Metal-Phthalocyanine-Based Advanced Catalysts for the Oxygen Reduction Reaction in Anion-Exchange Membrane Fuel Cells

Since the first Anion-Exchange Membrane (AEM) Fuel Cell (AEMFC) with practical performance was announced about a decade ago1, significant advances have been achieved in this field of research. In the past few years of intensive research on AEMFCs, remarkable progress has been reported, such as new highly stable functional groups for advanced AEMs2-5 and highly active PGM-free catalysts6-8. At the cell level, new AEMFCs based on CRM-free catalysts were successfully demonstrated9, AEMFC’s lifetime of 5,000-15,000 hours was theoretically demonstrated for the first time10-11, and a cell lifetime of 2,000 hours was experimentally proven12. Altogether, the research community has made very impressive progress in such a short time. However, many challenges still need to be overcome to achieve AEMFCs of industrial interest. Among them, cell performance with completely PGM-free catalysts and operation with ambient air, are the most critical ones.We, at Technion, have recently presented the first results of AEMFCs tested at cell temperatures above 100 ℃13-17. At these high temperatures, we could achieve not only high hydroxide ion conductivities close to 300 mS/cm18(!) but also improved cell stability (yes, a very counterintuitive result). We have also demonstrated a novel approach to achieve high AEMFC performance while using PGM-free catalysts in both electrodes. Altogether, these breakthroughs allow us for the first time to operate AEMFCs with ambient air and achieve record-high performance. This represents a significant landmark for this technology. In this talk, I will present the achievements and the new state-of-the-art H2-air AEMFC. References Dekel; Alkaline Membrane Fuel Cell (AMFC) Materials and System Improvement – State-of-the-Art; ECS Transactions, 50 (2) 2051-2052, 2013. Gjineci et al., Increasing the alkaline stability of N,N-diaryl-carbazolium salts using substituent electronic effects; ACS Appl. Mater. Interf. 12, 49617, 2020.Fan et al., Poly(bis-arylimidazoliums) possessing high hydroxide ion exchange capacity and high alkaline stability”; Nature Commun. 10(1), 2306, 2019.Gjineci et al., The reaction mechanism between tetraarylammonium salts and hydroxide; J. Org. Chem. 21, 3161-3168, 2020.Liu et al., Magnetic-field-oriented mixed-valence-stabilized ferrocenium anion-exchange membrane; Nature Energy 7, 329–339, 2022. Zion et al., Porphyrin aerogel catalysts for oxygen reduction reaction in anion-exchange membrane fuel cells; Functional Mater. 31(24), 2100963, 2021. Lilloja et al., Transition-metal and nitrogen-doped carbide-derived carbon/carbon nanotube composites; ACS Catalysis 11, 1920-1931, 2021. Kisand et al., Templated Nitrogen-, iron-, and cobalt-doped mesoporous nanocarbon derived from an alkylresorcinol mixture for AEMFC application; ACS Catalysis, 12, 14050-14061, Biemolt et al., An anion-exchange membrane fuel cell containing only abundant and affordable materials; Energy Technology 9, 2000909, 2021. Dekel et al., Predicting performance stability in anion exchange membrane fuel cells; Power Sources 420, 118-123, 2019. Yassin et al., Quantifying the critical effect of water diffusivity in anion exchange membranes for fuel cell applications; Membrane Sci. 608, 118206, 2020. Hassan et al., Achieving high-performance 2000h stability in AEMFCs; EnergyMater. 2001986, 2020. Douglin etal, A high-temperature anion-exchange membrane fuel cell; Power Sources Adv.5, 100023, 2020. Douglin et al., A High-Temperature AEMFC with a Critical Raw Material-free Nitrogen-doped Carbon Cathode; Chemical Engineering J. Adv. 8, 100153, 2021. Yassin et al., A surprising relation between operating temperature and stability of AEMFCs; Power Sources Adv. 11, 100066, 2021. Liu et al., Magnetic-field-oriented mixed-valence-stabilized ferrocenium anion-exchange membrane; Nature Energy 7, 329–339, 2022. Xue et al., High-temperature AEMFCs with remarkable stability; Joule 8, 1457-1477, 2024. Zhegur-Khais et al., Measuring the true hydroxide conductivity of anion exchange membranes; Membrane Sci. 612, 118461, 2020.

