Optimization of the protonic ceramic composition in composite electrodes for high-performance protonic ceramic fuel cells

A composite electrode in protonic ceramic fuel cells (PCFCs) is composed of an ionic conductor, an electronic conductor, and catalysts. To determine the contribution of the properties of the ionic conductor to the electrode performance, three different proton conductors: Ba(Ce_0.75Y_0.15)O_3−δ(BCY), Ba(Ce_0.45Zr_0.30Y_0.15)O_3−δ (BCZY), and Ba(Zr_0.75Y_0.15)O_3−δ (BZY), were used to fabricate composite electrodes for PCFCs. Moreover, their effects on the anode and cathode performances were investigated systematically. In the cathodes, the BCZY and BCY scaffolds showed a better performance than the BZY scaffold. However, in the anodes, the BZY scaffold showed a superior performance to the BCZY or BCY scaffold. This exhibited that the requirements of ion-conducting scaffolds in composite electrodes were different in cathodes and anodes and that the fuel cell performance could be optimized by choosing appropriate ionic conductors for each electrode.     

A high-performance ceramic composite anode for protonic ceramic fuel cells based on lanthanum strontium vanadate

The composite electrodes for protonic ceramic fuel cells (PCFC) were fabricated by infiltration of (La_0.8Sr_0.2)FeO_3−δ (LSF) cathode and (La_0.7Sr_0.3)V_0.90O_3−δ (LSV) anode into a porous protonic ceramic, Ba(Ce_0.51Zr_0.30Y_0.15Zn_0.04)O_3−δ (BCZY-Zn), respectively. Further, Pd-ceria catalysts were added into the composite anode. In the same method, the oxygen ion conducting fuel cells with the yttria-stabilized zirconia as an electrolyte (YSZ cell) were also fabricated. At 973 K, the non-ohmic area specific resistance (ASR) of PCFC (0.09 Ω cm²) was much smaller than that of the YSZ cell (0.28 Ω cm²) although the protonic conductivity of BCZY-Zn was slightly smaller than the oxygen ion conductivity of YSZ. According to the analysis of the symmetric cells with BCZY-Zn as an electrolyte, the LSV-composite anode showed better performance than the LSF-composite cathode at low temperatures.     

Carbon resistant Ni1-xCux-BCZY anode for methane-fed protonic ceramic fuel cell

This research aims to develop a better carbon resistant anode compared to conventional Ni-BCZY anode for methane fueled protonic ceramic fuel cell (PCFC). Solid-state reaction process is used to prepare alloy Ni_1-xCu_x-BCZY anode in PCFC. Ni is doped with Cu for better carbon resistance. Results show that, Ni_0·9Cu_0.1-BCZY anode calcined at 800 °C for 0.5 h exhibit an electrical conductivity of 2054 S/cm at 600 °C, which is 8.4% less than traditional Ni-BCZY anode. XPS, and Raman data show that Ni_0·9Cu_0.1-BCZY anode exhibit resistance to carbon deposition compared to traditional anode. The best carbon deposition resistance is observed for the Ni_0·7Cu_0.3-BCZY sample. This work demonstrates the suppression of carbon deposition and inhibition of anode deformation in methane fueled PCFC with Ni_1-xCu_x-BCZY anode. This work is helpful for development of carbon-resistant materials for energy generation with solid oxide fuel cells.     

Comparison of solid oxide fuel cell anode coatings prepared from different feedstock powders by atmospheric plasma spray method

Atmospheric plasma spray (APS) deposition of a high-performance anode coating, which is essential for obtaining high power density from a solid oxide fuel cell (SOFC), is developed. A conventional, micron-sized, nickel-coated graphite – yttria stabilized zirconia (YSZ) – graphite blend feedstock leads to a non-uniform layered coating microstructure due to the difference in the physical and thermo-physical properties of the components. In this research, new types of feedstock material received from a spray-drying method, which includes nano-components of NiO and YSZ (300 nm), are used. The microstructure and mechanical properties of a coating containing a nano composite that is prepared from spray-dried powders are evaluated and compared with those of a coating prepared from blended powder feedstock. The coating microstructures are characterized for uniformity, mechanical properties and electrical conductivity. The coatings prepared from spray-dried powders are better as they provide larger three-phase boundaries for hydrogen oxidation and are expected to have lower polarization losses in SOFC anode applications than those of coatings prepared from blended feedstock.     

