Activity and Durability Insights for Atomically Dispersed (AD)Fe-N-C Oxygen Reduction Catalysts

The effective utilization of clean energy and finding alternatives to fossil resources are highly important to ensure the sustainability of human society and are always among the major goals of both chemistry and material science research. Advanced electrochemical devices, such as fuel cells, water electrolysers and metal-air batteries, represent the most promising strategies for clean-energy utilization. In an electrochemical device, the redox reactions are spatially separated by a membrane, allowing direct extraction/transfer of electrons at an electrode-electrolyte interface, which leads to higher intrinsic energy conversion efficiencies, milder process conditions, easy product separation and excellent design features for coupling to renewable energy infrastructure. The performance of such electrochemical processes is fundamentally determined by the physicochemical properties of the electrochemical interfaces, encompassing both the electrocatalyst and the structure of the adjacent electrochemical double layer. Specifically, electrocatalysts play key roles in electrochemical reactions and often limit the performance of entire systems due to their insufficient activity, low durability or high cost. Ideally, the rate, efficiency, and selectivity of the above electrochemical reactions can be substantially improved by developing high-performance electrocatalyst. One of the central tasks for chemists and material scientists is to design and fabricate the high-efficient efficiency but low-cost electrocatalysts systems. The current promising electrochemical reactions mainly focus on the realization of the reversible conversion between chemical and electricity energy, e.g., the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen oxidation reaction (HOR), and hydrogen evolution reaction (HER). Coupling of the above electrochemical reactions provide a solid foundation for various essential electrochemical devices, such as direct hydrogen fuel cells (HOR + ORR); electrolysers (OER + HER); rechargeable zinc (Zn)-air battery (ORR + OER). Therefore, this thesis aims to design and synthesize high-performance electrocatalysts for HER, ORR and OER based on earth-abundant materials with proper hierarchical 2D or 3D nanostructures. Combined with the advanced characterization techniques and density functional theory (DFT) calculations, the relationship between the electrochemical activity and active sites of these earth-abundant electrocatalysts were detailedly explored and confirmed. Furthermore, to emphasize the hierarchical 2D or 3D nanostructures, the actual performance of these electrocatalysts was all evaluated in practical devices including Zn-air battery and proton exchange membrane fuel cell (PEMFC), specifically as follows: (1) The vast majority of the reported HER electrocatalysts performs poorly under alkaline conditions due to the sluggish water dissociation kinetics. In the first work, a hybridization catalyst construction concept is presented to dramatically enhance the alkaline HER activities of catalysts based on 2D transition metal dichalcogenides (TMDs) (MoS2 and WS2). A series of ultrathin 2D-hybrids are synthesized via facile controllable growth of 3d metal (Ni, Co, Fe, Mn) hydroxides on the monolayer 2D-TMD nanosheets. The resultant Ni(OH)2 and Co(OH)2 hybridized ultrathin MoS2 and WS2 nanosheet catalysts exhibit significantly enhanced alkaline HER activity and stability compared to their bare counterparts. The combined theoretical and experimental studies confirm that the formation of the heterostructured boundaries by suitable hybridization of the TMD and 3d metal hydroxides is responsible for the improved alkaline HER activities because of the enhanced water dissociation step and lowers the corresponding kinetic energy barrier by the hybridized 3d metal hydroxides. (2) Nitrogen-coordinated iron atoms on carbon matrix (Fe-N-C) materials are the most active Pt-group-metal-free ORR catalysts but still suffering their low stability and relatively lower activity compared to platinum-based materials. In the second work, Fe and Ni dual sites atomically dispersed in hierarchically ordered macroporous carbon support (Fe-Ni/N-HOMC) was designed and successfully prepared. Isolated atomic Fe- N4 and Ni-N4 active sites were confirmed via various characterizations. The ORR activity and stability of Fe-Ni/N-HOMC in both acid and alkaline electrolyte were much higher than commercial Pt/C and the mono-Fe doping counterpart, which was among the state-of-the-art ORR electrocatalysts. In addition, this 3D ordered interconnected macroporous structure with abundant mesopores and micropores could greatly increase the accessible ORR active site and also enhance the mass transport during the ORR process. When employed as cathodes for PEMFC, we found the excellent ORR activity of Fe-Ni/N-HOMC was completely translated to the cathode in the fuel cell. (3) High-performance bifunctional electrocatalysts with ORR and OER activity is the key to developing efficient rechargeable Zn-air batteries. In the third work, a high-performance bifunctional electrocatalysts for both OER and ORR were synthesized via further hybridizing as-prepared Fe-Ni/N-HOMC with NiFe layer double hydroxides (LDHs). Layered double hydroxides (LDHs) have been reported to be promising OER electrocatalysts with ultrahigh OER performances. The as-synthesized new composites exhibited almost the same ORR activity as Fe-Ni/N-HOMC, revealing that hybridization of NiFe-LDHs would not deteriorate the initial ORR activity. Moreover, the remarkable enhancement of OER activity was observed after the hybridization, which was attributed to the strong coupling of uniformly dispersed small NiFe-LDH nanoparticles with the carbon substrate. The prototype Zn-air battery was assembled using these new composites, which displayed the ultralow voltage gap and long-term stability. (4) Compared with Fe-N-C or Co-N-C based ORR electrocatalysts, the Cu-nitrogen-carbon composites were attracted little attention. However, the natural multicopper oxidases (MCOs) enzymes, such as laccase, can serve as efficient ORR catalyst with almost no overpotential. Inspired by their tris-copper centers in MCO, one novel Cu-nitrogen-carbon composite (Cu SAs/N-CS) with atomic Cu coordination sites were synthesized via the pyrolysis of the Cu-involved metal-organic-framework. The copper contents in Cu SAs/N-CS reaches as high as 3.17 wt.%, and the average distances of adjacent copper sites was around only 3.1 Å. Due to the synergetic effect of abundant single atomic copper active sites with closer distance and ultrathin carbon nanosheet structure, Cu SAs/N-CS exhibited superior ORR activity exceeding commercial Pt/C catalyst, methanol tolerance, and long-term stability in both alkaline and neutral electrolyte. In summary, four kinds of new composites were successfully designed and prepared as high-performance electrocatalysts for HER, ORR and OER. Multi-dimensional heterostructures, atomic metal coordination sites and 3D hierarchically porous structure were designed and observed, which contributed greatly to improve activities of these composites. This thesis suggests several new viewpoints in the design of electrocatalysts based on earth-abundant materials: (i) offering new strategies for the preparation of novel 2D and 3D heterostructures as electrocatalysts; (ii) expanding methods for the synthesis of atomic metal coordination sites and evaluating their activities for ORR; (iii) evaluating the practical performances of achieved electrocatalysts in proton exchange membrane fuel cell and Zn-air battery; (iv) attempting to explain reaction mechanisms of some electrocatalysts by DFT calculation.