In the past few years of intensive research on Anion-Exchange Membrane (AEM) Fuel Cells (AEMFCs), amazing progress has been reported. Novel highly stable functional groups for AEMs1-4 and PGM-free catalysts5-7 were developed, new AEMFCs based on CRM-free catalysts were successfully demonstrated8, AEMFC lifetime of 5,000-15,000 hours was theoretically demonstrated for the first time9-10, and cell lifetime of 2,000 hours was experimentally proven11. Altogether, the research community has made very impressive progress in such a short time. However, due to the degradation of AEMs, the operation of AEMFCs has been limited only to low temperatures, mainly below 80 ℃. We have recently presented the first results of AEMFCs successfully operated at cell temperatures above 100 ℃12-16. At these high temperatures, we could achieve hydroxide conductivities close to 300 mS/cm17. The first results are very encouraging and represent a significant landmark for the technology, opening a wide door for a new field of study we call the High-Temperature AEMFCs (“HT-AEMFCs”). In this talk, I will present the latest achievements in the HT-AEMFCs. References Gjineci et al., Increasing the alkaline stability of N,N-diaryl-carbazolium salts using substituent electronic effects; ACS Appl. Mater. Interf. 12, 49617, 2020.Fan et al., Poly(bis-arylimidazoliums) possessing high hydroxide ion exchange capacity and high alkaline stability”; Nature Commun. 10(1), 2306, 2019.Gjineci et al., The reaction mechanism between tetraarylammonium salts and hydroxide; J. Org. Chem. 21, 3161-3168, 2020.Liu et al., Magnetic-field-oriented mixed-valence-stabilized ferrocenium anion-exchange membrane; Nature Energy 7, 329–339, 2022. Zion et al., Porphyrin aerogel catalysts for oxygen reduction reaction in anion-exchange membrane fuel cells; Functional Mater. 31(24), 2100963, 2021. Lilloja et al., Transition-metal and nitrogen-doped carbide-derived carbon/carbon nanotube composites; ACS Catalysis 11, 1920-1931, 2021. Kisand et al., Templated Nitrogen-, iron-, and cobalt-doped mesoporous nanocarbon derived from an alkylresorcinol mixture for AEMFC application; ACS Catalysis, 12, 14050-14061, Biemolt et al., An anion-exchange membrane fuel cell containing only abundant and affordable materials; Energy Technology 9, 2000909, 2021. Dekel et al., Predicting performance stability in anion exchange membrane fuel cells; Power Sources 420, 118-123, 2019. Yassin et al., Quantifying the critical effect of water diffusivity in anion exchange membranes for fuel cell applications; Membrane Sci. 608, 118206, 2020. Hassan et al., Achieving high-performance and 2000 h stability in AEMFCs; Energy Mater. 2001986, 2020. Douglin et al., A high-temperature anion-exchange membrane fuel cell; Power Sources Advances 5, 100023, 2020. Douglin et al., A High-Temperature AEMFC with a Critical Raw Material-free Nitrogen-doped Carbon Cathode; Chemical Engineering J. Adv. 8, 100153, 2021. Yassin et al., A surprising relation between operating temperature and stability of AEMFCs; Power Sources Adv. 11, 100066, 2021. Liu et al., Magnetic-field-oriented mixed-valence-stabilized ferrocenium anion-exchange membrane; Nature Energy 7, 329–339, 2022. Xue et al., High-temperature anion-exchange membrane fuel cells with balanced water management and remarkable stability; Joule, in press (https://doi.org/10.1016/j.joule.2024.02.011), 2024. Zhegur-Khais et al., Measuring the true hydroxide conductivity of anion exchange membranes; Membrane Sci. 612, 118461, 2020.

Amazing progress has been achieved in the past two years of intensive research on Anion-Exchange Membrane (AEM) Fuel Cells (AEMFCs), bringing this technology significantly closer to the required levels for practical use in automotive (and other) applications. In material-related space, recent studies reported novel techniques for characterizing AEMs for fuel cells [1], as well as robust AEMs with hydroxide conductivities of 300 mS/cm [2]. In addition, new ionomeric materials and functional groups with increasing stability were introduced [3-5], and better Pt-free and PGM-free promising catalysts were developed [6-10]. On the fuel cells front, new AEMFCs based on CRM-free catalysts were successfully demonstrated [11-12], cells with record high power density outputs were obtained [13], materials able to operate under high-temperature AEMFC (HT-AEMFC) operation mode were reported [14], simulated materials and conditions to achieve AEMFC lifetime of 5,000-15,000 hours were theoretical demonstrated [15-16], and cell life time of 2,000 hours of continuous operation was already experimentally proven [17]. Altogether, the research community has made very impressive progress in such a short period of time. Having said that, we are not yet there; several remaining challenges should still be overcome in order to allow this technology to be a serious alternative to the mainstream PEMFC technology. To achieve that goal, we need (A) catalysts with higher activity towards hydrogen oxidation and oxygen reduction reactions to accomplish a full PGM-free (and even CRM-free) AEMFC; (B) a better understanding of carbonation issues while operating AEMFC with ambient air; and, (C) ionomeric materials with higher alkaline stability at higher temperatures. We, at Technion, focus our efforts on these (and other related) research topics, aiming to make a significant impact on the fuel cell research community. The latest achievements of our group in these AEMFC challenging fronts will be presented and discussed during the talk.

