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Oxygen reduction reaction (ORR) is one of the most important reactions in the field of electrocatalysis today. ORR represents a key cathodic reaction in hydrogen fuel cell, which typically needs to be promoted by the platinum group metals (PGMs), particularly Pt. The high cost of Pt adds significant barrier to the widespread implementation of the fuel cell technology. During the last two decades, substantially amount of effort has been invested in searching for low-cost replacements, or PGM-free catalysts for ORR. Although significant progress has been made, such catalysts still face major challenge in durability. By adding small amount of Pt over PGM-free catalytic substrate, we have found that both activity and stability will be significantly improved through synergistic interaction. [1] To better define synergistic effect in ORR catalysis, however, requires a carefully designed experiment that can separates multiple factors during the catalyst synthesis that can potentially influence the overall activity. In this report, we will discuss our recent study in understanding of the ORR catalysis synergy between Pt/PGM-free components in rationally designed catalyst systems. Another fast developing area of electrocatalysis is CO2 reduction reaction (CO2RR), which promises to electrochemically convert CO2 to fuels and chemicals using renewable electricity. While CO2RR via 2-electron transfer, such as the conversion to CO or formate, has been proven high selective with fast kinetics, conversions to C2+ chemicals require significantly stronger binding between the catalytic site and CO2 to complete multiple electron transfers (8 to 16) and C-C bond coupling steps, therefore are more challenging. More recently, we develop a new amalgamated lithium metal (ALM) synthesis method to preparing highly selective and active CO2RR catalyst for C2+ chemicals such as ethanol production. [2] In this presentation, we will discuss the hypothesis driven CO2RR catalyst design, combined with the mechanistic study for preparing effective catalysts. We will also share some critical insight on CO2RR mechanism through advanced structural characterization and computational modelling. Acknowledgement: This work is supported by U. S. Department of Energy, Hydrogen and Fuel Cell Technologies Office through Office of Energy Efficiency and Renewable Energy and by Office of Science, U.S. Department of Energy under Contract DE-AC02-06CH11357. [1] L. Chong, J. Wen, J. Kubal, F. G. Sen, J. Zou, J. Greeley, M. Chan, H. Barkholtz, W. Ding, and D.-J. Liu, “Ultralow-loading Platinum-Cobalt Fuel Cell Catalysts Derived from Imidazolate Frameworks,” Science (2018) 362, 1276 [2] “Highly selective electrocatalytic CO2 reduction to ethanol by metallic clusters dynamically formed from atomically dispersed copper” Haiping Xu, Dominic Rebollar, Haiying He, Lina Chong, Yuzi Liu, Cong Liu, Cheng-Jun Sun, Tao Li, John V. Muntean, Randall E. Winans, Di-Jia Liu and Tao Xu, (2020) Nature Energy, 5, 623–632

Low temperature water electrolysis represents a critical technology for green hydrogen production. Low temperature electrolysis can be operated using either proton exchange or alkaline membrane electrolyte. Compared to alkaline electrolyzer, proton exchange membrane (PEM) electrolyzer offers advantages of significantly higher current density and higher H2 purity, rendering it a preferred technology when high energy efficiency and low footprint are essential. Working in the oxidative and acidic environment under high polarization voltage, however, adds substantial demand to the electrode catalyst and the support. This is particularly the case at anode where the oxygen evolution reaction (OER) takes place. At present, the PGM materials such as Ir black or Ir oxide are catalysts of choice. Their high cost and limited reserve, however, adds a significant cost to PEM electrolyzer, which contributes to the overall expense of hydrogen production next only to the cost of electricity. Replacing Ir with earth-abundant transition metal oxides could help to reduce the electrolyzer system cost. These materials are known to be applicable in the alkaline electrolyte but not in acid due to dissolution. Since the traditional porous carbon cannot be used as the support under the oxidative potential during OER, their stand-alone conductivity represents another critical consideration. Argonne National Laboratory has recently designed and prepared a new class of PGM-free OER catalyst for PEM electrolyzer. The new catalysts are consisted of highly porous yet stable transition metal oxide derived from the metal-organic-frameworks (MOFs). Two catalyst series, ANL-Cat-A and ANL-Cat-B, were developed and investigated. The OER catalyst activity and durability were first measured by rotating disk electrode (RDE) method and in half-cell in the acidic media. Very promising OER activities were achieved. The catalyst durability was also measured through the multiple potential cycling from the voltage of 1.2 V to 2.0 V (vs. RHE) in the acidic electrolyte. Both ANL catalysts demonstrated promising activity and durability in the acidic medium. These PGM-free OER catalysts were also integrated into the membrane electrode assemblies and tested in PEM water electrolyzer under operating condition (60 °C to 80 °C and ambient pressure). Several MEAs demonstrated promising OER current density of 2000 mA/cm2 at 2.2 V iR-corrected . Extensive structural characterizations were carried out, both in static state and under the reaction condition using various tools such as high resolution electron microscopy and in situ X-ray absorption spectroscopy. Interesting correlation between the structure and property relationship was found. Computational modeling was also performed to understand the fundamental mechanism behind electron conductivity and the acid tolerance behind this new class of OER catalysts. Acknowledgement: This work is supported by U. S. Department of Energy, Hydrogen and Fuel Cell Technologies Office through Office of Energy Efficiency and Renewable Energy and by Office of Science, U.S. Department of Energy under Contract DE-AC02-06CH11357.

