Gradual Internal Reforming Research Articles

Progress in Solid Oxide Fuel Cells with Hydrocarbon Fuels

Solid oxide fuel cells (SOFCs)’ main advantage in fuel flexibility appears to be an interesting subject for further exploration. From the literature survey, direct utilisation of hydrocarbon as fuel for SOFCs has garnered attention with promising results reported. Various approaches, showcasing potential for using methane (CH4) and heavier hydrocarbons in SOFCs, have been described. The direct use of hydrocarbons can occur through either direct internal reforming or gradual internal reforming, with requisite precautionary measures to mitigate carbon formation. While the internal reforming process could proceed via steam reforming, dry reforming or partial oxidation, an exciting development in the direct use of pure hydrocarbons, seems to progress well. Further exploration aims to refine strategies, enhance efficiency and ensure the long-term stability and performance of hydrocarbon-fuelled SOFC systems. This review delves into the progress in this field, primarily over the past two decades, offering comprehensive insights. Regardless of fuel type, studies have largely concentrated on catalyst compositions, modifications and reaction conditions to achieve better conversion and selectivity. Finding suitable anode materials exhibiting excellent performance and robustness under demanding operating conditions, remains a hurdle. Alternatively, ongoing efforts are directed towards lowering working temperatures, enabling consideration of a wider range of materials with improved electrochemical performance.

Direct Ethanol Anode-Supported Solid Oxide Fuel Cell

Long term durability was demonstrated on high-performance direct ethanol solid oxide fuel cell operating in gradual internal reforming. Anode supported single cells, fabricated at Forschungszentrum Jülich, composed of (La,Sr)MnO3 cathode, 8 mol% yttria-stabilized zirconia (YSZ) electrolyte, and YSZ-Ni anode were used for long term testing on anhydrous (direct) ethanol. Gadolinia-doped ceria (CGO), with 0.1 wt.% of Ir, catalyst was produced by the impregnation of Ir salt in commercial CGO (Praxair) and mixed with organic additives. The CGO-Ir suspension was deposited onto the surface of the YSZ-Ni anode support with an air brush. Such a catalytic layer acts both as a physical barrier to avoid direct contact of the fuel with Ni-based anode and to promote the gradual internal reforming of ethanol. The CGO-Ir catalyst was designed for the reforming of the main compounds resulting from the thermal decomposition of ethanol at high temperature and to inhibit the formation of ethylene, which is a known source of carbon deposits. After deposition the sample was heated at 850ºC in inert atmosphere to ensure good adhesion between the catalytic layer and the anode. Gold grid and paint were used as current collectors in both cathode and anode sides. The single fuel cells were mounted in the test apparatus, sealed with gold rings and alumina cement and heated to the measuring temperature (850°C) under inert atmosphere. After gas tightness was checked by flowing air on the cathode side and argon on the anode side, the anode was reduced under hydrogen. The fuel cell was kept at 0.6 V while monitoring the current drained from the cell at 850 °C. Samples were initially operated in hydrogen for a few hours and fuel was switched to dry ethanol, carried by nitrogen. It is important to mention that no oxidizing agent was added to the fuel and that water produced by the electrochemical reaction of hydrogen at the anode promoted the reforming of the ethanol in the CGO-based layer, in the so-called gradual internal reforming. In such conditions the current output was recorded and observed to not be significantly different form that under hydrogen. Moreover, the direct ethanol fuel cell was continuously operated for 650 hours without major losses due to carbon formation. The experimental results demonstrate that the water released by the electrochemical oxidation of reformate hydrogen at the electrolyte/anode active interfaces is sufficient for the reforming of the primary fuel in the catalytic layer, provided that a minimum fuel utilization is respected. After the durability tests, energy dispersive X-ray spectroscopy and scanning electron microscopy analyses of the samples revealed no carbon deposit formation in the anode. The experimental results provided compelling evidence for the viability of gradual internal reforming of ethanol in high performance solid oxide fuel cells.

