Alkaline Exchange Membrane Fuel Cells Research Articles

Oxygen reduction reaction platinum group metal-free electrocatalysts derived from spent coffee grounds

The annual generation of coffee waste has overtaken 6 million metric tons, becoming a serious environmental problem. Herein, we report the fabrication of bimetallic electrocatalysts synthesized by 1) pyrolyzing spent coffee grounds (SCGs) at 400, 600, 800 and 1000 °C, 2) activating the as-obtained char with KOH and 3) functionalizing the activated carbon with iron(II) and manganese(II) phthalocyanine. The final electrocatalysts showed a high degree of amorphousness, defectivity (increasing with temperature) and high specific surface area (up to 1820 m2 g−1). In half-cell compartment (0.1 M KOH electrolyte), the top-notch material in terms of oxygen reduction reaction (ORR) activity and selectivity was CFeMn_600, which showed the same half-wave potential (E1/2) compared to Pt/C standard along with a lower peroxide production. These outstanding results could be attributed to a high surface area, a Fe-Mn synergy, and an abundance of C-N defects. The performance of CFeMn_600 as a cathode material in alkaline exchange membrane fuel cells (AEMFC) showed an open circuit voltage (OCV) of 0.890 V and power density of 30 mW cm−2. Notwithstanding, this research is one of few cases where a waste-derived electrocatalyst is tested in a real AEMFC, thus becoming a pioneer in the fuel cell study of waste-derived electrode materials.

Single-metal-atom-anchored RuN2 monolayers: A high-performance electrocatalyst for alkaline hydrogen oxidation reactions

The development of alkaline exchange membrane fuel cells (AEMFCs) is severely hampered by the scarcity of efficient Pt-free catalysts for the anodic hydrogen oxidation reaction (HOR). In this work, we systematically explored the HOR performance of single 3d transition metal atom-doped RuN2 monolayers (TM-RuN2, TM = Ti-Zn) by density functional theory calculations. Formation energy, oxidation potential, and electronic structure analyses indicate that the Ti, V, Fe, Co, and Ni-doped RuN2 not only have a good conductivity, but also possess strong thermodynamic and electrochemical stability. For TM-RuN2, the ortho-N and metal (TM or ortho-Ru) atoms form a dual-active site for the adsorption of H* and OH*, respectively, where the adsorption strength is fine-tunable via the TM-modulated electronic structure. The HOR occurs preferentially through the H2 + OH*-H* + OH* mechanism on the pristine and Co, Ni, Cu, and Zn-doped RuN2, and the Tafel − H* + OH* mechanism on the Ti, V, Cr, Mn, and Fe-doped RuN2. The precisely balanced H* and OH* adsorption strength of Fe-RuN2 results in the ultra-low free energy barriers to HOR. Benefiting from the strong thermodynamic and electrochemical stability, good conductivity, and excellent HOR activity, Fe-RuN2 exhibits a huge potential as HOR electrocatalysts for AEMFCs.

The Role of Discrepant Reactive Intermediates on Ru‐Ru2P Heterostructure for pH‐Universal Hydrogen Oxidation Reaction

AbstractDeveloping highly efficient electrocatalysts for hydrogen oxidation reaction (HOR) under alkaline media is essential for the commercialization of alkaline exchange membrane fuel cell (AEMFC). However, the kinetics of HOR in alkaline media is complicated, resulting in orders of magnitude slower than that in acid, even for the state‐of‐the‐art Pt/C. Here, we find that Ru‐Ru2P/C heterostructure shows HOR performance with a non‐monotonous variation in a whole pH region. Unexpectedly, an inflection point located at pH≈7 is observed, showing an anomalous behavior that HOR activity under alkaline media surpasses acidic media. Combining experimental results and theoretical calculations, we propose the roles of discrepant reactive intermediates for pH‐universal HOR, while H* and H2O* adsorption strengths are responsible for acidic HOR, and OH* adsorption strength is essential for alkaline HOR. This work not only sheds light on fundamentally understanding the mechanism of HOR but also provides new designing principles for pH‐targeted electrocatalysts.

The Role of Discrepant Reactive Intermediates on Ru-Ru2 P Heterostructure for pH-Universal Hydrogen Oxidation Reaction.

