High performance of direct methane-fuelled solid oxide fuel cell with samarium modified nickel-based anode

Natural gas is one of the most attractive fuels for solid oxide fuel cell (SOFC), while the anode activity for methane fuel has a great influence on the performance and stability of SOFC. Samarium is a good catalyst promoter for methane reforming. In this work, samarium is used to modify nickel catalyst, which results in small nickel oxide particles. The SmNi-YSZ (yttria-stabilized zirconia) anode has smaller particles and better interfacial contact between nickel and YSZ compared with conventional Ni-YSZ anode. The fine structure of SmNi-YSZ anode results in high activity for electrochemical oxidation of hydrogen and low polarization resistance of the cell. The performance of SmNi-YSZ anode cell with humidified methane as fuel is greatly improved, which is similar to that with hydrogen as fuel. The maximum power densities of SmNi-YSZ anode cell are 1.56 W cm⁻² for humidified hydrogen fuel and 1.54 W cm⁻² for humidified methane fuel at 800 °C. The maximum power density is increased by 221% when samarium is used to modify Ni-YSZ anode for humidified methane fuel at 650 °C. High cell performance results in good stability of SmNi-YSZ anode cell and the cell runs stably for more than 600 min for humidified methane fuel.     

Synthesis and characterization of NiO/GDC–GDC dual nano-composite powders for high-performance methane fueled solid oxide fuel cells

GDC (gadolinium-doped ceria) is well known as a high oxygen ionic conductor and is a catalyst for the electrochemical reaction with methane fuel leading to the oxidation of deposited carbon that can clog the pores of the anode and break the microstructure of the anode. NiO/GDC–GDC dual nano-composite powders were synthesized by the Pechini process, which were used as an AFL (anode functional layer) or anode substrates along with a GDC electrolyte and LSCF–GDC cathode. The anodes, AFL, and electrolyte were fabricated by a tape-casting/lamination/co-firing. NiO–GDC anode and NiO/GDC–GDC anode-supported unit cells were evaluated in terms of their power density and durability. As a result, the NiO/GDC–GDC dual nano-composite demonstrated an improved power density from 0.4 W/cm² to 0.56 W/cm² with H₂ fuel/air and from 0.3 W/cm² to 0.56 W/cm² with CH₄ fuel/air at 650 °C. In addition, it could be operated for over 500 h without any degradation with CH₄ fuel.     

Improving single-chamber performance of an anode-supported SOFC by impregnating anode with active nickel catalyst

In order to improve the single-chamber performance of a traditional anode-supported single-chamber solid-oxide fuel cell with NiO–ScSZ anode and ScSZ electrolyte, the modification of the anode with a fine nickel catalyst by impregnation method was exploited. Catalytic test demonstrated the nickel catalyst had higher catalytic activity than the severe sintered nickel–cermet anode between 700 and 900 °C, especially at the lower temperature range. SEM examination demonstrated the nickel catalyst impregnation increased the roughness of the nickel grains within the anode. Furthermore, some surfaces of the ScSZ grains are also covered with very fine nickel catalyst. By operating on a methane-air mixture gas with methane to oxygen ratio of 1.3:1, the cell with its anode impregnated with the nickel catalyst showed an open circuit voltage and peak power density of 0.954 V and 119 mW cm⁻² at a furnace temperature of 750 °C, respectively, as a comparison of 0.893 V and 79 mW cm⁻² for the cell without the nickel catalyst. The improved cell performance was attributed to the higher cell temperature and increased anode catalytic activity for methane partial oxidation.     