Effect of Catalyst Layer and Fuel Utilization on the Durability of Direct Methane SOFC

Among energy conversion systems, high temperature Fuel Cells are considered of great interest for delocalized, renewable and clean electricity and heat power production. The high operating temperature (500°C - 800°C) is likely to allow the use of various types of hydrocarbons instead of hydrogen as the fuel with high efficiency and flexibility. Theoretically, the fuel can be catalytically converted into hydrogen directly at the anodic side. Practically, the most important drawback is the formation of carbon deposits on the anode, poisoning the electrocatalytic activity of the electrode. Hence, one of the main current challenges remains the increase of the life-time of these systems (especially avoiding carbon deposition and anode pollution), and long term reliable operation with fuel flexibility. Such performances have not been achieved yet. We recently demonstrated the fundamental importance of the fuel utilization on the carbon deposition limits. The quantity of steam released by the anode is directly proportional to the current density, and then to the fuel utilization UF. Below a given value of UF, the system does not produce enough steam to ensure the internal catalytic conversion of the hydrocarbon flux, resulting in irreversible degradation of the cell by carbon methane cracking. This observation and the deep understanding of the anode operation in methane allowed us to achieve long term operation with pure hydrocarbons without carbon deposition at the surface of conventional Ni-YSZ anodes. The thermodynamical limits of carbon deposition as a function of fuel utilization were also investigated. Current developments and technological simplifications based on new principles of operation and original architectures designed in this finality will be presented. In particular the presentation will emphasize on the Gradual Internal Reforming and Electro-catalytic separation principles applied to the design of original anodic systems, and on the demonstration of the reliability of the systems in different pure hydrocarbons or carbon-based fuels (no H2O, CO2, O2 or carrier gas addition) [1-4]. The effect of the fuel utilization on the limits of carbon deposition will be discussed and the long term durability in pure dry methane will be demonstrated. The perspectives of direct operation of SOFC on waste fuels in order to decrease the amount of CO2 rejects in delocalized energy production systems will be discussed. 1. J-M. Klein et al., Journal of Power Sources 193, (2009) 331 2. S. D. Nobrega et al., Journal of Power Sources (2012) 156-159 4. S. Georges et al., ECS Transactions 57(1) (2013) 3023-3030 4. S.D. Nobrega et al., Journal of the Electrochemical Society, 161(3) (2014) F354-F359 5. J. Puig et al., Fuel Cells 14 (6) (2014) 1014-1021 6. K. Girona et al., Canadian Journal of Chemical Engineering 93 (2) (2015) 285-296

Direct Ethanol Anode-Supported Solid Oxide Fuel Cell

An anode-supported solid oxide fuel cell (SOFC) was continuously operated with direct (anhydrous) ethanol for ~600 hours, with a high current density. The operation of the SOFC under ethanol was made possible with the deposition of a ceria-based catalytic layer onto the cermet anode support, which efficiently converts the primary fuel in hydrogen. The catalytic layer associated with the gradual internal reforming (GIR) process avoids carbon deposition on the Ni surface. The results provide a significant advance towards the development of direct ethanol solid oxide fuel cells.

Modelling of gradual internal reforming process over Ni‐YSZ SOFC anode with a catalytic layer

AbstractMethane appears to be a fuel of great interest for solid oxide fuel cell (SOFC) systems because it can be directly converted into hydrogen by Internal Reforming within the SOFC anode. To cope with carbon formation, a new SOFC cell configuration combining a catalyst layer with a classical anode was developed. The rate of the CH4 consumption in the catalyst layer (Ir‐CGO) was determined experimentally for small values of steam to carbon ratios. This paper proposes a modelling and a simulation, using the CFD‐Ace software package, of the behaviour of a SOFC operated in Gradual Internal Reforming (GIR) conditions. This model of SOFC takes into account the kinetics of the steam reforming reaction in the catalyst layer in order to assess the influence of the steam to carbon ratio and the cell polarization. Because the risk of carbon formation is greater under GIR operation, a detailed thermodynamic analysis was carried out. Thermodynamic equilibrium calculations allowed us to predict the conditions of carbon formation occurrence.