Developing highly efficient electrocatalysts for hydrogen oxidation reaction (HOR) under alkaline media is essential for the commercialization of alkaline exchange membrane fuel cell (AEMFC). However, the kinetics of HOR in alkaline media is complicated, resulting in orders of magnitude slower than that in acid, even for the state-of-the-art Pt/C. Here, we find that Ru-Ru2 P/C heterostructure shows HOR performance with a non-monotonous variation in a whole pH region. Unexpectedly, an inflection point located at pH≈7 is observed, showing an anomalous behavior that HOR activity under alkaline media surpasses acidic media. Combining experimental results and theoretical calculations, we propose the roles of discrepant reactive intermediates for pH-universal HOR, while H* and H2 O* adsorption strengths are responsible for acidic HOR, and OH* adsorption strength is essential for alkaline HOR. This work not only sheds light on fundamentally understanding the mechanism of HOR but also provides new designing principles for pH-targeted electrocatalysts.

Enabling Low-PGM Anode Electrodes for Improved Cell Performance and Durability in Alkaline Exchange Membrane Fuel Cells

Anion exchange membrane fuel cells (AEMFCs) have gained great interest due to their potential to reduce cost relative to proton exchange membrane fuel cells (PEMFCs) as the alkaline working environment allows the reduction of precious metals and the use of non-precious metals as the oxygen reduction reaction catalysts. Significant progress in highly conductive and base stable anion exchange membranes has advanced the direction of research towards device level fuel cell performance and durability.1,2 High performing alkaline electrodes further improved AEMFC performance reaching to 3.4 W cm-2 and durability test over 2000 h at 0.6 A cm-2.3,4 In addition, maneuvering the operating window such as varied relative humidity of anode and cathode, gas flow rates, and operating temperature can further enable efficiency in fuel cell performance.5,6 Despite the significant improvements in AEMFC, the advanced performance is limited under certain conditions (e.g. H2/O2 operation, high gas stoichiometry and high PGM loading).7 Many of the fundamental performance and durability mechanisms remain poorly understood. Therefore, it is important to gain a better understanding of AEMFC electrode structures, catalyst-ionomer interactions, and degradation factors to further advance AEMFC towards commercially available.This talk will focus on MEA development emphasized in reducing anode PGM loading, using a perfluorinated AEM polymer (PFAEM) (jointly developed by 3M and the National Renewable Energy Lab)8 based MEA, in which PFAEM polymer is used as the membrane as well as the electrode ionomer. A combination of in-situ and ex-situ techniques are applied to understand structure-property relationships of the electrodes. Systematic study demonstrating our approach towards decreasing anode PGM loading will be presented. The results indicate that despite an 85% reduction in anode electrode’s PGM loading (0.7 mgPGM cm-2 to 0.1 mgPGM cm-2), peak power is able to be maintained by 70%, ~ 1.15 W cm-2 and with reasonable in-situ stability performance. This is accomplished by incorporating anode electrode’s electrocatalyst/ionomer integration and improving the electrode’s structure, leading for better water balance. This work is intended to provide practical methods and direction for improving AEMFC electrode’s structure and subsequently their fuel cell performance and durability.References C. G. Arges and L. Zhang, ACS Appl. Energy Mater., 1, 2991–3012 (2018).S. Gottesfeld, D. R. Dekel, M. Page, C. Bae, Y. Yan, P. Zelenay, and Y. S. Kim, Journal of Power Sources, 375, 170–184 (2018).G. Huang, M. Mandal, X. Peng, A. C. Yang-Neyerlin, B. S. Pivovar, W. E. Mustain, and P. A. Kohl, J. Electrochem. Soc., 166, F637–F644 (2019).N. U. Hassan, M. Mandal, G. Huang, H. A. Firouzjaie, P. A. Kohl, and W. E. Mustain, Advanced Energy Materials, 10, 2001986 (2020).T. J. Omasta, A. M. Park, J. M. LaManna, Y. Zhang, X. Peng, L. Wang, D. L. Jacobson, J. R. Varcoe, D. S. Hussey, B. S. Pivovar, and W. E. Mustain, Energy Environ. Sci., 11, 551–558 (2018).A. C. Yang-Neyerlin, S. Medina, K. M. Meek, D. J. Strasser, C. He, D. M. Knauss, W. E. Mustain, S. Pylypenko, and B. Pivovar, J. Electrochem. Soc. (2021) http://iopscience.iop.org/article/10.1149/1945-7111/abf77f.S. T. Thompson, D. Peterson, D. Ho, and D. Papageorgopoulos, J. Electrochem. Soc., 167, 084514 (2020).A. M. Park, Z. R. Owczarczyk, L. E. Garner, A. C. Yang-Neyerlin, H. Long, C. M. Antunes, M. R. Sturgeon, M. J. Lindell, S. J. Hamrock, M. Yandrasits, and B. S. Pivovar, ECS Trans., 80, 957–966 (2017).