Triple-component composite cathode for performance optimization of protonic ceramic fuel cells

The cathode of a protonic ceramic fuel cell must be able to facilitate ion and electron transfer, while simultaneously possessing a high catalytic activity for steam generation and the dissociation of gas-phase molecules. In this study, the performance of a cathode for protonic ceramic fuel cells is optimized by employing a triple-component composite cathode design, which integrates proton conductors, mixed electronic–ionic conductors, and a catalytic layer. Additionally, two other composite cathodes are fabricated for comparison. Owing to its higher electrical conductivity but lower catalytic activity, the composite cathode with protonic ceramic and (Ba_0.95La_0.05) (Fe_0.8Zn_0.2)O_3-δ (BLFZ) exhibits lower ohmic resistance but poor catalytic activity compared to the composite cathode with protonic ceramic and Ba(Co_0.4Fe_0.4Zr_0.1Y_0.1)O_3-δ (BCFZY). The triple-component cathode is fabricated by infiltrating BCFZY into a composite cathode composed of BLFZ and protonic ceramic, and both the ohmic and non-ohmic resistances of the cathode are optimized in CH₄ and H₂ fuels. In particular, the performance of CH₄ fuel is significantly improved by adopting a triple-component cathode. These results suggest a possible contribution of the oxygen reduction reaction at the cathode to the reformation of CH₄ at the anode.     

Optimized lithium-doped ceramic electrolytes and their use in fabrication of an electrolyte-supported solid oxide fuel cell

Lithium-gadolinium-doped ceria electrolytes (2–5 mol% of lithium) are prepared by fast and reliable one-pot sol gel combustion synthesis and sintered at low temperature. The aim is to improve the microstructure, electrochemical and power generation of electrolyte-supported intermediate temperature solid oxide fuel cells. Time-of-flight coupled secondary ions mass spectroscopy and transmission electron microscopy reveal the uniform distribution of lithium and the structural modification and surface change induced by the doping. Lithium addition reduces the sintering temperature to 950 °C, and the electrochemical properties compared to the pure gadolinium doped ceria are highly superior. A maximum of 3.59·10⁻²–1.41·10⁻¹ S·cm⁻¹ for total conductivity are achieved for 3 mol.% of lithium addition at intermediate operative temperature range. An electrolyte-supported solid oxide fuel cell is then fabricated and tested in different gas conditions and operative temperatures. The maximum power density is 359 mW·cm⁻² at 668 mA·cm⁻² (750 °C). The results demonstrate the reliability, the short time-to-product and the feasibility of both synthesis cycle and electrolyte production for industrial application to develop a cost-effective and marketable fuel cell technology.     

Preparation of nano-sized nickel as anode catalyst for direct urea and urine fuel cells

Nano-sized nickel with primary particle size of 2-3 nm has been successfully prepared for use as efficient anode catalysts in urea and urine fuel cells. XRD, SEM and TEM were used for characterisation of nano-sized nickel. Based on the previous communication, the performance of urea and urine fuel cells has been further improved when the relative humidity at the cathode was 100%. A maximum power density of 14.2 mW cm⁻² was achieved when 1 M urea was used as fuel, humidified air as oxidant. The performance of urine fuel cells operating above room temperature was also reported for the first time and a power density of 4.23 mW cm⁻² was achieved at 60 °C indicating potential application in urea-rich waste water treatment.     

Ameliorated performance of a microbial fuel cell operated with an alkali pre-treated clayware ceramic membrane

Clayware membrane amalgamated with 20% montmorillonite (M-20), acts as an excellent cost effective proton exchange membrane (PEM) for the application in field-scale microbial fuel cells (MFCs). In this investigation, M-20 membrane was pre-treated by acid (M-A), neutral water (M-N) and alkali (M-B), followed by the determination of the membrane properties to access their applicability in MFCs. With alkali treatment of M-20 membrane, maximum proton mass transfer coefficient of 6 × 10⁻⁶ cm s⁻¹ was obtained, which was nearly five times higher than M-A (1.15 × 10⁻⁶ cm s⁻¹) and four times higher than the control membrane, M-N. Proton conductivity was also found to be maximum for M-B (17.9 × 10⁻³ S cm⁻¹), which was four times higher than both M-N (4.4 × 10⁻³ S cm⁻¹) and M-A (4.6 × 10⁻³ S cm⁻¹). Oxygen mass transfer coefficient was found to be minimum for M-B (4.02 × 10⁻⁵ cm s⁻¹), which was considerably lesser than that observed for M-N (16.2 × 10⁻⁵ cm s⁻¹) and M-A (13.8 × 10⁻⁵ cm s⁻¹). Cation transport number of M-B (0.15 ± 0.01) was found to be two folds lower than M-N, demonstrating M-B is more selective towards proton transport compared to other cations. The MFC-B with M-B as PEM performed superior as compared with other MFCs, demonstrating coulombic efficiency (CE) of 10.2%, chemical oxygen demand (COD) removal efficiency of 88% and power density of 83.5 mW m⁻². On the other hand, MFCs using M-A and M-N as PEM, demonstrated mediocre performance with CE of 6% and 7.6%, COD removal efficiency of 80% and 83% and power density of 40.4 ± 6.2 mW m⁻² and 64.0 ± 5.8 mW m⁻², respectively. Hence, alkali treatment of clayware ceramic membrane elucidated its appropriateness for proliferating the efficacy of MFCs and these are recommended for scaling up of MFCs.     

