Electrochemical Performance of the Ni-Fe Based Metal-Support Solid Oxide Fuel Cell with Ba-Sr-Co-Fe-O and La-Sr-Mn-O Cathodes

The design of electrode microstructure is important to enhance performance and stability of solid oxide fuel cells (SOFCs). The most common material used for the fuel electrode is nickel-yttria stabilized zirconia (Ni-YSZ) composite, in which electron, ion and gas conduct in the metallic Ni phase, the ceramic YSZ phase and the pores, respectively. The electrochemical reaction therefore takes place at the triple-phase-boundary (TPB), hence the increase in TPB density improves electrode performance. Recently, the ceramic materials, which exhibits mixed ionic-electronic conductivity (MIEC) properties, are considered to be beneficial solution for the SOFC electrodes. They can greatly enhance the available reaction sites by introducing surface reactions on the double phase boundaries (DPB) between MIEC phase and pore. One of the promising materials is considered to be gadolinium doped ceria (GDC). GDC exhibits higher ionic conductivity compared to YSZ and has MIEC property in the reducing atmosphere. In the case of Ni-GDC composites, the electrochemical performance is supported by both DPB and TPB reactions. In general, the active DPB density increases with the share of GDC phase in the composite. On the other hand, the active TPB density achieves maximum value when the share of both solid phases is balanced. The optimal electrode design has to be determined by the ratio between DPB and TPB reactions and their kinetics. In the present study, electrolyte supported SOFC with Ni-Gd0.1Ce0.9O2-δ anodes with various phase fractions were fabricated and their polarization characteristics were experimentally investigated. The ratio of Ni and GDC was controlled by the initial powder composition, and the porosity was varied by isostatically pressing the anode after screen printing. Initially, NiO (AGC Seimi) and GDC (ShinEtsu) powders were mixed to achieve the target volume fractions of Ni:GDC = 70:30, 60:40, 50:50, 40:60, 30:70 vol%. The anodes were then screen-printed on the YSZ discs and calcinated at 1350oC. In order to modify the porosity of the anodes, some of the cells undergoes isostatic pressing treatment at 200 MPa for 30 minutes prior to the calcination. The LSCF (lanthanum strontium cobalt ferrite by Fuel Cell Materials) cathode with GDC (ShinEtsu) barrier layer were screen-printed and sintered on the other side of the electrolyte. Current – voltage curves and electrochemical impedance spectra were measured at 500 – 800 oC. Additionally, the anodes with optimal phase composition were discharged for 100 hrs. 3D microstructural analysis was conducted with the focused ion beam scanning electron microscopy (FIB-SEM). The microstructural parameters, such as phase volume fractions, particle intercept length, TPB and DPB densities and tortuosity factors were quantified. By evaluating the connectivity of each phase, the total and active TPB and DBP densities were calculated. Quantified microstructural parameters were correlated with the polarization characteristics. Neither the DPB reactions nor the TPB reactions could individually explain the measured polarization resistances of the composite anodes. In the case of screen-printed anode samples without isostatic pressing, the high porosity (ca. 52% for all of the samples) lead to low connectivity of the solid phases. The optimal composition of the cermet was found to be Ni:GDC = 0.4:0.6 vol%. Introducing isostatic pressing, improvements in both ohmic and polarization resistances are observed. The decrease in ohmic resistance is mainly attributed to the improved connectivity between the electrode and the electrolyte. The polarization resistance was influenced by the changes in active DPB and TPB densities. As the porosity is reduced and connectivities of the solid phases are enhanced by the isostatic pressing, not only the nominal values of active DPB and TPB densities increased, but also the ratio between them has changed. This effect is most significant for Ni:GDC = 0.3:0.7 vol% sample, which exhibits the smallest polarization resistance among all the investigated electrodes. The discharge testing showed the improved stability of the cells with the decreased porosity. It is therefore concluded that not only the ratio between Ni and GDC but also porosity is a very important parameter for the performance and stability of the anode. Figure 1