The activity of oxygen reduction reaction (ORR) catalysts often determine performance of polymer electrolyte fuel cells (PEFCs) as measured by their power output, open circuit voltage, and fuel conversion efficiency. Currently, Pt-nanoparticle catalysts, either supported on high surface-area carbons or prepared in a form of contiguous thin layer on conductive or non-conductive supports, represent the state of the art in ORR electrocatalysis at the PEFC cathode. However, the high and variable price and scarceness of Pt have limited its widespread implementation in the -temperature fuel cells to date, especially in automotive transportation. Under these circumstances, platinum group metal-free (PGM-free) ORR catalysts have received growing attention in recent years as a possible replacement for Pt-based formulations. The progress achieved since the development of the first nature-inspired electrocatalysts of oxygen reduction in the seminal work by Jasinski in the 1960s (Nature 201, 1212, 1964), which mostly happened through the broad implementation of the high-temperature synthesis approach, makes replacement of Pt in ORR electrocatalysts with earth-abundant elements, such as Fe, Co, N, and C, a realistic possibility. In this this presentation, we will summarize recent progress in research targeting development of high-performance PGM-free catalysts for oxygen reduction reaction (ORR) at Los Alamos National Laboratory. Two approaches will be discussed in a greater detail: (i) the approach involving fine-tuning of the catalyst porosity and surface area using pore-forming compounds and (ii) the method specifically focusing on the development of atomically dispersed transition metal moieties and avoiding the formation of transition metal-rich nanoparticles during the heat treatment of catalyst precursors. We will demonstrate the impact that porosity/surface area optimization, through the use of either pore formers (cyanamide, ZnCl2) precursor templating (metal organic frameworks) or both, can have on the fuel cell performance of PGM-free catalysts. We will also show how modifications to the electrode structure through the change in the ionomer content and ionomer equivalent weight can lead to substantial improvements in the fuel cell performance at both low- and high current densities (aerial power density of more than 0.50 W/cm2 in H2-air testing at 80°C). Finally, we will recapitulate the challenges still facing PGM-free research that, in spite of all the progress achieved in recent years, is yet to produce materials capable of competing with the incumbent Pt-based catalysts in terms of oxygen reduction activity, performance durability, and cost (specifically, when extended to the overall cost of a fuel cell stack). Acknowledgement Financial support for this research by DOE-EERE through Fuel Cell Technologies Office is gratefully acknowledged.

Nuclear resonance vibration spectroscopy (NRVS) is a novel technique capable of probing vibrational modes of Fe atoms in samples enriched in the Mössbauer-active nucleus of 57Fe. Compared to other vibrational spectroscopies, such as infrared or Raman, NRVS is not subject to the optical selection rules, affording full vibrational spectrum with limited spectroscopic noise. The NRVS intensity is directly related to the magnitude and direction of the motion, adding a unique quantitative capability to the spectral analysis. The technique provides insights into the dynamics of Fe atoms in the Fe-N-C catalysts for oxygen reduction reaction (ORR), which is not offered by other spectroscopic methods such as x-ray absorption spectroscopy (XAS), most commonly used for characterizing the atomic structure of Fe-sites in this class of platinum group metal-free (PGM-free) ORR catalysts. For NRVS to be successful, it is critical for iron in the catalyst to remain in a single chemical form and to minimize contribution to the spectra from complex Fe compounds such as Fe-rich nanoparticles and clusters, routinely present in iron-based PGM-free catalysts. Since NRVS relies on the Mössbauer effect, a studied catalyst needs to be enriched in 57Fe to maximize the signal-to-noise ratio. In this study, an (AD)Fe-N-C catalyst, fully 57Fe-enriched and containing exclusively atomically dispersed Fe sites, was synthesized from a metal organic framework (MOF) precursor. As a heterogeneous electrocatalytic process, ORR is a surface reaction. Demonstrating the presence of surface Fe and providing its chemical characteristics thus represent a major step towards a better understanding of the origins of the catalytic activity of Fe-N-C catalysts. While fundamentally a bulk technique, NRVS can be made surface-specific when combined with molecules or ions capable of selectively interacting with Fe sites on the catalyst surface. The use of molecular or ionic surface probes such as nitric oxide (NO, an O2 analog) or nitrite anion (NO2 -) allows for the discrimination between the bulk iron and surface Fe species of interest to ORR electrocatalysis. In this talk, we will summarize our NRVS study of the (AD) Fe-N-C ORR catalyst for oxygen reduction, which provides new and important information about the nature of Fe sites as the most likely active centers for oxygen reduction reaction on Fe-based ORR catalysts. Acknowledgements This research has been supported by DOE Fuel Cell Technologies Office through Electrocatalysis Consortium (ElectroCat). It used resources of the Advanced Photon Source (APS) at sector 3, a U.S. Department of Energy (DOE) Office of Science User Facility. Microscopy was performed as part of a user project supported by Oak Ridge National Laboratory’s Center for Nanophase Materials Sciences, a DOE Office of Science User Facility.