Nickel/gadolinium-doped ceria anode for direct ethanol solid oxide fuel cell

Abstract This report investigates the properties of nickel/gadolinium-doped ceria (Ni/GDC) as anode material for bio-ethanol fueled SOFC. The Ni/GDC cermets with 18 and 44 wt.% Ni were prepared by a hydrothermal method. Ethanol decomposition, steam reforming, and partial oxidation of ethanol were studied using a fixed-bed reactor at 1123 K. Carbon was formed only under dry ethanol for both catalysts. The addition of water or oxygen to the feed inhibited the formation of carbon. Ni/GDC was used as the anode current collector layer and as a catalytic layer in single cells tests. No deposits of carbon were detected in single cells with Ni/GDC catalytic layer after 50 h of continuous operation under direct (dry) ethanol. This result was attributed to the catalytic properties of the Ni/GDC layer and the operation mechanism of gradual internal reforming, in which the oxidation of hydrogen provides the steam for ethanol reforming, thus avoiding carbon deposition.

On the promoting effect of H2S on the catalytic H2 production over Gd-doped ceria from CH4/H2O mixtures for solid oxide fuel cell applications

In order to understand the exceptional tolerance of ceria to high sulfur levels in the fuel for further SOFC applications, the interaction of sulfur with a commercial Ce0.9Gd0.1O2−x (CGO, from Praxair) and its influence on H2 production from CH4/H2O mixture was studied. The activity tests were performed at 750°C, in the presence of H2S and under gradual internal reforming conditions (large excess of CH4 with respect to water vapor, 10:1). The presence of H2S in the reactant mixture promoted the catalytic activity of CGO. The nature of various species formed by sulfur–ceria interaction is discussed based on CH4-TPR, XRD, XPS, and in situ FTIR results. H2S reacts with ceria fraction in CGO and generates new catalytic sites with improved reactivity toward CH4. The formation and stabilization of oxygen vacancies by S-insertion in ceria lattice are evidenced and directly related to the improved activity. The detrimental effect of Ce2O2S phase, when formed, on the catalytic activity of doped ceria is confirmed.

A Fuel-Flexible Solid Oxide Fuel Cell Operating in Gradual Internal Reforming

An electrolyte supported solid oxide fuel cell (SOFC) was continuously operated with hydrogen, methane, and bioethanol for nearly 400 hours without adding water, O2, or CO2, and delivering a rather stable power output. Such a fuel-flexible SOFC was achieved by using both an anodic catalytic layer, which efficiently converts the primary fuel into hydrogen, and by the operation in gradual internal reforming conditions, which prevented degradation due to carbon formation.

SOFC Long Term Operation in Pure Methane by Gradual Internal Reforming

A solid oxide fuel cell was designed to be operated in pure methane, without external reforming or carrier gas. The fuel cell was built up from conventional NiO-YSZ anode supported cell with a specific Pt screen-printed anodic collecting system and a Ir-CGO catalytic layer. The operation principle is based on Gradual Internal Reforming. After an initiation in H2 for 30 minutes, the cell was operated for almost 2000 hours in pure and dry CH4 with a fuel utilization rate of 30 %. Intrinsic gradual degradation of 15 %/1000 h was observed, but no coking occurred at the anodic side.

Study of Ceria-Nickel Composites for Anode Catalytic Layer for Direct Ethanol SOFC

A hydrothermal route was used to synthesize gadolinia-doped ceria with highly dispersed Ni particles. The microstructural and electrical properties of the cermet revealed that Ni attained percolation at relatively low volume fraction. The cermet was used as a catalytic layer deposited onto the standard Ni-based anode and allowed for the stable operation under ethanol. No evidence of carbon deposits was identified after 50 hours of continuous operation under dry ethanol. Such a result was attributed to both the catalytic properties of the ceria layer and the operation mechanism of gradual internal reforming.

Renewable Fuels for SOFCs: Fuel Flexibility by Gradual Internal Reforming

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Direct ethanol solid oxide fuel cell operating in gradual internal reforming

An electrolyte supported solid oxide fuel cell (SOFC) using standard electrodes, doped-lanthanum manganite cathode and Ni-cermet anode, was operated with direct (anhydrous) ethanol for more than 100h, delivering essentially the same power output as running on hydrogen. A ceria-based layer provides the catalytic activity for the gradual internal reforming, which uses the steam formed by the electrochemical oxidation of hydrogen for the decomposition of ethanol. Such a concept opens up the way for multi-fuel SOFCs using standard components and a catalytic layer.