Since the first Anion-Exchange Membrane (AEM) Fuel Cell (AEMFC) with practical performance was announced about a decade ago1, significant advances have been achieved in this field of research. In the past few years of intensive research on AEMFCs, remarkable progress has been reported, such as new highly stable functional groups for advanced AEMs2-5 and highly active PGM-free catalysts6-8. At the cell level, new AEMFCs based on CRM-free catalysts were successfully demonstrated9, AEMFC’s lifetime of 5,000-15,000 hours was theoretically demonstrated for the first time10-11, and a cell lifetime of 2,000 hours was experimentally proven12. Altogether, the research community has made very impressive progress in such a short time. However, many challenges still need to be overcome to achieve AEMFCs of industrial interest. Among them, AEM degradation and AEMFC performance stability are of serious concern.We, at Technion, have recently presented the first results of AEMs and AEMFCs that can be operated at cell temperatures above 100 ℃13-17. At these high temperatures, we could achieve not only high hydroxide ion conductivities close to 300 mS/cm18(!) but also improved cell stability (yes, a very counterintuitive result). In turn, these high temperatures allow us to increase the catalyst activity towards both HOR and ORR, allowing the design of first high-performance high-temperature AEMFCs (HT-AEMFCs) made of PGM-free catalysts in both electrodes, and their operation with ambient air. This represents a significant landmark for this technology. In this talk, I will present the achievements and the new state-of-the-art of these HT-AEMFCs.

Developing a non-precious metal catalyst (NPMC) to replace Pt on the cathode of polymer electrolyte fuel cells is currently one of the most important challenges in electrocatalysis.1 In the recent years, incorporating transition metals, such as iron or cobalt into a nitrogen-doped carbon nanomaterial, thus forming active sites for the oxygen reduction reaction (ORR), has been shown to be a promising strategy for NPMC design. The debate on the exact active sites and the mechanism of the ORR in this type of catalysts is still ongoing, but many advances have been made by studying the effect of catalyst precursors (the sources for the carbon, nitrogen and transition metals) on the ORR activity of the final catalyst. Carbide-derived carbons (CDC) are carbon materials synthesized by removal of metals from metal carbides. By careful selection of synthesis conditions, the CDCs can be tuned to have specific pore size distributions and degrees of disorder. As a continuation of our previous work,2,3 where we studied nitrogen and transition metal doped highly microporous CDCs (M-N-CDC), we have now incorporated multiwall carbon nanotubes (MWCNT) into the M-N-CDC catalyst to form a composite catalyst (M-N-comp).4 The catalysts were synthesized in a two-step pyrolysis procedure: first the CDC was ball-milled along with iron(II)acetate and 1,10-phenanthroline. This mixture was pyrolyzed and then MWCNTs along with dicyandiamide and another amount of iron(II)acetate were added. The surface morphology and elemental composition of the final catalysts were investigated with scanning electron microscopy, N2 physisorption, inductively coupled plasma mass spectrometry and X-ray photoelectron spectroscopy along with rotating disk electrode (RDE) and single-cell anion-exchange membrane fuel cell (AEMFC) studies to give a thorough characterization of the physico-chemical properties of the catalysts and the relationships between them. The addition of MWCNTs was revealed to add mesoporosity as the MWCNTs filled the space in between the highly microporous CDC grains, thus increasing the ORR activity by providing more active sites and also facilitating mass transport. The ORR onset potential for the best catalyst, which had a CDC-to-CNT ratio of 2:1 in RDE mode was 0.99 V vs RHE in 0.1 M KOH and the maximum power density using this catalyst in a H2/O2 AEMFC with Tokuyama A201 anion exchange membrane was 120 mW cm‒2. However, the catalyst with lowest CDC-to-CNT ratio (1:2), which had more negative onset potential in RDE testing, performed better at higher current densities in the AEMFC and reached a maximum power density of 160 mW cm‒2, likely due to better mass transport in the thick catalyst layer. The best catalysts exceeded the activity of commercial Pt/C in both RDE and AEMFC testing, showing the excellent potential of CDC-based catalysts to replace costly Pt in AEMFC devices. References A. Sarapuu, E. Kibena-Põldsepp, M. Borghei, and K. Tammeveski, Electrocatalysis of Oxygen Reduction on Heteroatom-doped Nanocarbons and Transition Metal-Nitrogen-Carbon Catalysts for Alkaline Membrane Fuel Cells, J. Mater. Chem. A, 6, 776-804 (2018).S. Ratso, I. Kruusenberg, M. Käärik, M. Kook, R. Saar, P. Kanninen, T. Kallio, J. Leis, and K. Tammeveski, Transition Metal-Nitrogen Co-doped Carbide-Derived Carbon Catalysts for Oxygen Reduction Reaction in Alkaline Direct Methanol Fuel Cell, Appl. Catal. B Environ., 219, 276–286 (2017).S. Ratso, I. Kruusenberg, M. Käärik, M. Kook, L. Puust, R. Saar, J. Leis, and K. Tammeveski, Highly Efficient Transition Metal and Nitrogen Co-doped Carbide-Derived Carbon Electrocatalysts for Anion Exchange Membrane Fuel Cells, J. Power Sources, 375, 233–243 (2018).S. Ratso, M. Käärik, M. Kook, P. Paiste, V. Kisand, S. Vlassov, J. Leis, and K. Tammeveski, Iron and Nitrogen Co-doped Carbide-Derived Carbon and Carbon Nanotube Composite Catalysts for Oxygen Reduction Reaction, ChemElectroChem (2018). doi:10.1002/celc.201800132. Figure 1