Over the last two decades, platinum group metal-free (PGM-free) catalysts are attracting increasing attention and finding applications in several important process across many electrochemical energy technologies. Among those PGM-free materials, atomically dispersed (AD) transition metal-nitrogen-carbon (M-N-C) catalysts are gaining exceptional popularity as they demonstrate very high (for this class of materials) activity in oxygen reduction reaction (ORR)1 and are the only cathode catalysts suitable for both proton exchange membrane fuel cells (PEMFC) and alkaline, including anion/hydroxyl exchange membrane fuel cells (AFC, AEMFC/HEMFC). Over the last few years, M-N-C catalysts have shown promising activity in carbon dioxide reduction reaction (CO2RR).2 In this case, varying the transition metal in M-N-Cs opens routes for controlling the selectivity towards a list of C1 and C2 products. There are recent reports on catalytic activity of AD M-N-C materials in direct electro-reduction of molecular nitrogen (N2RR) or reactions of reduction of nitrates, nitrites or various nitrogen oxides (NOx). We have systematically investigated all these processes having as a base the M-N-C catalysts synthesized by sacrificial support method (SSM) – a hard template approach with transition metal salt and charge-transfer organic salt (nicarbazin) mixed by ball-milling, pyrolyzed at high temperature in inert atmosphere and then etched in HF after cooling. In most cases a secondary (similar) pyrolysis was performed to refine the material and ensure its AD character.The makeup and structure of the active site/sites of the AD M-N0C electrocatalysts, including geometry (coordination) and chemistry (composition and oxidation state) remain contentious to this day. There is an emerging agreement however, that the transition metal (at least for the 2nd row transitions meals) is immediately associated with (liganded by) the nitrogen functionalities, displayed on the surface if the carbonaceous substrate. It is almost universally accepted that N-coordinated AD transition metal ions, either as in-plane or edge-type defect in “graphene” sheet, are the main/principal active sites. This is often combined with a broadly accepted hypothesis that micro-porous surface area plays a critical role forming edge-type, intercalational active sites while meso-porous interface is most-likely associated with the in-plane, substitutional AD metal sites. Candidate structures participating in reativity towards O2, CO2 or nitrogen species include a list of nitrogen-containg and oxygen-containng moeties in the carbonaceous matrix. The carbon itself displays various degrees of graphitization, depending on the transition metal used in M-N-C synthesis. Additional complexity in this calss of caralysts study comes from the fact that many samples are not strictly AD materials. They often contain incorporated metal nano-particles, corresponding (native) oxides and/or carbides and nitrides (oxocabides and oxonitrides have been observed as well).These “unrefined” M-N-C materials are often used in practice and the corresponding nano-particle components of the de-facto nanocomposites do alter substantially the reactivity and selectivity of the catalysts in all these electro-reduction reactions.This talk discusses the mechanistic aspects of M-N-C catalysts in ORR, CO2RR, N2RR and electroreduction of nitrogen-containing oxo-species, obtained when cross-referencing electrochemical activity results obtained in rotating disk and rotating ring-disk electrodes setting (RDE/RRDE) with those observed in near-ambient pressure X-ray photo-electron spectroscopy (NAP-XPS) and supported by density functional theory calculations of the reagents adsorption on AD transition metal or nitrogen- or oxygen-containing moieties from the carbonaceous matrix of the M-N-Cs. The later are of particular importance as significant reactivity has been observed for most of those processes when metal-free, nitrogen-doped carbon (N-C) catalysts are used.3 We will present a case that outlines the reactivity of M-N-C in those important electro-reduction reactions in terms of (i) role of the AD transition metal, (ii) role of the surface N-groups as co-catalysts/alternative sites (iii) role of surface oxides as co-catalysts or hydrophilic/hydrophobic properties descriptor, the last being also critically dependent on morphology.4

Platinum group metal-free (PGM-free) catalysts for oxygen reduction reaction (ORR) in polymer electrolyte fuel cells have emerged as a promising alternative to PGM-based catalysts thanks to their abundance in the Earth crust and, consequently, low cost. Metal-nitrogen-carbon (M-N-C) catalysts possibly represent the most attractive PGM-free ORR materials. However, despite the significant progress accomplished in M-N-C catalyst development over the past two decades, this class of materials continues to face challenges that need to be overcome to narrow the performance gap to PGM-based catalysts.[1] Our team has made significant efforts to improve the activity and stability of M-N-C catalysts by developing novel synthesis approaches, such as the ‘dual-zone’ synthesis, targeting specifically improvements in catalyst stability.[2, 3] We have also established standardized protocols for the activity and stability evaluation of PGM-free catalysts under relevant operating conditions of the fuel cell.[4] Additionally, our modeling of PGM-free M-N-C ORR electrocatalysts has provided much needed insight into the materials and helped with their optimization. We have utilized machine learning methods coupled with high-throughput synthesis and characterization to optimize the conditions for a variety of synthesis approaches, which has led to substantial increase in experimentally realized activity.[5, 6] Our prior fundamental studies of ORR activity [1, 2, 7, 8] and materials stability [9] at the density functional theory (DFT) level are actively being linked to achieve simultaneously high activity and long-term stability through a Pareto optimization. Coupling machine learning and DFT efforts is presently underway.In this talk, we will summarize our recent progress in the development of PGM-free M-N-C catalysts for ORR, focusing on improvements in catalyst activity and stability from both experimental and theoretical perspectives. We will highlight various synthesis strategies for improving catalyst activity and stability, and key design principles for M-N-C catalysts, learned from DFT calculations and machine learning-driven, high-throughput catalyst synthesis. We will also discuss the challenges and opportunities in the development of PGM-free catalysts for ORR. Overall, PGM-free catalysts represent a promising pathway for the advancement of low-cost and efficient fuel cell technologies. References Martinez, U. et al., J. Electrochem. Soc., 2019. 166, F3136.Chung, H.T. et al., Science, 2017. 357, 479.Zelenay, P. and D. Myers, ElectroCat (Electrocatalysis Consortium); U.S. Department of Energy Hydrogen and Fuel Cell Program Annual Merit Review 2019. https://www.hydrogen.energy.gov/pdfs/review19/fc160_myers_zelenay_2019_o.pdf.Zhang, H. et al., Nat. Catal., 2022. 5 (5): 455.Kort-Kamp, W.J.M. et al. . J. Power Sources, 2023. 559: 232583.Karim, M.R. et al., ACS Appl. Energy Mater.. 2020. 3 (9): 9083.Holby, E.F., Curr. Opin. Electrochem., 2021. 25, 100631.Anderson, A.B. and E. F. Holby, J. Phys. Chem. C, 2019. 123 (30): 18398.Holby, E.F., G. Wang, and P. Zelenay, ACS Catal., 2020. 10 (24): 14527.

