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Nonstoichiometric CeO2and Ce0.25Zr0.75O2nanoparticles with varying surface concentrations of Ce3+were synthesized. Their surface Ce3+concentration was measured by XPS, and their surface oxygen vacancy concentrations and grain size were estimated using Raman spectroscopy. The surface oxygen vacancy concentration was found to correlate well with grain size and surface Ce3+concentration. When incorporated into a Nafion polymer electrolyte membrane (PEM), the added nonstoichiometric ceria nanoparticles effectively scavenged PEM-degradation-inducing free radical reactive oxygen species (ROS) formed during fuel cell operation. A 3-fold increase in the surface oxygen vacancy concentration resulted in an order of magnitude enhancement in the efficacy of free radical ROS scavenging by the nanoparticles. Overall, the macroscopic PEM degradation mitigation rate was lowered by up to 2 orders of magnitude using nonstoichiometric ceria nanoparticles with high surface oxygen vacancy concentrations

The present study aims to address the effect of the uniformity of particle size distribution on Pt stability. A theoretical model based on the chemical reactions of Pt oxidation and precipitation in the membrane is presented. The incorporation of a particle size distribution function and a population balance allows the investigation of different initial particle size distributions. Initial results demonstrate the change of platinum ions concentration across the electrode and membrane and reveal the shift of particle size distribution towards larger diameters under potential hold and potential cycling simulations.

The efficacy of metal oxide particles in mitigating vanadium ions crossover was investigated. 3 wt % SiO2 was incorporated within recast Nafion membrane from which membrane electrode assemblies were prepared by painting. The composite membranes exhibited proton conductivities slightly lower ([?]54-55 mS cm[?]1) than Nafion. However, the permeability of vanadium ions was lowered by 80-85%, while the performance was improved. These results demonstrated that loadings of SiO2 much lower than previously reported can mitigate vanadium-ion crossover. Additionally the direct application of the catalyst on the membrane was shown to be a viable MEA synthesis option.

This work aims to address the role of particle size distribution on Pt stability. A theoretical model is built based on modified Butler-Volmer equations, platinum oxide surface coverage and interparticle interactions between platinum oxide particles. Preliminary results demonstrate the change in platinum ions concentration across the electrode and membrane and reveal the effect of potential cycling on the particle size. Further research on the effect of particle size and potential cycling on electrochemically active surface area and its comparison with experimental data is in progress.

The efficacy of CeO2 nanoparticles in mitigating free radical induced PEM degradation is investigated. Commercially obtained CeO2 and nanoparticles synthesized in-house were incorporated within a recast Nafion(r) membrane. MEAs were prepared using Nafion(r) and Nafion(r)-CeO2 composite membranes (0.5wt%, 1wt%, and 3wt% CeO2). The composite membranes exhibited very similar proton conductivities (~35mS/cm) and hydrogen crossover (~1 mA/cm2) as Nafion(r). However, the fluoride emission rate (estimated from accelerated tests) was lowered by more than one order of magnitude upon addition of CeO2 into the Nafion(r) membrane, suggesting that CeO2 nanoparticles have potential to enhance membrane durability.

The efficacy of nanoparticles in mitigating free-radical-induced polymer electrolyte membrane (PEM) degradation is investigated. Commercially obtained and nanoparticles synthesized in-house were incorporated within a recast Nafion membrane. Membrane electrode assemblies were prepared using Nafion and composite membranes (0.5, 1, and ). The composite membranes exhibited very similar proton conductivities and hydrogen crossover as Nafion. However, the fluoride emission rate (from accelerated tests) was lowered by more than 1 order of magnitude upon addition of into the Nafion membrane, suggesting that nanoparticles have tremendous potential to greatly enhance membrane durability.

Pt/C/MnO2 hybrid catalysts were prepared by a wet chemical method. Rotating ring-disk electrode (RRDE) experiments were performed to estimate the amount of hydrogen peroxide (H2O2) formed during the oxygen reduction reaction (ORR) as a function of MnO2 content. Pt/C/ MnO2 (5% by weight of MnO2) hybrid electrocatalysts produced 50% less hydrogen peroxide than the baseline Pt/C electrocatalyst. The hybrid electrocatalysts were used to prepare membrane electrode assemblies that were tested at 90{degree sign}C and 50% RH at open circuit with pure hydrogen as fuel and air as the oxidant. The concentration of F- in the anode condensate over 24 hours was found to be reduced by a factor of 3-4 when Pt/C/MnO2 replaced Pt/C as the catalyst. Through cyclic voltammetry and RRDE kinetic studies, the lower ORR activity of the hybrid electrocatalysts was attributed to catalyst treatment with acid during MnO2 introduction.

