Ru Anode Research Articles

A Highly-Efficient Boron Interstitially Inserted Ru Anode Catalyst for Anion Exchange Membrane Fuel Cells.

Developing high-performance electrocatalysts for alkaline hydrogen oxidation reaction (HOR) is crucial for the commercialization of anion exchange membrane fuel cells (AEMFCs). Here, boron interstitially inserted ruthenium (B-Ru/C) is synthesized and used as an anode catalyst for AEMFC, achieving a peak power density of 1.37W cm-2 , close to the state-of-the-art commercial PtRu catalyst. Unexpectedly, instead of the monotonous decline of HOR kinetics with pH as generally believed, an inflection point behavior in the pH-dependent HOR kinetics on B-Ru/C is observed, showing an anomalous behavior that the HOR activity under alkaline electrolyte surpasses acidic electrolyte. Experimental results and density functional theory calculations reveal that the upshifted d-band center of Ru after the intervention of interstitial boron can lead to enhanced adsorption ability of OH and H2 O, which together with the reduced energy barrier of water formation, contributes to the outstanding alkaline HOR performance with a mass activity of 1.716mA µgPGM -1 , which is 13.4-fold and 5.2-fold higher than that of Ru/C and commercial Pt/C, respectively.

Non-stoichiometric tungsten-carbide-oxide-supported Pt–Ru anode catalysts for PEM fuel cells – From basic electrochemistry to fuel cell performance

Durability and cost of Proton Exchange Membrane fuel cells (PEMFCs) are two major factors delaying their commercialization. Cost is associated with the price of the catalysts, while durability is associated with degradation and poisoning of the catalysts, primarily by CO. This motivated us to develop tungsten-carbide-oxide (WxCyOz) as a new non-carbon based catalyst support for Pt–Ru–based anode PEMFC catalyst. The aim was to improve performance and obtain higher CO tolerance compared to commercial catalysts. The performance of obtained PtRu/WxCyOz catalysts was investigated using cyclic voltammetry, linear scan voltammetry and rotating disk electrode voltammetry. Particular attention was given to the analysis of CO poisoning, to better understand how WxCyOz species can contribute to the CO tolerance of PtRu/WxCyOz. Improved oxidation of COads at low potentials (E < 0.5 V vs. RHE) was ascribed to OH provided by the oxide phase at the interfacial region between the support and the PtRu particles. On the other hand, at high potentials (E > 0.5 V vs. RHE) CO removal proceeds dominantly via OH provided from the oxidized metal sites. The obtained catalyst with the best performance (30% PtRu/WxCyOz) was tested as an anode catalyst in PEM fuel cell. When using synthetic reformate as a fuel in PEMFC, there is a significant power drop of 35.3 % for the commercial 30% PtRu/C catalyst, while for the PtRu/WxCyOz anode catalyst this drop is around 16 %.

Electrochemical stability of RuO2(110)/Ru(0001) model electrodes in the oxygen and chlorine evolution reactions

RuO2 is commercially employed as an anodic catalyst in the chlor-alkali process. It is also one of the most active electrocatalysts for the oxidation of water, relevant to electrochemical water splitting. However, the use of RuO2 is limited by its low anodic stability under acidic conditions, especially at high overpotentials. In the present work, the electrochemical stability of model RuO2(110)/Ru(0001) anodes was investigated in order to gain a deeper understanding of the relation between structure and performance in Cl2 and O2 evolution reactions (CER and OER, respectively). Online electrochemical mass spectrometry was used to determine the onset potential of CER and OER in HCl and H2SO4 electrolytes, respectively. The onset potential of OER was higher in HCl than in H2SO4 due to competition with the kinetically more favorable CER. A detailed stability evaluation revealed pitting corrosion of the electrode surface with exposure of Ru(0001) metal substrate concomitant with the formation of a hydrous RuO2 in some areas regardless of the applied electrochemical treatment. However, despite local pitting, the RuO2(110) layer preserves its thickness in most areas. Degradation of the electrode was found to be less severe in 0.5 M HCl due to a decrease in the faradaic efficiency of RuO2 oxidation caused by competition with the kinetically more favorable CER.

