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Investigation Into Strategies for Enhanced Electrocatalytic Activities of Spinel-Based Transition Metal Oxide Nanoparticles

(Georgia Institute of Technology, 2022-12-02) Sewell, Christopher David

As the severity of global climate issues continues to build, the need for clean energy storage and conversion devices has become increasingly pressing. The production of green hydrogen through water electrolysis is a promising route to alleviating these challenges. However, the high cost and scarcity of the state-of-the-art noble metal-based electrocatalysts utilized in such processes represents one of the critical hurdles to be overcome prior to their practical implementation. A promising direction is to utilize transition metal-based nanoparticles (NPs), which offer superior electrocatalytic performance over their bulk counterparts. The work in this dissertation systematically investigates strategies to improve the electrocatalytic performance of transition metal-oxide NPs. Capping the surface of NPs with polymers is widely recognized as an effective means towards their dispersion and stabilization. However, it is often circumvented due to its tendency to lower the electrocatalytic activity of the ligated NPs. In this context, the first systematic investigation into the impact of the chain density and hydrophilicity of the surface-capping polymers, which can be judiciously regulated, on the oxygen evolution reaction (OER) activity is performed. By capitalizing on star-like diblock copolymers as nanoreactors, spinel CoFe2O4 (CFO) NPs permanently ligated with polymers of interest (i.e., varied chain density and characteristic) are crafted. The correlation between the chain density and hydrophilicity of surface-capping polymers and the OER activity of CFO NPs are scrutinized. Intriguingly, decreasing the number of surface-capping chains and increasing the chain hydrophilicity result in significantly decreased overpotential, caused by an increased exposure of the active material (CFO) to the electrolyte and reduced diffusion resistance. This study provides insight into the strategies for mitigating the activity-limiting properties of surface polymers and tailoring the electrocatalytic properties of polymer-ligated NPs. Recently, the use of externally applied magnetic fields has garnered significant attention as a promising strategy to enhance OER electrocatalytic performance. OER exhibits spin-dependent kinetics, producing triplet O2 from singlet reactants (OH-, H2O). Notably, magnetization can reduce this kinetic barrier by aligning the spin ordering of ferromagnetic (FM) electrocatalysts. Unfortunately, some of the most active OER catalysts, namely transition metal oxyhydroxides, are paramagnetic (PM). This can be circumvented by utilizing a spin pinning effect in FM/PM core/shell materials, which has already been successfully demonstrated in a bulk CFO/CoFeOxHy system. In this work, previous research is built upon by examining a similar system at the nanoscale. Star-like block copolymers prepared via sequential atom transfer radical polymerization were successfully utilized as nanoreactors to synthesize CFO nanoparticles. The surfaces of CFO nanoparticles were successfully doped with sulfur under mild conditions, enabling the successful surface reconstruction of S-doped CFO into a more active oxyhydroxide phase. Successful spin-pinning was verified by an observed increase in OER activity following the application and removal of a magnetic field; thus, confirming that spin-pinning remains a viable OER-enhancement technique even at the nanoscale. This study lays the groundwork for future systematic studies on the effects of NP size and core-to-shell ratio on the magnetic field-rendered OER enhancement. In addition to externally applied magnetic fields, other effects can be introduced during electrocatalysis to improve performance. Previous research has found that some spinel NPs, NiFe2O4 (NFO) for example, experience a photothermal effect upon near-infrared light irradiation which promotes the dynamic generation of active OER sites. Thus, in this dissertation, both the magnetic field-based enhancement and photothermal effect are collectively exploited to further improve the OER electrocatalytic ability of NFO NPs. Concurrent application of magnetic field and photothermal effect is demonstrated to further enhance the OER activity of NFO NPs. Interestingly, the significant increase in activity observed was primarily attributed to a greatly promoted surface reconstruction. It is determined that the application of a magnetic field during chronopotentiometry can promote surface reconstruction to a similar degree of inducing the photothermal effect. This work documents a new strategy to induce surface reconstruction in NiFe2O4, opening up the door for future studies employing different electrocatalytic materials and investigating the mechanisms of magnetic-field enhanced surface reconstruction. The findings in this dissertation serve as an important step towards the practical implementation of OER-limited devices, such as water electrolyzers. Various strategies to enhance the OER activity of metal-oxide nanoparticles have been presented. Excitingly, future work can build upon the investigated methods to enable low-cost, low-complexity electrocatalysts to serve as competitive alternatives to state-of-the-art noble-metal based catalysts.
Enhancing the Stability and Performance of Solid Oxide Cells by Tailoring Surfaces and Interfaces through Surface Modification

