushed MEA in its long term stability, which was observed in preliminary tests.     

Dynamic Simulation of Oxygen Transport Rates in Highly Ordered Electrodes for Proton Exchange Membrane Fuel Cells

Highly ordered Pt electrode has been recognized as an important technology for reducing Pt usage in fuel cells due to its improved oxygen transport capability. However, ordered Pt electrode can lead to the decrease in roughness of electrode, which in turn makes it unclear whether the improved oxygen transport can offset the decreased roughness of ordered electrode. Herein, we theoretically investigate the oxygen distribution, generated current, and minimum Pt loading of ordered Pt electrode based on kinetic model of oxygen transport. The results reveal that ordered Pt electrodes do not exhibit concentration polarization with the electrode thickness up to 100 μm. For ordered Pt electrode with diameter of nanorod of 60 nm, the limited current density reaches 110.2 A cm⁻² that is much higher than that for conventional electrode without considering Ohmic loss and mass transport loss outside electrode. To generate a current of 1.5 A cm⁻² at 0.67 V for fuel cell, the minimum Pt loading of cathode in PEMFC reaches 0.029 mg cm⁻² assuming that the electrocatalyst nanorods contain 1 nm Pt layer at the outmost surface.     

Synthesis and electrocatalytic oxygen reduction activity of graphene-supported Pt3Co and Pt3Cr alloy nanoparticles

Graphene-supported Pt and Pt₃M (M = Co and Cr) alloy nanoparticles are prepared by ethylene glycol reduction method and characterized with X-ray diffraction and transmission electron microscopy. X-ray diffraction depicted the face-centered cubic structure of Pt in the prepared materials. Electron microscopic images show the high dispersion of metallic nanoparticles on graphene sheets. Electrocatalytic activity and stability of the materials is investigated by rotating-disk electrode voltammetry. Oxygen reduction activity of the Pt₃M/graphene is found to be 3–4 times higher than that of Pt/graphene. In addition, Pt₃M/graphene electrodes exhibited overpotential 45–70 mV lower than that of Pt/graphene. The high catalytic performance of Pt₃M alloys is ascribed to the inhibition of formation of (hydr) oxy species on Pt surface by the alloying elements. The fuel cell performance of the catalysts is tested at 353 K and 1 atm. Maximum power densities of 790, 875, and 985 mW/cm² are observed with graphene-supported Pt, Pt₃Co, and Pt₃Cr cathodes, respectively. The enhanced electrocatalytic performance of the Pt₃M/graphene (M = Co and Cr) compared to that of Pt/graphene makes them a viable alternative to the extant cathodes for energy conversion device applications.     

Do not forget the electrochemical characteristics of the membrane electrode assembly when designing a Proton Exchange Membrane Fuel Cell stack

The membrane electrode assembly (MEA) is the key component of a PEMFC stack. Conventional MEAs are composed of catalyzed electrodes loaded with 0.1–0.4 mg_Pt cm⁻² pressed against a Nafion^® membrane, leading to cell performance close to 0.8 W cm⁻² at 0.6 V. Due to their limited stability at high temperatures, the cost of platinum catalysts and that of proton exchange membranes, the recycling problems and material availability, the MEA components do not match the requirements for large scale development of PEMCFs at a low cost, particularly for automotive applications.Novel approaches to medium and high temperature membranes are described in this work, and a composite polybenzimidazole–poly(vinylphosphonic) acid membrane, stable up to 190 °C, led to a power density of 0.5 W cm⁻² at 160 °C under 3 bar abs with hydrogen and air. Concerning the preparation of efficient electrocatalysts supported on a Vulcan XC72 carbon powder, the Bönnemann colloidal method and above all plasma sputtering allowed preparing bimetallic platinum-based electrocatalysts with a low Pt loading. In the case of plasma deposition of Pt nanoclusters, Pt loadings as low as 10 μg cm⁻² were achieved, leading to a very high mass power density of ca. . Finally characterization of the MEA electrical properties by Electrochemical Impedance Spectroscopy (EIS) based on a theoretical model of mass and charge transport inside the active and gas diffusion layers, together with the optimization of the operating parameters (cell temperature, humidity, flow rate and pressure) allowed obtaining electrical performance greater than 1.2 W cm⁻² using an homemade MEA with a rather low Pt loading.     