Atomic layer deposited YSZ overlayer on Ru for direct methane utilization in solid oxide fuel cell

We report on the fabrication of thin yttria-stabilized zirconia (YSZ) overlayers via atomic layer deposition (ALD) conformally coated on anodes of methane-fueled low-temperature solid oxide fuel cells. Nano-granular ALD YSZ overlayers that are broken into porous films at elevated temperature improved not only the initial electrochemical performance (35% increase in the maximum power density) but also the thermal stability of the porous Ru anodes by suppressing coarsening.

Supercritical, Freezing and Thermal Drying Process of Resorcinol‐Formaldehyde Polymer based Nano‐carbons and their Highly Loaded PtRu Anode Electrocatalyst for DMFC

AbstractThe capillary condensation is affected by micropore and nanopore of catalyst layer on fuel cell. Due to limitation of sluggish mass transport and electrocatalytic activity, to retain the pore skeleton of carbon and metal nanoparticles are very significant for enhanced utilizations of pore structure in electrochemical reaction. Besides, thickness of electrocatalyst layer is very crucial due to one of the factor affected by cell performance of direct methanol fuel cell. Highly loaded four Pt−Ru anode catalysts supported on resorcinol‐formaldehyde (RF) polymer based on meso‐porous carbons (80 wt.% Pt−Ru/carbon cryogel, 80 wt.% Pt−Ru/carbon xerogel and 80 wt.% Pt−Ru/carbon aerogel) and conventional carbon (80 wt.% Pt−Ru/Vulcan XC‐72) were prepared by colloidal method for direct methanol fuel cell. These catalysts were characterized by X‐Ray diffraction (XRD), High resolution transmission electron microscopy (HR‐TEM) and X‐ray photoemission (XPS). The results of CO stripping voltammetry, cyclic voltammetry (CV) and single cell test performed on DMFC show that Pt−Ru/carbon cryogel and Pt−Ru/carbon aerogel exhibits better performances in comparison to Pt−Ru/carbon xerogel and Pt−Ru/Vulcan XC‐72. It is thus considered that particle size, oxidation state of metal and electrochemical active surface area of these catalysts are important role in electrocatalytic activity in DMFC.

Pt–Ru Anode Catalyst to Suppress H2O2 Formation due to Oxygen Crossover

In addition to the oxygen reduction reaction that occurs at the cathode in polymer electrolyte fuel cells, oxygen transferred through the polymer electrolyte membrane (PEM) is reduced at the anode. The quantity of H2O2 generated on Pt-loaded carbon (Pt/C) and Pt–Ru alloy-loaded (Pt-Ru/C) catalysts in 0.5 M sulfuric acid solution was evaluated using a rotating ring-disk electrode method. H2O2 generation on Pt/C and PtRux/C with low Ru contents (x = 0.3, 0.5) steeply increased below 0.1 V vs. SHE. In contrast, H2O2 generation on PtRux/C with high Ru contents (x = 1.0, 1.5, 2.0) was suppressed, even below 0.1 V vs. SHE. PEM deterioration was evaluated by measuring the amount of fluorine emitted from lab-scale cells with anodes containing Pt/C and PtRux/C catalysts with different Ru contents. The amount of fluorine emitted from the cell with PtRux/C-containing anode decreased with increasing catalyst Ru content. PEM deterioration was suppressed by increasing Ru content in the anode catalyst due to decreased H2O2 generation.

Experimental investigation and mathematical modeling of triode PEM fuel cells

The triode operation of humidified PEM fuel cells has been investigated both with pure H2 and with CO poisoned H2 feed over commercial Vulcan supported Pt(30%)-Ru(15%) anodes. It was found that triode operation, which involves the use of a third, auxiliary, electrode, leads to up to 400% power output increase with the same CO poisoned H2 gas feed. At low current densities, the power increase is accompanied by an increase in overall thermodynamic efficiency. A mathematical model, based on Kirchhoff’s laws, has been developed which is in reasonably good agreement with the experimental results. In order to gain some additional insight into the mechanism of triode operation, the model has been also extended to describe the potential distribution inside the Nafion membrane via the numerical solution of the Nernst-Planck equation. Both model and experiment have shown the critical role of minimizing the auxiliary-anode or auxiliary-cathode resistance, and this has led to improved comb-shaped anode or cathode electrode geometries.

