A novel combined method using modified methane pulses and in-situ Raman spectroscopy together with mass spectrometry is applied to impregnated Ni/gadolinium-doped ceria (CGO). The partial oxidation of methane is deduced to proceed via a Mars-van-Krevelen type mechanism composed of initial methane decomposition together with carbon oxidation by oxygen from CGO. The critical role of the ceria surface and the bulk oxygen in the reaction is defined in detail. Oxygen is a necessary reactant in the reaction, as well as inhibiting carbon deposition. Oxygen spill-over is the driving force for the carbon oxidation and the ceria surface oxygen is resupplied by bulk oxygen after depletion. Bulk migration of oxygen to the surface is the rate-determining step. We also demonstrate that the ceria oxygen stoichiometry significantly affects the type of reaction and the rate of reaction between methane and Ni/CGO: The total oxidation of methane happens only when the oxygen stoichiometry is high while the oxygen spill-over rate decreases with decreasing oxygen stoichiometry, which reduces the rate of carbon elimination and results in reduction in the rate of methane oxidation. This work lays out a comprehensive evaluation methodology and provides important insights for future design of methane oxidation catalysts for solid oxide fuel cells, and more widely for methane reforming with different oxidants (steam, CO2, NO2 etc).

3D-printed Structural Pseudocapacitors Xinhua Liu*, Rhodri Jervis, Robert C. Maher, Ignacio J. Villar-Garcia, Max NaylorMarlow, Paul R. Shearing, Mengzheng Ouyang, Lesley Cohen, Nigel P. Brandon and Billy Wu* [*] Dr. X. Liu, Dr. Billy Wu Dyson School of Design Engineering, Imperial College London, UK E-mail: x.liu15@imperial.ac.uk, billy.wu@imperial.ac.uk Dr. R. Jervis, Prof. Dr. P. R. Shearing Department of Chemical Engineering, University College London, UK Dr. R. C. Maher, Prof. Dr. L. Cohen Department of Physics, Imperial College London, UK Dr. I. J. Villar-Garcia Department of Materials, Imperial College London, UK M. Naylor-Marlow Department of Mechanical Engineering, Imperial College London, UK M. Ouyang, Prof. Dr. N. P. Brandon Department of Earth Science and Engineering, Imperial College London, UK

The synergistic effect of cobalt oxide and Gd-CeO2 dual infiltration on SrO segregation in LSCF/CGO cathodes via commercial inkjet printing infiltration.

The key technical challenges that fuel cell developers need to address are performance, durability, and cost. All three need to be achieved in parallel; however, there are often competitive tensions, e.g., performance is achieved at the expense of durability. Stability and resistance to degradation under prolonged operation are key parameters. There is considerable interest in developing new cathodes that are better able to function at lower temperature to facilitate low cost manufacture. For anodes, the ability of the solid oxide fuel cell (SOFC) to better utilize commonly available fuels at high efficiency, avoid coking and sulfur poisoning or resistance to oxidation at high utilization are all key. Optimizing a new electrode material requires considerable process development. The use of solution techniques to impregnate an already optimized electrode skeleton, offers a fast and efficient way to evaluate new electrode materials. It can also offer low cost routes to manufacture novel structures and to fine tune already known structures. Here impregnation methodologies are discussed, spectral and surface characterization are considered, and the recent efforts to optimize both cathode and anode functionalities are reviewed. Finally recent exemplifications are reviewed and future challenges and opportunities for the impregnation approach in SOFCs are explored.

Nickel/gadolinium doped ceria (Ni/CGO) has been a popular SOFC anode material for decades for its superior mix conductivity and excellent oxygen storage capacity. However, the study of Ni/CGO in a realistic working condition is still lacking. Also, not much research has linked the chemical properties of CGO with the carbon resistance which is essential when using hydrocarbon as fuels. In this research, Ni/CGO powder was prepared via impregnation-calcination method. A novel pulse experiment has been conducted on impregnated powder. We did certain pulses of a fixed amount of methane into the sample at 600℃.The outlet gas was monitored by a quadrupole mass spectrometer. The product gas was composed of several species including hydrogen, steam, carbon monoxide, carbon dioxide, and methane that was not participated to the reaction. The major reaction was the partial oxidation of methane. With the increase of pulsing number, the product and shape of product peak changed a lot. Also, we observed a “tail” after each carbon monoxide production peak which was deduced to be the self-oxidation of carbon by the bulk migrated oxygen. After detailed quantitative analysis of the shape and intensity of the peaks and tails. We came up with a model in which the mechanism of methane partial oxidation was confirmed and so was the relation between carbon self-oxidation rate, surface oxygen and bulk oxygen migration rate of CGO. In-situ Raman spectroscopy was performed during the pulse experiment to monitor the change of CGO surface oxygen stoichiometry and deposited carbon. Thus we can confirm the conclusion deduced by pulse experiments and directly relate the carbon self-oxidation rate with bulk oxygen migration of CGO. The results would provide an insight into the design and modification of SOFC anode materials.