Polymer electrolyte fuel cells (PEFCs) are a key technology to realize a hydrogen-based economy in the transportation sector, expected to significantly reduce greenhouse gas emission. Platinum (Pt) continues to be the electrocatalyst of choice for oxygen reduction reaction (ORR) in PEFCs, despite the fact that the scarcity, high cost, and monopolized global distribution of this metal severely impede its large-scale commercialization. As an alternative approach, substantial efforts have been made to move towards PGM-free catalysts, the best performing of which are heat-treated iron, nitrogen, carbon (Fe-N-C) materials. While promising, the Fe-N-C catalysts face significant challenges on the way to becoming viable. One of the challenges is the need for identifying the ORR active site as a prerequisite for further development of Fe-N-C catalysts. The nature of the active site has puzzled researchers for decades, with the very presence of Fe being often questioned in the highly acidic environment of the PEFCs. Demonstrating the presence of surface Fe and its coordination environment would thus represent a major step towards a better understanding of the origins of catalytic activity in PGM-free catalysts. In this work, we applied Fe-specific characterization techniques, nuclear resonance vibrational spectroscopy (NRVS) and Mössbauer spectroscopy (MS) for the purpose of detecting Fe on the surface of Fe-N-C catalysts. While NRVS and MS are bulk methods, the use of a differential technique, in which the spectrum for catalyst recorded without an Fe-specific surface probe is subtracted from the probe-treated material, allows for obtaining spectrum representative of the surface Fe only. In the case described in this presentation, we applied this differential technique using NO (an O2 analog) as a probe of the surface Fe. Then, by combining the NRVS and MS signatures with DFT modeling we were able to obtain electronic and structural information for the surface Fe sites. For the described approach to be successful it is critical for Fe in the catalyst to remain in a single chemical form, relevant to the ORR. A majority of PGM-free synthesis methods based on heat-treatment of a mixture of iron, nitrogen, and carbon yield highly heterogeneous materials, containing Fe in various chemical forms, including in particular Fe-rich nanoparticles. These nanoparticles contribute to the NRVS and MS signals, making detection of the ORR-relevant atomically dispersed surface Fe species difficult or altogether impossible. To address this challenge, LANL recently developed a nanoparticle-free, metal organic framework (MOF)-derived PGM-free ORR catalyst, (AD)Fe-N-C. For the purpose of NRVS and MS experiments, this catalyst was also fully enriched with the 57Fe isotope of iron. The (AD)57Fe-N-C catalyst was then treated with NO as a probe of surface Fe sites and characterized using differential NRVS and MS. In this presentation, we will summarize the results of NRVS and MS experiments that attest to the presence of Fe sites on the surface of the atomically dispersed Fe-N-C catalysts for ORR. Acknowledgements This research is supported by DOE Fuel Cell Technologies Office, through the Electrocatalysis Consortium (ElectroCat). This research used resources of the Advanced Photon Source (APS) at sector 3, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract DE-AC02-06CH11357.

Platinum-based catalysts play an important role in electrocatalysis of the generally sluggish oxygen reduction reaction (ORR) at the polymer electrolyte fuel cell (PEFC) cathode. However, the expensive Pt-based catalysts contribute to more than 40% of the cost of the PEFC stack for automotive applications, constraining the commercialization of fuel cell power systems.1 To lower the fuel cell catalyst cost, non-platinum group (non-PGM) catalysts have drawn attention as a promising low-cost replacement for Pt-based ORR catalysts.2The development of non-PGM catalysts have been the focus of significant research effort for years, aimed at obtaining active and durable materials, typically via the heat treatment of N-containing organic compounds and transition metal salts in inert atmosphere. One of the keys to the ultimate success of those efforts is the selection of suitable nitrogen precursors for the synthesis. In this presentation, we will demonstrate a rational design of polyaniline-type (PANI-type) polymers, as the precursors for active and durable non-PGM catalysts for oxygen reduction. Recently, we have developed well-performing non-PGM catalysts by heat-treating PANI, Fe salts, and carbon in N2 atmosphere.3 The studies of this and similar non-PGM catalysts suggest that Fe-N defects in a carbon matrix may be vital for the ORR activity of such catalysts.4 If so, it is essential to promote the formation of Fe-N bonds during the catalyst synthesis. However, current approaches are still quite rudimentary, largely limited to screening of N-rich precursors and optimizing the Fe salt loading. The rationale behind selecting N-rich precursors is still lacking. In many cases, the N-containing groups in polymers, such as PANI, have poor affinity to Fe salts limiting Fe-N bond formation in the polymer precursor before the heat treatment. An approach to increasing the population of such bonds will be given in this presentation. The subject of this study are PANI-type polymers with N-containing side groups having high affinity to Fe. By this approach, we allow Fe-N bonds to form evenly in the precursor polymers before the subsequent heat treatment. A higher Fe-N bond content is observed compared to previously used PANI-Fe precursors. Following the precursor synthesis, the polymers are converted into a carbon-based non-PGM catalyst via a heat treatment under N2. The catalyst undergoes further characterization by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, and scanning transmission electron microscopy, followed by electrochemical characterization and fuel cell testing. The efficiency of the Fe uptake is also determined. This new approach paves the way to rational synthesis of non-PGM ORR catalysts via a rational design of polymer precursors with strong Fe-N interaction, ultimately resulting in a higher ORR active sites. Acknowledgement Financial support for this research by DOE-EERE through Fuel Cell Technologies Office is gratefully acknowledged. References Spendelow, J.; Marcinkoski, J., DOE Fuel Cell Technologies Office, Fuel Cell System Cost-2014, (2014).Wu, G.; Zelenay, P., Nanostructured Nonprecious Metal Catalysts for Oxygen Reduction Reaction. Acc. Chem. Res. 46, 1878-1889 (2013).Wu, G.; More, K. L.; Johnston, C. M.; Zelenay, P., High-Performance Electrocatalysts for Oxygen Reduction Derived from Polyaniline, Iron, and Cobalt. Science 332, 443-447 (2011).Holby, E. F.; Wu, G.; Zelenay, P.; Taylor, C. D., Structure of Fe–Nx–C Defects in Oxygen Reduction Reaction Catalysts from First-Principles Modeling. J. Phys. Chem. C 118, 14388-14393 (2014).