Carbon-tungsten oxide (C/WO3), Carbon-phosphotungstic acid (C/PTA) and Platinum/Carbon-PTA (Pt/C-PTA) hybrid catalysts were prepared by wet chemical methods. Rotating ring-disk electrode (RRDE) experiments were performed using these materials to estimate the amount of hydrogen peroxide (H2O2) formed during the oxygen reduction reaction (ORR). C-WO3 15 wt% and C-PTA hybrid catalysts produced 30-40% less hydrogen peroxide than C and Pt/C-PTA had 20-30% less peroxide production than the baseline Pt/C electrocatalyst. The hybrid catalysts were used to prepare membrane electrode assemblies that were tested at 90{degree sign}C and 30% RH at open circuit with pure hydrogen as fuel and oxygen as the oxidant. The concentration of F- in the anode condensate over 24 hours was found to be reduced by a factor of 50-60% when C-WO3 15wt% and C-PTA replaced C as the catalyst.

In this study electrochemical and XAS techniques are combined to monitor in situ oxide growth at long potential holds. The value of the potential has a greater effect than the length of the potential hold for large time scales. Evidence suggests that PtO2 is the dominant oxide phase under the experimental conditions.

The present study aims to address the effect of the uniformity of particle size distribution on Pt stability. A theoretical model based on the chemical reactions of Pt oxidation and precipitation in the membrane is presented. The incorporation of a particle size distribution function and a population balance allows the investigation of different initial particle size distributions. Initial results demonstrate the change of platinum ions concentration across the electrode and membrane and reveal the shift of particle size distribution towards larger diameters under potential hold and potential cycling simulations.

The efficacy of metal oxide particles in mitigating vanadium ions crossover was investigated. 3 wt % SiO2was incorporated within recast Nafion membrane from which membrane electrode assemblies were prepared by painting. The composite membranes exhibited proton conductivities slightly lower (∼54–55 mS cm−1) than Nafion. However, the permeability of vanadium ions was lowered by 80–85%, while the performance was improved. These results demonstrated that loadings of SiO2much lower than previously reported can mitigate vanadium-ion crossover. Additionally the direct application of the catalyst on the membrane was shown to be a viable MEA synthesis option.

This work aims to address the role of particle size distribution on Pt stability. A theoretical model is built based on modified Butler-Volmer equations, platinum oxide surface coverage and interparticle interactions between platinum oxide particles. Preliminary results demonstrate the change in platinum ions concentration across the electrode and membrane and reveal the effect of potential cycling on the particle size. Further research on the effect of particle size and potential cycling on electrochemically active surface area and its comparison with experimental data is in progress.

Preliminary results are presented in this study concerning i) the ex-situ identification of reactive oxygen species (ROS) within a model Fe+2/H2O2 solution using fluorescence spectroscopy; and ii) the effect of cerium oxide particle size on its radical scavenging properties and hence on the fluoride emission rate (FER) of composite Nafion® / CeO2 membranes. On the degradation diagnostics front, it is demonstrated that fluorescence fiber-optic measurements can sense the ex-situ formation of hydroperoxyl (HOO*) radicals in a Fe+2/H2O2 solution through a decrease in the fluorescence intensity in the presence of the radicals. Work to extend these studies for hydroxyl radicals and to achieve in-situ estimation is ongoing. On the degradation mitigation front, it is seen that lowering the CeO2 particle size leads further reduces the FER from composite membranes by 30-50%.

The efficacy of CeO2 nanoparticles in mitigating free radical induced PEM degradation is investigated. Commercially obtained CeO2 and nanoparticles synthesized in-house were incorporated within a recast Nafion® membrane. MEAs were prepared using Nafion® and Nafion®-CeO2 composite membranes (0.5wt%, 1wt%, and 3wt% CeO2). The composite membranes exhibited very similar proton conductivities (~35mS/cm) and hydrogen crossover (~1 mA/cm2) as Nafion®. However, the fluoride emission rate (estimated from accelerated tests) was lowered by more than one order of magnitude upon addition of CeO2 into the Nafion® membrane, suggesting that CeO2 nanoparticles have potential to enhance membrane durability.

