Molecule-electrode hybrid materials based on cobalt phthalocyanine (CoPc) supported on carbon nanostructures have emerged as highly effective electrocatalysts for the selective six-electron reduction of CO 2 to methanol (e-methanol). However, the strong π-stacking tendency of CoPc leads to poor solubility and hinders its uniform integration with conductive supports such as multiwalled carbon nanotubes (CNTs), limiting the controlled preparation of well-defined hybrid architectures. Here, we introduce a thermocleavable CoPc-ester precursor strategy that enables the synthesis of a highly dispersed CoPc-acid@CNT hybrid catalyst. Controlled thermal activation cleaves the solubilizing ester groups, generating insoluble CoPc-acid species that molecularly anchor onto the CNT surface. This approach promotes efficient active-site dispersion, confirmed through electron microscopy, and strengthens Co-CNT electronic coupling, as evidenced by operando IR spectroscopy, which reveals a steeper Stark tuning rate for the adsorbed *CO intermediate compared to conventionally prepared CoPc@CNT materials. The optimized hybrid catalyst delivers efficient aqueous CO 2 reduction to methanol, achieving a Faradaic efficiency (FE) of 44% and a total current density of 19 mA/cm², modestly surpassing the benchmark CoPc@CNT system (38%, 26 mA/cm²). To assess the commercial relevance of e-methanol electrolyzers employing such molecular hybrid catalysts, we also present a detailed techno-economic analysis (TEA) and life-cycle analysis (LCA). The TEA indicates that continued technical improvements could lower the minimum selling price of e-methanol to $0.41/kg, while the LCA shows a 34% reduction in carbon intensity (CI) relative to fossil-derived methanol, with the potential for near-zero CI when coupled with strategic renewable-energy integration. Collectively, these results highlight the promise of thermocleavable molecular precursors for achieving tailored catalyst anchoring and dispersion on conductive substrates, advancing the development of highly efficient and selective CO 2 -to-methanol electrocatalysts.

Nickel-based layered cathodes such as LiNiO2 offer high energy density for lithium-ion batteries, yet improvements in cycling performance and safety are required for practical use─often achieved through manganese and cobalt substitution as in LiNi0.80Mn0.10Co0.10O2 (NMC811). However, how such substitution impacts calcination, the key process that governs lithiation, structural ordering, crystallization, and ultimately the resulting material properties, remains unclear. Here, we investigate substitution-mediated calcination dynamics in NMC811 compared to LiNiO2 using multiscale-correlated in situ spectroscopy and atomistic-to-mesoscale modeling. While both systems progress through the same sequence of intermediates toward the thermodynamically favored layered phase, NMC811 exhibits an earlier onset of layering, concurrent with hydroxide decomposition followed by sluggish crystallization. Modeling reveals that Mn and Co lower the energy barrier for lithium incorporation and ordering but increase the penalty for interlayer gliding, thereby slowing crystal growth at elevated temperatures. This substitution-mediated decoupling of lithiation and crystallization explains the fine-grained microstructure observed in NMC811 versus coarsened particles in LiNiO2 and establishes a mechanistic framework for predictive microstructure engineering of Ni-based cathodes.

The oxygen evolution reaction (OER) is integral to several electrochemical energy conversion and storage technologies, including carbon dioxide reduction to value added fuels, nitrogen reduction to ammonia, reversible fuel cells, rechargeable metal-air batteries, and water electrolysis to produce hydrogen. One of the main challenges is optimizing the state-of-the-art IrO x -based catalysts’ OER activity and stability. This work investigates six commercial IrO x catalysts with diverse physicochemical properties with the goal of establishing how various structural and compositional variations influence OER activity and stabilityThe U.S. Department of Energy’s H2New consortium characterized these catalysts with a wide range of methods, collecting a combination of characterization techniques, including synchrotron X-ray scattering, X-ray diffraction, X-ray absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller pore and surface area analysis, electrical conductivity measurement, and aqueous electrochemical studies. While certain correlations are obvious, others may be missed, when dealing with such large parameter space. To address this, this work used principal component analysis (PCA) to identify the key correlations between variables extracted from various methods identifying key properties that govern performance and durability of the IrO x catalysts, providing insight to guide the rational design of robust, efficient IrO x OER catalysts. Parameters extracted from XPS showed clear correlations with electrochemical properties, however, assignments of XPS peaks, and precise nature of species are still debated. To address this, time of flight – secondary ion mass spectrometry (ToF-SIMS) analysis was conducted on the same samples, providing surface, subsurface and bulk information, complementary to information gained from XPS. PCA was then used to link specific peaks obtained by curve fitting XPS data and fragments detected in ToF-SIMS and correlate them with electrochemical metrics. Acknowledgements: Funding was provided by the U.S. Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office through the H2NEW Consortium. This work was authored in part by Argonne National Laboratory which is managed for the U.S. DOE by the University of Chicago Argonne, LLC under Contract No. DEAC02−06CH11357, by Oak Ridge National Laboratory, managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725, and by Lawrence Berekeley National Laboratory, managed by the University California under contract No. DE-AC02-0511231. The Advanced Light Source and the Advanced Photon Source are supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-05CH11231 and Contract No. DEAC02−06CH11357, respectively. The U.S. government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. government retains a nonexclusive, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for the U.S. government purposes.