Pyrolyzed platinum group metal free (PGM-free) oxygen reduction reaction (ORR) electrocatalysts are a promising class of earth-abundant materials for low-temperature polymer electrolyte fuel cell (PEFC) cathodes. Understanding of the atomic scale structure of PGM-free ORR active sites remains a key focus of research efforts with the aim of improving performance of these materials. The pyrolysis process leads to highly heterogeneous catalyst systems which complicates direct active site study. In particular, (i) understanding how these active sites give rise to ORR activity, (ii) how they interact with the environment during material degradation, (iii) their interactions with probe molecules for the purposes of active site quantification, and (iv) their spectroscopic signatures are all important aspects governed by atomic scale structure. Through the use of density functional theory (DFT), we investigate these four structure-function relationships. ORR activity, one of the greatest challenges faced by PEFCs, is explored via several binding energy parameterized descriptor models. These models include the computational hydrogen electrode (CHE) model which yields thermodynamic limiting potentials, and the linearized Gibbs energy relationship (LGER) model which yields reversible potentials for reaction steps. Additionally, kinetics of OOH bond dissociation via nudged elastic band (NEB) DFT calculations are also considered as this has been proposed by some groups to be rate determining for pathways that include binding to local C sites. Combined, these models give insight into how local arrangement of atoms affects reaction pathways and enables exploration of varied reaction pathways on and local to the active site. Durability of PGM-free electrocatalysts remains a key challenge in these materials. While a variety of degradation mechanisms have been proposed, the relation between environment and degradation mechanism has not been firmly established, complicating any mitigation strategies that might be applied. Through the use of an automated ab initio molecular dynamics (AIMD)-based model, the kinetics of bond breaking local to the active site is explored. Resulting degraded structures can then be studied via the activity models previously mentioned to show how such degradation affects calculated ORR activity descriptors. Additionally, the use of reaction rate models applied to activity loss curves can also enable some discrimination of degradation mechanism indicating either a single autocatalytic process or two mechanisms with different temporal behavior. Another issue faced by PGM-free electrocatalysts is the lack of a method for quantifying the number of ORR active sites. Unlike Pt-based systems where integration of charge transferred in the H adsorption/desorption region can give information about density of active sites, no such method has been fully established for determining the number of PGM-free active sites, a value required to deconvolute turn over frequency from ORR current densities. Promising approaches include use of probe molecules that, if bound to ORR active sites (and only ORR active sites) could provide insight into how many active sites are in a given sample. This is highly dependent on the specificity of binding for these molecules which can be explored via binding energy calculations with DFT. Finally, DFT can also be a valuable tool for understanding spectroscopic signatures of highly ORR active materials. The main issue faced in such studies is focusing on just the active sites which generally requires considering changes in the Fe states, particularly for so called atomically dispersed catalysts that exhibit the highest ORR activities to date. X-ray adsorption spectroscopy (XAS, in particular XANES and EXAFS) can give information about local structure and the state of Fe with and without probe molecules. DFT and related theoretical approaches can simulate these spectra as a function of local environment. Vibrational calculations with and without probe molecules give insight into Fe-specific nuclear resonance vibrational spectroscopy (NRVS). Calculation of energy density at the Fe nucleus and electric field gradient gives input regarding isomer shift and quadrupole splitting, giving much needed interpretation of Mössbauer spectroscopy, especially in instances where no standard exists or changes in measured parameters with ligands/probes are required. Combined, these coupled experimental/theoretical approaches give insight into the nature of active sites in PGM-free systems. In particular, in this contribution we will focus on the presence of spontaneously evolved ligands that, using DFT, are shown to be likely contributors to electrocatalyst activity in-situ and experimental signatures thereof.

The rising interest in polymer electrolyte fuel cell (PEFC) technology, part of the global shift in energy production to clean sources, is accompanied by efforts to drive down the cost of this technology, which focus primarily on the cathode catalyst, the most expensive PEFC component. While platinum-group metals (PGMs) continues to be the materials of choice for oxygen reduction reaction (ORR) catalysts, use of these materials in PEFCs must be significantly reduced or eliminated without a penalty in the overall cell performance for PEFC technology to become fully viable.The most promising class ORR catalysts that do not utilize PGMs (i.e., PGM-free catalysts), involve first-row transition metals, such as iron and cobalt incorporated in a nitrogen-doped carbon (M-N-C catalysts). While advancements in M-N-C activity have been impressive, the much sought-after improvement in durability has been impeded by limited information on changes in the PGM-free catalyst active site density, activity and its degradation rate during fuel cell testing. Currently, degradation of PGM-free catalysts during fuel cell operation is often quantified using the low-current region of polarization curves. While this approach is well established, it neglects complications from such factors as catalyst pore structure, membrane conductivity, ionomer content, nature of the support, and the inhomogeneity of active sites. Hence, there exists a critical need for a method with high specificity towards catalytic activity.In this presentation we will report for the first time on the use of Fourier-transform alternating current voltammetry (FTacV) as an electrochemical method for accurately quantifying the electrochemically active site density of PGM-free ORR catalysts and following their degradation in situ during operation of polymer electrolyte fuel cells. Using this method, we were able to detect changes in performance of electrochemically active species (electrocatalytic centers in this case), allowing us to calculate the electrochemical active site density (EASD) for the first time, which is necessary to elucidate the degradation mechanisms of PGM-free ORR catalysts that occur in situ fuel cells. large-amplitude FTacV, a well-established electrochemical method with distinct advantages over dc methods, was utilized to quantify the electrochemically active site density of PGM-free FeNC catalysts in situ in PEFC. First, we will demonstrate that an accurate measurement of the EASD can be made using this method. To further emphasize the strength of the technique, we will present our findings during degradation of commercial FeNC catalysts in operating PEFC. The peak currents from higher harmonics produced by this method are correlated to the fuel cell performance, and decrease after durability tests in a manner that indicates EASD loss may not be the only catalyst degradation mechanism, thus inviting further studies of yet-unknown degradation pathway(s).

