Metalorganic Precursors Research Articles

Hybrid molecular beam epitaxy of germanium-based oxides

Germanium-based oxides such as rutile GeO2 are garnering attention owing to their wide band gaps and the prospects of ambipolar doping for application in high-power devices. Here, we present the use of germanium tetraisopropoxide (GTIP), a metal-organic chemical precursor, as a source of germanium for the demonstration of hybrid molecular beam epitaxy for germanium-containing compounds. We use Sn1-xGexO2 and SrSn1-xGexO3 as model systems to demonstrate our synthesis method. A combination of high-resolution X-ray diffraction, scanning transmission electron microscopy, and X-ray photoelectron spectroscopy confirms the successful growth of epitaxial rutile Sn1-xGexO2 on TiO2(001) substrates up to x = 0.54 and coherent perovskite SrSn1-xGexO3 on GdScO3(110) substrates up to x = 0.16. Characterization and first-principles calculations corroborate that germanium occupies the tin site, as opposed to the strontium site. These findings confirm the viability of the GTIP precursor for the growth of germanium-containing oxides by hybrid molecular beam epitaxy, thus providing a promising route to high-quality perovskite germanate films.

Research progress on the application of derived porous carbon materials in solid-phase microextraction

固相微萃取是一种集采样、萃取、富集和进样于一体的样品前处理技术,其萃取效果与涂层材料密切相关。多孔碳材料具有比表面积大、多孔结构可控、活性位点多和化学稳定性好等优点,广泛应用于电池、超级电容器、催化、吸附和分离等领域,也是一种热门的用作固相微萃取探针的涂层材料。衍生多孔碳材料因种类丰富、可设计性强被广泛研究,研究主要集中在对衍生多孔碳材料的结构优化方面。但是衍生多孔碳材料在固相微萃取中的应用还存在如下问题:(1)共价有机框架衍生多孔碳材料的制备已取得较大进展,但将其应用于固相微萃取领域的研究仍较少;(2)有待进一步明确制备出的衍生多孔碳材料用作固相微萃取涂层表现出优异提取能力的机理;(3)有待进一步深入研究将衍生多孔碳材料用作固相微萃取涂层以实现对不同物理化学性质污染物的广谱高灵敏度分析。文章综述了近3年衍生多孔碳材料在固相微萃取中的应用研究,并展望了未来衍生多孔碳材料在固相微萃取中的研究前景。引用文献共56篇,主要来源于Elsevier。

Metal-Organic Precursor Synthesis, Structural Characterization, and Multiferroic Properties of GdFeO3 Nanoparticles.

GdFeO3 nanoparticles were fabricated by a facile metal–organic precursor method using citric acid as a complexing agent. The phase purity and structural analysis by powder X-ray diffraction and FTIR studies indicates that the material is highly crystalline with an orthorhombic structure. Electron microscopic (TEM and SEM) studies of rare earth ferrites reveal worm-shaped nanoparticles with an average grain size of 95 nm. The high-resolution TEM study provides an insightful image, which shows an interplanar spacing of approximately 0.12 nm that corresponds to the (112) crystalline plane. A high surface area of 231.5 m2 g–1 has been achieved with a mesoporous texture, which in turn gives a high dielectric constant. Well-defined hysteresis is obtained with a saturation magnetization of 17.5 emu g–1, remanent magnetization of 3.9 emu g–1, and coercive field of −446 Oe. Room-temperature ferroelectricity in GdFeO3 nanoparticles has been found for the first time with no leaky current and hence may be used in multistate memory devices.

Nanosheet-state cobalt-manganese oxide with multifarious active regions derived from oxidation-etching of metal organic framework precursor for catalytic combustion of toluene