Recent Advances in Electrocatalysts for Proton Exchange Membrane Fuel Cells and Alkaline Membrane Fuel Cells.

The rapid progress of proton exchange membrane fuel cells (PEMFCs) and alkaline exchange membrane fuel cells (AMFCs) has boosted the hydrogen economy concept via diverse energy applications in the past decades. For a holistic understanding of the development status of PEMFCs and AMFCs, recent advancements in electrocatalyst design and catalyst layer optimization, along with cell performance in terms of activity and durability in PEMFCs and AMFCs, are summarized here. The activity, stability, and fuel cell performance of different types of electrocatalysts for both oxygen reduction reaction and hydrogen oxidation reaction are discussed and compared. Research directions on the further development of active, stable, and low-cost electrocatalysts to meet the ultimate commercialization of PEMFCs and AMFCs are also discussed.

SnO2/CeO2 nanoparticle-decorated mesoporous ZSM-5 as bifunctional electrocatalyst for HOR and ORR

Developing highly efficient noble metal-free electrocatalysts for hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) in alkaline exchange membrane fuel cells (AEMFCs) is of great importance for the large-scale applications, which, however, still remains a great challenge. Here we present the synthesis of SnO2 and CeO2 nanoparticle-decorated mesoporous ZSM-5 (denoted as SnCe-ZSM) via electrostatic interaction, which, surprisingly, not only exhibits excellent catalytic activity towards HOR, but also largely enhance ORR performance. The strong electronic interaction between SnO2 and CeO2 nanoparticles synergistically leads to the electron-enrichment on SnO2 and oxygen vacancy accumulation on CeO2, which respectively enable the hydrogen and oxygen adsorption/activation concurrently, finally resulting in the significant enhancements of the electrocatalytic activity towards both HOR and ORR. Additionally, the SnCe-ZSM based zinc-air battery exhibits a remarkably high power density of 98 mW/cm2 and excellent stability during discharging/charging cyclic tests for 60 h. The SnCe-ZSM electrocatalyst provides a significant paradigm for designing bifunctional composite catalysts for applications in clean energy devices.

Polyetherimide based anion exchange membranes for alkaline fuel cell: Better ion transport properties and stability

Alkaline anion exchange membrane (AAEM) is the key component for alkaline exchange membrane fuel cells (AEMFCs). AAEMs with good ionic conductivity, excellent thermo-mechanical and alkaline stability were synthesized by chloromethylation and quaternization followed by alkalization of polyetherimide. Chloromethylation of polyetherimide, a key step in the synthesis of anion exchange membranes based on polyetherimide, frequently involves cancer-causing chemicals. Here, an approach towards the use of non-carcinogenic reagent has been implemented for the synthesis of AAEMs. Physiochemical properties of prepared membranes are tuned by varying tertiary amines. Derivatives during the membrane synthesis are characterized by proton NMR spectroscopy. FTIR spectroscopy confirms the successful quaternization of polyetherimide, and dense nature of membranes is cross-checked by SEM imaging. Synthesized anion exchange membranes show ionic conductivity in order of 2.68–3.22 × 10−2 S/cm complemented by ion exchange capacity of 1.58–2.07 meq/g. Under strong alkaline conditions 1 M KOH at 60 °C and 5 M KOH at room temperature, membranes are stable without losing their integrity. Based on preliminary studies, it is anticipated that functionalized polyetherimide may be a suitable candidate as an anion exchange membrane in fuel cell applications.