In the rapidly developing modern society, there is an urgent need for the wide-ranging availability of advanced and eco-friendly energy sources. One of the possible alternatives is the application of anion exchange membrane fuel cells (AEMFCs) with a catalyst reducing dioxygen efficiently. These promising devices can revolutionize the energy sector since they practically produce no pollution. However, to make them more widely used, several obstacles must be overcome. As a result, vast-ranging investigations focus on improving the properties of conductive polymer membranes [1] and catalysts for the oxygen reduction reaction (ORR) [2]. The durability of the membrane electrode assembly (MEA) is one of the critical requirements for the successful commercialization of anion exchange membrane fuel cells (AEMFCs). Despite significant impacts of nucleophilic degradation on ion-exchange capability and the anionic conductivity of investigated membranes, it is believed to affect only cationic sites of membrane polymers and thus cannot explain the reported loss in the mechanical strength of degraded AEMs. Such a phenomenon might be related to polymer backbone degradation caused by free radicals. This was widely described in the literature in the case of fuel cells using proton-conducting membranes [3] but barely mentioned for AEMFCs [4]. Since the oxidative degradation of hydrocarbon polymers is very well known, we aimed to comprehensively investigate the formation of the short-lived species generated during the operation of AEMFCs as well as stable radicals present in the polymer membranes.We investigated the LDPE-base membranes with Pt black, Pd black, PdAg, and Ag as the ORR catalysts, whereas for HOR the Pt black, Pd black, and NiFe catalysts were used. The in-situ measurements are performed with a micro-AEMFC inserted into a resonator of an electron paramagnetic resonance (EPR) spectrometer, which enables separate monitoring of radicals formed on the anode and cathode sides. The creation of radicals was monitored by the EPR spin trapping technique. In Figure 1 the EPR spectra of DMPO spin adducts trapped during operation of micro-fuel cell placed in EPR spectrometer cavity are presented. In this experiment, the LDPE-base membrane with platinum catalysts on both sides was used. The main detected adducts during the operation of the micro-AEMFC were DMPO-OOH and DMPO-OH on the cathode side and DMPO-H on the anode side. Additionally, we clearly show the formation and presence of stable radicals in AEMs during and after long-term AEMFC operation [5]. Preliminary results suggest that the creation of the short-living radicals during AEMFCs operation is independent of the used membrane. However, the applied catalysts determine the number of detected radicals. The EPR investigations indicate that, in addition to the known chemical degradation mechanisms of the cationic ammonium groups of the membrane, oxidative degradation, including radical reactions, has to be taken into account when the stability of an anion conductive polymer for AEMFCs is investigated. The formation of stable radicals in AEMs was proven for the first time in this study. All short-living radicals formed during the AEMFC operation were fully identified. The presence of radicals in the AEM after AEMFC testing indicates that reactive oxygen species may play a very important role in the degradation mechanism of the anion conducting polymers. Results from this study shed light on the understanding of radical formation and presence in the membranes during AEMFC tests, which in turn may help to solve the challenge of anion exchange membrane stability. Acknowledgments. This work was supported by the Polish National Science Centre (NCN) project OPUS-14, No. 2017/27/B/ST5/01004.