Introduction Ethanol has been extensively blended in gasoline as fuel to improve the combustion efficiency. Electrochemical CO2 reduction reaction (CO2RR) to ethanol and other value-added chemicals offers a promising “carbon-neutral” or even “carbon-negative” strategy1 when combined with renewable electricity, making the approach not only environmentally sound but also economically attractive. A key challenge for CO2RR is the lack of electrocatalyst that is capable of converting CO2 to a single product with high current efficiency, i.e. Faradaic efficiency (FE), low overpotentials and high durability2. Here, we report the preparation of commercial carbon-supported Cu SA catalysts by an amalgamated Cu–Li method. The catalysts demonstrated highly selective CO2-to-ethanol conversion with FE reaching ~91% at -0.7 V versus RHE and an onset potential as low as -0.4 V with FE of ~15%. The FE of the catalysts maintained at roughly 90% without degradation for 16 h. The CO2-to-ethanol FE is favored by high initial dispersion of single Cu atoms. Operando synchrotron X-ray absorption spectroscopy revealed that such dispersion played a critical role in a reversible transformation between Cu SA and Cu n (n= 3 and 4) as the active sites during the electrocatalytic reaction. Materials and Methods Preparing single atom catalyst starts with melting metal in liquid lithium in an Ar-filled glovebox. Lithium was heated to 200 °C, then the target metal (Cu in this case) was simultaneously added and kept for 4 h. The Li-Cu solid solutions were removed from the glovebox. The prepared amalgamated Cu-Li was oxidized to LiOH and mixed with carbon support materials before the LiOH was leached out with copious amounts of DI water, leaving the metal single atoms imbedded in the carbon support. Results and Discussion High-angle annular dark-field and aberration-corrected scanning transmission electron microscopy (HAADF-STEM), and X-ray absorption spectrum (XAS) are used to characterize the resulting samples. Figure. 1a shows a HAADF-STEM image of the atomically disperse Cu in sample Cu/C-0. Extended x-ray absorption fine structure (EXAFS) and x-ray absorption near-edge structure (XANES) are used to characterize the coordination structures and the electronic structure of the Cu atoms. Based on these XAS techniques, the Cu atoms are identified as being coordinated with four oxygens (Figure 1b). Figure 1c shows the FEs and CO2RR product distributions as the function of applied potentials from -0.4 V to -1.2 V over Cu/C-0.4. We detected the active potential for ethanol formation as low as -0.4 V with a decent FE of ~ 15%. The peak FE for ethanol is ~91% at a low potential of only -0.6 V and -0.7 V. To our knowledge, this value represents the highest FE for direct electrocatalytic CO2-to-ethanol conversion among Cu-based catalysts. The Cu/C-0.4 catalyst over a 16-hour span at -0.7 V showed an excellent stability in both current density and FE of CO2-to-ethanol over Cu/C-0.4 (Figure. 1d). Figure. 1e shows the FEs of the ethanol formation at different potentials obtained from individual catalyst studied. For Cu/C-0.1, Cu/C-0.4 and Cu/C-0.8, the FE for ethanol formation followed nearly identical profile with the active potential starting at as low as -0.4 V and reaching peak value > 90% at -0.7 V. Once the Cu loading reached to 1.6 wt.% or higher, however, the ethanol FE profile underwent a drastic reduction. Operando XAS study under the reaction conditions revealed a crucial dynamic catalytic mechanism, a reversible transformation between atomically dispersed Cu to Cun (n=3 or 4) clusters (Figure. 1f). Figure 1. (a) Representative HAADF-STEM images of Cu/C-0.4 showing the presence of isolated Cu species; (b) Fourier transform of k2-weighted R-space χ EXAFS data of the catalysts plus Cu(AcAc)2 as reference; (c) FE and the product distribution at different polarization potentials. The data were averaged over three repeated measurements with the standard deviations marked by black error bar for ethanol and red error bar for the total products; (d) FE and current density as the function of time during chronoamperometric electrolysis at -0.6 V; (e) FE of CO2-to-ethanol at different potentials over catalysts of different Cu loadings. (f) The hypothesised reaction mechanism suggested by the operando measurements. Significance Understanding the role of metal single atoms on the CO2 electrochemical reduction reaction is fundamentally important in designing new CO2RR catalyst for the large-scale production of value-added liquid fuels and chemicals. References 1. Xu, H. P. et al.; Highly selective electrocatalytic CO2 reduction to ethanol by metallic clusters dynamically formed from atomically-dispersed copper, Nature Energy, 2020, 5, 623-632. 2. Zhou, Y. S. et al. Dopant-induced electron localization drives CO2 reduction to C2 hydrocarbons. Nature Chemistry, 2018, 10, 974–980. Figure 1