Nitrogen-doped hollow carbon spheres as highly effective multifunctional electrocatalysts for fuel cells, Zn–air batteries, and water-splitting electrolyzers

Clean energy conversion technologies require low-cost multifunctional catalysts. In this work, nitrogen-doped hollow carbon spheres with nanoporous shells (NHCS–W) are prepared by using the ionic liquid 1-butyl-3-methylimidazolium chloride as a source of both carbon and nitrogen. A systematic investigation of the electrocatalytic performance and durability of NHCS–W reveals excellent performance and high stabilities for the oxygen reduction reaction, oxygen evolution reaction, and hydrogen evolution reaction in alkaline electrolytes. This multifunctionality facilitates promising practical applicability for NHCS–W. An alkaline exchange membrane fuel cell (AEMFC) with NHCS–W as the cathode electrocatalyst has a peak power density of 109 mW cm−2, which is 7 mW cm−2 higher than that of an AEMFC with Pt/C (20%) as the cathode electrocatalyst. By using NHCS–W as an air electrode, two rechargeable Zn–air batteries in series can power a 5 mm red light-emitting diode (~2.2 V). Moreover, a cell voltage of only 1.61 V is needed to achieve a current density of 10 mA cm−2 in a water-splitting electrolyzer employing NHCS–W as both the cathode and anode catalysts. This work reveals the potential of ionic liquid precursors for constructing nitrogen-doped carbon-based materials for a wide variety of electrocatalytic applications.

Combined Synchrotron Nano X-Ray Computed Tomography and XANES to Understand PGM-Free Anodes of Alkaline Fuel Cells

Combined chemical information and X-ray CT or X-ray radiography is a new paradigm in energy-conversion and -storage characterization. During electrochemical experiment chemical mapping can be used to differentiate elements within fuel cell catalyst layer. Polymer electrolyte fuel cells (PEFCs) and alkaline exchange membrane (AEM) fuel cells are both low temperature, high efficiency technologies that use hydrogen and air (oxygen) to produce electricity. Most of the current efforts have focused on PEFCs, as commercial availability of polymer electrolyte membrane (PEM), such as Nafion enabled wide-spread research. Recently, AEM fuel cells have shown to produce current densities that are compatible to PEFCs 1-2. The promise of AEM fuel cells is to be more cost-effective as they can use Earth-abundant materials as electrocatalysts. In the past decade platinum group metal-free (PGM-free) catalysts have been developed. We reported novel class of NiMo catalysts, supported on carbon blacks, that showed unprecedented power densities for fully PGM-free fuel cells 3. Understanding chemical oxidation states of Ni, Mo and Cu under applied potentials in hydrogen environment within AEM fuel cell anode is critical to advance the knowledge of this domain of electrocatalysts. NiCu and NiMo bi-metallic catalysts are dispersed onto porous, high surface area supports to achieve high electrochemical surface area and good dispersion. The catalysts clusters are micrometer sized domains composed of nano particles. As hydrogen oxidation reaction proceeds in anode of these AEM fuel cells, the surface of NiCu and NiMo are reduced and thus oxidation state can change depending on local conditions. Our micro X-ray CT results indicate significant difference in electrochemical behavior and morphology between NiMo and NiCu electrocatalysts1, 3. The micro-CT technique provides large field-of-view (FOV) but it is lacking in spatial resolution. Designing experiment with combined nano X-ray computed tomography, X-ray absorption near edge structure (XANES) and/or fluorescence spatial mapping of the electrocatalyst under operating conditions will provide unprecedented insight into structure-function relations of these catalyst layers. In this work we use nano-CT imaging at adsorption edges of Ni and Cu to show electrocatalyst distribution and its XANES spectra at 18-ID National Synchrotron Light Source II (NSLS II) (Figure 1). We are the first group to use operando hardware with gas lines and electric inputs at the 18-ID NSLS II. Figure 1 shows our most recent updated operando cell at the beamline. Using our Gen. 3 operando fuel cell hardware, spatial 2D mapping of Ni and Cu was achieved as a function of applied potential and time with XANES probes. References Roy, A.; Talarposhti, M. R.; Normile, S. J.; Zenyuk, I. V.; De Andrade, V.; Artyushkova, K.; Serov, A.; Atanassov, P., Nickel–Copper Supported on a Carbon Black Hydrogen Oxidation Catalyst Integrated into an Anion-Exchange Membrane Fuel Cell. Sustainable Energy & Fuels 2018.Serov, A.; Zenyuk, I. V.; Arges, C. G.; Chatenet, M., Hot Topics in Alkaline Exchange Membrane Fuel Cells. Journal of Power Sources 375, 149-157 2018 Kabir, S.; Lemire, K.; Artyushkova, K.; Roy, A.; Odgaard, M.; Schlueter, D.; Oshchepkov, A.; Bonnefont, A.; Savinova, E.; Sabarirajan, D. C., Platinum Group Metal-Free Nimo Hydrogen Oxidation Catalysts: High Performance and Durability in Alkaline Exchange Membrane Fuel Cells. Journal of Materials Chemistry A 2017, 5, 24433-24443 Figure 1. a) Our Gen. 4 operando fuel cell at nano TXM beamline at 18-ID NSLS II, b) CAD design of modular operando cell and a photograph of our manufactured cell. c) XANES spectra and 2D projections of NiCu/KB catalyst. Figure 1