(Georgia Institute of Technology, 2022-07-21) Kane, Nicholas John

Reversible solid oxide cells (RSOCs) are an extremely promising solution for efficient electric grid storage; however, breakthroughs in materials innovation are required for RSOCs to be implemented on a large scale, as several challenges remain to be fully resolved. The air electrode is one area of focus, as the kinetics of oxygen reduction and evolution reactions are notoriously sluggish, resulting in low energy efficiency. To combat these problems, a surface sol-gel (SSG) process was developed to achieve layer-by-layer deposition of catalytically active catalysts (e.g., PrOx and BaO) on the surface of a porous air electrode, reducing the polarization resistance while increasing the stability of the electrode. For example, the application of an SSG coating of PrOx to a La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) electrode reduced the polarization resistance from 1.136 to 0.117 Ω cm2 at 600 °C and the degradation rate from 1.13×10-3 to 2.67×10-4 Ω cm2 h-1 at 650 °C. The interface between the electrolyte and the air electrode is the other area of focus, where the electrolyte experiences degradation due to exposure to high concentrations of water during water electrolysis. Here, a dense and highly stable electrolyte composition, BaHf0.8Yb0.2O3 (BHYb), was deposited on the surface of a more conductive electrolyte, BaZr0.1Ce0.7Y0.1Yb0.1O3-δ, creating a bilayer electrolyte. The epitaxial, dense, and uniform BHYb layer is effective in preventing electrolyte degradation against high concentrations of steam and CO2 present in the air electrode, greatly enhancing the chemical stability while maintaining high electrochemical performance.
Development of Novel Electrode and Catalyst Materials for Solid Oxide Electrochemical Cells