Carbon dioxide emission from fossil fuel combustion has generated an on-going debate on its impact to the global environmental and ecological systems. New carbon capture, sequestration and conversion technologies are widely pursued as potential solutions to mitigate the concerns. The electrochemical CO2 reduction reaction (CO2RR) to hydrocarbon fuels and chemicals using renewable electricity offers an attractive “carbon-neutral” or even “carbon-negative” mitigation strategy. CO2 is an inexpensive carbon source and can be used as a feedstock for producing high value chemicals. Key challenges facing the current CO2RR electrocatalysis include improving energy efficiency by reducing the overpotentials; increasing the process selectivity by enhancing a single-product Faradaic efficiency (FE); and lowering the system operating cost by prolonging the catalyst stability. The U.S. produced 5.1 billion metric tons of CO2 in 2018 from industrial processes, posing a major concern on its impact to the climate.[1] The CO2 can be captured and used as raw material to produce to value-added chemicals. According to DOE’s “Bandwidth Study on Energy Use and Potential Energy Saving Opportunities in U. S. Chemical Manufacturing”,[2] C2+ chemicals such as ethanol (C2H5OH), acetic acid (CH3CO2H) and acetone (C3H6O) are among top 74 major chemicals produced in the US. Making these chemicals using sequestrated CO2 represents a huge opportunity for US manufacturing while improving the environment. Techno-economic analysis (TEA) of low-temperature electrochemical conversion of CO2 to C2+ chemical, particularly ethanol, has been conducted by several studies. All analyses indicate that profitable manufacturing of C2+ chemicals by electrochemical CO2 reduction reaction (CO2RR) depend strongly on conversion selectivity (Faradaic efficiency, or FE) and the difference between the actual and theoretical operating potentials (overpotential). Argonne National Laboratory, through collaboration with Northern Illinois University, recently prepared a series of highly active and durable electrocatalysts for CO2RR over commercial carbon support using a novel amalgamated lithium metal (ALM) synthesis technique.[3] The new electrocatalysts offer the several advantages in direct conversion to C2+ chemicals, including a) high FEs (all with peak FE > 90%) with one-step conversion to C2 (C2H5OH and CH3COOH) and C3 (C3H6O) chemicals; b) low voltage with the onset potential as low as -0.4 V and approaching to the theoretic limit; c) low cost catalysts made of earth-abundant transition metal; d) low operating temperature (< 80 °C) and pressure (one bar). including > 90% single-product FE, low onset potential (-0.4 V RHE for ethanol conversion) and excellent durability. In this presentation, we will report discuss the new electrocatalyst performance in terms of FE, onset potential and durability. The structure-function relationship with particular emphasis on CO2 to ethanol conversion and the mechanistic insight gained from operando X-ray absorption spectroscopy and computational modeling will also be reported. Acknowledgement: This work was supported by Argonne National Laboratory LDRD office. The works performed at Argonne National Laboratory’s Center for Nanoscale Materials, an U.S. Department of Energy Office of Science User Facility, is supported by Office of Science, U.S. Department of Energy under Contract DE-AC02-06CH11357. [1] https://www.eia.gov/environment/emissions/carbon/pdf/2019_co2analysis.pdf [2] https://www.energy.gov/sites/prod/files/2015/08/f26/chemical_bandwidth_report.pdf [3] Xu, H. P. et al.; Highly selective electrocatalytic CO2 reduction to ethanol by metallic clusters dynamically formed from atomically-dispersed copper, Nature Energy, 2020, 5, 623-632.

Capacitive deionization (CDI) represents one of the most thermodynamically efficient technologies for brackish water desalination, and its performance is highly dependent on the intrinsic properties of carbon materials. Ideally, CDI carbons should have high ion-accessible surface area, high porosity for ion mobility, great hydrophilic properties, excellent corrosion tolerance and good processability. Pyrolysis of precursory zeolitic-imidazolate frameworks (ZIFs) serves as a promising way to produce carbonaceous materials with great compositional and structural tunability. In this work, we systematically prepared an array of ZIFs (Zn(ligand)2) with different side-chain substitutions, which upon pyrolysis gave rise to carbon materials with variable elemental compositions, surface properties, wettability and graphitization levels; all are impacting the CDI performance. Zn(4abIm)2-C afforded the best salt adsorption capacity, while Zn(mIm)2-C showed the best overall salt adsorption capacity and rate; both exceeded the performance of the commercial carbon blacks. After careful correlation between the structures and the electrochemical results, it has been demonstrated that the CDI salt adsorption capacity increases with the carbon’s double layer capacitance. Additionally, graphitization level is significantly correlated with the CDI charge efficiency and energy consumption with more electronic conductive higher charge efficiency and lower energy consumption, which provides new insights to the field.

Carbon dioxide emission from fossil fuel combustion has generated an on-going debate on its impact to the global environmental and ecological systems. New carbon capture, sequestration and conversion technologies are widely pursued as potential solutions to mitigate the concerns. The electrochemical CO2 reduction reaction (CO2RR) to hydrocarbon fuels and chemicals using renewable electricity offers an attractive “carbon-neutral” or even “carbon-negative” mitigation strategy. CO2 is an inexpensive carbon source and can be used as a feedstock for producing high value chemicals. Key challenges facing the current CO2RR electrocatalysis include: a) how to improve energy efficiency by reducing the overpotentials; b) how to increase the process selectivity by enhancing a single-product Faradaic efficiency (FE); and c) how to lower the system operating cost by prolonging the catalyst stability. Argonne National Laboratory through collaboration with Northern Illinois University recently developed a series of highly active and durable single atom catalysts (SACs) for CO2RR prepared using a robust synthesis method over the commercial carbon support. The new electrocatalysts offer the several advantages including: a) direct conversion to C2 (C2H5OH and CH3CO2H) and C3 (C3H6O) chemicals in one-step electro-catalytic reaction without secondary upgrading; b) higher than 90% FE by suppressing the byproduct formation; c) high energy efficiency with the onset potential as low as 0.4 V observed for ethanol conversion; and d) good stability with no sign of activity loss during extended hours of chronoamperometry measurement. In this presentation, we will discuss the structure-function relationship of the new SACs with particular emphasis on CO2 to ethanol conversion. We will also share the mechanistic insight on catalysis as the catalyst transitioning from SAC to metal cluster. The catalyst performance in terms of FE, onset potential and durability will also be reported, combined with the catalyst structural properties obtained from various conventional and advanced characterization tools. Acknowledgement: The work performed at Argonne National Laboratory is supported by Office of Science, U.S. Department of Energy under Contract DE-AC02-06CH11357.

