Bimetallic icosahedral nanoframes have three-dimensional open structures, a high surface-area-to-volume ratio, and high surface site availability. Twin boundaries in these structures cause surface lattice expansion that leads to tensile strain over the nanoframes, which can improve their catalytic activity; however, robust methods for their synthesis in most metal systems are still lacking. In this work, we demonstrate a one-step synthetic strategy for the synthesis of both closed solid and hollow frame icosahedral PdRu nanoparticles (INPs) via a two-stage process of growth and dissolution. By extraction at different reaction times, INPs, concave-faceted icosahedral PdRu nanoparticles (CINPs), and icosahedral PdRu nanoframes (INFs) are obtained. High-angle annular dark-field scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy and inductively coupled plasma-optical emission spectrometry analyses show that the icosahedral nanostructures are PdRu alloys with similar to 5 at. % Ru relative to Pd. We also carried out the electrochemical ethanol oxidation reaction (EOR) and CO2 reduction reaction over three types of catalysts, PdRu INPs, PdRu CINPs, and PdRu INFs, as well as commercial Pd NPs, to examine their catalytic properties. PdRu INFs showed a much higher mass activity than PdRu INPs, PdRu CINPs, and Pd NPs in the EOR. PdRu INFs exhibited the highest Faradaic efficiency of CO gas (34%), which suggests that the expansive strain in the framework catalyst structure improves selectivity and activity for CO2 conversion.

Professor Chia-Kuang (Frank) Tsung made his scientific impact primarily through the atomic-level design of nanoscale materials for application in heterogeneous catalysis. He approached this challenge from two directions: above and below the material surface. Below the surface, Prof. Tsung synthesized finely controlled nanoparticles, primarily of noble metals and metal oxides, tailoring their composition and surface structure for efficient catalysis. Above the surface, he was among the first to leverage the tunability and stability of metal-organic frameworks (MOFs) to improve heterogeneous, molecular, and biocatalysts. This article, written by his former students, seeks first to commemorate Prof. Tsung's scientific accomplishments in three parts: (1) rationally designing nanocrystal surfaces to promote catalytic activity; (2) encapsulating nanocrystals in MOFs to improve catalyst selectivity; and (3) tuning the host-guest interaction between MOFs and guest molecules to inhibit catalyst degradation. The subsequent discussion focuses on building on the foundation laid by Prof. Tsung and on his considerable influence on his former group members and collaborators, both inside and outside of the lab.

The global ammonia yield is critical to the fertilizer industry as the global food demand is highly dependent on it, whereas, NH3 is also a key chemical for pharmaceutical, textile, plastic, explosive, and dye-making industries. At present, the demand for NH3 is fulfilled by the Haber-Bosch method, which consumes 1-3% of global energy and causes 0.5-1% CO2 emission every year. To reduce emissions and improve energy efficiency, the electrochemical nitrogen gas reduction reaction (N2RR) has received much attention and support after the funding announcement by the U.S. Department of Energy. In this work, we have created hollow CuAu nanoboxes with Cu-rich inner walls to improve the NH3 Faradaic efficiency in N2RR. These beveled nanoboxes are produced in different degrees of corner and edge etching, which produces both polyhedral and concave structures. In N2RR, the binary CuAu nanoboxes enhanced NH3 production compared to individual Au and Cu nanocubes. The results of DFT calculations suggest the Cu-rich inner walls in the hollow beveled CuAu nanoboxes play a major role in their performance by reducing the free energy ΔG*NNH for the potential-determining step to form *NNH (* + N2(g) + H+ + e- → *NNH). Meanwhile, the results in 10-cycle and solar-illuminated N2RR indicate the beveled CuAu nanoboxes are not only robust electrocatalysts but show promise in photocatalysis as well.