A solid oxide fuel cell (SOFC) is promising technology because of its high electrical efficiency and environmental performance. SOFC can utilize solid ceramic electrolyte, so it can avoid the problems like corrosion, leakage and electrolyte management that often occur in liquid electrolyte. However, these ceramic based SOFC has weakness in external impacts because of its brittleness and relatively low strength. For this problem, metal-supported SOFC has been suggested. Metal supported SOFC refers to SOFC which replace its ceramic support to metal support for enhancing mechanical strength. Metal-support SOFC includes higher mechanical strength, better resistance to vibrates and impacts than conventional SOFC. So, metal-supported SOFC can be applied to movable applications like automobile, train and ship as well as stationary power generation system. In this study, 3-layer metal-supported SOFC short stack was designed and developed for APU (Auxiliary Power Unit) application. The short stack was composed of metal-supported cells, interconnect plates, ceramic sealant, gasket and metal foams. The metal-supported SOFC cell was fabricated by sinter-joining method and dimension of metal-supported SOFC cell was 120 x 80 mm2 and active cathode area was 110 x 70 mm2. For the material of interconnect plates and metal supports, Crofer 22 APU alloy was used which has high resistance to oxidation, low rate of chrome vaporization and good electrical conductivity of its oxide layer. Also, hybrid sealing system of ceramic sealant and sealing gasket were applied for gas tightness. Electrochemical performance of the short stack was evaluated in 800 ℃. The I-V-P characteristics was measured in 1 L/min of hydrogen and 5 L/min of air. Open circuit voltage (OCV) of the short stack was 3.0 V and it showed stable value. The maximum electrical power of the short stack was 23.1 W. In I-V curve, it seems to nearly linear shape which means ohmic resistance governs overpotential of the short stack. This ohmic resistance may originated in current collection from electrodes and it will be further analyzed. Moreover, the short stack was operated for 120 hours in galvanostatic mode with 2.16 A of discharge current. In the beginning, the operation voltage of the short stack was 2 V and there was no rapid initial degradation. Over time, voltage of the short stack was slightly decreased. After 120 hours, voltage of the short stack was 1.81 V and its degradation rate was 9.5 % per 120 hours. This seems to be due to chrome poisoning of cathode and this problem also will be further analyzed. Figure 1

Life cycle assessment shows that retrofitting coal-fired power plants with fuel cells will substantially reduce greenhouse gas emissions

Most studies of solid oxide cell degradation during electrolysis or reversible current-switching operation have focused on the oxygen electrode.1 However, one recent study has shown that Nickel/yttria-stabilized-zirconia (Ni-YSZ) fuel electrodes coupled with YSZ electrolytes may also degrade when operated under applied electrolysis current.2 Most studies of Ni-YSZ degradation have focused on fuel cell operating conditions, including the effect of temperature3 and fuel gas composition.4 Currently, relatively little is known about the electrolysis operating conditions, e.g., temperature and current density, that lead to degradation, and no studies have been reported to date on current switching operation. In the present work, a degradation study of Ni-YSZ electrodes on YSZ electrolytes was carried out using a symmetric cell geometry. The cells are tape-cast co-fired structures consisting of thin YSZ electrolytes sandwiched between thick Ni-YSZ electrodes. This geometry is meant to mimic the structure of Ni-YSZ anode-supported cells, and has the advantages that: (1) the life tests are simplified compared to full cells, with no gas sealing required; (2) unlike full cells, there is no need to separate out responses from an oxygen electrode in impedance spectra; (3) in current-switched testing, both Ni-YSZ electrodes tend to evolve in the same way, such that the cells remain electrochemically symmetrical; and (4) in dc-current testing, results are obtained on both fuel cell and electrolysis operation, as one electrode operates under anodic conditions and the other operates under cathodic conditions. The Ni/YSZ|YSZ|Ni/YSZ cells were tested at 800 °C in 97% H2 – 3% H2O for up to 1000 h, with current density ranging from 0.2 to 1.2 A/cm2. Electrochemical impedance spectroscopy measurements were made periodically with the current set to zero, during short interruptions of the life tests. At 0.2 A/cm2, there was little change in the ohmic or polarization resistance during the tests, and post-test SEM microstructural evaluation showed no measurable change. At the higher current density of 0.8 A/cm2, on the other hand, substantial microstructural and electrochemical changes were observed. For current-switching operation, the ohmic resistance increased slightly, while the polarization resistance showed a decreasing tendency. The main microstructural change was the observation of nanoparticle formation in the Ni-YSZ electrode functional layers. The nanoparticles contain Ni, Yittria and zirconia, which potentially increased the triple phase boundary density, possibly explaining the decrease of polarization resistance. For dc current operation, the ohmic resistance increased relatively rapidly, while the polarization resistance dropped slowly. Nanoparticles were observed on both electrodes after the test, but with different morphologies. In addition, cross-sectional SEM images showed intergranular fracture within the YSZ electrolyte, due to grain boundary voids that formed during the dc current test, presumably explaining the observed electrolyte resistance increase. Reference 1 Call, A. V., Railsback, J. G., Wang, H. Q. & Barnett, S. A. Degradation of nano-scale cathodes: a new paradigm for selecting low-temperature solid oxide cell materials. Phys Chem Chem Phys 18, 13216-13222 (2016). 2 Chen, M. et al. Microstructural Degradation of Ni/YSZ Electrodes in Solid Oxide Electrolysis Cells under High Current. J Electrochem Soc 160, F883-F891, doi:10.1149/2.098308jes (2013). 3 Kennouche, D., Chen-Wiegart, Y. C. K., Cronin, J. S., Wang, J. & Barnett, S. A. Three-Dimensional Microstructural Evolution of Ni-Yttria-Stabilized Zirconia Solid Oxide Fuel Cell Anodes At Elevated Temperatures. J Electrochem Soc 160, F1293-F1304, doi:10.1149/2.084311jes (2013). 4 Matsui, T., Kishida, R., Muroyama, H. & Eguchi, K. Comparative Study on Performance Stability of Ni-Oxide Cermet Anodes under Humidified Atmospheres in Solid Oxide Fuel Cells. J Electrochem Soc 159, F456-F460, doi:10.1149/2.053208jes (2012).