In recent years infiltration of materials into porous ceramic scaffolds has been shown to be an effective way of creating catalytically active components for solid oxide fuel cells (SOFCs). However, the redox properties of these novel structures are not well understood. Here, we use X-ray photoelectron spectroscopy (XPS) and in-situ Raman spectroscopy to investigate the oxidation properties of yttria-stabilised zirconia (YSZ) scaffolds infiltrated with ceria (CeO2), gadolinium-doped ceria (GDC) and zirconia-doped ceria (ZDC), with and without Ni. XPS shows that doping ceria with zirconia increases the ratio of Ce3+ to Ce4+, while gadolinium doping results in a decrease of Ce3+. The presence of Ni increases the Ce3+/Ce4+ ratio for CeO2 and GDC, but had little effect on ZDC. We used the shift of the F-2g Raman peak to monitor in-situ, the oxidation state of ceria. In the as-made compounds, we show that while the gadolinium and zirconium dopants significantly change the oxidation characteristics of ceria, the resulting materials are only significantly reduced above 500 degrees C when co-infiltrated with Ni. In-situ Raman monitoring during reduction as a function of temperature showed that while ZDC reduces much more readily than undoped ceria or GDC, the presence of Ni dominated the reduction dynamics.

Structural energy storage devices have the potential to transform products such as aerial vehicles, cars and consumer electronics. In article number 1600167, Xinhua Liu, Billy Wu, and co-workers use direct metal laser sintering to create 3D hierarchical scaffolds with high mechanical strength. Functionalisation with MnOx-PEDOT:PSS imparts the structure with pseduocapacitive properties and multi-scale x-ray tomography highlights how this approach improves device performance and lifetime.

Reduced graphene oxide (rGO) suspended in an N,N-dimethylformamide (DMF) solvent underwent electrophoretic deposition (EPD) on carbon paper (CP) electrodes. X-ray computed micro-tomography (XMT) indicates a 24% increase in the specific surface area of CP modified with rGO in comparison to the untreated sample. Furthermore, XMT confirms that the deposition also penetrates into the substrate. Raman analysis shows that the rGO deposited is more amorphous than the CP electrode. A significant reduction in charge-transfer resistance of the VO2+/VO2+ reaction is also observed (from impedance measurements) in modified samples in comparison to untreated CP electrodes.

Direct metal laser sintering is used to create 3D hierarchical porous metallic scaffolds which are then functionalized with a co-electrodeposition of MnO2, Mn2O3, and doped conducting polymer. This approach of functionalizing metal 3D printed scaffolds thus opens new possibilities for structural energy storage devices with enhanced performance and lifetime characteristics.

Pseudocapacitors are energy storage devices which offer energy and power densities greater than supercapacitors and lithium-ion batteries respectively, however their mainstream adoption has been limited by poor lifetime and low areal capacitance. Of the pseudocapacitive materials, manganese oxides have received broad interest due to their relatively high gravimetric capacitances and low cost, however poor electronic conductivity results in low areal capacitance and thus impractical devices. To mitigate this, authors have combined manganese oxides with conductive additives in order to achieve higher mass loadings with high power rate capability. Of the conductive additives, doped polymers such as PEDOT:PSS are attractive as they are not only highly conductive but also exhibit pseudocapacitive behaviour, however the volume expansion observed upon charging/discharging results in limited electrode lifetime due to irreversible microstructural changes. 3D printing is a technology which has yet to be widely adopted within the development of electrochemical devices but could potentially offer new avenues for intelligently designed electrodes. Here we present a novel 3D printed pseudocapacitor, suitable for structural energy storage applications which exhibits improved performance and lifetime over traditional planar electrodes. Using direct metal laser sintering, we create intelligently designed scaffolds of stainless steel onto which we perform a co-deposition of manganese oxides (electrochemical deposition) and doped conducting polymer (electrophoretic deposition) to create a composite electrode with hierarchical porosity. Raman and x-ray photoelectron spectroscopy are used to confirm the presence of the manganese oxides and conducting polymers via the co-deposition process. Using a combination of scanning electron microscopy, multi-scale x-ray computed tomography and electrochemical tests, we then show new insights into how microstructural evolution relates to observed performance increases and decreases over the device lifetime. Through the creation of porous 3D printed scaffolds, we show that this approach can improve durability via mechanical confinement of the active material, minimising the detrimental effects of the volume expansion such as electrode delamination. High resolution x-ray computed tomography was then use to demonstrate how microstructural features such as the lamella like electrode structure and evolution of cracks in the electrode can explain the initial observed performance increase upon cycling due to an increase in accessible surface area. The figure below shows the reconstructed x-ray image of the 3D printed metal scaffold (grey) and co-deposited pseudocapacitive material (purple) with a orthogonal slice shown indicating the distribution of active material. The orthogonal slice of the high-resolution x-ray tomography image shows the lamella like structure, porous under-layer and cracks in the active material which contributes to changes in the electrochemical performance of the device. These novel insights can potentially open new routes for the design of future structural energy storage devices. Figure 1