Alkaline Exchange Fuel Cell Membrane Ionomers Containing Spirocyclic Repeat Units in an All Carbon Backbone for Enhanced Durability

Alkaline exchange membrane fuel cells (AEMFC)s continue to gain interest as a potential lower cost alternative to the commercially available proton exchange membrane fuel cells (PEMFC)s. Recently there have been significant advances in the performance of AEMFC systems achieving greater than 1 1-2, albeit with PGM catalysts. However, the incorporation of non PGM catalyst materials will significantly reduce costs. One of the more significant challenges to the commercialization of AEMFCs is demonstrating long term durability under operating conditions and over startup/shutdown cycles. Improving the durability of the ionomers employed in alkaline exchange membranes and catalyst ink formulations will enhance the long term durability of AEMFCs. Enhancing the durability of alkaline ionomers has focused on the installation of more stable cationic head groups3. Previous research has demonstrated the incorporation of spirocyclic repeat units into multiblock copolymers of polysulfone4. The research presented demonstrates the incorporation of the spirocyclic polymer poly(diallylpiperidinium hydroxide) into an all carbon backbone of hydrophobic/hydrophilic block copolymers. The synthesis, characterization and performance is pesented. Omasta, T. J.; Peng, X.; Miller, H. A.; Vizza, F.; Wang, L.; Varcoe, J. R.; Dekel, D. R.; Mustain, W. E., Beyond 1.0 W cm-2 performance without platinum: the beginning of a new era in anion exchange membrane fuel cells. J. Electrochem. Soc. 2018, 165 (15), J3039-J3044.Omasta, T. J.; Zhang, Y.; Park, A. M.; Peng, X.; Pivovar, B.; Varcoe, J. R.; Mustain, W. E., Strategies for Reducing the PGM Loading in High Power AEMFC Anodes. J. Electrochem. Soc. 2018, 165 (9), F710-F717.Marino, M. G.; Kreuer, K. D., Alkaline Stability of Quaternary Ammonium Cations for Alkaline Fuel Cell Membranes and Ionic Liquids. ChemSusChem 2015, 8 (3), 513-523.Strasser, D. J.; Graziano, B. J.; Knauss, D. M., Base stable poly(diallylpiperidinium hydroxide) multiblock copolymers for anion exchange membranes. J. Mater. Chem. A 2017, 5 (20), 9627-9640.

Boosting Hydrogen Oxidation Activity of Ni in Alkaline Media through Oxygen-Vacancy-Rich CeO2 /Ni Heterostructures.

The search for highly efficient platinum group metal (PGM)-free electrocatalysts for the hydrogen oxidation reaction (HOR) in alkaline electrolytes remains a great challenge in the development of alkaline exchange membrane fuel cells (AEMFCs). Here we report the synthesis of an oxygen-vacancy-rich CeO2 /Ni heterostructure and its remarkable HOR performance in alkaline media. Experimental results and density functional theory (DFT) calculations indicate the electron transfer between CeO2 and Ni could lead to thermoneutral adsorption free energies of H* (ΔGH* ). This, together with the promoted OH* adsorption strength derived from the abundance of oxygen vacancies in the CeO2 species, contributes to the excellent HOR performance with the exchange current density and mass activity of 0.038 mA cmNi -2 and 12.28 mA mgNi -1 , respectively. This presents a new benchmark for PGM-free alkaline HOR and opens a new avenue toward the rational design of high-performance PGM-free electrocatalysts for alkaline HOR.