(Georgia Institute of Technology, 2022-07-14) Zhang, Weilin

Solid oxide electrochemical cell (SOC), which offers a promising solution to a sustainable energy future, is a class of solid-state electrochemical devices for efficient energy storage and conversion. A SOC can operate on the fuel cell mode (solid oxide fuel cell, SOFC) to generate electricity from hydrogen or hydrocarbon fuels. It can also operate on the electrolysis cell mode (solid oxide electrolysis cell, SOEC) to produce valuable fuels by electrolyzing water or carbon dioxide. This dissertation focuses on the development of novel electrode, catalyst, and fabrication techniques for SOCs. The overall study can be separated into four parts. The first study focuses on the development of active and durable air electrode material for intermediate-temperature reversible solid oxide cells. To achieve high round-trip efficiency of SOCs, highly efficient and durable air electrode materials are needed to minimize energy loss associated with oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Here we report a bifunctional air electrode material, PrBa0.9Co1.96Nb0.04O5+δ, demonstrating outstanding electrochemical performance (e.g., achieving peak power densities of over 1.5 and 1 W cm−2, respectively, for Gd0.1Ce0.9O1.95 and BaZr0.1Ce0.7Y0.1Yb0.1O3-δ based fuel cells at 600 ºC) while maintaining excellent stability (e.g., having a degradation rate of 40 mV per 1,000 h for H2O electrolysis cells). The excellent property of the new electrode is attributed to the improved stability from Nb doping and the enhanced electrocatalytic activity from tuning Ba deficiency, as confirmed by experimental results and computational analysis. Following the first study, to lower the operating temperature of SOCs, the second study focuses on the development of triple conducting air electrode materials for low-temperature dual-ion conducting fuel cells. A series of materials candidates were designed by heavily doping transition metal and rare earth metal into BaHf0.8Y0.2O3-δ-based electrolyte material. The optimized composition Ba0.9Pr0.1Hf0.1Y0.1Co0.8O3-δ demonstrates an outstanding electrochemical activity on both BaZr0.1Ce0.7Y0.1Yb0.1O3-δ based symmetrical cells and single cells. X-ray diffraction and transmission electron microscopy results confirm that BPHYC is a mixture of three different phases, consisting of Y doped BaCoO3-δ (BYC), PrBaCo2O5+δ (PBC), and Y doped BaHfO3-δ (BHY). Detailed electrochemical analysis unravels that BYC and PBC phases play a synergistic effect on the ORR kinetics on oxygen-ion conducting cells, and BHY contributes to the proton conduction on proton-conducting cells. The triple conductivity of BPHYC was evaluated by the electrical conductivity relaxation measurement and the isotope exchange diffusion profile measurement. The long-term stability of BPHYC was also confirmed on both symmetrical cells and single cells under typical operating conditions. For the fuel electrode development, the third study focuses on the development of anode catalyst materials for SOFCs operated on hydrocarbon fuels. Conventional Ni-based cermet anode suffers from the coking issue when the hydrocarbon is used as the fuel. In this study, I designed and synthesized Ni and Ru co-doped BaZr0.8Y0.2O3-δ (BZYNR) as a promising anode catalyst material for SOFCs operated on various hydrocarbon fuels. When applied BZYNR on button cells with a conventional Ni-based anode, the single cells can operate on wet iso-octane (with 3 vol% H2O) for over 1,000 hours without obvious coking behavior. BZYNR was further applied on large-scale tubular cells with an effective area of about 38 cm2. World-record power output and durability were demonstrated on iso-octane, ethanol, and methane fuels. Two key properties of BZYNR contributed to its outstanding performance. First is that Ni and Ru cations are highly active sites for the hydrocarbon reforming process. The second is that BZYNR shows good water absorption capability, which benefits the water-mediated carbon removal process. The fourth study focuses on the fabrication techniques to create nanostructured electrodes for SOFCs. Durable, nanostructured electrodes fabricated via a simple, cost-effective method is effective to solve the performance and durability issues for SOFCs. In this work, both the nanostructured PrBa0.5Sr0.5Co1.5Fe0.5O5+δ (PBSCF) cathode and Ni−Ce0.8Sm0.2O1.9 (SDC) anode are fabricated on porous yttria-stabilized zirconia (YSZ) backbone via solution infiltration. Symmetrical cells with a configuration of PBSCF|YSZ|PBSCF show a low interfacial polarization resistance of 0.03 Ω cm2 with minimal degradation at 700 °C for 600 h. Ni-SDC|YSZ|PBSCF single cells exhibit a peak power density of 0.62 W cm−2 at 650 °C operated on H2 with good thermal cycling stability for 110 h. Single cells also show excellent coking tolerance with stable operation on CH4 for over 120 h. This work offers a promising pathway toward the development of high-performance and durable SOFCs to be powered by natural gas.
Enhancing air electrode performance of solid oxide cells by surface modification

(Georgia Institute of Technology, 2022-04-15) Evans, Conor

Reversible solid oxide cells based on proton conductors (P-rSOCs) offer an efficient and clean option for energy storage and conversion. However, one issue holding back this renewable technology is the sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) kinetics that take place at the air electrode. The air electrode in a P-rSOC is also subject to harsh environments (e.g., high concentration of steam) that can cause degradation over time. Catalyst infiltration into the air electrode offers a possible solution to each of these issues. Several catalyst candidates were investigated using the state-of-the-art double perovskite air electrode material, PrBa0.8Ca0.2Co2O5+δ (PBCC), as the air electrode backbone. Symmetrical cells with catalyst coated PBCC electrodes were primarily used to screen catalyst solutions and isolate the air electrode performance. Electrochemical impedance spectroscopy (EIS) was utilized to characterize the electrochemical performance and the long-term stability of catalyst infiltrated symmetrical cells under various testing conditions containing either steam and/or Cr contaminants. Electrochemical performance of single cells with a catalyst coated PBCC electrode was measured in both the fuel cell mode and the electrolysis cell mode. X- ray diffraction (XRD), scanning electron microcopy (SEM), and Raman spectroscopy were used to characterize phase composition, electrode microstructure and morphology, as well as surface chemistry to gain better understanding of the air electrode degradation mechanism during testing. Several catalysts were screened and optimized via symmetrical cell tests, including LaNiO3, La2NiO4, BaCoO3, LaNi0.6Fe0.4O3, La2Ni0.6Fe0.4O4, and PrCoO3. Symmetrical cells infiltrated with a PrCoO3 catalyst demonstrated particularly excellent stability and electrochemical performance (with a polarization resistance as low as 0.147 Ω cm2 and minimal degradation over 500 hours) against various sources of Cr contaminations at steam concentrations as high as 30% at 600 °C. Single cells infiltrated with PrCoO3 exhibit a peak power density of 2.02 W cm-2 at 650°C in the fuel cell mode, a 35.5% increase in performance from the single cells without catalyst modification. When run in electrolysis mode these same infiltrated single cells demonstrate a current density of 3.22 A cm-2 at 650 °C, a 22.4% improvement from the performance of the cells without catalyst modification. The single cell based on a PrCoO3 infiltrated cathode was among the best performing P-rSOCs ever reported in literature
Atomic Level Computational Studies of Ionic Defects and Transport Properties of Solid State Ionic Conductors