Composite cathodes based on Sm0.5Sr0.5CoO3−δ with porous Gd-doped ceria barrier layers for solid oxide fuel cells

Solid oxide fuel cells are high-temperature fuel cells which offer several advantages: high efficiency, fuel flexibility, high-quality waste heat, and the use of non-noble metal catalysts. Metal-supported solid oxide fuel cells, in which the ceramic mechanical support layer is replaced with the metal support, are considered as next-generation solid oxide fuel cells because of their enhanced mechanical/thermal ruggedness compared to conventional ceramic-supported solid oxide fuel cells. However, different thermomechanical behavior of metal support and ceramic layers during sintering makes metal-supported cells vulnerable to warping. Cell warpage must be minimized because it reduces not only uniformity of wet-chemical coating, but also actual contact area between electrode and interconnect, increasing the contact resistance.In this study, causes of metal-supported cell warpage are identified, and the design that can minimize cell warpage is suggested for successful scale-up of metal-supported solid oxide fuel cells. Through thermomechanical and residual stress analyses, it is found that residual stress derived from coefficient of thermal expansion mismatch between electrode layers and the metal substrate is the main cause of the warpage of metal-supported solid oxide fuel cells. Based on these results, a novel design that has thicker metal protection layer on the opposite side of the electrolyte is proposed for minimizing cell warpage due to residual stress. Through the design modification, vertical deformation of 2-inch metal-supported solid oxide fuel cell can be successfully controlled to 17.36% of the previous design. Furthermore, electrochemical evaluation showed a 21% decrease in ohmic ASR and a 25% increase in peak power density after the design modification, implicating reduction of contact resistance as a result of increased contact area by enhanced flatness.

Biomass-powered Solid Oxide Fuel Cells: Experimental and Modeling Studies for System Integrations