Boosting Hydrogen Oxidation Activity of Ni in Alkaline Media through Oxygen‐Vacancy‐Rich CeO2/Ni Heterostructures

AbstractThe search for highly efficient platinum group metal (PGM)‐free electrocatalysts for the hydrogen oxidation reaction (HOR) in alkaline electrolytes remains a great challenge in the development of alkaline exchange membrane fuel cells (AEMFCs). Here we report the synthesis of an oxygen‐vacancy‐rich CeO2/Ni heterostructure and its remarkable HOR performance in alkaline media. Experimental results and density functional theory (DFT) calculations indicate the electron transfer between CeO2 and Ni could lead to thermoneutral adsorption free energies of H* (ΔGH*). This, together with the promoted OH* adsorption strength derived from the abundance of oxygen vacancies in the CeO2 species, contributes to the excellent HOR performance with the exchange current density and mass activity of 0.038 mA cmNi−2 and 12.28 mA mgNi−1, respectively. This presents a new benchmark for PGM‐free alkaline HOR and opens a new avenue toward the rational design of high‐performance PGM‐free electrocatalysts for alkaline HOR.

(Invited) Ten Years on: Evolution, Status and Future of Alkaline Exchange Membrane Fuel Cell Systems

In 2009, CellEra Technologies began work on an Alkaline Exchange Membrane Fuel Cell (AEMFC) stack. Shortly thereafter, at a time when there was relatively little interest in the technology, a stack with 100 cm2 active area, yielding slightly under 100 mW/cm2, running on H2 and O2 was achieved. This result was the first demonstration of an AEMFC stack in operation and generated significant market interest. The membrane-electrode assemblies (MEA’s) used therein yielded up to 200 mW/cm2 in single-cell tests, a comfortably world-leading AEMFC power density at the time. Nevertheless, critical and potentially insurmountable obstacles were also in sharp focus: Low performance vs PEM fuel cells, low durability arising from chemical instability of ionomer in alkaline conditions, sensitivity to atmospheric CO2 and more. There exists in addition a special challenge of water management in the AEMFC. Though not traditionally assigned the same weight as the above obstacles in general AEMFC mythology, it was flagged as critical early on in our development program, and has since remained thematic, as it was determined to be a root cause in a large proportion, if not the majority, of identified device technology limitations. Active water consumption in the cathode electrode, ½O2 + H2O + 2e- → 2OH- (1) balanced by double the overall water generation rate at the anode, H2 + 2OH- → 2H2O + 2e- (2) leads to a wide variety of mutually reinforcing detrimental phenomena that must be mitigated holistically to achieve sustained high performance and durability. The existence of the additional reactant – water – in the cathode (Eq 1) is especially significant, with strong multi-scaled implications, from requirements for the chemistry of the component materials, to the design of catalyst layers, structural aspects of the MEA, optimization of operating conditions, design of flow fields and stack engineering. Even today, ten years on, this remains the core engineering and materials science challenge of the technology in spite of impressive progress made in the research field as a whole. In this talk we review the developments in, and understanding of, the PO-CellTech (formerly CellEra) MEA, stack and fuel cell system that have by now resolved all the fundamental questions of AEMFC viability as a technology, and allow us to target the nascent consumer automotive “FCEV” market: Ultra-low Platinum Group Metal (PGM) loadings, next-generation membrane technology, high areal (MEA) and volumetric (stack) power density, CO2 tolerance, and significant room for continued improvement. We will analyze the status and limitations of AEMFC power density, as well as the major outstanding challenge of device durability, with special reference to the ever-present water management imperative as well as increasingly stringent demands that need to be met, in order successfully to address a rapidly maturing exchange membrane fuel cell market.

(Invited) High Performance Alkaline Membrane Fuel Cells Powered By Direct Ammonia