One of the attractive applications for reversible Solid Oxide Cells (SOCs) is to convert CO2 into CO via high temperature electrolysis, which is particularly important for biogas upgrading. To improve biogas utility, the CO2 component can be converted into fuel via electrolysis. A significant issue for SOC operation on biogas is carbon-induced catalyst deactivation. Nickel is widely used in SOC electrodes for reasons of cost and performance, but it has a low tolerance to carbon deposition. Two different modes of carbon formation on Ni-based electrodes are proposed in the present work based on ex-situ Raman measurements which are in agreement with previous studies. While copper is known to be resistant towards carbon formation, two significant issues have prevented its application in SOC electrodes – namely its relatively low melting temperature, inhibiting high temperature sintering, and low catalytic activity for hydrogen oxidation. In this study, the electrodes were prepared through a low temperature metal infiltration technique. Since the metal infiltration technique avoids high sintering temperatures, Cu–Ce0.9Gd0.1O2−δ (Cu-CGO) electrodes were fabricated and tested as an alternative to Ni-CGO electrodes. We demonstrate that the performance of Cu-CGO electrodes is equivalent to Ni-CGO electrodes, whilst carbon formation is fully suppressed when operated on biogas mixture.

The redox properties of gadolinium doped ceria (CGO) and nickel oxide (NiO) composite cermets underpin the operation of solid oxide electrochemical cells. Although these systems have been widely studied, a full comprehension of the reaction dynamics at the interface of these materials is lacking. Here, in situ Raman spectroscopic monitoring of the redox cycle is used to investigate the interplay between the dynamic and competing processes of hydrogen spillover and water dissociation on the doped ceria surface. In order to elucidate these mechanisms, the redox process in pure CGO and NiO is studied when exposed to wet and dry hydrogen and is compared to the cermet behavior. In dry hydrogen, CGO reduces relatively rapidly via a series of intermediate phases, while NiO reduces via a single-step process. In wet reducing atmospheres, however, the oxidation state of pure CGO is initially stabilized due to the dissociation of water by reduced Ce(III) and subsequent incorporation of oxygen into the structure. In the reduction process involving the composite cermet, the close proximity of the NiO improves the efficiency and speed of the composite reduction process. Although NiO is already incorporated into working cells, these observations suggest direct routes to further improve cell performance.

Interest in the exfoliation of graphite to prepare few layer graphene (FLG) has seen significant growth. The electrochemical procedure has, unfortunately, remained rather elusive to scaling-up options. This work builds on recent results of employing acetonitrile (ACN) as a solvent for reducing the amount of expensive ionic liquids (ILs) used as electrolytes. In order to move towards a more environmentally friendly synthesis route, the yield and energy consumption of graphene exfoliation using the four main types of deep eutectic solvents (DESs) has been investigated. Best performance, in terms of the highest specific yield (graphene weight per unit energy consumed) of 0.307g/kJ, is observed when Type IV DES is employed as the electrolyte in ACN. Similar results, but with less specific yield, is observed when Type I DES is used (other DESs and the IL, BMPyrrBTA, did not provide high yields of graphene but produced more carbonaceous particles and rolled sheets instead). The physicochemical properties of the DESs also confirm that the best DES for exfoliation is the Type IV variant, which needs further investigation. The quality of graphene produced is excellent (4–5 layers, 80% transparency, specific surface area of 180m2/g, conductivity of 2.1×105S/m and a contact angle of 94° thereby displaying hydrophobicity) and comparable to most graphene produced via other means. While maintaining high quality, the application of ACN and DES is economically attractive compared to other methods.