Maximizing the platinum utilization represents a critical research area in the commercial PEM fuel cell development. This is particularly true at the fuel cell cathode where to promote sluggish oxygen reduction reaction (ORR) requires three to four times more Pt in the catalyst than its counterpart in anode. In the electrode, Pt should be highly dispersed to be fully accessible by the reactants. This becomes more important at the high fuel cell current density domain where a large influx of O2 must be converted. By simply dispersing platinum to smaller nanoparticles (NPs) has its limitation. Past studies indicate that the ideal NPs should have dimension in between 4 nm to 6 nm to balance the needs between high Pt exposure and low dissolution rate. At ultralow cathode loading of 0.03 mgPt/cm2 to 0.06 mgPt/cm2 in the PEM fuel cell, such size requirement adds a significant constraint to the available number of NPs for the effective oxygen conversion. At Argonne National Laboratory, we recently developed a new type of ORR catalyst by integrating ultralow loading of Pt (~3 wt.%) over PGM-free catalytically active support derived from the zeolitic imidazolate frameworks. [1] The new catalyst not only demonstrated excellent platinum mass activity and polarization current density in PEM fuel cell test at the cathodic Pt loading < 0.04 mg/cm2, but also showed very good durability during multiple fuel cell voltage cycling in the accelerated stress test (AST). Various characterization tools including XPS, XRD, XAS, TEM have identified the new catalyst containing highly strained Pt-Co core-shell NPs over hig-density and uniformly distributed Co/N/C and Co@graphene PGM-free active support. DFT calculation found two ORR catalytic routes over Pt and PGM-free active site with a crossover path at the formation of hydrogen peroxide, leading to synergistic catalysis. In this presentation, I will discuss the synergistic catalysis from the catalyst design perspective, supported by our recent experimental observation. I will also share our thoughts on the new research direction of this approach. Acknowledgement: This work is supported by U. S. Department of Energy, Fuel Cell Technologies Office through Office of Energy Efficiency and Renewable Energy. The works performed at Argonne National Laboratory’s Center for Nanoscale Materials, an U.S. Department of Energy Office of Science User Facility, is supported by Office of Science, U.S. Department of Energy under Contract DE-AC02-06CH11357. [1] L. Chong, J. Wen, J. Kubal, F. G. Sen, J. Zou, J. Greeley, M. Chan, H. Barkholtz, W. Ding, and D.-J. Liu, “Ultralow-loading Platinum-Cobalt Fuel Cell Catalysts Derived from Imidazolate Frameworks,” Science 362, 1276 (2018).

Abstract Single-atom catalysts (SACs) are recently emerging as a new frontier in heterogenous catalysis for their effectiveness in promoting catalytic reactions. We report herein the study of carbon-supported single-atom catalysts synthesized by a novelty method exhibit distinctive selectivity for some special electrochemical reactions during the electrolysis process. The aberration-corrected HAADF-STEM images combined with X-ray absorption spectroscopy identified the presence of single atoms. Theoretical density functional theory simulations of the best performing catalytic activity and selectivity could be attributed to the existence of single atoms in the catalysts. Introduction CO2 is a cheap resource of carbon that can be used as raw materials for fuel synthesis using renewable energy In 2005, 36.2 billion metric tons of CO2 was emitted to the atmosphere from anthropogenic sources, [1] which is corresponding to an increase in global mean temperature of around 0.1oC. New carbon capture, sequestration and conversion technologies are widely pursued as potential solutions to mitigate the concerns. The electrochemical CO2 reduction reaction (CO2RR) can combine carbon capture storage with renewable energy to convert CO2 into fuels and chemical feedstocks. Which is extraordinary significance for industry and is highly competitive with water electrolysis. Therefore, efficient electrocatalysts are required to reduce the reaction overpotential and improve the faradaic efficiency and selectivity for high value chemical products further. [2] The earth-rare, high price and low selectivity of precious metals prevent further large-scale commercial applications. Furthermore, these precious metal catalysts exhibit desirable products at highly cathodic potential window with high overpotential, which causes lot of energy consuming problem in application. Recently, single-atom catalysts (SACs) are emerging as a new frontier in heterogenous catalysis for their effectiveness in promoting catalytic reactions. [3] The unique electronic structure and unsaturated coordination environments in single atom catalysts (SACs) have been proven to enhance catalytic activity and excellent selectivity in a variety of reactions. In this work, the catalyst was prepared by a proprietary method currently under patent examination. Results and Discussion We report herein the study of carbon-supported SACs synthesized by a novel method that exhibit distinctive selectivity in electrochemical synthesis. The aberration-corrected HAADF-STEM images combined with X-ray absorption spectroscopy identified the presence of single atoms. Theoretical density functional theory simulations of the best performing catalytic activity and selectivity could be attributed to the existence of single atoms in the catalysts. The prepared metal single atoms dispersed on substrate catalysts showed high faradaic efficiency and selectivity of CO2 to C2 products conversion with low onset potential. Fig. 1a shows linear sweep voltammetry (LSVs) over M/C-0.1 before and after chronoamperometry measurements at different potentials. CV curves (Figure 1b) also displayed obvious activity toward CO2RR in the potential range from 0.5 V to -1.5 V vs RHE, and the current density remained stable with no apparent decay before and after electrolysis in CO2 saturated KHCO3 solution. The FE reached to as high as ~91.8% for ethanol at a low potential of -0.6 V when the metal loading is 0.1 wt% on carbon support. Figure 1. Electrochemical CO2RR over M/C-0.1. (a) LSV in a potential range of 0 to -1.5 V vs RHE in Ar and CO2 saturated 0.1 M KHCO3. (Scan rate: 50 mV s-1). (b) CV in a potential range of 0.5 to -1.5 V vs RHE in Ar and CO2 saturated 0.1 M KHCO3. (Scan rate: 50 mV s-1, (c) FEs of key byproduct as the function of potential over the catalysts of M/C-0.1 Significance Understanding the role of metal single atoms on the CO2 electrochemical reduction reaction is fundamental for design of an appropriated catalyst for the large-scale application of CO2 RR that aims the production of high energy liquid chemicals. References [1] Chen, C., Khosrowabadi Kotyk, J. F., Sheehan, S. W., Chem. 4, 2571-2586, (2018). [2] Zheng, X. L., Ji, Y. F., Tang, J., Wang, J. Y., Liu, B. F., Steinruck, H. G., Lim, K., Li, Y. Z., Toney, M. F., Chan, K. and Cui. Y. Nature Catalysis. 2, 55-61 (2019) [3] Wang, A. Q., Li, J., Zhang, T. Nature Reviews. 2, 65-81 (2018) Figure 1