Copper is an earth-abundant element that can be used to reduce the high cost and unsatisfactory durability of pure Pt catalysts by the formation of bimetallic Pt-M nanocrystals. Among CuPt nanostructures, nanocages attract great interest for catalysis as they allow passage of reactant species to their porous interiors, which provide a high fraction of surface sites. They may also enhance reactivity through an increase in collision frequency by enclosing reagents within nanoscale cavities and by lattice strain effects of the alloy. Recent reports apply solvothermal chemistry to obtain CuPt nanocages in one step. However, there is still a lack of understanding in the formation mechanism and its impact on catalytic activity for such hollow CuPt nanostructures. In this work, we adopt a two-step method in which we synthesize rhombic dodecahedral (RD) Cu-CuPt core-shell nanocrystals by the deposition of Pt on Cu nanocubes to form CuPt shells less than 2 nm in thickness, followed by removing Cu cores to obtain ultrathin octahedral (OCT) nanocages for catalytic applications. By adjustment to shorter and longer reaction time frames, the core-shell nanocrystals were also made into quasi-RD (QRD) and spiny-RD (SRD) morphologies, which lead to porous (POCT) and spiny (SOCT) OCT nanocages, respectively, upon etching. These three types of CuPt nanocages (POCT, OCT, and SOCT) were then examined in the electrocatalytic oxygen reduction reaction (ORR) and the hydrogen evolution reaction (HER) by the hydrolysis of NH3BH3 to study their performance. As a result, the SOCT CuPt nanocages exhibit the highest Pt mass activity (0.3 A/mg,) in the ORR, a 3-fold improvement over commercial Pt/C. They also show the lowest activation energy (24.3 kJ/mol) in the HER that is better than the commercial catalyst by a factor of 4. HER photocatalysis results show that the POCT and OCT nanocages have localized surface plasmon resonance (LSPR)-enhancement while the SOCT nanocages do not, which is attributed to inhomogeneity in Cu-Pt distributions at shorter reaction times.

We investigated lattice strain on alloyed surfaces using ∼10 nm core-shell nanoparticles with controlled size, shape, and composition. We developed a wet-chemistry method for synthesizing small octahedral PdPt alloy nanoparticles and Au@PdPt core-shell nanoparticles with Pd-Pt alloy shells and Au cores. Upon introduction of the Au core, the size and shape of the overall nanostructure and the composition of the alloyed PdPt were maintained, enabling the use of the electrooxidation of formic acid as a probe to compare the surface structures with different lattice strain. We have found that the structure of the alloyed surface is indeed impacted by the lattice strain generated by the Au core. To further reveal the impact of lattice strain, we fine-tuned the shell thickness. Then, we used synchrotron-based X-ray diffraction to investigate the degree of lattice strain and compared the observations with the results of the formic acid electrooxidation, suggesting that there is an optimal intermediate shell thickness for high catalytic activity.

Quantifying chemical compositions around nanovoids is a fundamental task for research and development of various materials. Atom probe tomography (APT) and scanning transmission electron microscopy (STEM) are currently the most suitable tools because of their ability to probe materials at the nanoscale. Both techniques have limitations, particularly APT, because of insufficient understanding of void imaging. Here, we employ a correlative APT and STEM approach to investigate the APT imaging process and reveal that voids can lead to either an increase or a decrease in local atomic densities in the APT reconstruction. Simulated APT experiments demonstrate the local density variations near voids are controlled by the unique ring structures as voids open and the different evaporation fields of the surrounding atoms. We provide a general approach for quantifying chemical segregations near voids within an APT dataset, in which the composition can be directly determined with a higher accuracy than STEM-based techniques.

PtCo/C and Pt/C catalyst powders were incorporated into electrospun nanofiber and conventional sprayed cathode membraneelectrode-assemblies (MEAs) at a fixed electrode loading of 0.1 mgPt/cm. The binder for PtCo/C nanofiber cathodes and Pt/C nanofiber anodes was a mixture of Nafion and poly(acrylic acid) (PAA), whereas the sprayed electrode MEAs utilized a neat Nafion binder. The structure of electrospun fibers was analyzed by scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS), which showed that the fibers were ∼30% porous with a uniform distribution of catalyst and binder in the axial and radial fiber directions. The initial performance of nanofiber MEAs at 80°C was 20% better than the sprayed electrode MEA (a maximum power density of 1,045 mW/cm2 vs. 869 mW/cm2). The benefit of the nanofiber electrode morphology was most evident at end-of-test (after a metal dissolution accelerated stress test), where power densities dropped by only 8%, after 30,000 square wave voltage cycles (0.6 V to 0.95 V), as compared to a 35% drop in the maximum power for the sprayed electrode MEA. The use of a recovery protocol improved the initial performance of a nanofiber MEA by ∼13%, to 1,070 mW/cm2 at 0.65 V, and increased the power after a metal dissolution stress test by 5–10% (e.g. 840 mW/cm2 at 0.65 V after 30,000 voltage cycles). At rated power, the nanofiber MEA generated more than 1,000 mW/cm2 at 99°C and a pressure of 250 kPaabs. The high performance and durability of PtCo/C nanofiber cathode MEAs is due to the combined effects of a highly active cathode catalyst and the unique nanofiber electrode morphology, where there is a uniform distribution of catalyst and binder (no agglomeration) and short transport pathways across the submicron diameter fibers (which lowers gas transfer resistance and facilitates water removal from the cathode). © The Author(s) 2019. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0151907jes]