In situ and ex situ Raman analyses of porous Ni/CGO electrodes reveal differences in the amount, location and type of carbon formed during CO/CO2 electrolysis. The results demonstrate the limitations of optical in situ techniques applied to Solid Oxide Cells (SOCs) operated in electrolysis conditions. Increased carbon deposition close to the electrode-electrolyte interface is likely to be the result of high chargetransfer current in that area. The positive effect of a CGO interlayer on reducing carbon formation on the fuel electrode is demonstrated.

The widespread technological introduction of graphene beyond electronics rests on our ability to assemble this two-dimensional building block into three-dimensional structures for practical devices. To achieve this goal we need fabrication approaches that are able to provide an accurate control of chemistry and architecture from nano to macroscopic levels. Here, we describe a versatile technique to build ultralight (density ≥1 mg cm −3 ) cellular networks based on the use of soft templates and the controlled segregation of chemically modified graphene to liquid interfaces. These novel structures can be tuned for excellent conductivity; versatile mechanical response (elastic-brittle to elastomeric, reversible deformation, high energy absorption) and organic absorption capabilities (above 600 g per gram of material). The approach can be used to uncover the basic principles that will guide the design of practical devices that by combining unique mechanical and functional performance will generate new technological opportunities.

Raman spectroscopy is a powerful characterization tool for improving the understanding of solid oxide fuel cells (SOFCs), capable of providing direct, molecularly specific information regarding the physical and chemical processes occurring within functional SOFCs in real time. In this paper we give a summary of the technique itself and highlight ex situ and in situ studies that are particularly relevant for SOFCs. This is followed by a case study of carbon formation on SOFC Ni‐based anodes exposed to carbon monoxide (CO) using both ex situ and in situ Raman spectroscopy combined with computational simulations. In situ measurements clearly show that carbon formation is significantly reduced for polarized SOFCs compared to those held at open circuit potential (OCP). Ex situ Raman mapping of the surfaces showed clear variations in the rate of carbon formation across the surface of polarized anodes. Computational simulations describing the geometry of the cell showed that this is due to variations in gas access. These results demonstrate the ability of Raman spectroscopy in combination with traditional characterization tools, to provide detailed understanding of critical processes occurring within functional SOFCs.

Carbon formation within nickel-based solid oxide fuel cell (SOFC) anodes exposed to carbonaceous fuels typically leads to reduced operational lifetimes and performance, and can eventually lead to catastrophic failure through cracking and delamination. In-situ Raman spectroscopy has been shown to be a powerful characterization tool for the investigation of the dynamics of physical processes occurring within operational SOFCs in real time. Here we investigate the dynamics of carbon formation on a variety of nickel-based SOFC anodes as a function of temperature, fuel and electrical loading using Raman spectroscopy. We show that the rate of carbon formation throughout the SOFC anode can be significantly reduced through a careful consideration of the SOFC anode material, design and operational conditions.

Raman spectroscopic maps were used to study the local properties of graphene films as grown on corrugated copper foils, by chemical vapour deposition, and after transfer onto SiO2(300 nm)/Si substrates. Analysis of the Raman peaks show the films exhibit a striped periodic pattern of single- and bi-layer graphene. By performing simultaneous AFM–Raman line maps of the as grown film on Cu we find that the layer growth shows a strong correlation to substrate topography. As a result, compressively strained non-AB stacked bi-layer graphene forms preferentially along the ridges, whilst single-layer graphene grows inside the trenches, of the Cu foil topography. These experimental results suggest that surface mobility is not the dominating factor determining control of layer number in such growth regimes.

A novel bulk acoustic wave (BAW) microgravimetric sensor based on gallium orthophosphate is demonstrated that it is capable of operation at high temperature (up to 900 degrees C). The sensor is applied to the detection of carbon deposition onto electrodeposited nickel from dry methane at 600 degrees C and used as an analogue for studying the coking of solid oxide fuel cell (SOFC) anodes. The degradation of electrochemical performance due to deposition of carbon onto symmetrical SOFCs with nickel/gadolinium doped ceria electrodes is measured using electrochemical impedance spectroscopy (EIS). Direct correlation is observed between the frequency shift of the sensor and the change in resistance to charge transfer of the SOFC anode. An induction period (similar to 2 h) following exposure to methane is observed where no significant carbon deposition occurs. (c) 2013 Elsevier B.V. All rights reserved.