Thermodynamic analysis and experimental study of electrode reactions and open circuit voltages for methane-fuelled SOFC

Natural gas is one of the most important fuels for solid oxide fuel cell (SOFC). The relationships among the reactions of methane over the nickel-based anode, fuel compositions, carbon deposition, electromotive force (EMF) and open circuit voltage (OCV) of SOFC are investigated in this work. With the increase of temperature, EMF and OCV of SOFC decrease gradually when the cell uses humidified hydrogen as fuel. Reactivity of methane increases gradually with the increase of temperature, which can affect the EMF and OCV of SOFC. When the humidified mixture of nitrogen and methane is used as the fuel, the EMF and OCV of SOFC increase gradually with the increase of temperature. EMF and OCV of SOFC with humidified mixture of hydrogen and methane (M_CH4: M_H2: M_H2O = 12.2: 85.3: 2.5) as fuel decrease gradually with the increase of temperature when the temperature is lower than 873 K, which is similar to that with humidified hydrogen as fuel. While when the temperature is higher than 923 K, the EMF and OCV of SOFC with humidified mixture of hydrogen and methane as fuel increase gradually with the increase of temperature, which is similar to that with humidified mixture of nitrogen and methane as fuel. OCV of SOFC is mainly affected by thermodynamic equilibriums for methane-fuelled SOFC when the anode activity is high enough, which is close to the EMF calculated according to the thermodynamic equilibriums. While with the increase of carbon deposition, the anode activity decreases apparently and the OCV of SOFC also decreases apparently, which shows that the OCV is affected by the anode activity for methane-fuelled SOFC when the anode activity is low.     

Self-humidified operation of a PEM fuel cell using a novel silica composite coating method

A proton exchange membrane fuel cell operating with no external humidification support was successfully reported using a novel silica composite layer on the anode side (Pt/C/SiO₂/Nafion). The nanosilica derived from tetramethoxy silane (TMOS) provided excellent porous morphology to retain water and hydrate protons. This layer provides a well-humidified environment for protons and easy proton transfer from the catalyst surface to the membrane electrolyte. The characteristics of the silica composite layer were investigated by various characterization methods: SEM, XRD, TEM, XPS, EIS, and TGA. A single cell fabricated with the anode containing this new silica composite layer showed a performance of 0.9 W/cm² which is two folds greater when tested with the commercial catalyst MEA (0.45 W/cm²). MEA delivered a constant output power (at 0.6 V) under dry and humidified gas conditions which shows excellent electrochemical stability and durability.     

Effect of metal particle size and Nafion content on performance of MEA using Ir-V/C as anode catalyst

Ir and Ir-V nanoparticles were synthesized in ethylene glycol using IrCl₃ and NH₄VO₃ as the Ir and V precursors, respectively. These nanoparticles were evaluated as anode catalysts in proton exchange membrane fuel cells (PEMFCs). A thermal treatment of the catalysts at 200 °C in a reducing atmosphere leads to very high electrocatalytic activity for the hydrogen oxidation reaction. The fuel cell performance reveals an optimal Nafion ionomer content of 25% in the catalyst layer used for the MEA fabrication. The electrocatalytic effects related to the change in the electrocatalyst structure are discussed based on the data obtained by X-ray diffraction (XRD) and transmission electron microscopy (TEM). In addition, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) techniques are used in-situ to assess the kinetics of hydrogen oxidation on the surface of these catalysts. A maximum power density of 1016.6 mW cm⁻² was obtained at 0.598 V and 70 °C with an anode catalyst loading of 0.4 mg (Ir) cm⁻². This performance is 50.7% higher than that for commercially available Pt/C catalysts under the same conditions. In addition, we also tested the anode catalyst with a low loading of 0.1 mg (Ir) cm⁻², the maximum power density is 33.8% higher than that of the commercial Pt/C catalyst with a loading of 0.4 mg (Pt) cm⁻².     

