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Anode flooding is one of the critical issues in proton exchange membrane (PEM)-based electrochemical hydrogen pump. One way to to mitigate it is to make the gas diffusion media highly hydrophobic. The coating mateirals much be compatible with other critical materials in the PEM electrolyzer.. It was discovered that a mixture of Nafion™ and oxidized carbon nanotubes (O-CNT) coated onto the porous gas diffusion medium can render it hydrophobic with an effective contact angle of 130°. Electrochemical pump testing has shown that, with the help of the coating, the flood-recovery performance of the hydrogen pump was greatly improved. A hydrogen pump cell with an uncoated GDL was not able to recover from a flooded state, while a hydrogen pump cell with a coated GDL was able to recover its performance within 100 secs.

In order to accurately predict the behavior or electrochemical devices, it is necessary to develop sophisticated models that take into consideration transport processes, electrochemical phenomena, mechanical stresses, and structural deformations on the operation of an electrochemical system. Many different models exist that can predict the electrochemical performance of these devices under a variety of operating and design conditions.[1-7] However, many of these models assume constant porosity and do not take into consideration the effects of a variable porosity on the porous electrode during cycling and what effects that may have on performance. In recent years, electrodes have been developed that show a significant volume change during intercalation and deintercalation, which are unable to be accurately predicted using these constant porosity models. Porosity and dimensional changes in an electrode can significantly affect the resistance of the battery during cycling and cause premature failure of the battery due to generated stresses. Previously, we have shown the ability to incorporate dimensional and porosity changes in a porous electrode into a model to predict volume changes in the active material during intercalation through the coupling of porous rock mechanics and porous electrode theory.[6] However, that model incorporated many assumptions in order to obtain an analytical solution, including the assumption of bulk stress, strain, and porosity. Here, we present a model that removes those assumptions and illustrates the coupling of porous electrode theory and rock mechanics in order to predict stress, strain, and porosity gradients across a porous electrode during cycling. 1. M. Jain and J. W. Weidner, J Electrochem Soc, 146, 1370 (1999). 2. M. Jain, G. Nagasubramanian, R. G. Jungst and J. W. Weidner, J Electrochem Soc, 146, 4023 (1999). 3. P. M. Gomadam and J. W. Weidner, J Electrochem Soc, 153, A179 (2006). 4. X. C. Zhang, A. M. Sastry and W. Shyy, J Electrochem Soc, 155, A542 (2008). 5. J. Christensen and J. Newman, J Solid State Electr, 10, 293 (2006). 6. T. R. Garrick, K. Kanneganti, X. Y. Huang and J. W. Weidner, J Electrochem Soc, 161, E3297 (2014). 7. K. Higa and V. Srinivasan, J Electrochem Soc, 162, A1111 (2015).

Modification of the support can alter the performance of electrocatalysts. Platinum is subject to poisoning in the anode of electrochemical cells operated at low temperatures required for many polymer electrolytes. Thus, very pure hydrogen is required which adds to the complexity and cost of these technologies. A process can be used to purify the fuel by pumping hydrogen protons through the membrane. This technique is also an excellent means of characterizing the tolerance of anode electrocatalysts. The surfaces become saturated with the impurity over time and electrochemical diagnostics allow us to probe this dynamic behavior with exposure. Over time, the activity is lost until the electrocatalyst is regenerated. Increasing the temperature, oxygen pressure, or potential are the best ways to remove the contamination. In this case, carbon monoxide (CO) is removed by cycling the potential. By this mechanism, the catalyst can be subject to similar driving forces causing corrosion in the cathode of the fuel cell. Through the design of a composite support, the goal is to provide a stable, connected platform for the platinum catalyst while also improving the tolerance to this common contaminant. Carbon blacks are used as a support to maintain high surface area and conductivity among other important reasons. Alternatively, graphitic multi-wall carbon nanotubes can be utilized to provide a more stable framework. Additionally, metal oxides may be added to their surface to promote a bifunctional mechanism for the CO oxidation. This may be a more robust method when compared to alloying catalysts with choice of other metals. The metal oxide can facilitate formation of hydroxyl groups in proximity to the Pt to aid the reaction in a similar way. Titania is chosen as an example for several reasons including its stability in this environment and also for the formation of a strong metal-support interaction. Addition of a donor dopant such as niobium may be chosen for ideal defect formation. Possible advantages and disadvantages of using similar transition metals in the electrocatalyst are discussed. Following the preparation of supports, the platinum catalyst is deposited by a polyol reduction. This low temperature reduction is selected to avoid the pitfalls of encapsulation that occur in strong metal-support interactions which can render catalysts inactive. After synthesis of precursor powders, the materials were characterized before being built into membrane electrode assemblies for full working cells. A suite of electrochemical diagnostics is applied to understand differences in the tolerance behavior that is fundamentally altered by the support structure. CO stripping (Fig 1.),chronoamperometric (Fig. 2) and chronopotentiometric (Fig. 3 a & b) tests are among the best ways to characterize the tolerance of these materials. Attempts to correlate the dynamics with impedance can give further insight into the deactivation. At higher currents, an oscillating phenomena is observed. Interesting transitions in the electrocatalysts arise that provide for stimulating discussion of its overarching principles which can guide support construction.