Since the publication of the classic paper by Mogensen et al. [1] on the physical properties of pure and doped ceria, many solid-oxide fuel cell (SOFC) development efforts have sought to take advantage of the high ionic conductivities of doped ceria such as Ce0.9Gd0.1O1.95-δ (GDC) to achieve high SOFC power densities at high cell operating voltages. However, high polaron-driven electronic conductivity of GDC at temperatures above 600 °C causes drops in cell voltages due in part to leakage currents, which also increase internal heat generation [2] and place tighter temperature limits on SOFC stacks with GDC electrolytes. To mitigate these challenges and achieve high power densities in GDC-based SOFCs, strategies must be developed to sustain maximum cell temperatures at approximately 650 °C to avoid high leakage currents while supporting relatively high power densities at sustainable cell voltages ≥ 0.7 V/cell. In the operation of an SOFC stack with co-flowing anode and cathode flows, high cathode excess air ratios (λ) can mitigate temperature rise across the stack, but at the expense of significant cathode-side pressure drops. With the operation of SOFC stacks on hydrocarbon fuels such as CH4, the ability to use internal endothermic reforming at realistic fuel utilizations > 60% provides an additional approach to reducing temperature rises over the length of the stack. A collaboration between the Univ. of Maryland, Colorado School of Mines, Alchemity, and RTX Technology Research Center has focused on the design, development and demonstration of high-power density GDC-based stacks for operation on CH4 with inline upstream pre-reforming to control stack inlet conditions such that temperatures across the stack at high power densities can be maintained to mitigate the effects of mixed ionic-electronic conductivity. This study presents down-the-channel modeling and experimental demonstrations of GDC-based SOFCs operating on CH4 with recycled anode exhaust to explore the range of inlet flow conditions that enable GDC-based electrolyte cells to maintain high-power densities > 0.5 W/cm2.Down-the-channel modeling of 10 × 10 cm SOFC cells with GDC or thin-film YSZ electrolytes are implemented using dusty-gas-models for porous media transport, heterogeneous and charge-transfer chemistry for the catalytic and electrochemical reactions in the anode and cathode, and mixed conducting submodels for oxide-ion and polaron transport through the electrolyte. Electrochemistry kinetic parameters forNi/GDC/SSC (strontium-doped samarium cobaltite) cells are calibrated against button-cell data from the Univ. of Maryland presented previously [3] and parameters for Ni/YSZ/LSM cells are calibrated against Elcogen cell test data [4]. To explore the effectiveness of lower inlet temperatures and CH4 internal reforming, baseline anode inlet feeds of CH4 mixed with anode exhaust to achieve a steam-to-methane ratio of 2 are set at temperatures up to 550 °C for GDC-based SOFCs and up to 600 °C for YSZ-based SOFCs. Excess air ratio λ varies to allow the mean cell temperature across the length of the stack to vary. Model results illustrated in Fig. 1 compare how the lower temperature GDC-based SOFC cells with their lower open circuit voltages but lower overpotentials can reach higher power densities than the thin-film YSZ-based SOFC cells for a given operating voltage, The model results show that the GDC cells have a peak density that is sustained at around λ= 5.0 wherein the cell is hot enough to support internal CH4 reforming but not so hot to drive high leakage currents that reduce the stack power density. The results indicate that GDC cell temperatures rise rapidly at slightly lower λ as leakage currents rapidly increase for mean cell temperatures. That allowable mean temperature increases with lower cell voltages due to the fact that lower cell voltage suppresses leakage current [2]. These modeling results are compared with tests of 10 × 10 cm SOFC cells with both GDC-electrolyte and with thin-film YSZ electrolytes and these tests reveal the effectiveness of internal reforming and lower inlet temperatures to mitigate the impact of leakage current on GDC-based cell performance and to achieve overall high power densities at cell voltages as high as 0.70 V/cell.

The design and development of highly conductive materials with wide electrolytic domain boundaries are among the most promising means of enabling solid oxide fuel cells (SOFCs) to demonstrate outstanding performance across low- and intermediate-temperature ranges. While reducing the thickness of the electrolyte is an extensively studied means for diminishing the total resistance of SOFCs, approaches involving an improvement in the transport behavior of the electrolyte membranes have been less-investigated. In the present work, a strategy for analyzing the electrolyte properties and their effect on SOFC output characteristics is proposed. To this purpose, a SOFC based on a recently developed BaCe0.5Zr0.3Dy0.2O3-δ proton-conducting ceramic material was fabricated and tested. The basis of the strategy consists of the use of traditional SOFC testing techniques combined with the current interruption method and electromotive force measurements with a modified polarization-correction assessment. This allows one to determine simultaneously such important parameters as maximal power density; ohmic and polarization resistances; average ion transport numbers; and total, ionic, and electronic film conductivities and their activation energies. The proposed experimental procedure is expected to expand both fundamental and applied basics that could be further adopted to improve the technology of electrochemical devices based on proton-conducting electrolytes.