Bimetallic Nickel/Ruthenium Catalysts Synthesized by Atomic Layer Deposition for Low-Temperature Direct Methanol Solid Oxide Fuel Cells.

Nickel and ruthenium bimetallic catalysts were heterogeneously synthesized via atomic layer deposition (ALD) for use as the anode of direct methanol solid oxide fuel cells (DMSOFCs) operating in a low-temperature range. The presence of highly dispersed ALD Ru islands over a porous Ni mesh was confirmed, and the Ni/ALD Ru anode microstructure was observed. Fuel cell tests were conducted using Ni-only and Ni/ALD Ru anodes with approximately 350 μm thick gadolinium-doped ceria electrolytes and platinum cathodes. The performance of fuel cells was assessed using pure methanol at operating temperatures of 300-400 °C. Micromorphological changes of the anode after cell operation were investigated, and the content of adsorbed carbon on the anode side of the operated samples was measured. The difference in the maximum power density between samples utilizing Ni/ALD Ru and Pt/ALD Ru, the latter being the best catalyst for direct methanol fuel cells, was observed to be less than 7% at 300 °C and 30% at 350 °C. The improved electrochemical activity of the Ni/ALD Ru anode compared to that of the Ni-only anode, along with the reduction of the number of catalytically active sites due to agglomeration of Ni and carbon formation on the Ni surface as compared to Pt, explains this decent performance.

The effects of hydrogen dilution, carbon monoxide poisoning for a Pt–Ru anode in a proton exchange membrane fuel cell

The effects of carbon monoxide (CO) poisoning and hydrogen dilution are investigated for a series of simulated reformate gases. A simple mathematical model with an internal air bleed term is proposed to understand the interaction between CO poisoning, hydrogen dilution, and the internal air bleed (IAB). According to the steady-state modeling results, the presence of nitrogen can be considered as a diluting agent for a relatively dilute H2–N2 mixture. For a CO–H2–N2 mixture, hydrogen dilution and CO poisoning “magnify” each other in their combined effect on the surface coverage of hydrogen. The beneficial effect of IAB was found to be affected by the competitive adsorption between CO and hydrogen. The steady-state surface coverage of CO is influenced by the adsorption and desorption of CO, the interaction between CO and the electro-oxidation of hydrogen, the interaction between IAB/hydrogen dilution/CO, the interaction between IAB/CO. However, the steady-state surface coverage of CO is largely determined by its own adsorption and desorption properties. Analytical solutions are also derived from the proposed mode for the transient surface coverage of hydrogen and CO. The mathematical treatment has been proved extremely effective for the understanding of the steady-state and transient behavior of the CO–H2 and CO–H2–N2 mixtures.

Reverse-Current Decay in Hydroxide Exchange Membrane Fuel Cells

In proton exchange membrane fuel cells (PEMFCs), the cathode carbon support corrodes during startup and shutdown by reverse-current decay (RCD). We show for the first time that hydroxide exchange membrane fuel cells (HEMFCs) also undergo RCD. We find that decreasing the oxygen reduction reaction (ORR) activity of the anode catalyst mitigates RCD: a Ru anode causes less corrosion than Pt, Ir, and Pd anodes, as expected from their ORR activities. After an intensive 6 h RCD test, an HEMFC based on Ru shows six times lower internal resistance compared to Pt (1.02 vs. 6.01 Ω cm2). Due to its enhanced ORR activity in base, carbon alone can sustain RCD. To minimize RCD the carbon support should be eliminated from the anode catalyst.