Cathode materials based on carbon nanotubes for high-energy-density lithium–sulfur batteries

The rational integration of conductive nanocarbon scaffolds and insulative sulfur is an efficient method to build composite cathodes for high-energy-density lithium–sulfur batteries. The full demonstration of the high-energy-density electrodes is a key issue towards full utilization of sulfur in a lithium–sulfur cell. Herein, carbon nanotubes (CNTs) that possess robust mechanical properties, excellent electrical conductivities, and hierarchical porous structures were employed to fabricate carbon/sulfur composite cathode. A family of electrodes with areal sulfur loading densities ranging from 0.32 to 4.77 mg cm⁻² were fabricated to reveal the relationship between sulfur loading density and their electrochemical behavior. At a low sulfur loading amount of 0.32 mg cm⁻², a high sulfur utilization of 77% can be achieved for the initial discharge capacity of 1288 mAh g_S⁻¹, while the specific capacity based on the whole electrode was quite low as 84 mAh g_{C/S+binder+Al}⁻¹ at 0.2 C. Moderate increase in the areal sulfur loading to 2.02 mg cm⁻² greatly improved the initial discharge capacity based on the whole electrode (280 mAh g_{C/S+binder+Al}⁻¹) without the sacrifice of sulfur utilization. When sulfur loading amount further increased to 3.77 mg cm⁻², a high initial areal discharge capacity of 3.21 mAh cm⁻² (864 mAh g_S⁻¹) was achieved on the composite cathode.     

Pt and Sn Doped Sputtered CeO2 Electrodes for Fuel Cell Applications

The interaction of Pt with CeO₂ layers was investigated by using photoelectron spectroscopy. Thirty‐nanometre‐thick Pt and Sn doped CeO₂ layers were deposited simultaneously by rf‐magnetron sputtering on a Si(001) substrate and a carbon diffusion layer of a polymer membrane fuel cell by using a composite CeO₂–Pt–Sn target. The laboratory XPS and synchrotron radiation soft X‐ray and hard X‐ray photoemission spectra showed the formation of cerium oxide with completely ionised Pt^2+,4+ species, and with Pt⁴⁺ embedded in the film bulk. Hydrogen/air fuel cell activity measurements normalised to the amount of Pt used revealed high specific power of up to 5.4 × 10⁴ mW mg^–1 (Pt). The activity of these materials is explained by the strong activity of embedded Ptⁿ⁺ cations.     

Mathematical analysis and experimental results of applying enhanced-surface-area packed-bed electrodes in electrogenerative sulfur dioxide oxidation

The results of applying enhanced-surface-area packed-bed (ESAP) electrodes in electrogenerative SO₂/O₂ cells are reported to illustrate their utility and potential applications. Mathematical analysis with parameters pertinent to the experimental conditions shows that all electrocatalyst sites in these electrodes are expected to be uniformly utilized for electrochemical SO₂ oxidation. Experimental results showed that ESAP electrodes (1 mg Pt/cm²) could provide at least 5 times higher SO₂ conversion at given cell voltages than graphite sheet electrodes (1.5 mg Pt/cm²).     