Alkaline exchange membrane fuel cells (AEMFCs) have gained significant attention in recent years owing to several advantages over the industry-standard proton exchange membrane fuel cells (PEMFCs) such as lower cost materials (e.g., non-PGM electro-catalysts, hardware, etc.) Less commonly cited are potential advantages of AEMFCs with respect to alternative fuels. Ammonia is a particularly attractive carbon-free fuel, being liquid at room temperature under ~7 atm, resulting in very high volumetric energy density and simplified distribution relative to hydrogen which is typically compressed to 200-700 atm. Furthermore, ammonia cannot be used as a fuel in PEMFCs since in the acidic environment ammonia exists primarily as ammonium which displaces the H+ ions that impart conductivity to the polyelectrolyte. One of the key challenges in direct ammonia fuel cells is to execute the sluggish ammonia oxidation reaction (AOR) effectively. Previous successful attempts at operating direct ammonia fuel cells, therefore, all utilized high-temperature approaches such as solid oxide fuel cells (SOFCs) operated at ~600-850 °C [1] or alternatively, alkaline fuel cells (AFCs) operated at ~140 °C with concentrated KOH solutions as the electrolyte [2]. Additionally, a few attempts have been made to operate at lower temperatures with ammonia as a fuel, yielding very low power densities (<20 mW/cm2) [3-4]. In this study, we report for the first time, a direct NH3/O2 AEMFCs operated completely free of liquid electrolyte – in both the membrane-electrode assembly and the fuel feed. Utilizing operating temperatures of 100-120 °C to minimize losses from the AOR, and optimizing operation conditions and MEA design, yielded a peak power density of 270 mW/cm2 with no added electrolyte, and 450 mW/cm2 with the addition of dilute (1M) KOH to the fuel feed. Optimization was also carried out to stabilize performance over several hours with minimal voltage loss, thereby demonstrating sustained ammonia oxidation in the absence of any hydroxide additives. This work thus demonstrates the applicability of a high-performance direct ammonia-powered AEMFCs. [1] Hagen A., "Use of alternative fuels in solid oxide fuel cells." Fuel 2.2H2 (2007): H2. [2] Simons E.L., Cairns E.J., Surd D.J., "The performance of direct ammonia fuel cells." Journal of The Electrochemical Society 116.5 (1969): 556-561. [3] Rong L., Tao S., "Direct ammonia alkaline anion-exchange membrane fuel cells." Electrochemical and Solid-State Letters 13.8 (2010): B83-B86. [4] Kuntke P., Sleutels T.H.J.A., Saakes M., Buisma C.J.N., "Direct ammonia fuel cell performance using PtIr/C as anode electrocatalysts." international journal of hydrogen energy 39.10 (2014): 5148-5152.

Pt-Mn/C and Pd-Mn/C Nanoparticles As ORR Electrocatalysts

The sluggish kinetics of the oxygen reduction reaction (ORR) at the cathode remains as one of the main challenges for commercial viability of alkaline exchange membrane fuel cells (AEMFCs). It is therefore, of great interest to explore the development of electrocatalysts with superior activity and stability relative to the conventional carbon supported Pt nanoparticles (NPs). In this work we have studied the effects and evolution of structure and surface composition of Pt-Mn and Pd-Mn NPs on their electrocatalytic activity for the ORR in alkaline media. Both Pt-Mn and Pd-Mn NPs were synthesized using solvothermal methods and were supported on C via impregnation. In the case of Pt-Mn an ordered intermetallic phase was obtained by heat treatment, while for Pd-Mn NPs heat treatment did not lead to an ordered alloy. We have investigated the crystalline structure of these NPs using X-ray diffraction (XRD) and their size, morphology and composition using TEM/STEM, EELS and EDX. Cyclic voltammetry (CV) and rotating disk electrode (RDE) voltammetry were used to assess their electrocatalytic activity and stability. The NPs were electrochemically dealloyed in acidic media, through potential cycling, leading to the formation of Pt and Pd shell on PtMn and PdMn core. The dealloyed nanocatalysts exhibited over 400% increase in mass activity and 500% increase in specific activity as compare to Pt/C. The stability of the electrocatalyst was tested after 4,000 potential cycles in alkaline media following the DOE protocol (0.6-1.0 V vs reversible hydrogen electrode). In alkaline media, Mn surface segregation ensued, leading to a lower electrocatalytic activity when compared to the freshly dealloyed catalyst.