Operational characteristics of thin film solid oxide fuel cells with ruthenium anode in natural gas

Direct utilization of hydrocarbons in low temperature solid oxide fuel cells is of growing interest in the landscape of alternative energy technologies. Here, we report on performance of self-supported micro-solid oxide fuel cells (μSOFCs) with ruthenium (Ru) nano-porous thin film anodes operating in natural gas and methane. The μSOFCs consist of 8 mol% yttria-stabilized zirconia thin film electrolytes, porous platinum cathodes and porous Ru anodes, and were tested with dry natural gas and methane as fuels and air as the oxidant. At 500 °C, comparable power densities of 410 mW cm−2 and 440 mW cm−2 were obtained with dry natural gas and methane, respectively. In weakly humidified natural gas, open circuit voltage of 0.95 V at 530 °C with peak power density of 800 mW cm−2 was realized. The μSOFC was continuously operated at constant voltage of 0.7 V with methane, where quasi-periodic oscillatory behavior of the performance was observed. Through post-operation XPS studies it was found that the oxidation state of Ru anode surfaces significantly differs depending on the fuel used, oxidation being enhanced with methane or natural gas. The nature of the oscillation is discussed based on the transition in surface oxygen coverage states and electro-catalytic activity of Ru anodes.

Pt–Ru decorated self-assembled TiO2–carbon hybrid nanostructure for enhanced methanol electrooxidation

Porous titanium oxide–carbon hybrid nanostructure (TiO2–C) with a specific surface area of 350 m2/g and an average pore-radius of 21 · 8 Å is synthesized via supramolecular self-assembly with an in situ crystallization process. Subsequently, TiO2–C supported Pt–Ru electro-catalyst (Pt–Ru/TiO2–C) is obtained and investigated as an anode catalyst for direct methanol fuel cells (DMFCs). X-ray diffraction, Raman spectroscopy and transmission electron microscopy (TEM) have been employed to evaluate the crystalline nature and the structural properties of TiO2–C. TEM images reveal uniform distribution of Pt–Ru nanoparticles (d Pt − Ru = 1·5–3·5 nm) on TiO2–C. Methanol oxidation and accelerated durability studies on Pt–Ru/TiO2–C exhibit enhanced catalytic activity and durability compared to carbon-supported Pt–Ru. DMFC employing Pt–Ru/TiO2–C as an anode catalyst delivers a peak-power density of 91 mW/cm2 at 65 °C as compared to the peak-power density of 60 mW/cm2 obtained for the DMFC with carbon-supported Pt–Ru anode catalyst operating under similar conditions.

Evidence of Nonelectrochemical Shift Reaction on a CO-Tolerant High-Entropy State Pt–Ru Anode Catalyst for Reliable and Efficient Residential Fuel Cell Systems

A randomly mixed monodispersed nanosized Pt-Ru catalyst, an ultimate catalyst for CO oxidation reaction, was prepared by the rapid quenching method. The mechanism of CO oxidation reaction on the Pt-Ru anode catalyst was elucidated by investigating the relation between the rate of CO oxidation reaction and the current density. The rate of CO oxidation reaction increased with an increase in unoccupied sites kinetically formed by hydrogen oxidation reaction, and the rate was independent of anode potential. Results of extended X-ray absorption fine structure spectroscopy showed the combination of N(Pt-Ru)/(N(Pt-Ru) + N(Pt-Pt)) ≑ M(Ru)/(M(Pt) + M(Ru)) and N(Ru-Pt)/(N(Ru-Pt) + N(Ru-Ru)) ≑ M(Pt)/(M(Ru) + M(Pt)), where N(Pt-Ru)(N(Ru-Pt)), N(Pt-Pt)(N(Ru-Ru)), M(Pt), and M(Ru) are the coordination numbers from Pt(Ru) to Ru(Pt) and Pt (Ru) to Pt (Ru) and the molar ratios of Pt and Ru, respectively. This indicates that Pt and Ru were mixed with a completely random distribution. A high-entropy state of dispersion of Pt and Ru could be maintained by rapid quenching from a high temperature. It is concluded that a nonelectrochemical shift reaction on a randomly mixed Pt-Ru catalyst is important to enhance the efficiency of residential fuel cell systems under operation conditions.