Fuel cells are appealing alternatives to combustion engines for efficient conversion of chemical energy to electrical energy, with the potential to meet substantial energy demands with a small carbon footprint. Intermediate temperature fuel cells (200-300 °C) combine the kinetic benefits and fuel flexibility of higher operating temperatures along with the flexibility in material choices that lower operating temperatures allow. Solid acid fuel cells (SAFCs) offer the unique benefit amongst intermediate temperature fuel cells of a truly solid electrolyte, specifically, CsH2PO4, which in turn, provides significant system simplifications relative to phosphoric acid or alkaline fuel cells. However, the power output of even the most advanced SAFCs has not yet reached levels typical of conventional polymer electrolyte or solid oxide fuel cells. This is largely due to poor activity of the cathodes. That is, while it has been possible to limit electrolyte voltage losses in SAFCs through fabrication of thin-membrane fuel cells (with electrolyte thicknesses of 25–50 μm), it has not been possible to attain high activity cathodes or to limit Pt loadings to competitive levels. In this thesis, the efficacy of non-precious metal catalysts in the solid acid electrochemical system is evaluated. In addition, an attractive synthesis route (specifically, the electrospray method) to fabricating high surface area electrodes with high catalyst utilization is presented. Elimination of Pt was pursued by the evaluation of carbon nanostructures as potential oxygen reduction reaction (ORR) catalysts in the solid acid electrochemical system. Multi-walled carbon nanotubes were the most consistently catalytically active in comparison with nano-graphite. It is demonstrated that the a) precursor partial pressure, b) seed catalyst size, c) growth temperature and d) chemical functionalization can be used to control the defect density and atomic composition of multi-walled carbon nanotubes (MWCNTs), all of which play a significant role on the measured ORR activity. Increasing the precursor partial pressure, decreasing the seed catalyst size, and decreasing the growth temperature increases the density of ORR active defects. In addition, the oxygen reduction reaction (ORR) electrochemical activity evaluated by symmetric cell AC impedance spectroscopy and fuel cell measurements, were significantly enhanced by chemical functionalization with oxygen containing functional groups. Area normalized impedance responses as low as 7 Ω cm2 were measured on symmetric MWCNT/ CsH2PO4 cells. However, it was discovered that these reactive MWCNTs also catalyze and are slightly consumed by steam reforming. Moreover, the orders of magnitude improvement with functionalization measured in impedance measurements is not replicated in fuel cell power output as a result of a decrease in open circuit voltage relative to standard cells. It is proposed that the loss in voltage results from hydrogen production at the cathode via the steam reforming reaction, although formation of hydrogen peroxide rather than water as the oxygen reduction product cannot be ruled out. This work has a significant contribution to catalysis, it demonstrates how carbon nanostructures can be designed by synthesis routes and chemical functionalization processes, to create active precious-metal-free ORR catalysts. It is also important that we have demonstrated potential ORR catalysts in acidic media. These catalysts have potential applications in phosphoric acid fuel cells and PEMFCs. In addition to the study of carbon nanostructures, oxides were evaluated as potential ORR catalysts. Specifically, TiOx nanoparticles were studied. Analysis shows that the activity is controlled by the oxidation state of Ti. The active site seems to be on or near slightly reduced Ti sites. In this study we have outlined synthesis routes to tune the oxidation state of Ti and enhance ORR activity in the solid acid fuel cell. Finally, the fundamentals of the electrospray process are explored to understand how the particle size ultimately resulting from electrospray synthesis depends on both solution properties and process parameters. This analysis presents a systematic way to control the fabrication of high surface area SAFC electrodes with increased throughput, catalyst utilization and consequently power density.

Manufacturing method of BSCF cathode for low-temperature solid oxide fuel cell-A review

Solid oxide fuel cells (SOFCs) have been considered as alternative energy conversion devices because of their high energy conversion efficiency, fuel flexibility, and cost efficiency without precious metal catalysts. In current SOFCs, the cermet anode consists of nickel and ion-conducting ceramic materials, and solid oxide electrolytes and ceramic cathodes have been used. SOFCs normally operate at high temperatures because of the lower ion conductivity of ceramic components at low temperatures, and they have weaknesses in terms of mechanical strength and durability against thermal shock originating from the properties of ceramic materials. To solve these problems, metal-supported solid oxide fuel cells (MS-SOFCs) have been designed. SOFCs using metal substrates, such as Ni-based and Cr-based alloys, provide significant advantages, such as a low material cost, ruggedness, and tolerance to rapid thermal cycling. In this article, SOFCs are introduced briefly, and the types of metal substrate used in MS-SOFCs, as well as the advantages and disadvantages of each metal support, are reviewed.