A high performance direct ammonia fuel cell using a mixed ionic and electronic conducting anode

A high performance direct ammonia fuel cell incorporating a doubly doped barium cerate electrolyte and a novel cermet anode consisting of europium doped barium cerate, a mixed ionic and electronic solid electrolyte, and Ni was studied. The catalytic activity of the cermet anodes was superior to that of Pt catalysts. The I–V and power density data suggest that the direct ammonia fuel cell could be operated at temperatures as low as 450 °C. The fuel cell was operated with ammonia as fuel in excess of 500 h without significant deterioration in performance.     

Improved PEM fuel cell performance with hydrophobic catalyst layers

Flooding of catalyst layers is one of the major issues, which effects performance of low temperature proton exchange membrane fuel cells (PEMFC). Rendering catalyst layers hydrophobic one may improve the performance of PEMFC depending on Pt percentage in the catalyst and Polytetrafluoroethylene (PTFE) loading on the electrode. In this study, effect of hydrophobicity in catalyst layers on performance has been investigated by comparing performances of membrane electrode assemblies prepared with 48% Pt/C. Ultrasonic coating technique was used to manufacture highly efficient electrodes. Power density at 0.45 V increased by the addition of PTFE, from 0.95 to 1.01 W/cm² with H₂/O₂ feed; while it slightly increased from 0.52 W/cm² to 0.53 W/cm² with H₂/Air feed. Addition of PTFE to catalyst layers while keeping Pt loading constant, enhanced performance providing improved water management. Kinetic activity increased by decreasing Nafion loading from 0.37 mg/cm² to 0.25 mg/cm² while introducing PTFE (0.12 mg/cm²) to the electrode. Electrochemical impedance spectroscopy (EIS) results proved that charge transfer resistance decreased with hydrophobic catalyst layers for H₂/O₂ feed. This is attributed to enhanced water management due to PTFE presence.     

Fabrication and evaluation of stable micro tubular solid oxide fuel cells with BZCY-BZY bi-layer proton conducting electrolytes

Anode-supported proton conducting micro tubular solid oxide fuel cells (MT-SOFCs) with the configuration of Ni–BaZr_0.1Ce_0.7Y_0.2O_3-δ (BZCY)/BZCY/BaZr_0.8Y_0.2O_3-δ (BZY)/La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF)-BZY have been prepared by a combination of phase inversion method and suspension-coating technique. The obtained Ni-BZCY anode hollow fiber presents a special asymmetrical structure consisting of a sponge-like layer and a finger-like porous layer, which is propitious to anode electrochemical process. Bi-layer electrolytes consisting of 5 μm thick BZCY and 3 μm thick BZY are successfully fabricated by suspension-coating technique. BZY electrolytes are placed at the cathode side, in order to improve the chemical stability against CO₂. The considerable electrochemical performance and good stability in the presence of CO₂ indicate that the construction of BZY-BZCY bi-layer electrolytes is an effective way for the development of stable proton conducting MT-SOFCs.     