(Georgia Institute of Technology, 2020-01-14) Zhang, Lei

Solid state ionic conductors (or electrolytes) are a vital component for electrochemical devices or systems for chemical and energy transformation. The chemical composition, crystal structure, defects, morphology, and electronic structure of these materials greatly affect their electrochemical properties such as ionic and electronic conductivity. Similar to barium zirconate (BaZrO3), barium hafnate (BaHfO3) is one of the most promising proton-conducting electrolytes for solid oxide fuel cells (SOFCs) because of their high proton conductivity at 400~700 °C. In this study, I have investigated dopant solubility, proton concentration, mobility, and chemical stability of A/B-site co-doped BaHfO3 using density functional theory calculations coupled with statistical thermodynamics. Specifically, I have calculated defect formation energy in charged supercells, finite temperature vibrational energy via phonon calculations in the harmonic approximation, proton migration energy via transition state theory, and defect-defect interactions via cluster-expansion method. A wide range of relevant properties are predicted, including the degree of hydration governed by hydration Gibbs free energy, proton diffusion coefficient derived from proton migration barrier search, and defect-defect interactions using cluster expansion method. These properties are sensitive to the type and amount of chemical dopants in the lattice, including Li, Na, K, Rb, and Cs on A-site and Sc, Y, La, Gd, Lu, Al, Ga, and In on B-site. The mismatch in the size of the dopant and the host ion induces local strain or elastic interactions. However, the electrostatic interactions between them are much less dependent on the ionic radius of dopant ions. Accordingly, the dependence of the dopant-proton binding energy on ionic radius of dopant has a “volcano” shape. In addition, the electronegativity of dopant ions also affect the affinity of acceptor-type dopants with donor-type protons. Hydration is promoted by both the A-site and the B-site dopants, although the effect of the latter is less pronounced. In general, a “trade-off” relation between proton concentration and mobility is observed in all cases, regardless of the ionic radius or the lattice site (A- or B-site) of the dopants. Defects play an important role in ionic transport and in enhancing catalytic activities for chemical and energy transformation processes. Thus, it is crucial to understand how to effectively enhance ionic transport by rationally design preferred defect structures, including 0D (point defects such as vacancies), 1D (dislocation), and 2D (grain boundary) defects. For example, local ion segregation may result in a space charge region, leading to accumulation of mobile charge carriers or improved mobility near those 1D/2D defects. The effect of the space charge layer, strain near 1D/2D defects, as well as collective defect-defect interactions pose an extreme challenge for both experiments and computations. In this study, the effect of an edge dislocation in Y:BaZrO3 on oxygen ion transport is evaluated. To probe the ion mobility, a reactive molecular dynamics simulation based on ReaxFF is utilized to simulate the super-large Y:BaZrO3 supercell with two edge dislocations. Radial distribution functions and thermal/chemical expansion coefficients are used to benchmark the local and global structure properties, and mean-square displacements are used to calculate diffusivity and conductivity. Dislocation is found to lower the activation energy of ionic transport, possibly because of distinct oxygen cage structures locally at the dislocation core. However, optimal Y% for oxygen ion conductivity is shifted to higher levels with increasing temperature. This could be due to the weakening of Y’s electrostatic “trapping effect”. Besides materials chemistry and microstructural features, the mechanical strain is another factor affecting ionic properties. Ceria (or CeO2) is a prototypical ionic material for catalyst and electrolyte applications. Chemo-mechanical coupling in ceria significantly affect the bulk defect properties of ceria. In this study, the effect of chemo-mechanical coupling is extended from the bulk to the (111) surface of ceria. There have been extensive theoretical and experimental research on the configurations of vacancies and polarons on the (111) surface, the dominantly exposed surface, which is crucial to surface catalytic activity. It was reported that surface oxygen vacancy on ceria’s (111) surface is not necessarily the most stable vacancy; however, the sub-surface vacancy could be. Similarly, polarons are not necessarily at the 1st-nearest-neighbor (1NN) of the corresponding vacancy either; they could be at the 2nd-nearest-neighbor (2NN). All those counter-intuitive phenomena were unveiled and validated both theoretically and experimentally. Inspired by previous research, I have identified a unique way of tuning defect configurations by applying tensile and compressive epitaxial strain on (111) slab. Across the magnitude of the applied strain from -5% compression to +5% tension, stability relationships of the surface vs. the sub-surface vacancy, the 1NN vs. the 2NN polaron, and the vacancy monomer vs. the dimer are surprisingly reversed. Elastic, electrostatic and electronic excitation energies are found to be dependent on defect-configuration. This gives us a new perspective to interpret the various vacancy patterns observed on (111) surface of the prepared ceria samples.
Enhancing Platinum-based Nanoarchitectures Electrocatalytic Activity and Durability for Oxygen Reduction Reaction at PEMFC: Investigating the Dual Role of Graphene as a Catalyst Support and Protective Cap