The oxygen evolution reaction (OER) is integral to several electrochemical energy conversion and storage technologies, including carbon dioxide reduction to value added fuels, nitrogen reduction to ammonia, reversible fuel cells, rechargeable metal-air batteries, and water electrolysis to produce hydrogen. Iridium oxide (IrO x ) is widely recognized as the benchmark OER catalyst for acidic environments. Despite widespread use of IrO x catalysts, most notably in proton-exchange membrane water electrolyzers (PEMWEs), a comprehensive understanding of the physicochemical properties of commercial catalysts and the impact of these properties on both the activity and stability of these catalysts is lacking. Here, we study commercial IrO x catalysts with different physicochemical properties, three nominally considered amorphous and three rutile, to elucidate how structural and compositional variations affect OER activity and stability. Utilizing standardized aqueous electrochemical protocols, time-resolved dissolution quantification using inductively-coupled plasma mass spectrometry, and physicochemical characterization, including multiple synchrotron X-ray techniques, we systematically correlate catalyst properties with OER performance and degradation behavior aided by principal component analysis (PCA). Our results demonstrate the general trend of amorphous IrO x having higher intrinsic activity but limited stability and crystalline rutile IrO2 having lower activity but enhanced stability against dissolution. The trends within the amorphous and rutile catalyst groups correlate with inherent material properties, including phase composition and structure, crystallinity, particle size, surface area, and surface structure/chemistry. Notably, we identify a rutile catalyst with the largest crystallite/domain sizes, moderate surface area, a small fraction of hydrous phase, and a favorable pore structure (trimodal distributions of pore sizes ranging from 2-5 nm) that exhibits the best balance between activity and stability among the six catalysts studied here. These findings illustrate a fundamental structure-governed trade-off between activity and stability and highlight the critical role of surface chemistry modification and structure engineering in IrO x catalyst optimization.

The synthesis of high value-added aromatics used in the chemical applications via CO2 modified Fischer-Tropsch synthesis (CO2-FTS) pathway is promising. Here, a copper modified Fe-based catalyst was synthesized, after mixing with HZSM-5 treated with polyethylene glycol (PEG), 86.92 % aromatics selectivity in the liquid was achieved. The effect of Cu promoter on the stability of oxides and its impact on zeolites due to migration were further investigated. It was Cu in oxygen removal and coke resistance on oxides and in adjusting the product distribution on zeolite that stabilized the active phase Fe5C2 and reduced the coke deposition on bifunctional catalysts, resulting in them running for 200 h without distinct deactivation. Based on the stability test, an empirical power-law kinetic model was established. To reduce the complexity of the model, the feedstock and products were divided into six lumps. Activation energy and pre-exponential factor of the reactions were determined by the Arrhenius equation. The comparison between the experimental and calculated results shows that this model can accurately predict the CO2 conversion and products distribution. Therefore, it provides a guidance for reactor design and simulation calculations.