For the first time, a nanosheet-state CoMnx mixed oxide with multifarious active regions was synthesized by oxidation-etching assembly of metal organic framework (MOF) precursor and applied for catalytic combustion of toluene at low temperatures. The obtained optimum catalyst denoted as CoMn6 showed excellent performance, which achieved 90% conversion of 1,000 ppm toluene under a weight hourly space velocity (WHSV) of 60,000 mL/(g·h) at 219 °C. While, it also exhibited long-term stability with strong water resistance property. The characterizations of physicochemical properties indicated that the oxidation-etching assembly process built an abundant mesoporous structure in the CoMnx catalyst, which greatly increased the specific surface area (SSA). Especially, potassium permanganate as oxidant and manganese source led to uniform dispersion and assembling of cobalt atoms, which caused the generation of low-crystallinity CoMnx mixed oxide with abundant dislocations, vacancies, phase interfaces and amorphous structures, resulting in excellent low-temperature reducibility, outstanding lattice oxygen mobility and abundant active species such as Mn3+, Co3+ and adsorbed oxygen species. Density functional theory (DFT) calculations demonstrated that gaseous oxygen with the longer bond length (1.406 Å) and stronger adsorption energy (−4.443 eV) could be adsorbed and activated well on the MnCo2O4.5 (311) plane, which is beneficial for the toluene oxidation. In situ diffuse reflectance infrared spectroscopy (DRIFTS) technique was applied to track the intermediates of toluene combustion under different atmospheres, which further deduced the contributions of different active regions and oxidation mechanism over the CoMnx catalyst. The present facile strategy of oxidation-etching assembly of the MOF precursor for the creating of novel catalyst with high performance could be applied in a wide variety of materials besides VOC combustion catalysts.

Hydrodeoxygenation of p-cresol over CuNi@C catalyst derived from metal-organic frameworks precursor

Catalytic hydrodeoxygenation is becoming more important industrially due to the urgent need for the conversion of oxygen-rich biomass into a renewable hydrocarbon energy source as means to tackle the climate change crisis. This research examined the catalytic hydrogenation of p-cresol as a model compound, using CuNi bimetallic nanoparticles incorporated into a carbon matrix (CuNi@C) as the catalysts, which were prepared using MOFs as the precursors. Various MOFs with varying molar content of nickel (Cu, CuNi0.2, CuNi0.5, CuNi0.8 and CuNi1.1) were prepared and used to derive the MOF-based bimetallic catalysts. The effect of the relative bimetallic compositions, surface morphology, and the oxidation of the metals of the catalysts was studied at different hydrogenation reaction temperatures varying from 200 to 300 °C. Advanced characterisations demonstrate that the MOF-derived Cu/Ni carbon nanocomposite catalyst at a Cu/Ni mole ratio of 0.5 (CuNi0.5/C) shows the highest catalytic activities at 300 °C, giving rise to a conversion rate of 80.3% and selectivity of 82.7% for the formation of 4-methylcyclohexanol (hydrogenation pathway). Cyclic hydrogenation tests also reveal that the CuNi0.5/C showed the highest thermochemical stability with a negligible decrease in catalytic activity despite the high temperature examined for a fast conversion. The preliminary results augur well for the sound promise of using corresponding MOFs derived novel catalysts for hydrogenation application.

Vapor-Phase Infiltration of Polymer of Intrinsic Microporosity 1 (PIM-1) with Trimethylaluminum (TMA) and Water: A Combined Computational and Experimental Study.

Vapor-phase infiltration, a postpolymerization modification process, has demonstrated the ability to create organic-inorganic hybrid membranes with excellent stability in organic solvents while maintaining critical membrane properties of high permeability and selectivity. However, the chemical reaction pathways that occur during VPI and their implications on the hybrid membrane stability are poorly understood. This paper combines in situ quartz crystal microbalance gravimetry (QCM) and ex situ chemical characterization with first-principles simulations at the atomic scale to study each processing step in the infiltration of polymer of intrinsic microporosity 1 (PIM-1) with trimethylaluminum (TMA) and its co-reaction with water vapor. Building upon results from in situ QCM experiments and SEM/EDX, which find TMA remains within PIM-1 even under long desorption times, density functional theory (DFT) simulations identify that an energetically stable coordination forms between the metal-organic precursor and PIM-1's nitrile functional group during the precursor exposure step of VPI. In the subsequent water vapor exposure step, the system undergoes a series of exothermic reactions to form the final hybrid membrane. DFT simulations indicate that these reaction pathways result in aluminum oxyhydroxide species consistent with ex situ XPS and FTIR characterization. Both NMR and DFT simulations suggest that the final aluminum structure is primarily 6-fold coordinated and that the aluminum is at least dimerized, if not further "polymerized". According to the simulations, coordination of the aluminum with at least one nitrile group from the PIM-1 appears to weaken significantly as the final inorganic structure emerges but remains present to enable the formation of the 6-fold coordination species. Water molecules are proposed to complete the coordination complex without further increasing the aluminum's oxidation state. This study provides new insights into the infiltration process and the chemical structure of the final hybrid membrane including support for the possible mechanism of solvent stability.