Single-atom catalysts (SACs) are recently emerging as a new frontier in heterogenous catalysis for their effectiveness in promoting catalytic reactions. We report herein the study of carbon-supported SACs synthesized by a novel method that exhibit distinctive selectivity in electrochemical synthesis. The aberration-corrected HAADF-STEM images combined with X-ray absorption spectroscopy identified the presence of single atoms. Theoretical density functional theory simulations of the best performing catalytic activity and selectivity could be attributed to the existence of single atoms in the catalysts.

Proton exchange membrane fuel cell (PEMFC) has been demonstrated as a highly efficient energy conversion technology. The sluggish oxygen reduction reaction (ORR) at the fuel cell cathode requires 3 to 5 times more catalysts than the hydrogen oxidation reaction at the anode.(1) Currently, platinum is still the catalyst material of choice. However, the heavy use of scarce Pt in the electrodes represents a major cost barrier to the commercialization of PEMFCs. Tremendous efforts have been dedicated to reduce or remove Pt usage through the development of Pt-transition metal catalysts, as highlighted recently by dealloyed PtNi (2), Mo-doped PtNi(3), and ordered PtCo(4); or through the development of transition metals-nitrogen-carbon based PGM-free catalysts (5, 6). In the fuel cell, catalysts should be highly dispersed over the electrode surface to be easily accessible by the reactants, especially at the high fuel cell current density where a large influx of O2 must be converted. For the Pt alloy catalyst of large crystallites, there won’t be enough crystallites available to spread over the electrode surface to encounter the incoming O2 if the total loading of platinum has to be maintained ultralow. Furthermore, unprotected Pt nano-alloys may lose their nanostructure and crystallinity from the dissolution and agglomeration during the ORR process. The PGM-free catalysts, on the other hand, have high catalytic site density with uniform distribution when prepared by homogenous precursors such as metal-organic framework or porous organic polymer, rendering them highly efficient in interacting with O2 flux. Their key drawback, however, is the poor stability operated under PEMFC condition. In this presentation, we will describe a method of preparing highly active yet stable electrocatalysts containing ultralow Pt content using Co or Co/Zn zeolitic imidazolate frameworks as precursors. The new catalysts contain Pt-Co core-shell nanoparticles (NPs) situated over the PGM-free catalytically active support (7). The ORR activities of the new catalysts were first tested in the O2 saturated acidic electrolyte by rotating ring disk electrode (RRDE) before fabricated into the membrane electrode assembly (MEA) and evaluated under fuel cell operating condition. The synergistic catalysis between Pt-Co NPs and PGM-free active substrate led to an unprecedented ORR performance in both RRDE and fuel cell. For example, the fuel cell test demonstrated a mass activity of 1.77 A/mgPt for the new catalysts and > 60% retention of the initial mass activity after 30,000 continuous voltage cycles from 0.6V – 1.0V. The characterizations of the fresh and the post-electrochemical test samples were investigated by x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD), x-ray absorption near-edge structure (XANES), extended x-ray absorption fine structure (EXAFS), transmission electron microscopy (TEM), Raman spectroscopy and BET surface analysis. We also performed DFT calculation on the ORR thermodynamic barriers over both Pt-Co NPs and PGM-free site as the descriptors for reaction pathway. The results reveal that the synergistic interaction between Pt-Co and PGM active substrate contribute significantly to both activity and durability enhancements. Acknowledgments: This work was supported by U.S. Department of Energy, Fuel Cell Technologies Office through Office of Energy Efficiency and Renewable Energy. LC wishes to thank Argonne National Laboratory for Maria Goeppert Mayer Fellowship. The works performed at Argonne National Laboratory’s Center for Nanoscale Materials and Advanced Photo Source, U.S. Department of Energy Office of Science User Facilities, is supported by Office of Science, U.S. Department of Energy under Contract DE-AC02-06CH11357. H. A. Gasteiger, N. M. Markovic, Just a Dream-or Future Reality? Science 324, 48-49 (2009). B. Han et al., Record activity and stability of dealloyed bimetallic catalysts for proton exchange membrane fuel cells. Energy & Environmental Science 8, 258-266 (2015). X. Huang et al., High-performance transition metal–doped Pt3Ni octahedra for oxygen reduction reaction. Science 348, 1230-1234 (2015 ). D. Wang et al., Structurally ordered intermetallic platinum-cobalt core-shell nanoparticles with enhanced activity and stability as oxygen reduction electrocatalysts. Nat Mater 12, 81-87 (2013). L. Chong et al., Investigation of Oxygen Reduction Activity of Catalysts Derived from Co and Co/Zn Methyl-Imidazolate Frameworks in Proton Exchange Membrane Fuel Cells. ChemElectroChem 3, 1541-1545 (2016). J. Shui, C. Chen, L. Grabstanowicz, D. Zhao, D. J. Liu, Highly efficient nonprecious metal catalyst prepared with metal-organic framework in a continuous carbon nanofibrous network. Proc Natl Acad Sci U S A 112, 10629-10634 (2015). L. Chong et al., Ultralow-loading platinum-cobalt fuel cell catalysts derived from imidazolate frameworks. Science, (2018).