Multifunctional macroporous solid oxide fuel cell anode with active nanosized ceramic electrocatalyst

In this work, an alternative anode material, consisting of perovskite-type manganese-doped lanthanum aluminate (La_1.5Al_0.33Mn_0.17O₃), was proposed and implemented. The solid oxide fuel cell anode was produced by the wet impregnation of nanoparticles into a macroporous electrolyte-based scaffold material. The produced cell was characterized by X-ray diffraction and scanning electron microscopy, from which the morphology of the scaffold, the particle size distribution, and porosity were extensively performed and discussed. Electrochemical and electrocatalytic tests were accounted by recording i-V plots with hydrogen or methane as fuels, and by measuring methane conversion rates and C₂ hydrocarbons selectivity.The particle size distribution was confirmed to be submicrometric with the presence of nanoparticles. High levels of porosity (30–35%) were achieved at the scaffold and the cells were able to operate with hydrogen and methane as fuels delivering a power density of around 150 mW.cm⁻² and yielding 30–70% C₂ hydrocarbons selectivity, depending on operational conditions.     

System analysis of a protonic ceramic fuel cell and gas turbine hybrid system with methanol reformer

The performance of a methanol-fed protonic ceramic fuel cell (PCFC)/gas turbine (GT) hybrid system is investigated in this work. To build the system, Thermolib software is employed with input parameters obtained from references. Effects of air stoichiometry on system performance are analyzed. Results show that, as air stoichiometry is increased, the reformer temperature and CO concentration decrease, while H₂ concentration increases. High air stoichiometry decreases PCFC temperature and performance. GT output power increases with increasing air flow. But, the power consumption by compressor also increases. Overall, to achieve higher system efficiency for this hybrid system, the optimum values of air stoichiometry are from 2.7 to 2.9. An additional heat recovery steam generator can also improve the overall system efficiency from 66.5% to 71.7%. This work helps in understanding the modeling and optimum functioning parameters of high power generation systems.     

Fabrication and characteristics of anode as an electrolyte reservoir for molten carbonate fuel cell

In order to design the anode of a molten carbonate fuel cell (MCFC) to serve as an additional electrolyte reservoir, the surface of a conventional Ni-10 wt.% Cr anode is modified with bohemite sol by means of a dip-coating method. After coating the bohemite sol on the nickel surface, the surface layer is change into lithium aluminate particles during the course of cell operation. This results in good electrolyte wettability compared with a bare nickel surface. Consequently, the surface modification makes it possible to increase the electrolyte filling contents in the anode pores from 25–30 to 50–60 vol.%. In addition, the anti-sintering ability is induced due to the presence of lithium aluminate particles between the nickel particles. These findings show that the surface modification can increase both the structural stability and the electrolyte loading of the anode.     

A novel design for humidifying an open-cathode proton exchange membrane fuel cell using anode purge

The low performance of open-cathode proton-exchange-membrane fuel cells (OCPEMFCs) is attributed to the low-humidity ambient air supplied to the cathode using electric fans. To improve the OCPEMFC performance, this paper proposes a novel humidification method by collecting water purged from the anode and supplying it to the open cathode. The OCPEMFC performance is evaluated at various humidifier distances from the cathode inlet, and it is compared with that where no humidifier is used when the OCPEMFC operates under three different current levels of 1, 5, and 8 A. The results show that the novel design improves the stack power, and optimal performance is achieved at a humidifier distance of 2 cm. The energy efficiency achieves an improvement between 1.4% and 1.8% when a humidifier is used.     

Fabrication of solid oxide fuel cell anode electrode by spray pyrolysis

Large triple phase boundaries (TPBs) and high gas diffusion capability are critical in enhancing the performance of a solid oxide fuel cell (SOFC). In this study, ultrasonic spray pyrolysis has been investigated to assess its capability in controlling the anode microstructure. Deposition of porous anode film of nickel and Ce_0.9Gd_0.1O_1.95 on a dense 8 mol.% yttria stabilized zirconia (YSZ) substrate was carried out. First, an ultrasonic atomization model was utilized to predict the deposited particle size. The model accurately estimated the deposited particle size based on the feed solution condition. Second, effects of various process parameters, which included the precursor solution feed rate, precursor solution concentration and deposition temperature, on the TPB formation and porosity were investigated. The deposition temperature and precursor solution concentration were the most critical parameters that influenced the morphology, porosity and particle size of the anode electrode. Ultrasonic spray pyrolysis achieved homogeneous distribution of constitutive elements within the deposited particles and demonstrated capability to control the particle size and porosity in the range of 2-17 μm and 21-52%, respectively.     