Cover Picture: Flow Synthesis of Single and Mixed Metal Oxides (Chem. Methods 8/2022)

The Front Cover shows a versatile flow synthesis strategy for continuous manufacturing of single- and mixed-metal oxide particles with a high degree of size monodispersity. The flow-focusing microreactor equipped with an online photo-crosslinking module enables facile production of a broad range of monodispersed metal oxide particles (ZnO, SnO2, CeO2, LaPrO3) using metal organic precursors beyond metal alkoxides. More information can be found in the Research Article by Zachary S. Campbell et al..

Electronic Tuning of Core-Shell CoNi Nanoalloy/N-Doped Few-Layer Graphene for Efficient Oxygen Electrocatalysis in Rechargeable Zinc-Air Batteries.

The discovery of highly efficient, durable, and affordable bifunctional ORR/OER electrocatalysts is of great significance for the commercialization of rechargeable metal-air batteries. Herein, we synthesized uniformly sized CoNi alloy nanoparticles encapsulated with N-doped few-layer graphene (N-FLG) sheets via pyrolysis of a CoNi dual metal-organic framework precursor. The developed CoNi/N-FLG catalyst exhibited excellent oxygen reduction activity (comparable to a commercial 20 wt % Pt/C catalyst) and outstanding oxygen evolution activity (superior to a commercial 20 wt % IrO2/C catalyst), thus enabling efficient bifunctional oxygen electrocatalysis and stability when applied in prototype rechargeable zinc-air batteries. The remarkable electrochemical properties of CoNi/N-FLG originate from its unique core-shell structure and favorable electron penetration effects, thereby optimizing the adsorption/desorption strengths of intermediates formed during the oxygen reduction and oxygen evolution reactions.

Plasma enhanced atomic layer deposition and atomic layer etching of gallium oxide using trimethylgallium

Atomic layer etching driven by self-limiting thermal reactions has recently been developed as a highly conformal and isotropic technique for low damage atomic scale material removal by sequential exposures of vapor phase reactants. Gallium oxide (Ga2O3) is currently among the materials of interest due to a large variety of applications including power electronics, solar cells, gas sensors, and photon detectors. In this study, Ga2O3 was deposited by plasma enhanced atomic layer deposition using trimethylgallium [TMG, Ga(CH3)3] and O2 plasma at a substrate temperature of 200 °C. We report a newly developed method for Ga2O3 thermal atomic layer etching, in which surface modification is achieved through HF exposure resulting in a gallium fluoride surface layer, and then removed through volatile product formation via ligand exchange with TMG. Saturation of the precursor exposure at a substrate temperature of 300 °C resulted in an etch rate of 1.0 ± 0.1 Å/cycle for amorphous Ga2O3. Uniformity and conformality of the atomic layer etching process were confirmed via atomic force microscopy with a measured surface roughness of 0.55 ± 0.05 nm that remains unchanged after etching. The use of TMG for etching may expand available precursors for atomic layer etching processes, while allowing for both etching and deposition of Ga2O3 using the same metalorganic precursor.

“Host-Guest” crystalline Mo/Co-framework induced phase-conversion of MoCx in carbon hybrids for regulating absorption of electromagnetic wave

Unveiling the structural design and synthesizing mechanism of the metallic crystalline precursors is of great significance for constructing hetero-interfaces and enhancing the EW attenuation in electromagnetic wave absorbing materials (EWAMs). Herein, two diverse crystalline Mo-species incorporated metal-organic framework precursors were designed for studying the phase conversion during the high-temperature treatment and evaluating their electromagnetic wave (EW) absorbing mechanism. The MoO4 as the node on the framework and the Mo12O40 cluster as guest in the framework derived β-Mo2C and η-MoC in MoCx/Co@NC hybrids, respectively. The EW absorbing performance results indicated a superior RLmin of −47.72 dB at 11.76 GHz at the thickness of 2.0 mm and a wide effective absorption bandwidth (EAB) of 4.58 GHz (7.44–12.02 GHz) covering the whole X-band at the thickness of 2.5 mm for η-MoC/Co@NC. The “Host-Guest” precursor induced the uniformly distributed η-MoC and metallic Co nanoparticles in the N-doped carbon matrix, generating abundant 3d/4d hetero-interfaces and intense synergistic interaction. The crucial role of thermal stability of the crystalline framework and phase conversion among multi-components were investigated, which lighten the structural design of the high-performance EWAMs in the future.