Advances in new systems of organic-inorganic hybrid nanocomposites are less prevalent, owing to a lack of facile strategies for precise control of their structures, compositions, and, hence, their properties. In this work, Au-BINOL hybrid nanocomposites with eccentric and concentric nanostructures were produced. The hybrid nanocomposites containing two distinct moieties of inorganic Au nanocrystals and organic BINOL nanospheres were applied to the catalytic hydrogenation of 4-nitrophenol with NaBH4 in the aqueous phase with and without the illumination of visible light. Here, we demonstrate that the existence of Au-BINOL interfaces offers benefits to their performance. The eccentric nanostructures made with CTAC show the superior activity from large Au-BINOL interfaces formed between the BINOL nano spheres and the faces of Au nanoplates. They further exhibit a high Au localized surface plasmon resonance (LSPR)-enhancement effect on the photoreduction of 4-nitrophenol, which is attributed to the strong LSPR absorption of exposed Au nanocrystals unaffected by the coverage of BINOL shells.

Significant mass-transport resistances in polymer-electrolyte-fuel-cell catalyst layers (CLs) impose a lower limit on Pt-loading levels, hindering wide-spread fuel-cell commercialization. The origin of this resistance remains unclear. Minimization of CL mass-transport resistance is imperative to achieve better CL design and performance. In this paper, an operando method based on H-2 limiting current is used to characterize and quantify CL resistance in traditional porous Pt/carbon-based electrodes. CL sub-resistances are isolated using continuum multiscale modeling and experiments, investigating the effects of reactant molecular weight, pressure, and ionomer to carbon weight ratio. The results expose CL resistance including both interfacial and transport components, although the majority of the CL resistance is ascribed to a local resistance close to the Pt reaction sites, which includes interfacial resistance and local transport resistance. Variations in temperature, humidity, and primary particle loading (Pt:C ratio) highlight the impact of operating conditions and CL design parameters on CL sub-resistances. The observed trends guide optimization of CL design to achieve novel low-loaded fuel-cell electrodes. (C) The Author(s) 2019. Published by ECS.

The distribution of tantalum and oxygen ions in electroformed and/or switched TaO x-based resistive switching devices has been assessed by high-angle annular dark-field microscopy, X-ray energy-dispersive spectroscopy, and electron energy-loss spectroscopy. The experiments have been performed in the plan-view geometry on the cross-bar devices producing elemental distribution maps in the direction perpendicular to the electric field. The maps revealed an accumulation of +20% Ta in the inner part of the filament with a 3.5% Ta-depleted ring around it. The diameter of the entire structure was approximately 100 nm. The distribution of oxygen was uniform with changes, if any, below the detection limit of 5%. We interpret the elemental segregation as due to diffusion driven by the temperature gradient, which in turn is induced by the spontaneous current constriction associated with the negative differential resistance-type I- V characteristics of the as-fabricated metal/oxide/metal structures. A finite-element model was used to evaluate the distribution of temperature in the devices and correlated with the elemental maps. In addition, a fine-scale (∼5 nm) intensity contrast was observed within the filament and interpreted as due phase separation of the functional oxide in the two-phase composition region. Understanding the temperature-gradient-induced phenomena is central to the engineering of oxide memory cells.

Development of Pt catalysts alloyed with transition metals has led to a new class of state-of-the-art electrocatalysts for oxygen reduction at the cathode of proton exchange membrane fuel cells; however, the durability of Pt-based alloy catalysts is challenged by poor structural and chemical stability. There is a need for better understanding of the morphological and compositional changes that occur to the catalyst under fuel cell operation. Here, we report in-depth characterization results of a Pt-Co electrocatalyst incorporated in the cathode of membrane electrode assemblies, which were evaluated before and after accelerated stress tests designed specifically to enhance catalyst degradation. Electron microscopy, spectroscopy, and 3D electron tomography analyses of the Pt-Co nanoparticle structures suggest that the small- and intermediate-sized Pt-Co particles, which are typically Pt-rich in the fresh condition, undergo minimal morphological changes, whereas intermediate- and larger-sized Pt-Co nanoparticles that exhibit a porous "spongy" morphology and initially have a higher Co content, transform into hollowed-out shells, which is driven by continuous leaching of Co from the Pt-Co catalysts. We further show how these primary Pt-Co nanoparticle morphologies group toward a lower Co, larger size portion of the size vs. composition distribution, and provide details of their nanoscale morphological features. (C) The Author(s) 2018. Published by ECS.