A sophisticated design of the interface structure between the cathode and the electrolyte is essential to improve the performance of solid oxide fuel cells (SOFCs). It is because the interface is the place where it directly affects both the ohmic resistance and the polarization resistance as interface contact and interface reaction, respectively. To improve interface properties, electrolyte surface treatment or inserting interface functional layer between the cathode and the electrolyte have been applied. They improved cell performance by effectively enhancing the interfacial characteristics such as interface bonding and interface reaction area. However, although both ohmic and polarization resistance greatly contributed to the improved cell performance, a detailed analysis related to ohmic resistance compared to polarization resistance is insufficient. Unlike polarization resistance which can quantify interface reaction related resistance using distribution of relaxation time (DRT) model, there is no proper methodology to quantify interface resistance in the case of ohmic resistance. The interface resistance has been analyzed to the extent that it belongs to the remaining resistance except for the electrolyte resistance from total ohmic resistance in consideration of the ionic conductivity and thickness of the electrolyte, which still not completely separate the interface resistance from the total ohmic resistance. Furthermore, in recent years, the electrolyte thickness has gradually decreased to less than 5 μm for high-performance and the electrolyte resistance has been significantly reduced, increasing proportion of interface resistance in total ohmic resistance. Therefore, we need to reduce the interface resistance for further cell improvement. Also, quantifying the interface resistance and having a deeper understanding of the correlation between interface resistance and interface structure should be supported.Here, to realize the interface resistance from the ohmic resistance, we designed several types of interface structure using electrostatic spray deposition (ESD) which can precisely control the particle size and be used to fabricate a thin functional layer. Using the different interface properties and equivalent circuit models, we separate the interface resistance from the ohmic resistance quantitatively. Our results can suggest a simple and effective interface analysis method for achieving high performance SOFCs. Figure 1

Numerical evaluation of oxide growth in metallic support microstructures of Solid Oxide Fuel Cells and its influence on mass transport

Keywords: Triode fuel cells, oxygen reduction, auxiliary electrode, overpotential minimization, SOFC, PEMFC INTRODUCTIONThe power output and thermodynamic efficiency of electrochemical power producing devices, batteries and fuel cells, depend critically on the minimization of overpotential losses at the anode and cathode [1]. Significant overpotential, caused by inefficient electrocatalysis at the anode and cathode, remains the main obstacle for commercialization of the technologies of solid oxide fuel cells (SOFC) and polymer electrolyte membrane (PEM) fuel cells [1]. < style="text-align: justify;"> EXPERIMENTAL The introduction of a third electrode together with an auxiliary circuit which is run in the electrolytic mode permits fuel cell operation under previously inaccessible anode-cathode potential difference. This introduces a new controllable variable in fuel cell operation and can lead to significant reduction of the anodic and cathodic overpotential and thus in an enhancement of power output and overall thermodynamic efficiency. The triode operation has been tested both with SOFC and with PEMFCs, the latter with CO poisoned H2 feeds. In both cases significant, up to 800% and 400% respectively increases in power output have been obtained [2,3]. The new design is shown schematically in Figure 1 for the case of a PEM fuel cell. In the present study two reference electrodes added in order to measure the anodic and cathodic overpotential. RESULTS AND DISCUSSIONTwo parameters have been introduced to quantify the results of triode operation. The first is the power enhancement ratio, rP, defined as:ρp=Pfc /Po fc (1)where Po fc is the cell power output for normal (Iaux=0) operation. The second parameter is the power gain ratio, ΛP , defined as ΛP=(Pfc - Po fc)/Paux (2) When ΛP>1 then the thermodynamic efficiency of the triode unit is higher than that corresponding to conventional fuel cell operation. In the case of PEM fuel cells it has been found [3] that the cell power output can be enhanced by a factor of four with a concomitant 30% increase in thermodynamic efficiency. It was found that the applied auxiliary potential affects the charged transfer kinetics both at the anode and at the cathode and can enhance significantly the cathodic reduction of oxygen. CONCLUSIONS The triode fuel cell appears to be a promising concept under conditions of significant anodic or cathodic overpotential.Significant enhancement in cell performance is possible only when anode and cathode are is at least partly polarizable. Mathematical modeling is underway to optimize cell geometry. Application of the triode operation in suitably modified PEMFC stacks also appears feasible [3]. Figure 1.Schematic of the triode fuel cell, showing (a) the fuel cell and auxiliary circuits. (b) The exact geometry of the triode PEM fuel cell tested [3] and the electrical circuits. The fuel cell cathode acts simultaneously as an electrode of the auxiliary circuit where current or potential are controlled via a galvanostat-potentiostat.ACKNOWLEDGMENTWork supported under the ARISTEIA Programme. ReferenceS [1] W. Vielstich, A. Lamm and H. Gasteiger, in Handbook of Fuel Cells, Fundamentals Technology and Applications, Vol. 2, Wiley, New York (2003).[2] S.P. Balomenou and C.G. Vayenas, J. Electrochem. Soc., 151(11) (2004) A1874.[3] F.M. Sapountzi, S.C. Divane, M.N. Tsampas, C.G. Vayenas, Electrochim. Acta 56 (2011) 6966.