Nanostructured Anodes for Direct Methane Thin Film Solid Oxide Fuel Cells

This proceedings manuscript describes in brief representative results on porous Ru anodes incorporated into thin film solid oxide fuel cells (SOFCs). Thin film of 8 mol% yttria-stabilized zirconia (YSZ) was fabricated as free-standing electrolytes, with porous platinum (Pt) and porous Ru deposited as cathode and anode electrodes, respectively. μSOFCs were tested with methane as the fuel and air as the oxidant, exhibiting an open circuit voltage of 0.71 V and a peak power density of 450 mW/cm2 at 500 °C. Anode electrodes were investigated for structural change and was found that morphology evolution in anode electrodes were strongly dependent on the fuels used. Auger electron spectroscopy was carried out on Ru anodes before and after methane operation, and revealed minimal amount of carbon existing on Ru surface, possibly being reaction intermediates. On-going studies on Ru-CGO composite anodes are discussed.

Low temperature thin film solid oxide fuel cells with nanoporous ruthenium anodes for direct methane operation

Thin film micro-solid oxide fuel cells (µSOFCs) utilizing nanoporous ruthenium (Ru) anodes were fabricated and investigated for direct methane operation for the first time. The µSOFCs consist of 8 mol% yttria-stabilized zirconia (YSZ) thin film electrolytes, porous platinum (Pt) cathodes and porous Ru anodes, fabricated on silicon platforms by physical vapor deposition. The fuel cells, tested with methane as the fuel and air as the oxidant, exhibited an open circuit voltage (OCV) of 0.71 V and a peak power density of 450 mW cm−2 at 500 °C without visually detectable carbon deposition. Structural investigations revealed that the morphology evolution in nanoporous Ru anodes was strongly dependent on the fuels (namely, methane or hydrogen) used, and possible mechanisms leading to the observations are discussed. Results presented here project insights to enable direct use of hydrocarbons with high performance, and are of potential relevance to advancing low temperature micro-fuel cell technology for portable power.

Analysis of Spatio-temporal Pattern Formation in a PEM Fuel Cell with Pt ∕ Ru Anode Exposed to H2 ∕ CO Mixtures

In 2005 Zhang and Datta published a model for describing autonomous potential oscillations in a -catalyst-polymer electrolyte membrane (PEM) fuel cell operated with CO rich reformate [ J. X. Zhang and R. Datta , J. Electrochem. Soc. , 152 , A1180 (2005) ]. In the present contribution, we simplify a spatially extended version of this model in order to relate appearing pattern formation to electrochemical coupling mechanisms described by Krischer [ K. Krischer , in Advances in Electrochemical Science and Engineering, Wiley (2003) ]. It is concluded that mean-field- and migration-coupling are the fundamental mechanisms dictating pattern formation in the studied system. By artificially separating the electrical coupling terms it is found that large mean-field-coupling leads to a frequency entrainment and migration-coupling to a spatio-temporal intermittency scenario. It is argued that each of the situations can be found under realistic conditions, depending on the membrane conductivity and the system dimensions.

Effect of heat treatment on stability of gold particle modified carbon supported Pt–Ru anode catalysts for a direct methanol fuel cell

Carbon supported Au–PtRu (Au–PtRu/C) catalysts were prepared as the anodic catalysts for the direct methanol fuel cell (DMFC). The procedure involved simple deposition of Au particles on a commercial Pt–Ru/C catalyst, followed by heat treatment of the resultant composite catalyst at 125, 175 and 200 °C in a N 2 atmosphere. High-resolution transmission electron microscopy (HR-TEM) measurements indicated that the Au nanoparticles were attached to the surface of the Pt–Ru nanoparticles. We found that the electrocatalytic activity and stability of the Au–PtRu/C catalysts for methanol oxidation is better than that of the PtRu/C catalyst. An enhanced stability of the electrocatalyst is observed and attributable to the promotion of CO oxidation by the Au nanoparticles adsorbed onto the Pt–Ru particles, by weakening the adsorption of CO, which can strongly adsorb to and poison Pt catalyst. XPS results show that Au–PtRu/C catalysts with heat treatment lead to surface segregation of Pt metal and an increase in the oxidation state of Ru, which militates against the dissolution of Ru. We additionally find that Au–PtRu/C catalysts heat-treated at 175 °C exhibit the highest electrocatalytic stability among the catalysts prepared by heat treatment: this observation is explained as due to the attainment of the highest relative concentration of gold and the highest oxidation state of Ru oxides for the catalyst pretreated at this temperature.