Electrode Kinetics of Solvated Electrons in Liquid Ammonia

Electrode reaction of ammoniated electrons was investigated with voltammetry, potentiometry and chronoamperometry. Experiments were conducted on Pt, Au and W electrodes in 0.5 M LiI, NaI, KI, CsI and KBr solutions of liq. NH₃. The results in dilute solutions (< 10<⁻⁴ M) do not reflect the differences in alkali metal, electrode metal and supporting electrolyte and are explained by a simple one-electron transfer process whose transferring species is a free solvated electron and its ion-pair with a metal cation in a rapid equilibrium. The formal standard potential is −2.155 ± 0.005 V vs. Pb/Pb(NO₃)₂ (0.05 M) at −40°C in liq. NH₃ involving 0.5 M alkali metal iodide. The lower limit of the averaged diffusion coefficient is 0.7 × 10⁻⁴ cm² s⁻¹. At higher metal concentrations (> 10⁻² M), a two-electron transfer process tends to prevail, which is explained by considering the dimer of ion-pairs as the diffusing species.     

Nanostructured membrane electrode assemblies from layer‐by‐layer composite/catalyst containing membranes and their fuel cell performances

In this study, two approaches are compared to develop nanostructured membrane electrode assemblies (MEA) using layer‐by‐layer (lbl) technique. The first is based on the direct deposition of polyallylamine hydrochloride (PAH) and sulfonated polyaniline (sPAni) on Nafion support to prepare lbl composite membrane. In the second approach, sPAni is coated on the support in the presence of platinum (Pt) salt, Nafion solution and Vulcan for obtaining catalyst containing membranes (CCMs). SEM and UV–vis analysis show that the multilayers are deposited on both sides of Nafion successfully. Although H₂/O₂ single cell performances of acid doped lbl composite membrane based MEA are found to be at the range of 126 and 160 mW cm^?2 depending on the number of deposited layers, the cell performance of MEA obtained from catalyst containing lbl self‐assembled thin membrane (PAH/sPAni‐H⁺)_10‐Pt is found to be 360 mW cm^?2 with a Pt utilization of 720 mW mgPt^?1. This performance is 82% higher as compared to original Nafion^®117 based MEA (198 mW cm^?2). From the cell performance evaluations for different structured MEAs, it is mainly found out that the use of lbl CCMs instead of composite membranes and fabrication of thinner electrolytes result in a higher H₂/O₂ cell activity due to significant reduction in ohmic resistivity. Also, it is observed that the use of sPAni slightly improves the cell performance due to an increased probability of the triple phase contact and it can lead to superior physicochemical properties such as conductivity and thermal stability. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40314.     

Palladium-based electrodes: A way to reduce platinum content in polymer electrolyte membrane fuel cells

To decrease the Pt content, a polymer electrolyte membrane fuel cell (PEMFC) was formed using a carbon supported Pd₉₆Pt₄ catalyst as the anode material, and a carbon supported Pd₄₉Pt₄₇Co₄ catalyst as the cathode material. The as-obtained Pd-based PEMFC with an overall Pd:Pt:Co atomic composition of electrodes (anode + cathode) = 72:26:2 exhibited a performance not too far from that of the fuel cell with the conventional 100% Pt electrodes. With a Pt content of 35 wt% of that of the cell with full Pt electrodes, at a current density of 1 A cm⁻² the performance loss of the cell with the Pd-based catalysts was only 11%, with 6% ascribed to the anode catalyst and 5% to the cathode catalyst. The maximum power density of the Pd-based cell was 76% of that of the cell with Pt catalysts.     

Achieving 360 NL h−1 Hydrogen Production Rate Through 30‐Cell Solid Oxide Electrolysis Stack with LSCF–GDC Composite Oxygen Electrode

A 30‐cell solid oxide electrolysis (SOE) stack consisting of 30‐cell planar Ni–YSZ hydrogen electrode‐supported single cell with La_0.6Sr_0.4Co_0.2Fe_0.8O_3–δ–Ce_0.9Gd_0.1O_1.95 (LSCF–GDC) composite oxygen electrodes, interconnects, and sealing materials was tested at 750 °C in steam electrolysis mode for hydrogen production. The direction of gas flow in the stack was a cross‐flow configuration, and the stack configuration was designed to open gas flow channels at the air outlet. The electrolysis efficiency of the stack was higher than 100% at 90/10H₂O/H₂ ratio under <0.5 A cm⁻² current density. During hydrogen production, the stack was operated at 750 °C under 0.5 A cm⁻² constant current density for more than 500 h with 4.06% k h⁻¹ degradation rate. Up to 73% steam conversion rate and 91.6% current efficiency were obtained; the net hydrogen production rate reached as high as 361.4 NL h⁻¹. Our results suggested that the SOE stack that was designed with LSCF–GDC composite oxygen electrode could be used to conduct large‐scale hydrogen production.     