Low temperature water electrolysis represents one of the critical technologies in distributed hydrogen production. It produces clean hydrogen with fast response time and works well when coupled with renewable but intermittent power sources such as wind and solar. Low temperature electrolysis can be operated using either proton exchange or alkaline membrane electrolyte. Compared to alkaline electrolyzer, proton exchange membrane (PEM) electrolyzer offers advantages of significantly higher current density (x5 improvement) and higher H2 purity, rendering it a preferred technology when high energy efficiency and low footprint are essential. Working in the oxidative and acidic environment under high polarization voltage, however, adds substantial demand to the electrode catalyst and the support. This is particularly the case at anode where the oxygen evolution reaction (OER) takes place. At present, the PGM materials such as Ir black or Ir oxide are catalysts of choice. Their high cost and limited reserve, however, limit the broad implementation of PEM electrolyzer in the renewable energy landscape. Low-cost transition metal based catalysts are known to be active toward OER in alkaline electrolyte but not in acid. Furthermore, traditional catalyst support such as porous carbon cannot sustain the oxidative potential before being oxidized to CO2. Argonne National Laboratory has recently designed and synthesized a new class of PGM-free OER catalyst for PEM electrolyzer. The new catalysts are consisted of highly porous yet stable transition metal composite derived from the metal-organic-frameworks (MOFs). The new catalysts are also integrated into a porous nano-network electrode architecture to improve the conductivity, mass transport and durability against oxidative corrosion. Two catalyst series, ANL-Cat-A and ANL-Cat-B, were developed and investigated. The OER catalyst activity and durability were first measured by the catalytic layer coated over rotating disk electrode (RDE) method or carbon paper in half-cell containing strongly acidic media. Very promising OER activities were achieved. For example, the half-cell OER current density as the function of the polarization potential of a representative ANL-Cat-A (catalyst loading of 2 mg/cm2) was compared with that of Ir-black (catalyst loading of 0.2 mg/cm2). ANL-Cat-A achieved an OER potential of 1.584 V vs. RHE at the current density of 10 mA/cm2, which is only 29 mV higher than that of Ir black benchmark. The catalyst durability was measured through the multiple potential cycling from the voltage of 1.2 V to 2.0 V (vs. RHE) in the acidic electrolyte. The percentage of current density retention against the initial value was measured as the gauge for stability. Both ANL catalysts demonstrated excellent activity and durability over most of PGM-free catalysts in acidic medium. For example, one ANL-Cat-A catalyst retained 90% and 80% current densities at 1.8 V and 2.0 V after 2,000 voltage cycles, respectively. In contrast, the percentage of the current density retention for Ir black was dramatically decreased after only 1000 voltage cycles. Several catalysts from ANL-Cat-A and –B series were also integrated into membrane electrode assemblies and tested in PEM electrolyzer at Giner Inc. under operating condition (60 °C and ambient pressure). Important processing parameters, such as anode catalyst loading, ionomer-to-catalyst ratio, pretreatment and application methods, have been systematically studied. Several MEAs demonstrated OER current density > 200 mA/cm2 at 1.8 V. This work collaborates with DOE HydroGen Consortium in computational modeling, surface property characterization and advanced electron microscopic imaging. Acknowledgement: This work is supported by U. S. Department of Energy, Fuel Cell Technologies Office through Office of Energy Efficiency and Renewable Energy. The works performed at Argonne National Laboratory’s Center for Nanoscale Materials, an U.S. Department of Energy Office of Science User Facility, is supported by Office of Science, U.S. Department of Energy under Contract DE-AC02-06CH11357.