With increasing demand for energy, the development of the energy storage and conversion technologies has become the focus of an intensive research effort in recent years. Among various technologies, fuel cells, batteries, supercapacitors, and water electrolyzers have been recognized as potentially feasible and efficient devices for portable, stationary, and transportation applications. For both the fuel cells and metal-air batteries, the oxygen reduction reaction (ORR) cathode catalysts play a major role in the device performance characteristics, as determined based on the power output, open circuit voltage, charge-discharge rate, energy efficiency, cycling life (for batteries), etc. Currently, Pt-nanoparticle catalysts, supported on high surface-area carbons, represent the state-of-the-art electrocatalysts for hydrogen oxidation reaction (HOR) and ORR at the polymer electrolyte fuel cell (PEFC) anode and cathode, respectively. However, the prohibitive price and scarcity of Pt have limited its widespread implementation in the PEFC, especially at the cathode, which accounts for approximately 80% of the Pt loading in fuel cells. As a result, non-precious metal catalysts (NPMCs) for the ORR have received more attention in recent years as a possible replacement of precious-metal catalysts.A successful ORR catalyst must combine high activity with good long-term stability – a major challenge in the strongly acidic environment of the PEFC cathode. Since the early work of Jasinski in the 1960s (Nature 201, 1212, 1964), recent breakthroughs in the synthesis of high-performance non-precious metal catalysts (NPMCs) (e.g., Lefèvre et al., Science 324, 71, 2009; Wu et al., Science 332, 443, 2011) make replacement of Pt in ORR electrocatalysts with earth-abundant elements, such as Fe, Co, N, and C, a realistic possibility, though the activity and especially durability of the resulting catalysts need to be improved before the technology can become viable.The NPMC performance depends on the selection of precursors, the synthesis chemistry; and especially the catalyst nanostructure. In addition to those, the CNx structures likely play a major role in the performance of ORR active site(s). Apart from possible direct participation in the active site, the transition metal is crucial to in-situ formation of carbon nanostructures (nanotubes, onion-like structures, graphene) by catalyzing the decomposition of the nitrogen/carbon precursor(s) at a high temperatures (800-1000°C). The formation of different carbon and nitrogen-doped carbon nanostructures can be controlled during the synthesis of such NPMCs. The highly-graphitized carbon nanostructures likely serve as a matrix for the formation of the ORR-active groups with improved catalytic activity and durability, containing nitrogen and possibly also metal atoms.Future NPMC synthesis approaches are certain to focus on the precise control of interactions between precursors of the metal and carbon/nitrogen during the heat treatment, with the main purpose being the maximizations of the population of active sites, optimization of nitrogen doping levels, and generation of carbon morphologies capable of hosting active and stable ORR sites. This is evident not only in catalysts developed for PEFCs but also in materials specifically designed for alkaline fuel cells (Chung et al., Nat. Commun. 4:1922 doi:10.1038/ncomms2944, 2013). In the end, however, the much needed progress in ORR electrocatalysis at NPMCs, especially in acid media, will be decided by better understanding of the origin of the NPMC activity and the nature of the active site. That key part of NPMC development will be addressed in this presentation along with the summary of the progress achieved to date and challenges still awaiting non-precious metal electrocatalysis in polymer electrolyte fuel cells. Acknowledgment Financial support from DOE-EERE Fuel Cell Technologies Office and Los Alamos National Laboratory Laboratory-Directed Research and Development (LDRD) Program and is gratefully acknowledged.