Performance and stability of Pt-based ternary alloy catalysts for PEMFC

Carbon-supported Pt-based ternary alloy electrocatalysts were prepared by incipient wetness method in order to elucidate the origin of the enhanced activity of oxygen reduction reaction in PEMFC. To measure the catalytic activity and stability of the cathode alloy catalysts (electrodes containing Pt loading of 0.3 mg/cm², 20 wt.% Pt/C, E-TEK), the I-V polarization curves were obtained. All alloy catalysts showed higher performances than Pt/C. It can be concluded that as platinum formed alloys with transition metals, the electronic state of Pt and the nearest neighbor Pt-Pt distance changes, which significantly influence the electrocatalytic activity for oxygen reduction.Long-term stability test was performed with the Pt₆Co₁Cr₁/C alloy catalyst for 500 h. According to XPS analysis, the lower oxide component with Pt₆Co₁Cr₁/C electrocatalyst provides a large portion of platinum in metallic species in the electrocatalyst and it seems to be mainly responsible for its enhanced activity towards oxygen reduction.     

Real electrode surface area by Zn2+ adsorption and electrocatalytical reactivity for the oxygen reduction reaction. Comparison of the electrocatalytical reactivity of pure and composite spinel oxide Cu1 + xMn2−xo4(0 < x < 0.4) electrodes

Zn²⁺ adsorption was used to determine the electrochemically active surface area (EASA) of spray pyrolized (SP) film electrodes and of powders prepared by decomposition of metal salts (DMS) in composite graphite and teflon bonded electrodes of spinel oxide Cu_{1 + x}Mn_2−xO₄ (0 < x < 0.4) (DMSGT). It is shown that both SP and DMS materials are nanosized with particle diameters in the range 50–80Å and EASAs per unit loading mass M (EASAM) 1300–2200cm²mg⁻¹. The lesser intrinsic reactivity in the case of DMSGT electrodes is attributed to modification of the surface reactivity of pure oxide particles in contact with graphite and teflon.     

A Study on Process Parameters of Direct Ethanol Fuel Cell

Ethanol is one of the promising future fuels of Direct Alcohol Fuel Cells (DAFC). The electro‐oxidation of ethanol fuel on anode made of carbon‐supported Pt‐Ru electrode catalysts was carried out in a lab scale direct ethanol fuel cell (DEFC). Cathode used was Pt‐black high surface area. The membrane electrode assembly (MEA) was prepared by sandwiching the solid polymer electrolyte membrane, prepared from Nafion^® (SE‐5112, DuPont USA) dispersion, between the anode and cathode. The DEFC was fabricated using the MEA and tested at different catalyst loadings at the electrodes, temperatures and ethanol concentrations. The maximum power density of DEFC for optimized value of ethanol concentration, catalyst loading and temperature were determined. The maximum open circuit voltage (OCV) of 0.815 V, short circuit current density (SCCD) of 27.90 mA/cm² and power density of 10.30 mW/cm² were obtained for anode (Pt‐Ru/C) and cathode (Pt‐black) loading of 1 mg/cm² at a temperature of 90°C anode and 60°C cathode for 2M ethanol.     

H2/Cl2 fuel cell for co-generation of electricity and HCl

A H₂/Cl₂ fuel cell system with an aqueous electrolyte and gas diffusion electrodes has been investigated and the effects of electrolyte concentration and temperature on the open circuit voltage (OCV) and cell performance have been evaluated. Furthermore, the kinetics and long-term stability of Pt as electrocatalyst have been studied under various conditions. In addition, the long-term stability of Rh electrocatalyst has been evaluated. The OCV obtained showed that the Cl₂ reduction is more reversible than O₂ reduction. The ohmic drop was determining the cell performance at high current densities. An output power of about 0.5 W cm^–2 was achieved with this system.     