Methane internal steam reforming in solid oxide fuel cells at intermediate temperatures

The internal steam reforming of methane (CH₄) on conventional solid oxide fuel cell (SOFC) anode (nickel-yttria stabilized zirconia or Ni-YSZ) offers significant advantages compared to the external reforming process. However, the technology is currently facing some major issues such as coking and oxidation of anode during operation. Here we report a low-temperature sinterable catalyst, Ce_0·77Ni_0·2Mn_0·03O_2-δ (CNMnO), applied on top of Ni-YSZ to perform the steam reforming reaction. A single cell with CNMnO/Ni-YSZ/YSZ/GDC/LSC configuration produces a peak power density of 492 mW cm^?2 in wet hydrogen and 371 mW cm^?2 in wet methane, at 600 °C. The cell also shows exceptional durability against Ni oxidation when tested in wet methane under 0.2 A cm^?2 for 100 h. The improved performance and durability of the catalyst layer has been attributed to the nanosized precipitated Ni and Mn particles distributed on the surface of individual CNMnO particles.     

Performance and carbon deposition over Pd nanoparticle catalyst promoted Ni/GDC anode of SOFCs in methane,methanol and ethanol fuels

The electrochemical performance and carbon deposition on palladium catalyst promoted Ni/Gd_0.1C_0.9O_1.95 (Ni/GDC) anode in methane and alcohol fuels like methanol and ethanol are investigated at open circuit potential and under dc bias using electrochemical impedance spectroscopy technique. Presence of Pd nanoparticle catalyst significantly promotes the electrocatalytic activity of Ni/GDC for the electrooxidation reaction in methane and in particularly in methanol and ethanol fuels. For instance, in the case of methanol oxidation reaction, there is clear separation of the impedance arcs at high and low frequencies and activation energy for the reaction is reduced by ∼33% on a 0.15 mg cm⁻² PdO impregnated or infiltrated Ni/GDC anode. The transitional impedance response study when the inlet gas is switched from hydrogen to methane or alcohol fuels indicates that the oxidation reaction in methane and alcohol fuels is most likely dominated by adsorption, dissociation and diffusion steps of the reaction. Carbon deposition is also observed on Pd-infiltrated Ni/GDC in methanol and ethanol, but different from that observed in methane, there is no filament carbon fibers formation on the Pd-impregnated Ni/GDC surface in methanol fuel.     

A high-performance integrated electrode for anion-exchange membrane direct ethanol fuel cells

We propose a new anode electrode structure that is composed of a nickel foam layer with thin catalyst films coated onto the skeleton of the foam. This innovative design of the anode electrode enables the integration of the catalyst and diffusion layers, thereby extending the electrochemical active surface area and facilitating the transport of species. The experimental results indicate that the use of the integrated electrode in an anion-exchange membrane direct ethanol fuel cell can significantly improve the cell performance as compared with the use of the conventional electrode that has separated catalyst and diffusion layers; a peak power density of 130 mW cm⁻² and a maximum current density of 1060 mA cm⁻² are achieved at 80 °C.     

Boosting the performance of alkaline direct ethanol fuel cell with low-Pd-loading nickel foam electrode via mixed acid-etching

Nickel foam has been widely used as an electrode supporting material for alkaline direct ethanol fuel cells (ADEFC). However, the smooth skeleton surface of pristine nickel foam results in low specific surface area, such that a high-load catalyst is required to deal with ethanol oxidation, which limits its application as a catalyst support. Therefore, efforts to enhance the roughness of skeleton surface and reduce the catalyst loading have been intensively made. One of the conventional approaches is hydrochloric acid (HCl) etching method, which can remove the inert layer but does not change the surface roughness. In this paper, a mixed acids treated nickel foam anode with low Pd loading (0.35 mg cm^?2) is prepared by simply soaking for three times for ADEFC performance testing. The peak power density reaches 30 mW cm^?2, which is double the performance of the HCl treated anode. The performance improvement is attributed to the micro-holes produced by mixed acids etching, which enhance the roughness of skeleton and improve electrochemical active surface area (ECSA) of the catalyst. This work opens a new platform for in-depth exploration on metal foam electrodes in fuel cells.     