Understanding the fundamental insights of electrochemical reactions, particularly the oxygen evolution reaction (OER) in low-temperature proton-exchange membrane water electrolyzers (PEMWE), is crucial for enhancing corresponding overall cell performance, including both activity and stability. 1 Iridium oxide (IrO x ) is the standard OER electrocatalysts for electrochemical water splitting in the acidic environment of PEMWE due to its sustained OER activity over time versus more active, but less durable alternatives such as RuO x . 2,3 Within the IrO x class of OER catalysts, there are three broad classes categorized by their atomic structure and crystallinity: rutile, amorphous, and hydrous. Understanding the impact of the physicochemical properties on the electrochemical performance and durability of IrO x -based catalysts within these classes is essential for developing strategies to maximize the efficiency and durability of PEMWE systems. This presentation explores six commercial IrO x catalysts with varying morphologies (e.g., particle size and surface area) and atomic structures (e.g., amorphous hydrous and rutile forms) to examine how these factors influence OER behavior. The activity and stability of these catalysts are evaluated using rotating disk electrode techniques, which involve analyzing their redox features and estimating OER activity based on variations in electrochemical capacitance, phase composition, and morphology. The identified most active and the most stable IrO x -based catalysts are further investigated to design a promising OER anode with a unique gradient electrode architecture for PEMWE applications. This study provides insights into the relationship between morphology, atomic structure, and OER mechanisms in commercial IrO x catalysts, paving the way for the development of more efficient and durable electrocatalysts for water splitting. Acknowledgements This research is supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office under the auspices of the H2NEW Consortium. Argonne National Laboratory is managed by the U.S Department of Energy by the University of Chicago Argonne, LLC, also under contract DE-AC-02-06CH11357. Reference "Technical Targets for Proton Exchange Membrane Electrolysis", https://www.energy.gov/eere/fuelcells/technical-targets-proton-exchange-membrane-electrolysis Gao, G. et al. Recent advances in Ru/Ir-based electrocatalysts for acidic oxygen evolution reaction. Applied Catalysis B: Environmental 343 , 123584 (2024). Xu, J. et al. IrO x ·nH 2 O with lattice water–assisted oxygen exchange for high-performance proton exchange membrane water electrolyzers. Science Advances 9 , eadh1718 (2023).

A deeper understanding of the thermodynamics and kinetics governing the lithiation and layering mechanisms of NMC cathode materials (LiNi x Mn y Co z O2, where x + y + z = 1) offers valuable insights for enhancing synthesis methods and improving cathode performance. By employing atomistic and mesoscale approaches informed by in situ powder X-ray diffraction (PXRD) experiments, critical parameters for comprehending lithiation and layering processes and reaction rates were identified. The mesoscale approach captured the evolution of the phases and crystallite size observed in the in situ PXRD, revealing the differences in reaction rates with the use of different lithium salts and starting precursors. Ab initio molecular dynamics (AIMD) underscored the importance of vacancies and structural defects in promoting ion mobility and facilitating the nucleation of a layered domain. This nucleation disrupts the symmetry of disordered phases, ultimately creating a strained phase that serves as a buffer between layered and disordered regions. The lithiation and layering processes reflect a dynamic balance between the thermodynamic drive for a low-energy layered structure and the kinetic of diffusion, which is influenced by temperature and lithium vacancy concentration. Overall, reaction mechanisms are driven by the inherent defects of the intermediate phase that differ for NMC cathode materials. The lithium salts impact the rates of lithiation and layering, with a much slower process for Li2CO3.

To enable further adoption of proton exchange membrane water electrolysis (PEMWE), we must continue to advance our fundamental understanding of the activity and degradation mechanisms of state-of-the-art iridium-based oxide catalysts for the oxygen evolution reaction (OER). Here, we employ synchrotron-based X-ray diffraction (XRD), pair distribution function (PDF), in situ and operando X-ray absorption spectroscopy (XAS) of commercial iridium oxide catalysts to i) explore the potential dependence of the iridium oxidation state and local coordination structure and correlate these findings with dissolution data and a reaction model, and ii) understand the physiochemical nature of numerous commercially available products toward informing the selection of a catalyst to enable studies of materials integration and degradation mechanisms of PEMWEs within the framework of the U.S. Department of Energy H2NEW consortium. Among the sources of degradation of OER catalysts that currently hinder more widespread adoption of PEMWEs is the dissolution of Ir, resulting in the loss of catalytic activity over time. Kasian et al. proposed reaction mechanisms for Ir dissolution that vary with potential – at low overpotentials, Ir 3+ dissolution following O 2 release is in competition with re-oxidation to Ir 4+ O 2 . At high overpotentials, IrO 2 OH is oxidized to Ir 6+ O 3 , which may dissolve as IrO 4 2- after reacting with water. 1 In this work, we investigate the oxidation state and local coordination environment of Ir in two commercially available IrO x catalysts through in situ and operando Ir L 3 -edge XAS; we then correlate these results with Ir dissolution measured using inductively coupled plasma mass spectrometry for hydrous IrO x under varying applied potentials. We find that in hydrous IrO x , Ir continues to oxidize up to a certain potential, above which the oxidation state plateaus. We compare this finding with experimental dissolution data in addition to a reaction model developed from proposed mechanisms, both of which display a decrease in Ir dissolution above the same potential. This result diverges from the conventionally observed activity-stability tradeoff and affirms the theory that a passivating oxide is formed at high overpotentials. Furthermore, we have characterized six commercially available iridium oxide catalysts using ex situ XAS, synchrotron XRD, and PDF measurements to detect differences in crystallinity, structure, and oxidation state and correlate these differences with OER performance. From these techniques, there are two distinct groups of catalysts: i) amorphous or hydrous Ir oxides exhibiting local ordering, and ii) crystalline Ir oxides with varying crystallite sizes. These characteristics are found to correlate with electrochemical redox behavior and OER activity. This work improves our understanding of the dissolution mechanisms of iridium oxide catalysts and lays the groundwork for improved understanding of the impact of anode catalyst properties on the performance and durability of PEMWEs. References (1) Kasian et al., Angewandte Chemie International Edition 2018 , 57 (9), 2488-2491.