In suit Investigation of Anode Support on Cell Performance Reduced under Various Temperatures for Planar Solid Oxide Fuel Cells

The performance of anode support of Ni‐YSZ reduced from room temperature (T_R) to working temperature (T_w) and at T_w in anode‐supported planar solid oxide fuel cell was investigated quantitatively in situ. A 2 μm thick Pt voltage probe was embedded at the interface between the anode support and the function anode in the cell. Results showed that the power densities of the stack that was reduced from T_R to T_w (stack 1) and stack reduced at T_w (stack 2) were 0.343 W cm⁻² and 0.583 W cm⁻² with the corresponding fuel utilization of 36.28% and 63.87%, respectively, under the operating voltage of 0.8 V. The degradation rate of stack 1 was 7.76 times more than that of stack 2 when the stack was discharged under a constant current of 0.476 Acm⁻² for 100 h. Ni particles agglomerated in the anode support of the cell inside stack 1, whereas Ni particles in the anode support of the cell inside stack 2 were evenly distributed. The performance of stack 1 was poor mainly because of the increasing ohmic and polarization resistances caused by Ni agglomeration and decreasing porosity of the anode support.     

Synergistic mechanism of isolated Fe3+ and highly dispersed Ptδ+ over zeolite for boosting propane dehydrogenation

Pt-based catalysts have been widely investigated in propane dehydrogenation (PDH) owing to their high activity in C H activation, while it suffers from Pt sintering and coke deposition. We develop a transition metal Fe and zeolite support synergistic-modified method to realize the highly dispersed and stable Pt species inside zeolite over Pt/Fe-silicate-1. And it shows the excellent PDH performance with propylene generation rate of 51.6 mol C₃H₆ g_Pt⁻¹ h⁻¹ and low deactivation rate constant k_d of 0.017 h⁻¹ as well as a high TOF_Pt of 37.6 s⁻¹ at 550°C. The systematic characterizations reveal the isolated Fe³⁺ species could significantly improve Pt dispersity and regulate Pt electronic density to realize a more positive Pt^δ+ species inside Silicalite-1 pore. And the further in situ DRIFTS experiments demonstrate that the synergistic effect between the appropriate acidic Fe sites and the highly dispersed Pt^δ+ species around Fe species are responsible for the superior PDH performance.     

Sr2Fe1.5Mo0.5O6–δ – Zr0.84Y0.16O2–δ Materials as Oxygen Electrodes for Solid Oxide Electrolysis Cells

The high‐temperature solid oxide electrolysis cell (SOEC) is one of the most promising devices for hydrogen mass production. To make SOEC suitable from an economical point of view, each component of the SOEC has to be optimized. At this level, the optimization of the oxygen electrode is of particular interest since it contributes to a large extent to the cell polarization resistance. The present paper is focused on an alternative oxygen electrode of Zr_0.84Y_0.16O_2–δ‐Sr₂Fe_1.5Mo_0.5O_6–δ (YSZ‐SFM). YSZ‐SFM composite oxygen electrodes were fabricated by impregnating the YSZ matrix with SFM, and the ion‐impregnated YSZ‐SFM composite oxygen electrodes showed excellent performance. For a voltage of 1.2 V, the electrolysis current was 223 mA cm⁻², 327 mA cm⁻² and 310 mA cm⁻² at 750 °C for the YSZ‐SFM10, YSZ‐SFM20, and YSZ‐SFM30 oxygen electrode, respectively. A hydrogen production rate as high as 11.46 NL h⁻¹ has been achieved for the SOEC with the YSZ‐SFM20 electrode at 750 °C. The results demonstrate that YSZ‐SFM fabricated by impregnating the YSZ matrix with SFM is a promising composite electrode for the SOEC.