(Georgia Institute of Technology, 2020-01-03) Mahmoud, Ali Ahmed Abdelhafiz

Energy demand-supply relationship is a big concern with world’s consumption increased over 65% through the past two decades. Polymer Electrolyte Membrane Fuel Cell (PEMFC) possess high energy density with zero carbonaceous emissions. One of the major challenges in PEMFC is concerned with the oxygen reduction reaction (ORR) at the cathode side, where low mass activity and poor stability are key challenges to overcome. Catalyst architectures are composed of two distinctive components: catalyst material and catalyst support. Herein, our objectives are enhancing catalyst stability, catalyst-support interaction, and maximizing catalyst active surface area. In the presented thesis, strain-tuned atomically precise hybrid catalyst architectures are synthesized. Mixed single atomically dispersed up-to a few thick atomic layers Pt catalyst architecture are synthesized using electrochemical layer by layer synthesis or magnetron DC-sputtering techniques. Graphene, due to its mechanical and chemical stability, is used to demonstrating its role as a platform for Pt growth (i.e. catalyst support) and as a protective cap. Graphene/Pt vicinity dictates Pt adatoms structure. Templated Pt adatoms growth is dictated by graphene epitaxy. TEM analysis shows ripening-free of low-dimensional Pt adatom deposited on graphene, where Pt is fully wetting graphene at ~1 nm thick layer over 1 cm2 area. Pt/Graphene epitaxy induces compressive strain on Pt-Pt bond distance up to 4%. Compressive strain enhances ORR activity due to down-shifting the d-band center of Pt adatoms, weakens reactions intermediates adsorption at Pt surface. Templated Pt adatoms grown on graphene shows higher stability due to covalent chemical bond formation between Pt adatoms and underlying graphene substrate. Single layer graphene utilized as a protective cap shows chemical transparency to ORR electroactivity and suppresses catalytic deactivation, wherein graphene does not restrict the access of the reactants but does block Pt from dissolution or agglomeration. Single layer graphene cap enables survival of Pt active surface area by almost zero-loss after 1K testing cycles with on observable mass activity loss within marginal error bars. Sandwiching Pt adatoms between two sets of multi-layered graphene sheets boosts ORR activity and catalyst stability. Thickness of graphene cap influences ORR activity, 3-layers graphene thick marks the threshold to observe ORR activity, where 5-layers graphene shows blockage or ORR activity. Three-layers graphene/Pt Sandwich retains 460% of ECSA after 15K testing cycles and 975% higher mass activity, compared to state-of-the-art commercial Pt/carbon catalyst. Ex-situ Raman analysis suggests catalyst degradation to occur when sufficient point defects are generated within graphene structure, through which Pt single atoms hop through towards the surface. DFT based calculations suggests that dissolution of trapped Pt adatoms at defect-center is activated by Pt clustering right underneath the defect.
A new family of proton conducting electrolytes with enhanced stability for reversible fuel cell operation: BaHfxCe0.8-xY0.1Yb0.1O3