Evaluation of the polarization resistance of protonic ceramic electrolysis cells with a triple-component composite electrode

Steam-electrolysis performance of protonic ceramics cells with Ni-cermet and triple-component composite electrodes composed of protonic ceramics, mixed proton–electron conductor, and catalysts was evaluated under different operating atmospheres at 500 °C to determine the effects of the catalysts on the electrode performance and electrochemical reaction mechanisms of steam splitting and hydrogen evolution. Here, Ba(Ce_0.3Zr_0.5Y_0.1Yb_0.1)O_3-δ, (Ba_0.95La_0.05) (Fe_0.8Zn_0.2)O_3-δ, and La_0.8Sr_0.2CoO_3-δ were used as the protonic ceramics, mixed proton–electron conductor, and catalyst, respectively. Under a fuel-cell atmosphere, the steam vapor pressure (pH₂O) at the airside and hydrogen partial pressure (pH₂) at the fuel side were held constant at equal levels. In contrast, pH₂O was higher and pH₂ was lower under the electrolysis atmosphere. The higher pH₂O at the airside decreased the air electrode impedance, but the lower pH₂ at the fuel side significantly increased the fuel electrode impedance. The La_0.8Sr_0.2CoO_3-δ catalyst facilitated the adsorption and dissociation of steam. Based on the study results, the mechanisms for steam splitting/dissociation at the triple-component composite electrode and hydrogen evolution at the Ni-cermet electrode are suggested.     

Fabrication of integrated BZY electrolyte matrices for protonic ceramic membrane fuel cells by tape-casting and solid-state reactive sintering

Integrated porous/dense/porous tri-layer BaZr_0.8Y_0.2O_3-δ (BZY) electrolyte asymmetrical matrices were designed for protonic ceramic membrane fuel cells (PCMFCs) and fabricated by multilayer tape-casting and solid-state reactive sintering. The effects of pore-former, sintering aid and sintering program on the microstructure of integrated electrolyte matrices (IEMs) were studied. Graphite and NiO were appropriate pore-former and sintering aid, respectively, and an accelerated heating program was more desirable. The conductivities of the IEM with designed microstructure in different atmospheres were measured by AC impedance spectroscopy at 400–600 °C. The highest conductivity of 6.9 × 10^?3 S cm^?1 at 600 °C was obtained in wet air atmosphere, and the corresponding activation energy was 0.602 eV. Gas-tightness of the IEM was confirmed by a stable open circuit voltage (OCV) of 0.97 V at 600 °C from a button fuel cell with impregnated NiO anode and BaCo_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ (BCFZY) cathode. These indicate that the fabricated BZY-based IEM has great potential for PCMFC application.     

Effective factors improving catalyst layers of PEM fuel cell

Cathode catalyst layer has an important role on water management across the membrane electrode assembly (MEA). Effect of Pt percentage in commercial catalyst and Pt loading from the viewpoint of activity and water management on performance was investigated. Physical and electrochemical characteristics of conventional and hydrophobic catalyst layers were compared. Performance results revealed that power density of conventional catalyst layers (CLs) increased from 0.28 to 0.64 W/cm² at 0.45 V with the increase in Pt amount in commercial catalyst from 20% to 70% Pt/C for H₂/Air feed. In the case of H₂/O₂ feed, power density of CLs increased from 0.64 to 1.29 W/cm² at 0.45 V for conventional catalyst layers prepared with Tanaka. Increasing Pt load from 0.4 to 1.2 mg/cm², improved kinetic activity at low current density region in both feeding conditions. Scattering electron microscopy (SEM) images revealed that thickness of the catalyst layers (CLs) increases by increasing Pt load. Electrochemical impedance spectroscopy (EIS) results revealed that thinner CLs have lower charge transfer resistance than thicker CLs. Inclusion of 30 wt % Polytetrafluoroethylene (PTFE) nanoparticles in catalyst ink enhanced cell performance for the electrodes manufactured with 20% Pt/C at higher current densities. However, in the case of 70% Pt/C, performance enhancement was not observed. Cyclic voltammetry (CV) results revealed that 20% Pt/C had higher (77 m²/g) electrochemical surface area (ESA) than 70% Pt/C (65 m²/g). In terms of hydrophobic powders, ESA of 30PTFE prepared with 70% Pt/C was higher than 30PTFE prepared with 20 %Pt/C. X-Ray Diffractometer (XRD) results showed that diameter of Pt particles of 20% Pt/C was 2.5 nm, whereas, it was 3.5 nm for 70% Pt/C, which confirms CV results. Nitrogen physisorption results revealed that primary pores of hydrophobic catalyst powder prepared with 70% Pt/C was almost filled (99%) with Nafion and PTFE.