Fe-N-C catalysts are the most promising platinum group metal (PGM) free electrocatalysts for oxygen reduction reaction (ORR). Significant progress has been made in understanding the active site structure and activity and improving the ORR performance. It is generally accepted that the Fe-N-C sites are associated with FeN x centers embedded in a defective nitrogen-doped graphene. As reported in literature, both pyrrolic N and pyridinic N can support Fe single site; however, it is difficult to distinguish between the two. Furthermore, experimental characterization, such as in-situ X-ray absorption spectroscopy (XAS) and Mössbaruer, has elucidated the redox behavior of Fe 2+ to Fe 3+ during the reaction. Interestingly, in different acidic environments, the ORR activity exhibits differently. For instance, in comparison between H 2 SO 4 and HClO 4 solutions at the same pH value, the Fe redox happens at lower potential in H 2 SO4; however, the right shift of half-wave potential (E 1/2 ) of ORR in H 2 SO 4 , compared with HClO 4 , indicates higher ORR activity. This indicates that the electrolyte systems have a significant impact on ORR activity. To further understand the active site structure and their ORR activity, density functional theory (DFT) calculations utilizing explicit solvation effect are carried out. XANES simulation using FDMNES suggests that as prepared catalysts could consist of Fe single atom sites supported by both pyrrolic and pyridinic N atoms; however, the pyrrolic species are not as stable as pyridinic species in solution. As presented by DFT simulation, the anions in solutions can interact with FeN 4 site differently. SO 4 2- binds strongly with the FeN 4 center, while HSO 4- and ClO 4- interact rather weakly. Furthermore, the redox potential and limiting potential are evaluated via mechanistic study. By focusing on more stable Fe center supported by pyridinic N, the results suggest that the transformation of Fe 2+ to Fe 3+ happens at 0.52 V in H 2 SO 4 , which is lower than that in HClO 4 , 0.69V. More interestingly, the limiting potential (activity) of ORR in H 2 SO 4 is higher than that in HClO 4 (0.94 vs 0.68 V). DFT simulation indicated that the anions in electrolyte can impact the Fe redox behavior and ORR performance, which agrees well with the experimental investigation. This work also provides significant guidance to further improve ORR activity of Fe-N-C catalysts.