Gradual Internal Reforming of Ethanol in Solid Oxide Fuel cells

Electrolyte (yttria-stabilised zirconia, YSZ) supported solid oxide fuel cells (SOFCs) were fabricated using spin coating of standard LSM cathode and Ni-YSZ cermet anode. A ceria-based catalytic layer was deposited onto the anode with a special current collector design. Such a single cell configuration allows operation by gradual internal reforming of direct carbon-containing fuels. First, the fabricated single cells were operated with hydrogen to determine the optimised conditions of fuel concentration and flow rate regarding faradaïc efficiency. Then, the fuel was switched to dry ethanol and the cells were operated for several hours (100h) with good stability. Post-operation electron microcopy analyses revealed no carbon formation in the anode layer. The results indicate that the gradual internal reforming mechanism is effective, opening up the way to multi-fuel SOFCs, provided that a suitable catalyst layer and cell design are available.

Modeling of a SOFC Fuelled by Methane: Influence of the Methane Steam Reforming Kinetics

Methane appears to be a fuel of great interest for SOFC systems because it can be directly converted into hydrogen by Gradual Internal Reforming (GIR) within the SOFC anode with a new cell configuration. This study proposes a model of SOFC which takes into account the kinetics of the reforming reaction on the catalyst in order to assess the limitations under current of this new configuration of the SOFC cell.

Study of thermal effects on the performance of micro-tubular solid-oxide fuel cells

Mathematical modeling of methane-fed anode-supported micro-tubular solid-oxide fuel cell (MT-SOFC) is developed. Steam reforming of methane is considered in two cases of: direct internal reforming (DIR) and gradual internal reforming (GIR). The polarization curves and temperature distribution of a cell fed with three variations of fueling (i.e., DIR and GIR of methane and pure hydrogen) are compared with each other. The simulation results are verified through temperature and performance measurements of a MT-SOFC sample operating on above three variations of fueling. In DIR operating condition, a drop in the anode gas temperature at a short distance after entering the cell takes place which results in high temperature gradient. In GIR operating condition, the temperature distribution in axial direction is steadier. The ohmic loss is lower in the case of pure hydrogen fuel than internal reforming of methane, but the concentration loss is lower in methane-fed operating conditions.

Ir/Ce 0.9Gd 0.1O 2− x as a new potential anode component in solid oxide fuel cells integrating the concept of gradual internal reforming of methane

Ce 0.9Gd 0.1O 2− x -supported iridium catalyst containing 0.1 wt% Ir was prepared and studied in the steam reforming of methane under water deficient conditions (H 2O/CH 4 = 0.1) in order to evaluate its potential use as anode material in solid oxide fuel cells directly fed with methane and integrating a gradual internal reforming (GIR) concept. Catalytic activity of Ce 0.9Gd 0.1O 2− x (CGO) and Ir/Al 2O 3 (0.1 wt% Ir) was also measured. Attention was paid to carbon deposition. Catalysts were characterized by temperature programmed reaction experiments in dry methane (TPR-CH 4) followed by mass spectrometry. Adding Ir to CGO was shown to result in a catalyst much more active than CGO and Ir/Al 2O 3, being stable and extremely resistant to carbon deposition. Different mechanisms and/or rate determining steps are proposed and discussed to explain the observed different catalytic behaviours depending on the catalyst.