Finding viable alternative catalysts for the oxygen reduction reaction (ORR) is a key issue in modern electrocatalysis. Traditional Pt/C catalysts are not viable in the long term and thus much effort has been focused on non-precious metal catalysts (NPMCs). Metal-nitrogen doped carbon materials (MNCs) have emerged as the main candidate for replacing the platinum-based catalysts. Among these materials, carbide-derived carbon (CDC), which is a type of carbon materials produced by removing the metal atoms from a carbide lattice, stand out as exceptional candidates due to easily variable porosity. The specific surface areas of CDC materials can reach around 1000-2000 m2 g−1 and the textural characteristics can be tuned by selection of carbides and synthesis conditions, with reproducible large-scale syntheses already shown.1 In this work, we propose a method to introduce nitrogen and metals into a carbide derived carbon material with little loss of porosity using dicyandiamide (DCDA) and either cobalt or iron salts (Figure 1b). The CDC is derived from titanium carbide and then doped by pyrolyzing a mixture of the CDC, DCDA and either CoCl2 or FeCl3. The textural properties of the catalysts are probed with N2 physisorption, the morphology with scanning electron microscopy, the surface elemental composition with X-ray photoelectron spectroscopy (XPS) and the structure with Raman spectroscopy. The catalysts‘ activity towards ORR along with the stability during 1000 cycles and methanol tolerance in 0.1 M KOH is assessed using the rotating disk electrode (RDE) method and compared to that of commercial Pt/C catalysts (Figure 1a). The catalysts are also utilized in a alkaline direct methanol fuel cell (ADMFC)2 and an H2/O2 anion exchange membrane fuel cell (AEMFC). The catalysts are shown to retain their microporous structure after the pyrolysis with successful doping of up to 5.3 at.% of nitrogen into the surface layer of the materials as determined by XPS. The catalysts show excellent activity in 0.1 M KOH rivaling that of commercial platinum-based catalysts and are very stable during 1000 potential cycles, with the iron-based catalysts somewhat more active. Up to 3 M methanol concentration also has very minimal effect on the activity of the catalysts. In an ADMFC using the Fuma-Tech FAA3 membrane the MNC catalysts show better performance than Pt/C (Figure 1c) and in an AEMFC with the Tokuyama A201 membrane as the polymer electrolyte they also rival the Pt/C catalyst. Overall, we show that transition metal and nitrogen-doped CDCs present a viable alternative to commercial Pt/C catalysts for oxygen reduction in alkaline conditions and alkaline membrane fuel cells.

Platinum group metal (PGM)-free catalysts for oxygen reduction reaction (ORR) have shown high oxygen reduction reaction activity in alkaline media. In order to reduce the overpotential losses in anion-exchange membrane fuel cells (AEMFCs), PGM-free catalysts need to have a high site density to compensate for their which will enable reaching high cell current and power densities. Herein, we will present our work on the synthesis, characterization, and utilization of heat-treated iron porphyrin aerogels as cathode catalysts in AEMFCs. The heat treatment effect was thoroughly studied using several techniques, and the best performing aerogel was showing an excellent performance in AEMFCs, reaching a peak power density of 580 mW cm-2 and a limiting current density of as high as 2.0 A cm-2, which can be considered as the state-of-the-art for PGM-free based AEMFCs.

Non-precious metal catalysts (NPMCs) with high activity and stability are developed for oxygen reduction reaction (ORR) in alkaline membrane fuel cell (AMFC). A variety of important parameters determining the performance of AMFC are systematically investigated, including the ratio of catalyst to ionomer at cathode, the flow rates of oxygen and air, and the fuel cell operating temperatures. An optimum catalyst/ionomer ratio range of 7:3 to 8:2 was found for the NPMC-based cathode in both H2/O2 and H2/air cases. The operating temperature was demonstrated to play the crucial role in determining the AMFC performances.

Recently a major effort in fuel cell research and development have been undertaken to displace platinum with platinum-free or even better, totally metal free catalyst materials. With the possibility of using heteroatom doped carbon-based materials as electrocatalysts for oxygen reduction reaction (ORR) instead of Pt, anion exchange membrane fuel cells (AEMFCs) have big advantage over other low-temperature fuel cells. Beside other carbon nanomaterials, carbon nanotubes and graphene have shown good electrocatalytic and catalyst supporting properties for different fuel cell cathode catalysts. Graphene and/or carbon nanotubtube doping with heteroatoms is a common strategy to increase the electrocatalytic activity of these materials towards the ORR [1]. Different heteroatoms, such as nitrogen, phosphorous, sulfur and boron have been studied as promising dopants to prepare electrocatalysts for ORR in alkaline media [2]. In this work the electrocatalytic activity of nitrogen and sulfur co-doped MWCNT/rGO was studied towards the ORR in alkaline media (0.1 M KOH) using the rotating disc electrode (RDE) method. The catalyst materials were prepared by doping of MWCNT/rGO with N and S via simple one-pot synthesis method using high-temperature pyrolysis in inert gas atmosphere. The resulting catalyst material exhibited excellent electrocatalytic activity towards the ORR in alkaline media. Catalyst samples were characterized also by transmission electron microscopy, X-ray photoelectron spectroscopy and energy-dispersive X-ray spectroscopy methods. Fuel cell experiments were carried out using Fumatech Fumapem® FAA anion-exchange membrane and FAA ionomer. Methanol tolerance and long-term stability tests were performed. The results revealed remarkable catalytic activity of nitrogen and sulfur co-doped carbon towards the ORR in alkaline media, as well good methanol tolerance. Composition analysis with different physical characterization methods confirmed that nitrogen and sulfur have been grafted onto the carbon support. RDE tests demonstrated highly improved catalytic activity in comparison with undoped MWCNT/rGO and fuel cell tests showed a great potential of N and S doped carbon as alternative cathode catalyst and catalyst carrier for anion exchange membrane fuel cells.