Hydrogen production through water electrolysis is a crucial technology to enable the transition to a carbon neutral, hydrogen-based economy. One of the primary types of electrolyzers is the low-temperature proton-exchange membrane water electrolyzer (PEMWE). As with the analogous proton-exchange membrane fuel cells, platinum group metal electrocatalysts are utilized due to their activity and stability in acidic environment. Electrocatalysis R&D efforts for PEMWEs primarily focus on the oxygen evolution reaction (OER) since it is several orders of magnitude kinetically slower than the hydrogen evolution reaction (HER).1 Iridium-based metal oxides (IrOx) are regarded as the best PEM electrolyzer electrocatalysts as they balance activity and stability.2 However, improvements are needed in both areas to enable minimization of Ir loading to meet system cost targets while also meeting challenging performance and lifetime targets.3 An understanding of the factors affecting both the activity and stability of Ir-based OER catalysts is needed to develop strategies to enable both high OER activity and long-term stability of the PEMWE anode catalyst. This presentation will describe our studies of the effects of perfluorosulfonic acid (PFSA) binder on the OER kinetics and the factors influencing the stability of two commercial Ir-based OER catalysts, one comprised of IrOx only and the other also containing TiOx. Measurements of OER kinetics as a function of ionomer to catalyst ratio utilizing rotating disc electrode and cavity microelectrode methods in an acidic aqueous electrochemical environment will be described. Dissolution and loss of Ir under the operating conditions of the PEMWE anode is considered to be one of the main PEMWE anode degradation mechanisms.4 To understand the factors affecting this phenomenon, the potential and time-dependence of Ir (and Ti) were determined using an electrochemical flow cell system connected to an inductively-coupled plasma-mass spectrometer (ICP-MS) capable of detecting trace concentrations ( Acknowledgements This research is supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office under the auspices of the H2NEW Consortium. Argonne National Laboratory is managed for the U.S Department of Energy by the University of Chicago Argonne, LLC, also under contract DE-AC-02-06CH11357. References A. Raveendran, M. Chandran, and R. Dhanusuraman, RSC Adv., 13 (2023) 3843. J. Ouimet, J.R. Glenn, D.D. Porcellinis, A.R. Motz, M. Carmo, K.E. Ayers, ACS Catalysis, 12 (2022) 6159. "Technical Targets for Proton Exchange Membrane Electrolysis", U.S. Department of Energy, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office, March, 2023. Zeng, R. Ouimet, L. Bonville, A. Niedzwiecki, C. Capuano, K. Ayers, A.P. Soleymani, J. Jankovic, H. Yu, R. Maric, et al., J. Electrochem. Soc., 169(5) (2022) 054536.

Minimization of bulk and surface free energy acts as the driving force for precipitation of transition metal carbonates. Thermodynamically dominated precipitates form single crystals, and kinetically controlled deposits show spherical morphology.

Calcination is a solid-state synthesis process widely deployed in battery cathode manufacturing. However, its inherent complexity associated with elusive intermediates hinders the predictive synthesis of high-performance cathode materials. Here, correlative in situ X-ray absorption/scattering spectroscopy is used to investigate the calcination of nickel-based cathodes, focusing specifically on the archetypal LiNiO2 from Ni(OH)2. Combining in situ observation with data-driven analysis reveals concurrent lithiation and dehydration of Ni(OH)2 and consequently, the low-temperature crystallization of layered LiNiO2 alongside lithiated rocksalts. Following early nucleation, LiNiO2 undergoes sluggish crystallization and structural ordering while depleting rocksalts; ultimately, it turns into a structurally-ordered layered phase upon full lithiation but remains small in size. Subsequent high-temperature sintering induces rapid crystal growth, accompanied by undesired delithiation and structural degradation. These observations are further corroborated by mesoscale modeling, emphasizing that, even though calcination is thermally driven and favors transformation towards thermodynamically equilibrium phases, the actual phase propagation and crystallization can be kinetically tuned via lithiation, providing freedom for structural and morphological control during cathode calcination.

Iron nitrogen carbon (Fe-N-C) electrocatalysts remain the most promising platinum group metal-free (PGM-free) catalysts for the oxygen reduction reaction (ORR) in polymer electrolyte fuel cells (PEFCs). Although significant progress has been made in recent years in improving both the ORR activity and stability of the Fe-N-C catalysts, further enhancement in the catalyst durability while maintaining the activity is imperative for the practical applications. One of the major factors that hinders the further enhancement of the catalysts is the lack of clear understanding of the nature of the active sites and density of the active sites in the Fe-N-C catalysts due to the complexity of the Fe-N-C catalysts’ composition and structure. Gaseous nitric oxide was proven to be a suitable probe molecule that can bond to Fe and impede the ORR of the Fe-N-C catalysts. In recent years, we have studied the effects of gas-phase adsorption and desorption of nitric oxide on the redox features and ORR activity on Fe-N-C catalysts synthesized by different methods. We have used various characterization tools to quantify the amount of nitric oxide adsorbed and to identify the adsorption sites and geometry, including electrochemical stripping, temperature programmed desorption, and in situ X-ray techniques. The corresponding results obtained will be summarized in this talk. The implication of these results on the nature of the ORR active sites of the Fe-N-C catalysts will be discussed. Acknowledgements This work was supported by the U.S. Department of Energy (DOE), Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office (HFTO) under the auspices of the Electrocatalysis Consortium (ElectroCat 2.0). This work utilized the resources of the Advanced Photon Source, a U.S. DOE Office of Science user facility operated by Argonne National Laboratory for DOE Office. This work was partially authored by Argonne, a U.S. Department of Energy (DOE) Office of Science laboratory operated for DOE by UChicago Argonne, LLC under contract no. DE-AC02-06CH11357.