(Georgia Institute of Technology, 2019-08-21) Murphy, Ryan Joe

Solid oxide fuel cell (SOFC) technology has the potential to be one of the most efficient energy conversion technologies and the same technology can be used to efficiently produce several chemical species such as hydrogen and syngas through reverse operation, known as solid oxide electrolysis cells (SOEC). However, the long-term performance of these systems is often limited by degradation of the electrolyte. In this study, a new family of proton conducing electrolyte materials, BaHfxCe0.8-xY0.1Yb0.1O3 (BHCYYb), have been developed, which demonstrate much improved stability while maintaining similar or higher conductivities than current state-of-the-art materials. The performance of the SOFCs based on these new electrolytes rivals that of the current best performance reported in literature, but with better durability. In addition, BHCYYb has been shown to possess higher stability through long term chemical stability and conductivity tests. Further, solid oxide cells based on BHCYYb have also been operated in the reverse mode, as SOECs for CO2-H2O co-electrolysis. Finally, a number of dopants have been introduced to the BaHfO3-based system in order to further improve the conductivity and stability.
Stability of double perovskite cathodes under high humidity for solid oxide fuel cells

(Georgia Institute of Technology, 2019-05-06) Liu, Yuchen

Solid Oxide Fuel Cells (SOFCs) can directly convert a wide variety of fuels to electricity efficiently. They can also be run in reverse as Solid Oxide Electrolysis Cells (SOECs) to produce hydrogen (and carbon-containing fuels) from electrolysis of water (and carbon dioxide). However, the kinetics of oxygen reduction reaction (ORR) on the cathode is often hindered by various contaminants, which may react with the cathode to form insulating phases and degrade fuel cell performance. The stability and performance of the cathode in moisture is critical to the cell performance as SOFCs and SOECs. Several state-of-the-art cathode materials are investigated in a high moisture environment to uncover their performance and degradation mechanism. First, powders of electrode materials were analyzed for any degradation before and after long-term moisture exposure using XRD to probe the bulk and Raman Spectroscopy to probe the surface. SEM was also used to characterize any morphological changes during the exposure. Second, electrochemical impedance spectroscopy (EIS) was used to monitor the long-term performance of symmetric cells under various conditions. Finally, current-voltage relationships of symmetric cells were acquired under typical operating conditions for SOFCs and SOECs to determine the polarization resistance, stability and durability of the cathode materials.
Development and characterization of materials for intermediate temperature solid oxide fuel cell anodes

(Georgia Institute of Technology, 2019-04-30) Deglee, Ben

Solid Oxide Fuel Cells (SOFCs) are devices capable of directly converting chemical energy into electrical energy through high temperature electrochemical oxidation of fuels, but there remain serious obstacles before these devices can be fully implemented into the modern energy infrastructure. The operation of SOFCs with hydrocarbon fuels has the highest potential for commercial impact, but the activity of state-of-the-art materials toward these fuels is relatively low compared to hydrogen, and SOFCs can quickly degrade due to the deposition of solid carbon (coking). Lowering SOFC operating temperatures to less than 600 °C would expand the application of SOFCs while dramatically reducing system complexity and cost, but device performance at these temperatures remains prohibitively low. To address these obstacles, this work focuses on two key issues in SOFC technology development: improvement of SOFC materials and advancement of SOFC characterization techniques. First, a high performing SOFC was designed and demonstrated, uniquely suited for low temperature direct methane operation through the addition of an internal reforming catalyst layer. In situ spectroscopy was used extensively to evaluate the defect and surface structure of the reforming catalyst, directly relating the material structure to device performance. The second issue was addressed through the development of a novel testing platform for quantitative comparison of different anode surface coatings, as well as the design and fabrication of new operando equipment which increases the current testing capability of the SOFC community.
Towards rational design of solid oxide fuel cell electrodes through surface modification