Sol–gel synthesis of Pt-Ru-Os-Ir based anode electro-catalysts for direct methanol fuel cells

A high specific surface area (∼95 m 2/g) Pt 44Ru 41Os 10Ir 5 based anode electro-catalysts for direct methanol fuel cell, synthesized by a novel complexed sol–gel (CSG) process, shows better catalytic activity in comparison to pure equi-atomic compositions of Pt-50 at.% Ru anode catalysts synthesized by similar sol–gel processes. A homogeneous amorphous gel was successfully synthesized by complexing platinum(II) acetylacetonate, ruthenium(III) acetylacetonate, iridium(III) acetylacetonate and osmium(III) chloride with tetramethylammonium hydroxide (TMAH) used as a complexing agent. Phase-pure Pt(Ru,Os,Ir) and Pt(Ru) solid solutions possessing high specific surface area (SSA) (∼90–120 m 2/g) were successfully synthesized by thermal decomposition of the amorphous gel followed by controlled removal of carbonaceous species present in the thermally treated powders. The controlled removal of carbon, present in the thermally treated Pt-Ru-Os-Ir powder, has been successfully achieved by conducting precise thermal treatments of the thermally treated powders using controlled oxidizing atmospheres. Results indicate that the nano-crystalline pure Pt(Ru,Os,Ir) solid solution of nominal composition Pt-41 at.%Ru-10 at.%Os-5 at.% Ir possessing good chemical homogeneity exhibit excellent catalytic activity, demonstrating the potential of the novel complexed sol–gel process for synthesizing high-performance Pt-Ru-Os-Ir based catalysts for direct methanol fuel cells.

Electronic structure of Pt–Co cathode catalysts in membrane electrolyte assembly observed by X-ray absorption fine structure spectroscopy with different probing depth

Electronic structures of Pt–Co cathode and Pt–Ru anode catalysts in membrane electrolyte assemblies (MEAs) for polymer electrolyte fuel cell have been investigated using X-ray absorption near edge structure (XANES) spectroscopy, and the changes of electronic structures accompanied with degradation have been observed by comparison between spectra obtained by fluorescence-yield (FY) and conversion-electron-yield (CEY) methods, probing depths of which are several hundreds μm and ∼100 nm, respectively. The Co K XANES spectra of the as-fabricated MEA show that the Co atoms in the cathode are metallic and oxidized Co ions exist at the interface between the cathode and electrolyte. The spectra of the long-time operated MEA suggest that the oxidation of Co makes progress with degradation of the cathode catalysts. In contrast to the Co K XANES spectra, the line shape of the Ru K XANES spectra is unchanged even after the long-time operation.

The problem of Ru dissolution from Pt–Ru catalysts during fuel cell operation: analysis and solutions

Platinum–ruthenium catalysts are widely used as anode materials in polymer electrolyte fuel cells (PEMFCs) operating with reformate gas and in direct methanol fuel cells (DMFCs). Ruthenium dissolution from the Pt–Ru anode catalyst at potentials higher than 0.5 V vs. DHE, followed by migration and deposition to the Pt cathode can give rise to a decrease of the activity of both anode and cathode catalysts and to a worsening of cell performance. A major challenge for a suitable application of Pt–Ru catalysts in PEMFC and DMFC is to improve their stability against Ru dissolution. The purpose of this paper is to provide a better knowledge of the problem of Ru dissolution from Pt–Ru catalysts and its effect on fuel cell performance. The different ways to resolve this problem are discussed.