An additional layer in an anode support for internal reforming of methane for solid oxide fuel cells

Anode supported solid oxide fuel cells (SOFCs) have been extensively investigated for their ease of fabrication, robustness, and high electrochemical performance. SOFCs offer a greater flexibility in fuel choice, such as methane, ethanol or hydrocarbon fuels, which may be supplied directly on the anode. In this study, SOFCs with an additional Ni–Fe layer on a Ni–YSZ support are fabricated with process variables and characterized for a methane fuel application. The addition of Ni–Fe onto the anode supports exhibits an increase in performance when methane fuel is supplied. SOFC with a Ni–Fe layer, sintered at 1000 °C and fabricated using a 20 wt% pore former, exhibits the highest value of 0.94 A cm⁻² and 0.85 A cm⁻² at 0.8 V with hydrogen and methane fuel, respectively. An impedance analysis reveals that SOFCs with an additional Ni–Fe layer has a lower charge transfer resistance than SOFCs without Ni–Fe layer. To obtain the higher fuel cell performance with methane fuel, the porosity and sintering temperature of an additional Ni–Fe layer need to be optimized.     

Performance analysis of hollow fibre-based micro-tubular solid oxide fuel cell utilising methane fuel

Solid oxide fuel cell (SOFC) has been studied as one of the most amazing development in energy production that could work directly with hydrocarbon fuel without reforming procedure. This study was conducted to analyse the micro-tubular solid oxide fuel cell (MT-SOFC) in terms of its performance by utilising methane as the fuel, subsequently compared with hydrogen. MT-SOFC that was investigated in this work consisted of thin cathode layer, coated onto co-extruded anode/electrolyte dual-layer hollow fibre (HF); in which its anode was made of nickel (Ni), coupled with cerium-gadolinium oxide (CGO) as an electrolyte, whereas the cathode was lanthanum strontium cobalt ferrite (LSCF) and CGO. The physical analyses carried out were three-point bending test and scanning electron microscopy (SEM). X-ray diffraction (XRD) analysis was further conducted to examine the carbon deposition in HFs. In evaluating the performance of HFs, current-voltage (IV) measurement, as well as impedance analysis of various temperatures range from 500 °C to 700 °C were performed. Based on the results, the OCV, maximum power density and ohmic ASR of MT-SOFC exposed to methane fuel, were at 0.79 V, 0.22 W cm⁻² and 0.31 Ω cm²; compared to the other that was exposed to hydrogen fuel, recorded at 0.89 V, 0.67 W cm⁻² and 0.19 Ω cm² respectively. This indicates that there was a significant reduction in cell performance when methane was used as the fuel, due to the carbon deposition as proven by SEM, three-point bending and XRD.     

Anode bleeding experiments to improve the performance and durability of proton exchange membrane fuel cells

Cost, durability, efficiency and fuel utilization are important issues that remain to be resolved for commercialization of proton exchange membrane fuel cells (PEMFC). Anode flow mode, which includes recirculation, dead-ended and exit bleeding operation, plays an important role in fuel utilization, durability, performance and the overall cost of the fuel cell system. Depending on the flow mode, water and nitrogen accumulation in the anode leads to voltage transients and local fuel starvation, which causes cell potential reversal and carbon corrosion in the cathode catalyst layers. Controlled anode exit bleeding can avoid the accumulation of nitrogen and water and improve fuel utilization. In this study, we present a method to control the bleed rate with high precision in experiments and demonstrate that hydrogen utilization as high as 0.9988 for a 25 cm² single cell and 0.9974 for an 8.17 cm² single cell can be achieved without significant performance loss. In the experiments, anode pressure is kept at 1 bar higher than the cathode pressure to decrease nitrogen crossover from the cathode, decreasing the crossover from the cathode. Moreover, four load cycle profiles are applied to observe the cumulative loss in the electrochemical surface area (ECSA), which are acquired from cyclic voltammetry (CV) analysis. Experiments confirm that the ECSA loss and severe voltage transients are indicative of fuel starvation induced by prolonged dead-ended or low exit-bleed operation modes whereas bleed rates that are larger than the predicted crossover rate are sufficient to operate the fuel cell without voltage transients and detrimental ECSA loss.     