Recent development of chemically stable anion exchange membranes and ionomers resulted in substantial increase in research and development in the field of Anion Exchange Membrane Fuel Cells (AEMFCs) [1]. One of the advantages of AEMFC technology is the possibility to use completely platinum group metal-free (PGM-free) electrocatalysts for the cathode (Oxygen Reduction Reaction, ORR) and the anode (Hydrogen Oxidation Reaction, HOR) [2, 3]. High performance of Membrane Electrode Assemblies (MEAs) with PGM-free catalysts was achieved using M-N-C type of materials (M=Fe, Co or Ni) [4]. The cathodic electrocatalysts consisted of transition metal, nitrogen and carbon matrix can be prepared by several methods: treatment of carbons with transition metal in ammonia atmosphere, high temperature pyrolysis of Metal Organic Framework (MOF) compounds or through templating approach (Sacrificial Support Method, SSM) [5, 6]. In contrast to massive research in the ORR for AEMFCs, the development of PGM-free catalysts for HOR is still in the early stage, with majority of electrocatalysts tested in Rotating Disk Electrode (RDE) conditions. The only publications in open literature on integration of PGM-free anodic materials (nickel-based) are limited to NiW and NiMo supported on carbon blacks [7, 3]. In a present contribution the design, synthesis and scale-up of different Ni-based anodic materials for AEMFC application is reported. The electrocatalysts were synthesized by thermal reduction of nickel and second metal precursors on the surface of commercial and in house prepared carbon supports (in house carbon supports are denoted as Engineered Catalyst Supports, ECS). Several important synthetic parameters such as ratio between metals, type of carbon support, reduction temperature etc. were optimized in order to achieve the highest performance in fuel cell tests. As-obtained electrocatalytically active anodic materials were integrated into the catalyst layer by proprietary method practiced at EWII Fuel Cells [8]. The catalyst layer variations included different catalyst:ionomer ratio, loading of the Ni-based catalysts in the MEA and other parameters. Fuel cell tests performed at Pajarito Powder and EWII Fuel Cells revealed high performance of PGM-free materials similar to reported earlier (Figure 1) [3]. Figure 1. Fuel cell performance of MEA with NiCu/C anode using different loadings in catalyst layer. Conditions: A: NiCu/C, C: Pt/C, Tcell = 60°C, 100% RH, flow rates = 200 ccm, backpressure = 10 psig. The future directions on improvement of fuel cell performance will be discussed. Acknowledgements: Department of Energy, Hydrogen Oxidation Reaction in Alkaline Media, Control Number: 0966-1624, Award Number: DE-EE0006962 (PI A. Serov) and ARPA-E DE-AR0000688 (PI B. Zulevi). References. [1] A. Serov, I. V. Zenyuk, C. G. Arges, M. Chatenet "Hot topics in alkaline exchange membrane fuel cells" J. of Power Sources (2017) DOI: doi.org/10.1016/j.jpowsour.2017.09.068 [2] Md M. Hossen, K. Artyushkova, P. Atanassov, A. Serov "Synthesis and characterization of high performing Fe-NC catalyst for oxygen reduction reaction (ORR) in Alkaline Exchange Membrane Fuel Cells" J. Power Sources (2017) DOI: 10.1016/j.jpowsour.2017.08.036 [3] S. A. Kabir, K. Lemire, K. Artyushkova, A. Roy, M. Odgaard, D. Schlueter, A. Oshchepkov, A. Bonnefont, E. Savinova, D. Sabarirajan, P. Mandal, E. Crumlin, I. V. Zenyuk, P. Atanassov, A. Serov "Platinum Group Metal-free NiMo Hydrogen Oxidation Catalysts: High Performance and Durability in Alkaline Exchange Membrane Fuel Cells" J. Mater. Chem. A (2017) DOI: 10.1039/C7TA08718G [4] R. Janarthanana, A. Serov, S. Kishore Pilli, D. A. Gamarra, P. Atanassov, M. R. Hibbs, A. M. Herring "Direct Methanol Anion Exchange Membrane Fuel Cell with a Non-Platinum Group Metal Cathode based on Iron-Aminoantipyrine Catalyst", Electrochim. Acta 175 (2015) 202-208. [5] J. K. Dombrovskis, A. E. C. Palmqvis "Recent Progress in Synthesis, Characterization and Evaluation of Non-Precious Metal Catalysts for the Oxygen Reduction Reaction" Fuel Cells 16 (2016) 4–22. [6] A. Serov, M. J. Workman, K. Artyushkova, P. Atanassov, G. McCool, S. McKinney, H. Romero, B. Halevi, T. Stephenson "Highly stable precious metal-free cathode catalyst for fuel cell application", J. Power Sources 327 (2016) 557-564. [7] Q. Hu, G. Li, J. Pan, L. Tan, J. Lu, L. Zhuang "Alkaline polymer electrolyte fuel cell with Ni-based anode and Co-based cathode" Int. Journal of Hydrogen Energy 38 (2013) 16264-16268. [8] T. Reshetenko, M. Odgaard, D. Schlueter, A. Serov "Analysis of alkaline exchange membrane fuel cells performance at different operating conditions using DC and AC methods" J. of Power Sources (2017) DOI: /doi.org/10.1016/j.jpowsour.2017.11.030 Figure 1