A large overpotential of oxygen reduction reaction (ORR) at a cathode in polymer electrolyte fuel cells (PEFCs) is one of the serious problems to decrease the energy conversion efficiency. Nørskov’s group reported that even Pt which is currently used as an ORR catalyst cannot reach the theoretical oxygen electrode potential of 1.23 V at 298 K [1]. On the other hand, Yamamoto et al. recently suggested that noble metal doped titanium dioxides (TiO2) can reach the theoretical potential by changing the absorption energies of the ORR intermediates according to the first-principle calculations [2]. However, the first-principle calculations did not consider the continuous electron supply to proceed the ORR. It is difficult to form the sufficient electron conduction path from supports to active sites on the TiO2 because TiO2 has low conductivity due to a large band gap. Therefore, we focused on the formation of the active sites on the TiO2 surface by doping noble metal such as Rh and Pd and the electron conduction path from carbon supports to the active sites by preparing the titanate nanosheets.Na2Ti3O7 was synthesized as precursor of anionic titanate nanosheets([Ti3O7]2- ;TiNS) according to the previous paper [3]. Na2Ti3O7 was treated through ion-exchange reaction with hydrochloric acid and tetramethylammonium aqueous solution, finally TiNS were obtained. A TEM observation revealed that the formation of very large sheet-like materials with a size of approximately upwards of ten micrometers, resulting that TiNS were completely synthesized.Next, we focused on the formation of the electron conduction path through nanosheets from supports using the electron tunneling effect. When the nanosheets were directly supported on the glassy carbon electrode, the ORR activity was the same as that of GC, and almost no ORR current flowed even low potential region. Then, vapor grown carbon fibers (VGCFs) as purchased, with immersion of mixed acid (MA; H2SO4 and HNO3) at 170 oC for 24 h and PDDA (Poly(diallyl dimethylammonium chloride)) as polycation were attempted to use as supports. The TiNS were immersed in the distilled water dispersed with the treated VGCFs to be supported by them. These catalysts were designated as TiNS/VGCF, TiNS/VGCF(MA), and TiNS/VGCF(MA-PDDA).The ORR current of TiNS/VGCF(MA-PDDA) was larger than that of TiNS/VGCF, TiNS/VGCF(MA). In addition, the ORR onset potential of the TiNS/VGCF(MA-PDDA) increased by 0.3 V compared to that of TiNS/VGCF. These results suggest that surface treatment of VGCFs was effective to form the electron conduction path from VGCF to active sites of nanosheet surface. The electrostatic interaction between VGCF surface positively charged by PDDA and anionic TiNS contributed the formation of the electron conduction path. However, according to the TEM observation, TiNS were partially contacted with VGCF and some TiNS were agglomerated. It is necessary to obtain higher ORR activity that a control of size of TiNS and contact with supports such as VGCF.On the other hand, we attempted to dope Rh and Pd to TiNS through solid-state reaction. Rh-,Pd-doped TiNS (designated as Rh-TiNS and Pd-TiNS) were synthesized the same way as previous paper [3]. XRD patterns of the precursors revealed that Rh2O3 or PdO were existed with Na2Ti3O7 above the addition of 5 atomic %. Rh-TiNS and Pd-TiNS were supported by VGCF(MA-PDDA) after Rh-TiNS and Pd-TiNS were treated TMAOH aqueous solution. The ORR activities of the samples with the addition of 5at% Rh or 10at% Pd were higher than those of the samples which Rh2O3 or PdO were not observed in XRD patterns. The ORR active sites were estimated by Rh2O3 or PdO deposited on the surface of the TiNS. This result showed that an amount of doped Rh or Pd was limited to Na2Ti3O7. The limitation of doped Rh or Pd was 5at% or 10at%, respectively. Therefore, the doped amounts of noble metals such as Rh or Pd to TiNS should be appropriately controlled.AcknowledgementThe authors thank the New Energy and Industrial Technology Development Organization (NEDO) for financial support. This work was partly supported by TOKYO CITY UNIVERSITY Interdisciplinary Research Center for Nano Science and Technology for instrumental analysis.Reference(1) A. Kulkarni et al., Chem. Rev., 118, 2302 (2018).(2) Y. Yamamoto et al., J. Phys. Chem. C., 123, 19486 (2019).(3) W. Soontornchaiyakul et al., RSC Adv., 7, 21790 (2017). Figure 1

A Durable Platinum Group Metal-free Oxygen Reduction Catalyst for Polymer Electrolyte Fuel Cells Hanguang Zhang, Hoon T. Chung, Ulises Martinez, Edward F. Holby, and Piotr Zelenay Materials Physics and Applications Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA Performance of platinum group metal-free (PGM-free) catalysts for oxygen reduction reaction (ORR) in polymer electrolyte fuel cells (PEFCs), especially high-temperature metal-nitrogen-carbon (M-N-C) materials, has improved a lot in the last two decades,1, 2 however, their durability continues to present a big challenge. PGM-free catalysts typically suffer a 40-80% activity loss during the first 100 hours of operation in the low-temperature fuel cell cathode, which is way short of the 8,000-hour lifetime target for PEFCs.3, 4 Significant improvements to PGM-free catalyst performance durability are thus required before they can be considered for practical PEFCs.In this presentation, we will introduce a ‘dual-zone’ approach to high-temperature synthesis of PGM-free catalysts, which results in modifications to the catalyst surface and, ultimately, in very significant improvements to their durability. In H2-air fuel cell testing, the ‘dual-zone’ fuel cell catalyst has shown a minimal performance loss during up to 80,000 voltage cycles using standardized PGM-free durability test protocol developed in ElectroCat consortium and approved by DOE. The catalyst has also retained 70% of its initial activity in a 600-hour constant-voltage fuel cell test at 0.70 V.We will report fuel cell performance data in the first part of this presentation, followed by discussion of possible origins of the much improved performance durability imparted by the ‘dual-zone’ approach. Acknowledgement This research was supported by the U.S. DOE, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office under the auspices of the Electrocatalysis Consortium (ElectroCat). References Wu, G.; More, K. L.; Johnston, C. M.; Zelenay, P., High-performance electrocatalysts for oxygen reduction derived from polyaniline, iron, and cobalt. Science 2011, 332, 443-447.Chung, H. T.; Cullen, D. A.; Higgins, D.; Sneed, B. T.; Holby, E. F.; More, K. L.; Zelenay, P., Direct atomic-level insight into the active sites of a high-performance PGM-free ORR catalyst. Science 2017, 357, 479-484.Shao, Y.; Dodelet, J.-P.; Wu, G.; Zelenay, P., PGM-Free Cathode Catalysts for PEM Fuel Cells: A Mini-Review on Stability Challenges. Mater. 2019, 31, 1807615.U.S. DRIVE Fuel Cell Technical Team Roadmap; Department of Energy, US, 2017.