Methoxy methane (dimethyl ether) as an alternative fuel for direct fuel cells

The electrooxidation of methoxy methane (dimethyl ether) was studied at different Pt-based electrocatalysts in a standard three-electrode electrochemical cell. It was shown that alloying platinum with ruthenium or tin leads to shift the onset of the oxidation wave towards lower potentials. On the other hand, the maximum current density achieved was lower with a bimetallic catalyst compared to that obtained with a Pt catalyst. The direct oxidation of dimethoxy methane in a fuel cell was carried out with Pt/C, PtRu/C and PtSn/C catalysts. When Pt/C catalyst is used in the anode, it was shown that the pressure of the fuel and the temperature of the cell played important roles to enhance the fuel cell electrical performance. An increase of the pressure from 1 to 3 bar leads to multiply by two times the maximum achieved power density. An increase of the temperature from 90 to 110 °C has the same effect. When PtRu/C catalyst is used in the anode, it was shown that the electrical performance of the cell was only a little bit enhanced. The maximum power density only increased from 50 to 60 mW cm⁻² at 110 °C using a Pt/C anode and a Pt_0.8Ru_0.2/C anode, respectively. But, the maximum power density is achieved at lower current densities, i.e. higher cell voltages. The addition of ruthenium to platinum has other effect: it introduces a large potential drop at relatively low current densities. With the Pt_0.5Ru_0.5/C anode, it has not been possible to applied current densities higher than 20 mA cm⁻² under fuel cell operating conditions, whereas 250 and almost 400 mA cm⁻² were achieved with Pt_0.8Ru_0.2/C and Pt/C anodes. The Pt_0.9Sn_0.1/C anode leads to higher power densities at low current densities and to the same maximum power density as the Pt/C anode.     

A tolerance criterion for tar concentration in a model wood gas for a nickel/scandia-stabilized zirconia cermet anode in a solid oxide fuel cell

Durability of a nickel and scandia-stabilized zirconia cermet anode against toluene in hydrogen was evaluated in this paper. Anode deterioration was judged by the loss of elemental nickel from a surface of an anode. Elemental nickel loss was observed when the toluene concentration was 3 or 10 g/Nm³, steam to carbon ratio was 1, and current density was 0.5 A/cm² at both temperatures: 1073 K and 1173 K. Therefore the tolerance criterion must be less than 3 g/Nm³ in hydrogen in the experimental conditions. However, the deterioration can be mitigated to some extent by increasing the operating temperature, steam-to-carbon ratio, or current density. Anode deterioration was also mitigated when hydrogen concentration in the fuel gas was nearly identical to that of wood gas. The influence of hydrogen concentration in the fuel gas on deterioration may be substantial. The loss of elemental nickel could not be detected instantaneously by electrochemical diagnosis.     

Ir-Pt/C composite with high metal loading as a high-performance anti-reversal anode catalyst for proton exchange membrane fuel cells

Voltage reversal induced by hydrogen starvation can severely corrode the anode catalyst support and deteriorate the performance of proton exchange membrane fuel cells. A material-based strategy is the inclusion of an oxygen evolution reaction catalyst (e.g., IrO₂) in the anode to promote water electrolysis over harmful carbon corrosion. In this work, an Ir-Pt/C composite catalyst with high metal loading is prepared. The membrane-electrode-assembly (MEA) with 80 wt% Ir-Pt(1:2)/C shows a first reversal time (FRT) of up to 20 hours, which is about ten times that of MEA with 50 wt% Ir-Pt(1:2)/C does. Furthermore, the MEA with 80 wt% Ir-Pt(1:2)/C exhibits a minimum cell voltage loss of 6 mV@1 A/cm² when the FRT is terminated in 2 hours, in which the MEA with 50 wt% Ir-Pt(1:2)/C exhibits a voltage loss of 105 mV@1 A/cm². Further physicochemical and electrochemical characterizations demonstrate that the destruction of anode catalyst layer caused by the voltage reversal process is alleviated by the use of the composite catalyst with high metal loading. Hence, our results reveal that the combination of OER catalyst on the Pt/C with high metal loading is a promising approach to alleviate the degradation of anode catalyst layer during the voltage reversal process for PEMFCs.     