The U.S. Department of Energy (DOE) set the 2020 durability target for polymer electrolyte membrane fuel cell transportation applications at 5000 hours. Since it is impractical to test every fuel cell for this length of time, there is ever increasing interest in developing accelerated stress tests (ASTs) that can accurately simulate the material component degradation in the membrane electrode assembly (MEA) observed under automotive operating conditions, but over a much shorter time frame. In this work, a square-wave catalyst AST was examined that shows a 5X time acceleration factor over the triangle-wave catalyst AST and a 25X time acceleration factor over the modified wet drive-cycle catalyst durability protocol, significantly decreasing the testing time. These acceleration factors were correlated to the platinum (Pt) particle size increase and associated decrease in electrochemical surface area (ECSA). This square-wave AST has been adopted by the DOE as a standard protocol to evaluate catalyst durability. We also compare three catalyst-durability protocols using state-of-the-art platinum-cobalt catalysts supported on high surface area carbon (SOA Pt-Co/HSAC) in the cathode catalyst layer. The results for each of the three tests showed both catalyst particle size increase and transition metal leaching. Moreover the acceleration factors for the alloy catalysts were smaller due to Co leaching being the predominant mechanism of voltage decay in similar to 5 nm PtCo/C catalysts. Finally, an extremely harsh carbon corrosion AST was run using the same SOA Pt-Co/HSAC catalyst. This showed minimal change in particle size and a low percentage Co loss from the cathode catalyst particles, despite a significant loss in catalyst layer thickness and cell performance. The carbon corrosion rates during these various ASTs were directly measured by monitoring the CO2 emission from the cathode, further confirming the ability of the square-wave AST to evaluate the electro-catalyst independently of the support. (C) The Author(s) 2018. Published by ECS.

The control of morphology in the synthesis of Rh nanocrystals can be used to precisely tailor the electronic surface structure; this in turn directly influences their performance in catalysis applications. Many works have brought attention to the development of Rh nanostructures with low-index surfaces, but limited effort has been devoted to the study of high-index and surface defect-enriched nanocrystals as they are not favored by thermodynamics because of the involvement of high-energy surfaces and increased surface-to-volume ratios. In this work, we demonstrate an aqueous synthesis of concave Rh nanotetrahedra (CTDs) serving as efficient catalysts for energy conversion reactions. CTDs are surface defect-rich structures that form through a slow growth rate and follow the four-step model of metallic nanoparticle growth. Via the tuning of the surfactant concentration, the morphology of Rh CTDs evolved into highly excavated nanotetrahedra (HETDs) and twinned nanoparticles (TWs). Unlike the CTD surfaces with abundant adatoms and vacancies, HETDs and TWs have more regular surfaces with layered terraces. Each nanocrystal type was evaluated for methanol electrooxidation and hydrogen evolution from hydrolysis of ammonia borane, and the CTDs significantly showed the best catalytic performance because of defect enrichment, which benefits the surface reactivity of adsorbates. In addition, both CTDs and HETDs have strong absorption near the visible light region (382 and 396 nm), for which they show plasmon-enhanced performance in photocatalytic hydrogen evolution under visible light illumination. CTDs are more photoactive than HETDs, likely because of more pronounced localized surface plasmon resonance hot spots. This facile aqueous synthesis of large-surface-area, defect-rich Rh nanotetrahedra is exciting for the fields of nanosynthesis and catalysis.