SOFC fuelled by methane without coking: optimization of electrochemical performance

In recent years, fuel cell technology has attracted considerable attention from several fields of scientific research as fuel cells produce electric energy with high efficiency, emit little noise, and are non-polluting. Solid oxide fuel cells (SOFCs) are particularly important for stationary applications due to their high operating temperature (1,073–1,273 K). Methane appears to be a fuel of great interest for SOFC systems because it can be directly converted into hydrogen by direct internal reforming (DIR) within the SOFC anode. Unfortunately, internal steam reforming in SOFC leads to inhomogeneous temperature distributions which can result in mechanical failure of the cermet anode. Moreover this concept requires a large amount of steam in the fed gas. To avoid these problems, gradual internal reforming (GIR) can be used. GIR is based on local coupling between steam reforming and hydrogen oxidation. The steam required for the reforming reaction is obtained by the hydrogen oxidation. However, with GIR, Boudouard and cracking reactions can involve a risk of carbon formation. To cope with carbon formation a new cell configuration of SOFC electrolyte support was studied. This configuration combined a catalyst layer (0.1%Ir–CeO2) with a classical anode, allowing GIR without coking. In order to optimise the process a SOFC model has been developed, using the CFD-Ace+ software package, and including a thin electrolyte. The impact of a thin electrolyte on previous conclusions has been assessed. As predicted, electrochemical performances are higher and carbon formation is always avoided. However a sharp decrease in the electrochemical performances appears at high current densities due to steam clogging.

Direct methane solid oxide fuel cell working by gradual internal steam reforming: Analysis of operation

A solid oxide fuel cell was designed to be operated with pure hydrocarbons, without additive or carrier gas, in order to bring technological simplifications, cost reductions and to extend the fuel flexibility limits. The cell was built-up from a conventional cell (LSM/YSZ/Ni-YSZ), to which was added a Ir–CeO2 catalyst layer at the anode side and an original current collecting system. The cell was first operated with steam in gradual internal reforming (GIR) conditions (R = [H2O]/[CH4] < 1) with carrier gas at the anode. The optimal operating parameters were determined in terms of flow rates, cell potential, and fuel utilisation. The cell was finally operated with pure dry methane at 900 °C at 0.6 V yielding current density of about 0.1 A cm−2 at max power for 120 h. Small but abrupt deterioration of the performances was observed, but no carbon deposition. Electrical and chemical analysis of this degradation are provided. At total, the fuel cell was operated for more than 200 h in pure dry methane, demonstrating that gradual internal reforming actually occurred efficiently in the anode compartment, which make possible operation without reforming agent such as H2O or CO2 for other hydrocarbon fuels.

Modeling of a SOFC Fueled by Methane:Anode Barrier to Allow Gradual Internal Reforming Without Coking

Natural gas appears to be a highly attractive fuel for solid oxide fuel cell systems. To avoid the cooling effect occurring in direct internal reforming, gradual internal reforming (GIR) can be used. GIR is based on local coupling between steam reforming and hydrogen oxidation. The steam required for the reforming reaction is obtained from hydrogen oxidation on the anode side. Previous studies have demonstrated that the cooling effect has disappeared. However, with GIR, the risk of carbon formation is greater. To deal with this issue, a different cell configuration was studied. This configuration combines a catalyst layer with a cermet anode, allowing GIR without coking. The study comprised simulations, using the CFD Research Corporation software package, of the behavior of a tubular solid oxide fuel cell when using GIR. A thermodynamic study based on the partial pressure distributions within the cell was also carried out to investigate the occurrence of carbon formation. A parametric analysis of the reforming rate and the thickness of the layer were then performed. The simulations indicate that the risk of carbon deposition is strongly reduced if the configuration is used for a catalyst layer of and at a reforming rate in the catalyst only ten times higher than the reforming rate in nickel.

A Solid Oxide Fuel Cell Operating in Gradual Internal Reforming Conditions under Pure Dry Methane

A planar solid oxide fuel cell (SOFC) was designed to be operated in gradual internal reforming conditions under pure dry methane. Stable operation was achieved for about 30 h. This result was obtained by deposition onto a Ni–yttria-stabilized zirconia cermet of a highly active and carbon-deposition-resistant catalyst layer consisting of Ir/CeO 2 . The performances of this layer were first evaluated in situ at open-circuit voltage, and then the principle of gradual internal reforming associated with electrocatalytic dissociation was demonstrated. The best cell performances with CH 4 /H 2 O=1/4 were 0.1 A cm −2 at 0.55 V (about 55 mW cm −2 ) at 1173 K.