Design of industrially scalable microtubular solid oxide fuel cells based on an extruded support

The current work describes the adaptation of an existing lab-scale cell production method for an anode supported microtubular solid oxide fuel cell to an industrially ready and easily scalable method using extruded supports. For this purpose, Ni–YSZ (yttria stabilized zirconia) anode is firstly manufactured by Powder Extrusion Moulding (PEM). Feedstock composition, extruding parameters and binder removal procedure are adapted to obtain the tubular supports. The final conditions for this process were: feedstock solid load of 65 vol%; a combination of solvent debinding in heptane and thermal debinding at 600 °C. Subsequently, the YSZ electrolyte layer is deposited by dip coating and the sintering parameters are optimized to achieve a dense layer at 1500 °C during 2 h. For the cathode, an LSM (lanthanum strontium manganite)–YSZ layer with an active area of ∼1 cm² is deposited by dip coating. Finally, the electrochemical performance of the cell is measured using pure humidified hydrogen as fuel. The measured power density of the cell at 0.5 V was 0.7 W cm⁻² at 850 °C.     

Response to Disselkamp: Direct peroxide/peroxide fuel cell as a novel type fuel cell

Besides hydrogen peroxide is known as conventionally oxidizer, it is both a fuel and a source of ignition. Platinum is not suitable catalyst for oxidation and reduction of hydrogen peroxide, because it directly converts the hydrogen peroxide to oxygen gas. In this study, the oxidation mechanism of peroxide is investigated and a fuel cell operating with acidic peroxide as oxidant and basic peroxide as fuel is constructed. The peroxide oxidation reaction in novel alkaline direct peroxide/peroxide fuel cell (DPPFC), shown feasible here using less expensive carbon supported Nickel catalyst, makes the alkaline direct peroxide/peroxide fuel cell a potentially low cost technology compared to PEM fuel cell technology, which employs platinum catalysts. The power density of 3.75 mW cm⁻² at a cell voltage of 0.55 V and a current density of 14 mA cm⁻² was achieved in our fuel cell.     

Highly active lanthanum doped nickel anode for solid oxide fuel cells directly fuelled with methane

Lanthanum doped nickel and YSZ composite anode (LaNi–YSZ) exhibited a greatly reduced polarization resistance and high performance for electrochemical oxidation of hydrogen and methane, which resulted from a fine anode structure with a high dispersion of nickel catalyst and a high catalytic activity towards methane.     

Ceria-Co-Cu-based SOFC anode for direct utilisation of methane or ethanol as fuels

Nickel-free solid oxide fuel cell anodes are an object of study for applications that aim at utilising primary carbonaceous fuels to generate power. In this study, a ceria-Co-Cu anode is produced and tested with hydrogen, methane and ethanol fuels at various temperatures.The produced catalysts were characterised by X-ray analysis and H₂ temperature-programmed reduction (TPR). Catalytic tests were performed and compared with the material under electrochemical operation. The cells were electrochemically characterised by recording i-V plots. The samples were assessed post-test for eventual carbon deposits by Raman spectroscopy investigations and temperature-programmed oxidation (TPO) analysis.The cells were able to operate with hydrogen, methane as well as ethanol, directly fed to the anode, with maximum power densities ranging from 400 to 540 mW.cm⁻², depending on the fuel stream utilised. The cells also kept their integrity demonstrating coking resistance for over 24 h of continuous operation. Important discussions and conclusions are drawn about carbon formation and the role of each compound in the anode composition. The bimetallic cell (ceria-Co-Cu) is herein compared to monometallic ones (ceria-Co and ceria-Cu) that served as baselines. The advantages of the bimetallic composition are listed and evaluated throughout the discussions.