Anion exchange membrane fuel cells (AEMFCs) have recently received significant attention as a future high efficiency, environmentally energy conversion device. This attention is due to the potential advantages that AEMFCs can offer compared the much more common, and commercialized, proton exchange membrane fuel cells (PEMFCs) – most notably lower cost. However, there are several remaining roadblocks for the AEMFC technology to be widely adopted, such as: i) the stability of the anion exchange membranes (AEMs) and anion exchange ionomer (AEIs); ii) the development of highly active low-platinum group metal (PGM) for non-PGM catalysts; iii) the discovery of water management strategies to prevent from electrodes flooding or drying out; and iv) reducing the negative effect of CO2 on the AEMFC performance. In an AEMFC operating on ambient air, CO2 reacts with the OH- anions created from the oxygen reduction reaction at the cathode, forming HCO3- and CO3 2-. These carbonates are transported from the cathode to the anode during operation. The presence of carbonate anions has multiple impacts on the operating AEMFC; carbonates decrease the conductivity and water uptake of AEM, introduce additional charge transfer resistance at the hydrogen oxidation anode and change the anode pH (resulting in a thermodynamic decrease in the cell operating voltage). In total, the CO2-related overpotential can be up to 400 mV, which is unacceptable from a practical perspective. Unfortunately, to date, only very few (especially experimental) studies have focused on quantifying the effect of CO2 on AEMFC performance. This poster will present an extensive array of experiments that deconvolutes the fundamental electrochemical mechanism for carbonate “poisoning” in AEMFCs. We also investigate the dynamics of CO2 uptake and removal and dynamics in these systems – with a particular focus on the impact of CO2 concentration in the reacting gas, temperature, AEM thickness and AEM chemistry. Finally, strategies to reduce the CO2 related overpotential below 100 mV will be shown.

Electrocatalytic activity of the oxygen reduction reaction (ORR) on carbon-supported metallophthalocyanine (MPc/C, M = Fe, Co, Ni, and Mn) catalysts was studied with a rotating disk electrode (RDE) and a rotating ring-disk electrode (RRDE) in 0.1 M NaOH solutions. FePc/C shows better ORR activity than CoPc, NiPc, and MnPc in 0.1 M NaOH solutions. Density functional theory (DFT) calculations were performed to study the adsorption of O2, H2O, OH, HOOH, and H2OO molecules on FePc, CoPc, NiPc, and MnPc molecule catalysts. Investigations using various MPc/C molecules as the cathode catalyst in anion exchange membrane fuel cells (AEMFCs) revealed that the catalysts, such as FePc/C, with high ORR activities observed with a RDE in 0.1 M NaOH solutions, do not warrant the high performance observed in the AEMFCs. DFT calculation results indicate that the FePc molecules are favorable for the adsorption of OH− rather than O2 or H2O, especially under AEMFC operation conditions. Electrochemical impedance (EIS) spectra obtained while operating the AEMFCs revealed that the resistance of OH− transportation from the cathode to the anode depends on the cell potentials and the nature of the MPc molecules. As predicted by the DFT calculation results, the FePc/C catalyst shows the highest OH− transport resistant at a high current and a low cell voltage region. The bonding strength between OH− and MPc molecules is a critical factor that determines the performance of the MPc molecules in AEMFCs. The fundamental discrepancy between ORR activities observed with an RDE in a standard three-electrode cell and ORR activities observed in an AEMFC is discussed.