Sulfur-modulated FeNi nanoalloys as bifunctional oxygen electrode for efficient rechargeable aqueous Zn-air batteries

Currently, FeNi nanoalloys have received considerable attention for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in rechargeable aqueous zinc (Zn)-air batteries (ZABs) because of their high content and good chemical stability. However, their poor electronic conductivity, small surface area, and sluggish activity seriously hinder their catalytic performance. Herein, S-modulated FeNi nanoalloys supported by hierarchically porous carbon (S-FeNi/PC) are synthesized through the thermal treatment of metal-organic precursors for efficient bifunctional oxygen catalysis. S decoration endows S-FeNi/PC with a superior OER performance while maintaining an ORR performance that is comparable to that of Pt/C. Hence, S-FeNi/PC exhibits excellent bifunctional oxygen catalytic activity, outperforming the noble-metal-based composite catalysts of Pt/C and RuO2. Notably, the ZABs assembled with S-FeNi/PC exhibit high specific capacity (792 mA h g−1), high peak power density (123.5 mW cm−2), and remarkable durability for 700 charge/discharge cycles at 10 mA cm−2, which surpasses the performance of commercially available Pt/C-RuO2 and other catalysts in previously reported studies. This study will provide not only new bifunctional oxygen electrodes for efficient ZAB devices but also new insights into the design of FeNi-based materials for a wide range of catalytic applications.

Elucidating the Reaction Mechanism of Atomic Layer Deposition of Al2O3 with a Series of Al(CH3)xCl3-x and Al(CyH2y+1)3 Precursors.

The adsorption of metalorganic and metal halide precursors on the SiO2 surface plays an essential role in thin-film deposition processes such as atomic layer deposition (ALD). In the case of aluminum oxide (Al2O3) films, the growth characteristics are influenced by the precursor structure, which controls both chemical reactivity and the geometrical constraints during deposition. In this work, a systematic study using a series of Al(CH3)xCl3-x (x = 0, 1, 2, and 3) and Al(CyH2y+1)3 (y = 1, 2, and 3) precursors is carried out using a combination of experimental spectroscopic techniques together with density functional theory calculations and Monte Carlo simulations to analyze differences across precursor molecules. Results show that reactivity and steric hindrance mutually influence the ALD surface reaction. The increase in the number of chlorine ligands in the precursor shifts the deposition temperature higher, an effect attributed to more favorable binding of the intermediate species due to higher Lewis acidity, while differences between precursors in film growth per cycle are shown to originate from variations in adsorption activation barriers and size-dependent saturation coverage. Comparison between the theoretical and experimental results indicates that the Al(CyH2y+1)3 precursors are favored to undergo two ligand exchange reactions upon adsorption at the surface, whereas only a single Cl-ligand exchange reaction is energetically favorable upon adsorption by the AlCl3 precursor. By pursuing the first-principles design of ALD precursors combined with experimental analysis of thin-film growth, this work enables a robust understanding of the effect of precursor chemistry on ALD processes.

“One-for-two” strategy: The construction of high performance positive and negative electrode materials via one Co-based metal organic framework precursor for boosted hybrid supercapacitor energy density

In this work, using a Co-based metal organic framework (Co-MOF) array as precursor, the high performance supercapacitor positive electrode (CNVS: Ni/V-doped Co3S2@Co/Ni-doped VS2 hetero-structure) and negative electrode (CNFS: Fe/V-doped Co3S2@Co/Fe-doped VS2 hetero-structure) are successfully constructed by a “one-for-two” synthesis strategy. Benefiting from their unique hollow triangular arrays, rich mesoporous structure constructed by M3S2/MS2 heterogeneous interface, abundant active centers originating from the defect of elements doping, the optimized CNVS and CNFS can improve the transfer ratio of electrons and electrolytes for fast kinetics, and provide more electroactive sites for deeply redox reaction. Therefore, an outstanding specific capacitance of 6556 mF cm−2 (910.56 μA h cm−2) is achieved by CNVS electrode under 0–0.5 V (vs. Hg/HgO) at 2 mA cm−2, and the CFVS electrode displays a high specific capacitance of 6195 mF cm−2 (1720 μA h cm−2) under −0.1 to −1.1 V range (vs. Hg/HgO) at 5 mA cm−2. Furthermore, a high-performance hybrid supercapacitor (HSC) is assembled with CNVS as the positive electrode, and CFVS as the negative electrode, which presents an ultrahigh energy density of 0.83 mWh cm−2 at a power density of 4.56 mW cm−2, and excellent cycle performance of maintaining 79.6% initial capacity after 5000 cycles.