Highly conductive and chemically stable alkaline anion exchange membranes via ROMP of trans-cyclooctene derivatives

Alkaline anion exchange membranes (AAEMs) are an important component of alkaline exchange membrane fuel cells (AEMFCs), which facilitate the efficient conversion of fuels to electricity using nonplatinum electrode catalysts. However, low hydroxide conductivity and poor long-term alkaline stability of AAEMs are the major limitations for the widespread application of AEMFCs. In this paper, we report the synthesis of highly conductive and chemically stable AAEMs from the living polymerization of trans-cyclooctenes. A trans-cyclooctene-fused imidazolium monomer was designed and synthesized on gram scale. Using these highly ring-strained monomers, we produced a range of block and random copolymers. Surprisingly, AAEMs made from the random copolymer exhibited much higher conductivities than their block copolymer analogs. Investigation by transmission electron microscopy showed that the block copolymers had a disordered microphase segregation which likely impeded ion conduction. A cross-linked random copolymer demonstrated a high level of hydroxide conductivity (134 mS/cm at 80 °C). More importantly, the membranes exhibited excellent chemical stability due to the incorporation of highly alkaline-stable multisubstituted imidazolium cations. No chemical degradation was detected by 1H NMR spectroscopy when the polymers were treated with 2 M KOH in CD3OH at 80 °C for 30 d.

Enhancement of Palladium HOR Activity in Alkaline Conditions through Ceria Surface Doping

Hydrogen oxidation reaction (HOR) electrocatalysis suffers from slow kinetics at the anode of alkaline exchange membrane fuel cells (AEMFCs). A series of Pd-CeO2-x catalyst was synthesized at low temperature by the decomposition of cerium ammonium nitrate (CAN) on Pd. This simple method yields palladium with sub-stoichiometric amorphous CeO2-x islands which nucleate and grow on the surface of Pd. The vertical growth is preferred: ceria on ceria vs. ceria on palladium as evidenced by the constant values of Pd electrochemical surface areas observed for all ceria contents. The HOR activity is enhanced compared to pristine Pd. At 0.1 V vs. RHE, the specific and mass activities could be increased by a factor of 100 and 50 respectively for the highest content ceria samples. These results show that high ceria doping is requested to activate the HOR activity of palladium in alkaline medium, which can be achieved by cerium ammonium nitrate low temperature decomposition.

Structure of Active Sites of Fe-N-C Nano-Catalysts for Alkaline Exchange Membrane Fuel Cells.

Platinum group metal-free (PGM-free) catalysts based on transition metal-nitrogen-carbon nanomaterials have been studied by a combination of ex situ and in situ synchrotron X-ray spectroscopy techniques; high-resolution Transmission Electron Microscope (TEM); Mößbauer spectroscopy combined with electrochemical methods and Density Functional Theory (DFT) modeling/theoretical approaches. The main objective of this study was to correlate the HO2− generation with the chemical nature and surface availability of active sites in iron-nitrogen-carbon (Fe-N-C) catalysts derived by sacrificial support method (SSM). These nanomaterials present a carbonaceous matrix with nitrogen-doped sites and atomically dispersed and; in some cases; iron and nanoparticles embedded in the carbonaceous matrix. Fe-N-C oxygen reduction reaction electrocatalysts were synthesized by varying several synthetic parameters to obtain nanomaterials with different composition and morphology. Combining spectroscopy, microscopy and electrochemical reactivity allowed the building of structure-to-properties correlations which demonstrate the contributions of these moieties to the catalyst activity, and mechanistically assign the active sites to individual reaction steps. Associated with Fe-Nx motive and the presence of Fe metallic particles in the electrocatalysts showed the clear differences in the variation of composition; processing and treatment conditions of SSM. From the results of material characterization; catalytic activity and theoretical studies; Fe metallic particles (coated with carbon) are main contributors into the HO2− generation.

Leveraging Commercial Silver Inks as Oxidation Reduction Reaction Catalysts in Alkaline Medium

Alkaline exchange membrane fuel cells (AEMFCs) development is impeded by the lack of low-cost processes for fabricating catalyst layers. One bottleneck lies in using large amounts of precious group metals during the layer deposition process by spray-painting. One possible solution would be to leverage inkjet printing technologies known for their full recovery of the printed material. Recent advances in printed electronics has led to the commercialization of silver (Ag) inks. We demonstrate the electrocatalytic properties (oxygen reduction reaction (ORR)) of Ag ink. Moreover, we show that a simple galvanic replacement reaction (GRR) on the Ag ink yields Ag0.9M0.1 (M = Pt or Pd) hollow nanoparticles. The resultant electrocatalyst demonstrated high activity for the ORR in alkaline medium. The Ag colloidal dispersion (the ink) reacted with a minute amount of platinum group metals precursors (PGMs). X-ray diffraction (XRD) and electron microscopy confirmed the hollow morphology and the formation of Pt or Pd-ri...