Previous ionomer adsorption (Figure 1) explorations in our group have shown significantly lower adsorption (lower Keq) of ionomer when platinum (Pt) nanoparticles are present on the carbon support.1 Such differences can suggest a higher affinity of the polymer chain to carbon, which could suggest that acidic groups on the carbon surface might participate in hydrogen bonding on dipole-dipole interactions with the hydrophilic unit in the polymer.1,2 This disagrees with many recent suggestions that the interactions with ionomer are driven by specifc adsorption of sulfonic acid or sulfonate on the Pt. Understanding such interactions can be key to further improve the Pt/Carbon/ionomer electrodes structure and, consequently, proton exchange membrane fuel cell (PEMFC) performance. In this study, the adsorption of ionomer on a series of Pt:C (0:100, 30:70, 50:50 and 70:30) ratios using Vulcan XC-72 Carbon and Ketjenblack (KJB) supports were evaluated to further understand this interaction. The adsorption properties of water-dissolved 3M 825 equivalent-weight (EW) ionomer on both the carbon supports and the series of carbon-supported platinum (Pt/C) catalysts were studied with 400 MHz 19F Nuclear Magnetic Resonance Spectroscopy (NMR) and Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). A detailed structure characterization of the pristine supports and catalyst materials was achieved through Brunauer-Emmet-Teller (BET) nitrogen adsorption-desorption, transmission electron microscopy (TEM) and X-ray diffraction (XRD). The adsorbed ionomer structure was also explored through NMR and Fourier-Transform Infrared (FTIR). These results will be reported along with context from other studies of ionomer-supported catalyst interactions in the actual catalyst layer. Acknowledgements NMC gratefully acknowledges the support from a Fulbright Fellowship as well as the Office of Naval Research. Research was supported at ORNL by the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy. References N. M. Cantillo, L. Li, J. Peng, G. A. Goenaga, and Thomas A. Zawodzinski ECS Trans., 80, 259–268 (2017) http://ecst.ecsdl.org/content/80/8/259.full.pdf. S. Ma, Q. Chen, F. H. Jøgensen, P. C. Stein, and E. M. Skou, Solid State Ionics, 178, 1568–1575 (2007). Figure 1

The synthesis of monodisperse size- and shape-controlled Au nanocrystals is often achieved with cetyltrimethylammonium bromide (CTAB) surfactant; however, its role in the growth of such tailored nanostructures is not well understood. To elucidate the formation mechanism(s) and evolution of the morphology of Au nanocrystals in the early growth stage, we present an in situ liquid-cell scanning transmission electron microscopy (STEM) investigation using electron beam-induced radiolytic species as the reductant. The resulting particle shape at a low beam dose rate is shown to be strongly influenced by the surfactant; the Au nanocrystal growth rate is suppressed by increasing the CTAB concentration. At a low CTAB concentration, the nanoparticles (NPs) follow a reaction-limited growth mechanism, while at high a CTAB concentration the NPs follow a diffusion-limited mechanism, as described by the Lifshitz-Slyozov-Wagner (LSW) model. Moreover, we investigate the temporal evolution of specific NP geometries. The amount of Au reduced by the electron beam outside the irradiated area is quantified to better interpret the nanocrystal growth kinetics, as well as to further develop an understanding of electron beam interactions with nanomaterials toward improving the interpretation of in situ measurements.

The durability of Pt-Co alloy cathode catalysts supported on high surface area carbon is investigated by subjecting them to accelerated stress tests (ASTs). The catalysts had different initial Co contents and nanoparticle morphologies: a "spongy" porous morphology for the high-Co (H) content catalyst, and a fully alloyed crystalline morphology for the medium-Co (M) and low-Co (L) content catalysts. The specific activity of the catalysts depends on their initial Co content, morphology and nanoparticle size, and remained higher than 1000 mu A/cm(2)-Pt after 27-50% Co loss. The H-catalyst electrode showed the smallest kinetic overpotentials (eta(c)(s)) due to higher initial Pt loading than the other two electrodes, but it had the fastest increase in eta(c)(s) with AST cycling due to lower Co retention; the L-catalyst electrode showed higher eta(c)(s) due to a lower initial Pt loading, but had a smaller increase in.cs with aging due to higher Co retention; the M-catalyst electrode showed a similar increase in eta(c)(s) with aging, but this increase was due to the combined effects of Co dissolution and electrochemically active surface area (ECSA) loss. The modeled increase in mass transfer overpotentials with aging correlates with the initial Pt loading, ECSA loss and the initial catalyst morphology. (C) The Author(s) 2018. Published by ECS.