Renewable hydrogen generation using the low-temperature proton-exchange membrane water electrolyzer (PEMWE) represents a crucial technology for achieving global zero-carbon emissions. Iridium oxide (IrOx) stands out as a primary platinum group metal catalyst for the anode in electrochemical water splitting due to a balance in activity and stability in acidic environments.1 However, the anode catalyst performance is still predominately hampered by the sluggish kinetics of the oxygen evolution reaction (OER) compared to the hydrogen evolution reaction (HER) at the Pt cathode.2 Therefore,understanding the factors influencing the OER kinetics of Ir-based catalysts is essential for developing strategies to achieve high OER activity in the PEMWE anode electrocatalysts. This presentation will delve into our investigation of how the perfluorosulfonic acid (PFSA) binder affects the anode catalyst OER behaviors, specifically the corresponding kinetics and activity of two commercial Ir-based OER catalysts, IrOx from Alfa Aesar and TiO2-decorated IrOx (IrTiOx) from Umicore, as a function of the PFSA ionomer-to-catalyst (I/C) ratio. We combined the cavity microelectrode (CME) technique, which offers a direct approach to study OER kinetics without the ionomer,3 with the rotating disc electrode (RDE) technique, which allows to assess the impact of PFSA on OER kinetics and activity at varied I/C ratios in an acidic electrolyte. The study provided valuable insights into ionomer dependent OER mechanisms, elucidating the intricate interactions among the ionomer, catalyst, and reaction intermediates. Acknowledgements This research is supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office under the auspices of the H2NEW Consortium. Argonne National Laboratory is managed by the U.S Department of Energy by the University of Chicago Argonne, LLC, also under contract DE-AC-02-06CH11357. Reference S. M. Alia, M.-A. Ha, G. C. Anderson, C. Ngo, S. Pylypenko and R. E. Larsen, Journal of The Electrochemical Society, 2019, 166, F1243. E. Oakton, D. Lebedev, M. Povia, D. F. Abbott, E. Fabbri, A. Fedorov, M. Nachtegaal, C. Copéret and T. J. Schmidt, Acs Catalysis, 2017, 7, 2346-2352. J. Behnken, M. Yu, X. Deng, H. Tüysüz, C. Harms, A. Dyck and G. Wittstock, ChemElectroChem, 2019, 6, 3460-3467.

The iron redox behavior and oxygen reduction reaction (ORR) activity of Fe-N-C ORR electrocatalysts synthe-sized by a variety of techniques were investigated as a function of the identity of the electrolyte anion (bisulfate/ sulfate or perchlorate) at a constant pH. In situ X-ray absorption spectroscopy data support the assignment of the redox peaks in the voltammograms to the Fe3+/Fe2+ redox couple. It was found that for a given Fe-N-C catalyst, there is a correlation between the Fe redox couple peak potential and the ORR activity in perchloric acid electrolyte, but not in sulfuric acid electrolyte. While a higher Fe redox couple potential (>= 110 mV higher) was observed in perchloric acid electrolyte, a higher ORR activity was obtained in sulfuric acid electrolyte. The higher ORR activity observed in sulfuric acid than perchloric acid was correlated with the higher peak current and larger faradaic charge for the Fe redox couple. A study of the Fe redox behavior using a cavity microelec-trode, eliminating the impact of ionomer, showed that the interaction of H2SO4 with Fe-N-C is stronger than that of HClO4 and that Fe redox in both electrolytes is a reversible surface electrochemical reaction.