8 mol % Y2O3-ZrO2 [YSZ] has been widely used as electrolyte material in SOFCs. (Sc2O3)0.1(CeO2)0.01(ZrO2)0.89 [SCSZ] has higher ionic conductivity in the intermediate temperature range (600oC - 800oC) compared to YSZ, but YSZ has better chemical and phase stability. In this work YSZ and SCSZ were used in developing layered electrolytes with a unique design to incorporate both materials, resulting in an electrolyte with enhanced ionic conductivity and improved robustness. The design involved placing SCSZ layers between two outer YSZ layers, so as to produce four- and six-layered electrolytes. Tape casting, lamination and pressureless sintering techniques were used in the development of the electrolytes. Due to the mismatch of the coefficient of thermal expansion between the two materials, thermal residual stresses arise between the layers. These stresses contribute to an enhancement of the ionic conductivity of the layered electrolytes. In addition, the compressive residual stress significantly affects the mechanical properties of layered electrolytes, and improves the electrochemical performance. Biaxial flexure strength was measured using ring-on-ring strength testing at room temperature and 800oC. A finite element method was employed to calculate the maximum principal stress at fracture. The results showed that the layered YSZ/SCSZ/YSZ electrolytes have improved flexure strength at both room temperature and 800 oC because of the appearance of compressive residual stresses in the outer YSZ layers of the electrolyte. The calculated compressive stress values were also verified using Weibull statistics of strength data measured at room temperature.

Multi-layered (Y2O3)0.08(ZrO2)0.92 / (Sc2O3)0.1(CeO2)0.01(ZrO2)0.89 (YSZ/SCSZ) electrolytes were designed for intermediate temperature Solid Oxide Fuel Cells (SOFCs), so that the inner SCSZ layers provided superior ionic conductivity and the outer YSZ layers provided chemical and phase stability. A total of nine electrolyte designs were developed and tested. Due to the mismatch in the thermal expansion coefficients between the two electrolyte materials, residual stresses develop between the layers. It was noticed that the ionic conductivity of the electrolytes is enhanced due to the presence of residual stresses. To study the electrochemical performance of the SOFC with different electrolyte materials and configurations, an electrolyte-supported planar button SOFC is modeled using COMSOL Multiphysics® 4.3. The main governing equations include the charge conservation equation, Maxwell-Stefan diffusion model, Butler-Volmer equation, and Brinkman equation. The cathode and anode materials used are (La0.6Sr0.4)0.95-0.99Co0.2Fe0.8O3 and Ni-YSZ respectively. Validation of the model was done against experimental results of another planar SOFC by Joongmyeon et al. (Journal of Power Sources, 2007). The simulations show that SOFCs with 3-layered pure SCSZ electrolyte produced the highest power density while the single cell with 6-layered pure YSZ electrolyte produced the least power density. These results make sense, since the increase in the electrolyte thickness increases the ohmic losses. The model developed can be used in further studying the behavior of the cells. In order to study the mechanical properties of the electrolytes, biaxial flexure tests were performed via a ring-on-ring method at room temperature and 800 °C. Due to the high deflection of the electrolytes, a non-linear dependence between stress and load was observed. Therefore, the geometric non-linearity feature was utilized in the modeling to calculate the maximum tensile stress in the specimen at a given load. Results showed that layered electrolytes have higher biaxial flexure strength. This is theorized to be due to the presence of compressive stresses at the outer YSZ layers. Weibull statistics was used on stress calculations to verify the results.

In polymer electrolyte cells, an approach is shown for construction of resilient electrocatalysts. In the anode where the hydrogen oxidation reaction is subject to poisoning from fuel impurities like carbon monoxide (CO), increased tolerance and stability for the catalyst is revealed by modification of the support structure and properties. A carbon nanotube framework serves as the foundation for metal oxide addition, namely titania and niobium doped form. The corrosion resistant transition metal oxides form a strong bond with platinum catalysts through unique electronic interactions, measured by XPS. Several other material characterizations are also included to make comparisons between composites. Composite supports contribute improved reactivity towards oxidation of CO, especially in reduced titania. Carbon corrosion resistance is also measured and shown to be the greatest for this support. Synergistic combination of effects is observed directly by preparation of electrocatalysts into working membrane electrode assemblies measured for their performance & durability.

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Most modeling work of the polymer electrolyte membrane fuel cell (PEMFC) assumes an equilibrium relationship between membrane water content and proton conductivity. However, evidence is provided which shows that deviations from the equilibrium relationship exist during the transient hydration and dehydration cycles. Although Nafion® membranes follow a nearly symmetric water uptake and loss, dry membranes gain conductivity much faster than they absorb water while wet membranes lose conductivity at about the same rate they desorb water. This asymmetric behavior should be accounted for when predicting the transitional behavior of PEMFCs.

The core of a polymer electrolyte membrane fuel cell stacks are membrane electrode assemblies (MEAs). Manufacturing processes for MEA have significant impact on their performance and durability. The authors report an ultrasonic atomization and spraying technique to deposit catalyst layer directly onto the membrane to realize membrane electrode assemblies. Electrochemical test of as-fabricated MEAs indicated very good performance and reasonable stability. The Platinum yield of the fabrication process was found to be around 89%.

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