Synthesis and characterization of SnO2 thin films using metalorganic precursors

Tetrakis (dimethylamino) tin(IV) (TDMASn) is a metal organic precursor used for fabricating transparent conducting tin oxide (SnO2) thin films via atomic layer deposition process (ALD). This study reported for the first time, a spin coating fabrication process of transparent conducting SnO2 thin films using TDMASn as the precursor for electrode materials of solar cells substrate. The samples were prepared using sol–gel spin-coating process and annealed at different temperatures to form metastable crystal structured SnO2 thin films. The manufactured thin films consequently underwent X-ray diffraction (XRD), scanning electron microscope (SEM), UV–vis spectroscopy, and resistivity analysis. The XRD analysis certified the films to be of polycrystalline structure, with the SEM results revealing variations in film thicknesses. The UV–vis analysis demonstrated a peak absorption band at 250 nm, while the highest transmittance of 83.2% in the visible range was noticed at the 550 °C sample.

Morphology and composition dependence of multicomponent Cu-based nanoreactor for tandem electrocatalysis CO2 reduction

Multicomponent heterogeneous catalysts present excellent catalytic performance attributed to the synergistic effect of multi-sites. Nevertheless, identifying the composition of the multi-sites and exploring the synergistic catalytic mechanisms for the multiple active sites in electrocatalytic CO2 reduction reaction (CO2RR) still lack intensive study. This work regulates the chemical composition of Cu-based nanoreactors readily by adjusting the geometrical morphology of metal-organic frameworks precursor. The obtained cuboctahedron nanoreactor containing Cu-N4/Cu2O/Cu multiple active sites exhibits excellent CO2RR selectivity towards deep reduction product (80%) with high current density. Moreover, the tandem catalytic mechanism of multicomponent active sites has been studied intensively. The CO2 molecule is firstly reduced in Cu-N4 sites to form CO and then the CO is transfered to Cu2O/Cu sites for further deep reduction. The high concentration of CO provided by Cu-N4 sites decreases the free energy of rate-determining step for CH4 products in Cu2O sites. This work provides a promising direction for designing and synthesizing multicomponent Cu-based tandem catalysts to access high efficiency and selectivity in the electrocatalytic CO2 reduction reaction.

Monte Carlo simulation of the surface-assisted self-assembly of metal-organic precursors comprising phenanthrene building blocks

Surface-assisted fabrication of carbon-based covalent architectures has been a promising pathway to low-dimensional materials with special physicochemical properties and functions. In this contribution, the Monte Carlo simulation method was used to predict the formation of metal-organic precursors preceding the covalent Ullmann coupling of halogenated phenanthrene monomers. To that end, the coarse-grained model of adsorbing (111) surface, phenanthrene molecules and linking adatoms was proposed, in which the monomers were equipped with active centers providing directional metal-linker interactions. The simulations performed for various intramolecular distributions of active centers in the phenanthrene unit (corresponding to halogen positions) resulted in diverse metal-organic superstructures, including chains, ring oligomers, triangular and windmill trimers, ladders, and periodic and aperiodic networks. For those molecules which were chiral in 2D the corresponding calculations in enantiopure and racemic overlayers were also carried out. These simulations resulted in characteristic examples of both advantageous and adverse effect of the opposite enantiomer on the ordering in racemic systems. Our theoretical findings provided some hints on how to halogenate monomeric phenanthrene units to create polymeric architectures with presumed structural features, such as topology, periodicity, connectivity, ramification and porosity.

Selective Hydration of Rutile TiO2 as a Strategy for Site-Selective Atomic Layer Deposition.