(Georgia Institute of Technology, 2017-11-14) Doyle, Brian

Solid oxide fuel cells represent a scalable energy generation technology capable of operating at high efficiencies on multiple fuel sources. However, wide-spread implementation of SOFCs has been limited by the high degradation rate at current operating temperatures of 800-1000°C. Lowering the operating temperature to an intermediate range of 500-700°C will decrease the degradation phenomena, but will also decrease the catalytic activity of the electrodes. Modifying the surface of the electrodes is one method to increase the catalytic activity at these relatively low operating temperatures. This dissertation seeks to understand the role of surface modification on solid oxide fuel cell electrodes through conformal and non-conformal coatings. The first part of this dissertation demonstrates an asymmetric cell testing platform that is used to better understand the effects of conformal film deposition. Depositing a conformal thin film into a porous cathode is nontrivial and requires exhaustive optimization of either solution or gas phase deposition techniques. Even then, if the backbone material and the coating material aren’t very similar (in crystal structure, thermal expansion, etc), then the film will no longer be conformal after reaching SOFC operating temperatures. The asymmetric testing platform in this work was designed to focus on the effect of the thin film modification, which was accomplished by depositing a dense LSCF cathode on one side of an SDC electrolyte support with an accompanying porous LSCF counter electrode. Because of the high surface area of the counter electrode, the polarization resistances measured were dominated by the dense LSCF thin film. The planar dense film allows for precise control over the modification with conformal thin films via RF sputtering. The first part of the dissertation describes the fabrication and electrochemical characterization of this testing platform, which demonstrated the ORR activity was the dominant feature in the impedance spectra. The second part of the dissertation describes the surface modification with undoped ceria and samarium doped ceria. First, infiltration was used to modify the surface and it was seen that a change in morphology influenced the ORR activity. More specifically, for the undoped ceria, a more conformal morphology as opposed to a more dispersed, nanoisland morpohology lead to lower impedance for the ORR. Using the asymmetric testing platform and sputtered ceria, it was found that the thickness of the conformal ceria influenced the ORR. Thinner films showed an increase polarization resistance, while thicker films showed a decreased polarization resistance. The increase in polarization resistance for the thinner films was explained by an increase in vacancy concentration as demonstrated through comparison of the impedance behavior under bias to a doped ceria thin film. Second, it was found infiltration with samarium doped ceria decreased the polarization resistance. Interestingly, the performance increase was independent of the mol% of the samarium doped into ceria. This goes against the conventional thinking that increasing ionic conductivity (by increasing samarium mol %) will lead to increasing surface exchange properties. Thin film conformal deposition of 20SDC demonstrated an overall increase in polarization resistance with increasing resistance correlating to film thickness. These last two results suggest that the ionically conducting surface modification reduces the oxygen through a surface mediated process that requires high surface nanoparticles The third part of the dissertation describes the work using praseodymium doped ceria as the modification material to better understand the role of ionic and electronic conductivity in the ORR catalytic activity. Doping praseodymium into ceria increases both the ionic and electronic conductivity. Through infiltration, it was found that the optimal performance occurs at 50 mol% praseodymium in ceria even though 70 mol % exhibits higher electronic and ionic conductivities. Through XPS and TGA, it was found that amount of Ce3+ (i.e. reduced ceria) changes non-linearly with praseodymium dopant concentration. The 50 mol% doped ceria showed more Ce4+ available relative to the 30 and 70 mol% praseodymium concentration. Thus, it was found that oxygen ion vacancy concentration and electronic conductivity are not the only material properties relevant to increasing ORR activity. Instead, the results indicate a more nuanced view of oxygen reduction reaction and the correlation to bulk material properties. In the end, this work describes a platform for the characterization of conformal thin film surface modification and demonstrates the potential to increase material performance beyond bulk material properties. Importantly, this work has shown the nuanced performance enhancement beyond traditional correlations to ionic and electronic conductivity.