Since the electrode/catalyst materials contribute to nearly half of a fuel cell stack cost, there is an urgent need to reduce or replace PGM usage. Among all the non-PGM candidates explored so far, transition metal doped nitrogen-carbon (TM-N-C) composites appear to be the most promising ones. Generally, these materials are prepared by forming TM-N4 molecular complex over amorphous carbon support, followed by thermal activation. Since non-PGM catalysts are known to have lower turn-over frequency per catalytic site comparing to platinum, their active site densities must be substantially higher to deliver a comparable performance. Using carbon support dilutes the active site density. The new approaches that could circumvent such limitation without the need of inert carbon support include the use of metal-organic framework (MOF) [1-3] and porous organic polymer (POP) [4] as the catalyst precursors. The materials derived from these rationally designed precursors can serve as high efficiency non-PGM catalysts directly or be further modified to low-PGM catalysts. To maximize the utilization of non-PGM or low-PGM catalytic centers requires an electrode structure that ensures efficient mass transport of reactant and product to and from the active site. Furthermore, the catalyst must be durable under accelerated aging conditions. . At Argonne National Laboratory, we pioneered the research of using MOFs and POPs as the precursors for non-PGM catalyst synthesis [1, 3, 4, 5]. MOFs have clearly-defined lattice structures through the metal-ligand coordination chemistry. The TM-N4 entities can be grafted into MOFs with very high ligation site densities. During thermal activation, the organic linkers are converted to electro-conductive carbon while maintaining porous framework, leading to catalysts with high surface areas and uniformly distributed catalytic sites. We demonstrated that zeolitic imidazolate framework, subclass of MOF, can used to prepare low-cost, highly active non-PGM catalysts. More recently, we developed a “one-pot” solid-state synthesis method which produces non-PGM catalyst using low-cost material without the need of solvent and separation [5]. Parallel to MOFs, we also developed another class of non-PGM catalysts using the porous organic polymers (POPs). [4] POPs are prepared by cross-linking the monomers containing strong TM-N binding site through polymerization. Similar to MOFs, POPs have high surface areas and uniformly distributed active sites inside the pours framework. The cathode catalysts prepared by MOF or POP have produced some major catalytic activity breakthroughs, generating the highest current and power densities among those reported in the literature. To improve mass and charge transfer for non-PGM catalysts, we have recently invented a new method to produce non-PGM catalyst with nano-network electrode architecture. [6] The MOF-based catalysts are incorporated into individual nano-fibers connected by a graphitic network. High micro-pore volume and surface area are maintained whereas the meso-pores in the conventional powder catalysts were no longer necessary and eliminated. Mass transport is improved through macro-pores inside the nano-network while the charge transfer is accomplished through the network of graphitic fibers. The new nano-network non-PGM catalyst has achieved excellent fuel cell performances in both activity and durability. Catalyst durability under fuel cell operating condition represents another critical challenge facing non-PGM and low-PGM catalyst development. We have recently developed a new approach to stabilize the catalyst performance. The new catalyst demonstrated less than 12% loss of mass activity at 0.9 V after 30,000 voltage cycles in a fuel cell test following DOE test protocol. Acknowledgement: The authors wish to thank Chen Chen and Lauren Grabstanowicz for her assistance in the MEA preparation. The work performed at Argonne is supported by DOE Fuel Cell Technologies Office and Office of Science. References: [1] Shengqian Ma, Gabriel Goenaga, Ann Call and Di-Jia Liu, Chemistry: A European Journal 17, 2063 (2011) [2] Eric Proietti, Frédéric Jaouen, Michel Lefèvre, Nicholas Larouche, Juan Tian, Juan Herranz & Jean-Pol Dodelet, Nature Comm. 2, 416 (2011) [3] D. Zhao, J.-L. Shui, C. Chen, X. Chen, B. M. Reprogle, D. Wang and D.-J. Liu, Chem. Sci., 2012, 3 (11), 3200 – 3205 [4] S. Yuan, J.-L. Shui, L. Grabstanowicz, C. Chen, S. Commet, B. Reprogle, T. Xu, L. Yu and D.-J. Liu, Angew. Chem. Int. Ed., 2013, 52(32), 8349–8353 [5] Dan Zhao, Jiang-Lan Shui, Lauren R. Grabstanowicz, Chen Chen, Sean M. Commet, Tao Xu, Jun Lu, and Di-Jia Liu, Advanced Materials, 2014, 26, 1093–1097 [6] J. Shui, C. Chen, L. R. Grabstanowicz, D. Zhao and D.-J. Liu, Proceedings of National Academy of Sciences, 2015, vol. 112, no. 34, 10629

Proton exchange membrane fuel cells (PEMFCs) represent the future powertrain for the automotive application due to their high efficiency, high power density, and emission of only water from the vehicle. Technology advancements are needed to enable the widespread commercialization of fuel cell-powered vehicles, including increased durability and decreased cost. Platinum is currently the electrocatalyst of choice for PEMFCs, contributing a significant fraction of the overall fuel cell stack cost [1]. There is an imperative need to develop inexpensive, non-platinum group metal (PGM) material as alternative catalysts. At Argonne National Laboratory, we are developing new methods of preparing non-PGM materials as potential substitutes for platinum cathode electrocatalysts for PEMFCs. Our approaches focus on transition metal and nitrogen-doped carbon composites prepared from highly porous organic precursors as electrocatalysts for the oxygen reduction reaction (ORR). One such method involves the use of metal-organic frameworks (MOFs) as sacrificial templates [2-4]. For example, we reported recently a one-pot solid-state synthesis technique to prepare Fe-doped zeolitic imidazolate frameworks (ZIFs), a sub-class of MOFs, which are subsequently pyrolyzed to yield highly-active ORR catalysts [4]. Although the one-pot synthesis method has been successfully demonstrated, we found that the catalyst activity could be substantially improved by optimizing the processing conditions of individual steps from synthesis, thermal activation, to post-treatment. For example, a major factor influencing catalytic activity are the heat treatment conditions. Optimizing pyrolysis time has proven to dramatically enhance ORR activity. Increased catalyst conductivity is another factor contributing to catalyst performance improvement. Furthermore, we also found that MOF synthesis conditions can significantly influence precursor structure and the resulting ORR activity of the catalyst. The improved catalyst activity has to be ultimately demonstrated in membrane-electrode assemblies (MEAs) of fuel cells. The engineering process of preparing MEAs using MOF-based non-PGM catalyst is, to certain degree, difference from that of conventional carbon-supported catalysts. Parameters such as the catalyst loading, perfluorosulfonic acid ionomer to catalyst ratio, affect the catalyst performance at the fuel cell level. In this presentation, we will also describe our effert in optimizing the MEA fabrication process. These improvements at both catalyst and MEA levels have yielded impressive ORR activity when tested in a fuel cell system, moving towards the performance targets set by U.S. DOE for the automotive application. The work performed at Argonne National Laboratory is supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office. References: [1] B. James et al., “Fuel Cell Transportation Cost Analysis,” presentation at the 2013 U.S. DOE Hydrogen and Fuel Cells Program Annual Merit Review and Peer Evaluation. http://www.hydrogen.energy.gov/pdfs/review13/fc018_james_2013_o.pdf [2] Shengqian MA, Gabriel Goenaga, Ann Call, and Di-Jia Liu, Chemistry: A European Journal 17, 2063 (2011). [3] Dan Zhao, Jiang-Lan Shui, Chen Chen, Xinqi Chen, Briana M. Reprogle, Dapeng Wang, and Di-Jia Liu, Chem. Sci., 3(11), 3200 (2012). [4] Dan Zhao, Jiang-Lan Shui, Lauren R. Grabstanowicz, Chen Chen, Sean M. Commet, Tao Xu, Jun Lu, and Di-Jia Liu, Advanced Materials 26, 7 (2014).