Platinum metal group (PMG) catalysts are used for oxygen reduction reaction (ORR) at cathodes in state-ofthe-art polymer electrolyte fuel cells (PEFCs). Since the PMG catalysts contain expensive rare metals, they should be replaced with rare-metal-free catalysts for widespread PEFCs. Recently, electrocatalysts synthesized from carbon and transition metal complexes have been studied [1,2]. It is known that ORR catalysts with multi-nuclear-active sites have high ORR activity [3]. It is also known that natural ORR catalysts such as laccases have a multinuclear copper complex as an active center and show high ORR activity [4], suggesting that laccase-inspired artificial ORR catalysts prepared from carbon and a multinuclear copper complex would show high ORR activity. In the present work, we incorporated a trinuclear copper complex ([Cu3(trz)3(μ3-OH)]Cl2·6H2O) [5] into graphene nanosheets to synthesize laccase-inspired electrocatalysts for ORR, where grapheme nanosheets worked as an electrical conductive material and the trinuclear copper complex with a triangle core imitated the active center of laccases. The trinuclear copper complex was prepared from copper chloride and 1,2,4-triazole according to the literature [5]. This copper complex and graphene oxide (GO) were mixed and then reduced in two methods. The first method is heat treatment at high temperature for a short time. The second method is electrochemical reduction on a glassy carbon (GC) electrode (-1.1 V vs. Ag|AgCl, 300 s). We carried out powdery X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma atomic emission spectroscopy (ICP-AES) to characterize the catalysts. In situX-ray absorption fine structure (XAFS) spectroscopy was also carried out to estimate the molecular structure during ORR. For electrochemical measurements of the catalysts, the powdery catalyst was suspended in an ethanol-Nafion mixture to make ink containing the catalyst. The catalyst ink was put on a GC electrode and dried under the air at room temperature. Linear Sweep Voltammetry (LSV) was carried out under a saturated O2atmosphere using a rotary disk electrode to obtain current-potential curves. Britton-Robinson buffered solutions were used as electrolyte solutions. The heat reduction improved ORR activity. The catalyst obtained after the heat treatment showed higher ORR activity than that obtained after the electrochemical reduction. This result indicated that the two reduction methods might give different structures of ORR active sites. XPS spectra of the catalyst before and after the heat treatment were recorded to obtain information on structural changes. A peak originating from C-O was observed before the heat treatment. It disappeared after the heat treatment. This result indicated that GO was reduced to rGO by the heat treatment. The Cu2p spectra showed that CuII was also reduced to CuI. A new peak was observed in N1s spectra after the heat treatment. This peak might be attributed to new configuration that triazole rings were incorporated into graphene nanoshheets. In situ XAFS spectra clarified that the multi-copper arrangement was partially kept even after heat reduction and contributed to the higher ORR activity than other copper catalysts. References. [1] K. Kamiya, K. Hashimoto, S. Nakanishi, Chem. Commun., 2012, 48, 10213–10215. [2] T. Taniguchi, et al., Part. Part. Syst. Charact., 2013, 30, 1063-1070. [3] M. Thorum, J. Yadav, A. Gewirth, Angew. Chem. Int. Ed., 2009, 48, 165–167. [4] N. Mano, V. Soukharev, A. Heller, J. Phys. Chem. B, 2006, 110, 11180–11187. [5] T. Yamada, G. Maruta, S. Takeda, Chem. Commun., 2011, 47, 653–655

The kinetically sluggish oxygen reduction reaction (ORR) at the cathode of polymer electrolyte membrane fuel cells (PEFCs) requires higher content of platinum at the cathode than the facile hydrogen oxidation at the anode. Due to the scarcity and high cost of platinum, the development of inexpensive platinum group metal-free (PGM-free) ORR catalyst is one of the most urgent needs in the PEFC field. Transition metal-nitrogen-carbon (M-N-C) catalysts obtained by heat-treating transition metals, nitrogen, and carbon precursors have been viewed as the promising PGM-free catalysts for PEFC cathodes though not yet meeting all the performance characteristics required. High ORR activity, excellent mass-transport properties and practical long-term durability must be achieved simultaneously for PGM-free catalyst to replace platinum-based catalysts in the PEFC system. Specific catalyst precursors and heat-treatment conditions are critical to obtaining PGM-free catalysts with the desired structure. Iron- and cobalt-based zeolitic imidazolate frameworks (ZIFs), with uniformly distributed transition metals coordinated by N-containing ligands, have been viewed as highly suitable precursors for ORR catalysts. However, catalysts derived from these ZIFs often have low surface area and porosity, which are not conducive to efficient mass transport. On the contrary, ZIF-8, a zinc based ZIF, yields carbon with high surface area and porosity. Dodelet et al. used ZIF-8 as a microporous host for Fe and N precursors [1]. Following a heat-treatment at a relatively high temperature of 1050 ºC, they obtained an ORR catalyst with enhanced fuel cell performance. Unlike Fe and Co in Fe- and Co-based ZIFs, zinc in ZIF-8 is volatile during high-temperature treatment, likely acting as pore-forming agent. Base on that assumption, we used in this work a zinc salt instead of zinc ZIF as a precursor responsible for the formation of micropores in the catalyst. By using high heat-treatment temperature we also achieved more corrosion-resistant catalysts, while increasing the porosity and specific surface area from 315 m2 g-1 to 910 m2 g-1due to Zn evaporation. Fe-CM-PANI(Zn) catalyst was synthesized using the two nitrogen-precursor (cyanamide and PANI) approach, developed previously by LANL[2]. ZnCl2 was mixed with nitrogen precursors and heat-treated at 1000 ºC to ensure complete removal of Zn. The resulting CM-PANI-Fe(Zn) catalyst had much higher surface area than the catalyst obtained without Zn under the same conditions. The half-wave potential (E½ ) for CM-PANI-Fe(Zn) in RDE testing in acidic electrolyte, 0.79 V vs. RHE, was similar to that obtained with Zn-free CM-PANI-Fe heat-treated at 900 ºC (optimal heat-treatment temperature for the Zn-free system), but by 0.16 V higher than E½ measured with the Zn-free catalyst heat-treated at 1000 ºC (Figure 1). While no immediate increase in the activity can be demonstrated with CM-PANI-Fe(Zn), this catalyst promises to have much improved stability thanks to being treated at a much higher temperature. Electrochemical and fuel cell testing of the Zn-derived catalyst, focusing in particular on the durability, is underway, as is the catalyst structure optimization. The results will be present at the meeting.

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.