The efficacy of CeO2nanoparticles in mitigating free-radical-induced polymer electrolyte membrane (PEM) degradation is investigated. Commercially obtained CeO2and nanoparticles synthesized in-house were incorporated within a recast Nafion membrane. Membrane electrode assemblies were prepared using Nafion and Nafion–CeO2composite membranes (0.5, 1, and 3wt%CeO2). The composite membranes exhibited very similar proton conductivities (∼35mS/cm)and hydrogen crossover (∼1mA/cm2)as Nafion. However, the fluoride emission rate (from accelerated tests) was lowered by more than 1 order of magnitude upon addition of CeO2into the Nafion membrane, suggesting that CeO2nanoparticles have tremendous potential to greatly enhance membrane durability.

Carbon-tungsten oxide (C–WO3)and platinum/carbon-tungsten oxide (Pt∕C–WO3)catalysts were prepared by chemical methods. The WO3loading in the catalyst was 15wt%. C–WO3catalysts produced ∼60%less hydrogen peroxide than baseline Cand Pt∕C–WO3electrocatalysts produced ∼30%less hydrogen peroxide formation than baseline Pt∕C. Membrane electrode assemblies (MEAs) were prepared using Pt∕Cand Pt∕C–WO3electrocatalysts and subjected to accelerated durability tests at 90°Cand 30% relative humidity (RH) at open circuit with hydrogen as fuel and oxygen as oxidant. The fluoride emission rate (in μmolF−∕h-cm2) over 24hwas found to be reduced by ∼70%at the anode and ∼60%at the cathode condensate when Pt∕C–WO3replaced Pt∕Cin the electrode. Fuel cell polarization data was obtained using Pt∕Cand Pt∕C–WO3in the cathode at 80°Cand 75, 50, and 25% RH, with air and oxygen as oxidants and hydrogen as fuel. For all the test conditions, the performance of MEAs with Pt∕C–WO3was found to be lower than that of MEAs with Pt∕C. Through electrochemical impedance spectroscopy experiments and polarization data analysis, the lower performance was attributed to (i)lower catalytic activity, and (ii)higher ionic and transport resistances in the electrodes.

Pt/C/MnO2 hybrid catalysts were prepared by a wet chemical method. Rotating ring-disk electrode (RRDE) experiments were performed to estimate the amount of hydrogen peroxide (H2O2) formed during the oxygen reduction reaction (ORR) as a function of MnO2 content. Pt/C/ MnO2 (5% by weight of MnO2) hybrid electrocatalysts produced 50% less hydrogen peroxide than the baseline Pt/C electrocatalyst. The hybrid electrocatalysts were used to prepare membrane electrode assemblies that were tested at 90{degree sign}C and 50% RH at open circuit with pure hydrogen as fuel and air as the oxidant. The concentration of F- in the anode condensate over 24 hours was found to be reduced by a factor of 3-4 when Pt/C/MnO2 replaced Pt/C as the catalyst. Through cyclic voltammetry and RRDE kinetic studies, the lower ORR activity of the hybrid electrocatalysts was attributed to catalyst treatment with acid during MnO2 introduction.

Carbon-tungsten oxide (C/WO3), Carbon-phosphotungstic acid (C/PTA) and Platinum/Carbon-PTA (Pt/C-PTA) hybrid catalysts were prepared by wet chemical methods. Rotating ring-disk electrode (RRDE) experiments were performed using these materials to estimate the amount of hydrogen peroxide (H2O2) formed during the oxygen reduction reaction (ORR). C-WO3 15 wt% and C-PTA hybrid catalysts produced 30-40% less hydrogen peroxide than C and Pt/C-PTA had 20-30% less peroxide production than the baseline Pt/C electrocatalyst. The hybrid catalysts were used to prepare membrane electrode assemblies that were tested at 90{degree sign}C and 30% RH at open circuit with pure hydrogen as fuel and oxygen as the oxidant. The concentration of F- in the anode condensate over 24 hours was found to be reduced by a factor of 50-60% when C-WO3 15wt% and C-PTA replaced C as the catalyst.