Anion exchange membrane fuel cells (AEMFC) have gained increasing research interest because its alkaline chemistry enables non-platinum group metal (non-PGM) catalysts to be used. Despite this opportunity, many researchers still focus on PGM material due to their performance. Often the approach is to minimize PGM content by using non-PGM supporting substrates, such as Pt-Ni foam and Pt-Ni/Ni-B catalysts in order to mitigate cost [1] [2]. Although the performances of both PGM and non-PGM catalysts have been thoroughly researched, their stability under an AEMFC environment is seldom questioned. This is because PGM materials, typically Pt, are noble metals and many non-PGM materials are considered stable under alkaline conditions, especially nickel. However, the Pt stability in PEMFCs has been severely challenged during fuel cell operations. Ferreira et al. reported the Pt catalyst particle aggregation with decreased PEMFC performance [3]. Helmly et al. reported Pt dissolution in a PEM electrolyte. In alkaline fuel cell operation, the amount of dissolved Pt was reported to be even higher than from PEM FC operation [4]. Hence, the Pt stability is of concern under AEMFC conditions. On the other hand, Ni stability does not appear to have been reported. Therefore, the focus of this study is to examine catalyst stability of Pt and Ni under identical AEMFC operating conditions. This study focuses on pure Pt and Ni carbon supported catalysts, which have been conventionally used to operate AEMFCs. To study and compare the two materials under the same test condition, both Ni/C and Pt/C catalysts were applied on the same AEMFC in separate locations as shown in Fig.1. A sandwiched AEM was used so that catalyst migration could be studied without interference from direct catalyst contact. The AEMFC was held at 0.9V by a potentiostat with H2 and O2 gas flowing at each specific electrode. Once per day, the cell open circuit potential (OCP) was measured without the imposed voltage. To identify any catalyst morphology change after 30 days (~500hrs) operation, scanning electron microscopy (SEM) was conducted on a cross section of each catalyst layer; transmission electron microscopy (TEM) was used to observe catalyst particles from each layer; inductively coupled plasma (ICP) analysis was used to determine if any catalyst could be detected in the middle AEM. The OCP was found to have dropped by 0.2V during the 30 day operation. Significant catalyst morphology changes were found at the cathode for both Ni/C and Pt/C catalysts. SEM analysis showed that the Ni material was found to develop a band like structure at the AEM-catalyst layer interface. The TEM analysis confirmed that the Ni nanoparticles developed a smeared shape on the carbon substrate, which was verified as a Ni oxide species using energy-dispersive X-ray (EDX) mapping. The SEM images showed that the Pt signal from the cathode catalyst layer was much weaker than the one from the anode. TEM analysis showed that the Pt remained as nanoparticles on the carbon substrate, but that the nanoparticle density appeared lower than on the anode, consistent with Pt dissolution. The ICP analysis showed both Ni and Pt in the middle AEM. The results indicate, substantial morphology changes occurred on both Ni/C and Pt/C catalysts during AEMFC operation. Additional research is needed to investigate the change of morphology mechanisms, which is key to developing enhanced stability of AEMFC catalysts. [1] Daping He, Libo Zhang, Dongsheng He, Gang Zhou, Yue Lin, Zhaoxiang Deng, Xun Hong, Yuen Wu, Chen Chen & Yadong Li, Amorphous nickel boride membrane on a platinum–nickel alloy surface for enhanced oxygen reduction reaction, Nature Communications volume 7, Article number: 12362 (2016) [2] Julia van Drunen, Brandy K. Pilapil, Yoseif Makonnen, Diane Beauchemin, Byron D. Gates, and Gregory Jerkiewicz, Electrochemically Active Nickel Foams as Support Materials for Nanoscopic Platinum Electrocatalysts, ACS Applied Materials & Interfaces 2014 6 (15), 12046-12061 [3] P. J. Ferreira, G. J. la O,, Y. Shao-Horna, D. Morgan, R. Makharia, S. Kocha, and H. A. Gasteiger, Instability of Pt ∕ C Electrocatalysts in Proton Exchange Membrane Fuel Cells A Mechanistic Investigation J. Electrochem. Soc. 2005 volume 152, issue 11, A2256-A2271 [4] Serhiy Cherevko, Aleksandar R. Zeradjanin, Gareth P. Keeley and Karl J. J. Mayrhofer, A Comparative Study on Gold and Platinum Dissolution in Acidic and Alkaline Media J. Electrochem. Soc. 2014 volume 161, issue 12, H822-H830 Figure 1

Anion exchange polyelectrolytes for membranes and ionomers