The feasibility of a site-selective hydration strategy that enables site-selective atomic layer deposition (ALD) is investigated among four rutile TiO2 facets [(110), (100), (101) and (001)] and their most prevalent step edges. First-principles simulations of asymmetric slab models were utilized to create accurate representations of pristine terrace and step edge sites. The adsorption free energies for molecular and dissociative adsorption of H2O were calculated to evaluate this strategy as a viable route to step edge selectivity. We predict that selective hydroxylation is possible on the 110 and 001 step edges and further computationally evaluate three metalorganic ALD precursors for their compatibility with the selective hydration strategy. Experimental evidence for delayed nucleation of ALD on rutile (001), (110), and (100) TiO2 single crystals corroborates predictions of the dehydration of the surface and suggests the possibility of site-selective ALD.

Achieving efficient toluene oxidation over metal–organic framework-derived Pt/CeO2-Co3O4 catalyst

Pt/CeO2-Co3O4 catalyst (Pt/CeCo) was prepared by anchoring Pt species on the CeO2-Co3O4 support that derived from metal-organic framework precursor. The Pt/CeCo catalyst exhibited an eminent toluene catalytic activity compared with Pt/Co3O4. The improvement of catalytic performance for Pt/CeCo catalyst was attributed to surface Co3+ sites and Pt0 species by the enhanced SMSI, where Co3+ sites were benefical for the toluene activation and Pt0 species were conducive to oxygen activation. Moreover, the high mobility of surface active oxygen, excellent low-temperature reducibility and plentiful oxygen vacancies further ensured the exceptional catalytic performance. The in situ DRIFTS demonstrated that the ring-opening of benzoic acid into maleic anhydride was the rate-determining step and that the Pt/CeCo catalyst underwent an accelerated toluene oxidation process compared with Pt/Co3O4 catalyst.

Plasma diagnostics and modeling of lithium-containing plasmas

Thin-film deposition from chemically reactive multi-component plasmas is complex, and the lack of electron collision cross-sections for even the most common metalorganic precursors and their fragments complicates their modeling based on fundamental plasma physics. This study focuses on understanding the plasma physics and chemistry in argon (Ar) plasmas containing lithium bis (trimethylsilyl) amide used to deposit Li x Si y thin films. These films are emerging as potential solid electrolytes for lithium-ion batteries, and the Li-to-Si ratio is a crucial parameter to enhance their ionic conductivity. We deposited Li x Si y films in an axial flow-through plasma reactor and studied the factors that determine the variation of the Li-to-Si ratio in films deposited at various points on a substrate spanning the entire reactor axis. While the Li-to-Si ratio is 1:2 in the precursor, the Li-to-Si ratio is as high as 3:1 in films deposited near the plasma entrance and decreases to 1:1 for films deposited downstream. Optical emission from the plasma is dominated by Li emission near the entrance, but Li emission disappears downstream, which we attribute to the complete consumption of the precursor. We hypothesized that the axially decreasing precursor concentration affects the electron energy distribution function in a way that causes different dissociation efficiencies for the production of Li and Si. We used Li line intensities to estimate the local precursor concentration and Ar line ratios to estimate the local reduced electric field to test this hypothesis. This analysis suggests that the mean electron energy increases along the reactor axis with decreasing precursor concentration. The decreasing Li-to-Si ratio with axially decreasing precursor concentration may be explained by Li release from the precursor having lower threshold energy than Si release.

Half-cell electrode assessments of a crossover-tolerant direct methanol fuel cell with a platinum group metal-free cathode

In this work, a platinum group metal- free (PGM-free) Fe-N-C oxygen reduction reaction (ORR) catalyst derived from metal organic framework precursors (Fe-MOF) is evaluated at the cathode side of a direct methanol fuel cell (DMFC). A wide range of methanol concentrations were used, and the performance of the DMFC using air was evaluated and compared to a commercial Pt/C cathode. We conducted our tests with a custom, integrated H2 reference electrode that separately provided the anode and cathode overpotentials. This allowed us to perform a Tafel analysis on both electrodes and understand the dominant polarizations involved at the PGM-free cathode and the PtRu/C anode. Overall, we achieved a high cell performance using a Fe-N-C based catalyst under liquid methanol and air operation with a peak power density of 111 mW/cm2, where the cathode presented a markedly larger contribution to the voltage loss versus the anode. Additionally, we used nanoscale X-ray computed tomography (nano-CT) to image the Fe-N-C cathode and investigate the ionomer and pore size distributions allowing us to identify areas of improvement for catalyst layer fabrication.