The most active class of platinum group metal-free (PGM-free) oxygen reduction reaction (ORR) electrocatalysts in acidic electrolytes are those synthesized by heat treatment of iron, carbon, nitrogen precursors (Fe-N-C). Due to the large number of possible precursor compounds, a small fraction of the synthesis variable space has been explored. Correlation of synthesis variables with Fe speciation and ORR activity has been limited. In this work, an automation platform and a multi-port ball-milling were utilized to evaluate the effects of synthesis variables, such as identity of iron precursor, iron loading, and carbon and nitrogen sources on the ORR activity of iron-nitrogen-carbon catalysts in acidic electrolyte. The ORR activity is correlated with catalyst Fe speciation determined using Fe K-edge X-ray absorption spectroscopy (XAFS).

Reducing human reliance on inefficient energy systems and fossil fuels has become more urgent due to the consequences of global climate change. However, traditional trial-and-error approaches have hampered our ability to accelerate the discovery and implementation of functional materials for efficient energy conversion devices, such as polymer electrolyte fuel cells (PEFCs). To address this, we develop an adaptive learning framework that integrates machine learning and state-of-the-art capabilities in high-throughput synthesis to achieve expedited optimization of iron-nitrogen-carbon PEFC oxygen reduction reaction (ORR) electrocatalysts. We use statistical inference, uncertainty quantification, and global optimization to build a computational designof-experiment tool that identifies the optimum compositions to be investigated next to reduce the demands placed on experimental materials discovery. We benchmark the ability of the proposed strategy to discover optimum catalyst synthesis conditions in a six-dimensional search space when starting with a thirty-six-sample database. By following the adaptive learning strategy, we synthesize fourteen new catalysts from approximately ten billion unique compositions and discover four catalysts that outperform all original samples. The best machine learning-optimized catalyst is 33% more active than the highest-performing one in the initial database, showing an ORR activity seven times larger than those typically reported for the same class of materials.

Increasing the capacity of cathode materials used for lithium-ion batteries is desirable, as it ultimately enhances the energy density. Due to their lower cost and reversible cycling capacity of 250 – 300 mAh/g, Li- and Mn-rich LMR-NMC oxides are strong candidates as next generation cathodes used in lithium-ion batteries. Apart from the atomic structure, morphology of the cathode particles also influence their performance. LMR-NMC cathode particles are usually constructed through a two-step cathode fabrication process, which involves initial coprecipitation of the Mn-rich carbonate based cathode precursors, and later calcination of these precursors with a lithium salt at elevated temperatures. The secondary particles generally maintain their as precipitated precursor morphologies even after high temperature calcination. Even though the primary particles do change their size during calcination, the rate of oxidation and lithiation experienced by the transition metal precursors depend substantially on the primary particle morphology. Hence, it is critical to understand and control both the primary and secondary particle morphologies obtained after the coprecipitation process. In the present context, carbonate based NMC cathode precursors containing only Mn, only Ni and only Co, is precipitated, along with equal amount of the transition metals (Ni 0.33 Mn 0.33 Co 0.33 CO 3 ), using conventional batch reactors. NH 4 HCO 3 is used as the source of carbonate anions during the coprecipitation process, and the entire reaction is conducted at 50°C. The obtained particle morphologies for different transition metals are shown in Figure 1(a) as visualized using high resolution TEM techniques. Except MnCO 3 , all other transition metals demonstrate aggregated morphologies, which most probably form through surface growth mechanisms. Competition between growth rate and surface energies that leads to the formation of single crystalline particles for MnCO 3 , and particulate features for other transition metals, are demonstrated in Figure 1(b). Multiscale computational methodologies are developed to elucidate the impact of reaction kinetics and thermodynamics on determining the overall primary and secondary particle morphologies. Influence of transition metal content and ammonia concentration in determining the final particle size and size distribution will be discussed as part of this study. Figure 1

Nanoscale morphology has a direct impact on the performance of materials for electrochemical energy storage. Despite this importance, little is known about the evolution of primary particle morphology nor its effect on chemical pathways during synthesis. In this study, operando characterization is combined with atomic‐scale and continuum simulations to clarify the relationship between morphology of cathode primary particles and their lithiation during calcination of LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC‐811). This combined approach reveals a key role for surface oxygen adsorption in facilitating the lithiation reaction by promoting metal diffusion and oxidation, and simultaneously providing surface sites for lithium insertion. Furthermore, oxygen surface termination is shown to increase the activation energy for sintering, leading to smaller primary particle sizes at intermediate temperatures. Smaller particles provide both shorter diffusion lengths for lithium incorporation and increased surface site density for lithium insertion. These insights provide a foundation for more tailored syntheses of cathode materials with optimized performance characteristics.