The combined functionality of components in organic inorganic hybrid nanomaterials render them efficient nanoreactors. However, the development in this field is limited due to a lack of synthetic avenues and systematic control of the growth kinetics of hybrid structures. In this work, we take advantage of an ionic switch for regio-control of Au-BINOL(1,1'-Bi-2-naphthol) hybrid nanostructures. Aromatic BINOL molecules assemble into nanospheres, concomitant with the growth of the Au nanocrystals. The morphological evolution of Au nanocrystals is solely controlled by the presence of halides in the synthetic system. Here we show that quaternary ammonium surfactants (CTAB or CTAC), not only bridging Au and BINOL, but also contributing to the formation of concentric or eccentric structures when their concentrations are tuned to the range of 10(-5) to 10(-3) M. This facile strategy offers the potential advantage of scalable production, with diverse functional organic inorganic hybrid nanocomposites being produced based on the specific archetype of Au-BINOL hybrid nano composites.

Platinum-based alloys are known to demonstrate advanced properties in electrochemical reactions that are relevant for proton exchange membrane fuel cells and electrolyzers. Further development of Pt alloy electrocatalysts relies on the design of architectures with highly active surfaces and optimized utilization of the expensive element, Pt. Here, we show that the three-dimensional Pt anisotropy of Pt-Ni rhombic dodecahedra can be tuned by controlling the ratio between Pt and Ni precursors such that either a completely hollow nanoframe or a new architecture, the excavated nanoframe, can be obtained. The excavated nanoframe showed ∼10 times higher specific and ∼6 times higher mass activity for the oxygen reduction reaction than Pt/C, and twice the mass activity of the hollow nanoframe. The high activity is attributed to enhanced Ni content in the near-surface region and the extended two-dimensional sheet structure within the nanoframe that minimizes the number of buried Pt sites.

The activity and durability of both platinum group metal (PGM)-free and low-PGM catalysts rely heavily on the interaction of the active species with the support structure [1]. These carbon-based supports can be tailored in a number of ways to impact the morphology and performance of the electrocatalyst. Visualizing these interactions by scanning transmission electron microscopy (STEM) in two and/or three dimensions can provide valuable multi-scale insight, which can be leveraged towards maximizing catalyst utilization and durability. In this work, quantitative analytical STEM characterization is performed at high spatial resolution on a number of Pt-based and PGM-free catalyst and support systems to elucidate the nature of these critical interactions. The interplay between carbon graphitization and Pt loading was examined in three dimensions by quantitative electron tomography. The initial Pt dispersion and subsequent agglomeration following accelerated stress tests were quantified for high surface area carbon, Vulcan, and low surface-area carbons, with Pt catalyst loadings ranging from 5 to 40 wt.%. Higher degrees of graphitization in the carbon support led to a poor initial Pt dispersion, which in turn resulted in increased agglomeration during cycling. These results showed that in order to improve the mass activity and durability of the corrosion-resistance graphitized carbons, steps must be taken to improve initial Pt dispersion. To this end, a series of nitrogen-doped graphitized carbon supports were synthesized to study possible interactions between the nitrogen-doped surfaces and Pt nanoparticles. Low-voltage, aberration-corrected STEM coupled with electron energy loss spectroscopy (EELS) was used to probe these interactions in an effort to improve Pt dispersion and stability on corrosion-resistance supports. Such catalyst-support interactions are perhaps best epitomized in the atomic-level interplay found in heat-treated metal-nitrogen-carbon (M-N-C) catalysts in fuel cells with PGM-free cathodes [2]. The resulting atomic-level structures derived from zeolitic imidazolate frameworks (ZIFs) and hybrid cyanamide-polyaniline precursors were visualized at the atomic level by the low-voltage, aberration-corrected STEM. The composition of catalytic oxygen reduction reaction (ORR) active sites and other structures explored by STEM-EELS complement electrochemical measurements to further guide synthesis protocols as efforts continue to produce high-performance and durable PGM-free based fuel cells. References L. Du, Y. Shao, J. Sun, G. Yin, J. Liu, Y. Wang, Nano Energy 29 (2016) 314. G. Wu, K. L. More, C. M. Johnston, P. Zelenay, Science 332 (2011) 443. Acknowledgements Research sponsored by the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy (DOE), and through a user project supported by ORNL’s Center for Nanophase Materials Sciences (CNMS), which is a DOE Office of Science User Facility. A portion of this research was performed using instrumentation provided by the U.S. DOE Office of Nuclear Energy, Fuel Cycle R&D Program, and the Nuclear Science User Facilities. Figure 1