Li-O2 battery has attracted a great deal of attentions recently due to its high theoretical energy density.[1] Many studies were reported on the investigation of catalysts and cathode structures to the battery performance.[2] They revealed that the actual redox mechanism in Li-O2 battery could be significantly more complicated than originally thought. During the discharge-charge cycling, cathodic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) occur in Li-O2 battery. Various catalysts were disclosed in attempts to promote ORR and OER processes at lower overpotentials therefore higher overall round-trip efficiency. However, little information is available on the catalytic mechanism. For example, it is commonly accepted that lithium peroxide, Li2O2, serves as a redox intermediate during cycling reactions. Li2O2 is nearly insoluble in the organic electrolytes and precipitates on the surface of the cathode once formed. How a solid-state catalyst could promote not only Li2O2 formation during ORR, but also its dissipation during OER is completely unclear. Such catalytic reactions would require a solid-solid interaction with limited or no mass-transport. How the catalytic transition intermediates can be formed under such condition remains a mystery. Without a better understanding of the catalytic mechanism, it is difficult to rationally design and improve the next generation Li-O2battery. At Argonne National Laboratory, our team has explored a low-cost, high surface area Fe/N/C composite as the cathode catalyst for Li-O2 battery application, inspired by the non-precious metal catalyst study for the proton exchange membrane fuel cell.[3] The catalyst demonstrated reduced ORR and OER overpotentials in the discharge-charge cycle and minimized the electrolyte decomposition. We also developed a holistic approach in studying electrochemical processes in Li-O2 battery using various characterization tools, such as SEM, TEM, FTIR, XRD, etc..[4] Particularly, we introduced a microfocused synchrotron X-ray diffraction (m-XRD) and a micro-tomographic techniques (µ-CT) for the spatiotemporal study on the phase and structural change in Li-O2 battery under actual cell cycling condition.[5] The m-XRD has a spatial resolution at micron level with the complete penetration and sampling from cell’s radial direction, rendering it possible to probe battery’s composition layer-by-layer under in situconditions. The data collection at any given position usually takes a few seconds, making the method particularly suitable to study the dynamic change inside the battery in real time. In this presentation, we will focus on our recent operando, spatiotemporal investigation on the catalytic processes at the Li-O2 battery cathode using the m-XRD technique. We prepared an in situ Li-O2 battery using the representative material and cell design and studied formation, dissipation and distribution of the lithium redox intermediate under the multiple discharge-charge cycling condition in the entire cathode region. We demonstrated, for the first time, the evolutions of the grain size, concentration and spatial distribution of lithium peroxide as the functions of ORR/OER potentials and capacity. A new “self-propagating” catalytic mechanism was derived from the experimental data and compared to the similar electrocatalytic processes in fuel cell. The new finding could clarify some of the on-going controversies on the redox mechanism. More importantly, it shed lights on the new structural and material research directions for better cycloability and durability of the Li-O2battery. Acknowledgement: The work performed at Argonne is supported by DOE under Contract No. DE-AC02-06CH11357 by UChicago Argonne, LLC. References: [1] G. Girishkumar, B. McCloskey, A. C. Luntz, S. Swanson, W. Wilcke, J. Phys. Chem. Lett. 2010, 1, 2193. [2] a) K. M. Abraham, Z. Jiang, J. Electrochem. Soc. 1996, 143, 1; b) A. Débart, A. J. Paterson, J. Bao, P. G. Bruce, Angew. Chem. Int. Ed. 2008, 47, 4521; c) B. D. McCloskey, D. S. Bethune, R. M. Shelby, G. Girishkumar, A. C. Luntz, J. Phys. Chem. Lett. 2011, 2, 1161. [3] Jiang–Lan Shui, Naba K. Karan, Mahalingam Balasubramanian, Shu–You Li and Di–Jia Liu, J. Am. Chem. Soc. 2012 , 134 (40), 16654 [4] Jiang-Lan Shui, John S. Okasinski, Dan Zhao, Jonathan D. Almer and Di-Jia Liu, ChemSusChem, 2012, 5, 2421 [5] a) Jiang-Lan Shui, John S. Okasinski, Peter Kenesei, Howard A. Dobbs, Dan Zhao, Jonathan D. Almer, and Di-Jia Liu, Nature Comm. 2013 4, 2255; b) Jiang-Lan Shui, John S. Okasinski, Chen Chen, Jonathan D. Almer and Di-Jia Liu, ChemSusChem 2014 , 7, 543

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The impact to the Li-O2 battery performance from the insoluble lithium salts formed from the electrolyte decomposition during discharge-charge cycle was investigated by a microfocused synchrotron X-ray diffraction (m-XRD) technique, together with the conventional imaging and spectroscopic methods. Lithium alkyl carbonate deposit was found throughout the battery. Surprisingly, the concentration of Li2CO3 in the separator is significantly higher than that in both electrodes. Imaging method such as Scanning electron microscopy revealed that the precipitates grew on the separator fiber surface, ultimately obstructing the pores serving as the ion-transport channel. A model based on finite-element analysis was developed to qualitatively illustrate the possible chemical/physical processes leading to high accumulation of insoluble precipitates in the separator region.

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