bluuebunny/crossref_metadata_2025 huggingface dataset:
Design and Optimization of Commercially-Relevant CO2 Electrolyzers
Authors: Weng Lien-Chun , Romiluyi Oyinkansola , Bell Alexis T. , Weber Adam Z.
Published: February 2020

The electrochemical reduction of CO2 (CO2R) to value-added products is an attractive technology for tackling the rising atmospheric CO2 levels and storing intermittent renewable energy into chemical bonds. Fundamental understanding of CO2R has progressed significantly in recent years and is critical in the development of industrial scale CO2R electrolyzers.1 However, most of our understanding has been drawn from experiments optimized for aqueous-phase CO2R systems. These systems can be limited by mass transfer at fairly low current densities (~10 mA cm-2) due to unfavorable CO2/OH- interactions and large diffusion lengths.2

To achieve commercially-relevant CO2R rates (> 100 mA cm-2), gas-diffusion electrodes (GDEs) play an important role as they can decrease the diffusion length of CO2 to as small as 10 nm.3 The thin diffusion boundary layers in GDEs allow higher CO2R current densities and CO2R to occur under environments with higher OH- concentrations.4 However, with such drastic changes in operating condition and local environment, it is necessary to explore and better understand the transport and reaction overpotential intricacies in GDEs. For instance, conventional cell designs optimized for planar electrodes will suffer from large ohmic drops across the cell due to the higher current density; product distribution will also vary arising from higher CO2 and OH- concentrations near the catalyst.5

In this talk, we present a multiphysics modelling framework to design and optimize GDE systems performing CO2R. We then explore the performance and limitations of various cell designs guided by simulation results and examine potential methods for improving water management and tuning catalyst selectivity. Finally, we discuss the disparities in local environments between aqueous and GDE devices and propose strategies to reduce the gap in knowledge between the two systems.

Acknowledgements

This material is based upon work performed by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under Award Number DE-SC0004993. We thank David Larson for providing experimental data for CO2 reduction on membrane-electrode assembly devices.

D. Raciti and C. Wang, ACS Energy Lett., 2018, 3, 1545-1556.

T. Burdyny and W. A. Smith, Energy Environ. Sci., 2019, DOI: 10.1039/c8ee03134g.

L. C. Weng, A. T. Bell and A. Z. Weber, Phys. Chem. Chem. Phys., 2018, 20, 16973-16984.

S. Verma, X. Lu, S. Ma, R. I. Masel and P. J. Kenis, Phys. Chem. Chem. Phys., 2016, 18, 7075-7084.

C. T. Dinh, T. Burdyny, M. G. Kibria, A. Seifitokaldani, C. M. Gabardo, F. P. G. de Arquer, A. Kiani, J. P. Edwards, P. De Luna, O. S. Bushuyev, C. Q. Zou, R. Quintero-Bermudez, Y. J. Pang, D. Sinton and E. H. Sargent, Science, 2018, 360, 783-787.
Tuning the Sensitivity of CO2 Electroreduction on Copper Surfaces Via Electrolyte Engineering
Authors: Akhade Sneha A , Weitzner Stephen Eric , Lucci Felicia , Feaster Jeremy T. , Ivanovskaya Anna N , Wood Brandon C. , Varley Joel Basile , Baker Sarah E , Duoss Eric B
Published: February 2020

With growing increase in energy demand and chemical production, electrochemical reduction (ER) of CO2 can potentially pave the route for generation of sustainable drop-in fuels using renewable wind and solar energy sources. Cu has been identified as a promising electrocatalyst for CO2 conversion to methane and ethylene, albeit the rates of the electrocatalytic reactions are strongly influenced by the reaction environment and the operating conditions [1,2]. Electrolytic ions are known to impact the rates of electrocatalytic reactions, though a molecular understanding of such impact is not comprehensively understood. Here, we employ a coupled quantum mechanics/molecular mechanics (QM/MM) scheme [3] to investigate the role played by the electrolytic ions under applied potential on the activity-selectivity relationships for CO2 ER. By varying the concentration and identity of electrolytic salts, we investigate their effect on the reaction energetics and binding strength of reaction intermediates in the CO2 ER pathway. Using a high throughput combinatorial approach that spans a wide range of electrolytes, we attempt to create design principles for electrolyte-based tuning of CO2 ER selectivity and compare with experimentally measured CO2 ER selectivities. The results of these studies provide a rationale for improved environment driven design and screening, and allow computation of reaction energetics using nuanced, dynamical models of the electrochemical double layer.*

[1] Y. Hori, in Handbook of Fuel Cells: Fundamentals, Technology and Application (VHC Wiley, Chichester, 2003), Vol. 2, 720-733.

[2] A. Murata & Y. Hori, Product selectivity affected by cationic species in electrochemical reduction of CO2 and CO at a Cu electrode. Bulletin of the Chemical Society of Japan (1991), 64(1), 123-127.

[3] J. Haruyama, T. Ikeshoji and M. Otani, Electrode potential from density functional theory calculations combined with implicit solvation theory. Physical Review Materials (2018), 2(9), p.095801.

*This work was performed under the auspices of the U.S. DOE by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344.
Studies of Electrochemical CO2 Reduction in Membrane-Electrode Assemblies
Authors: Romiluyi Oyinkansola , Weng Lien-Chun , Larson David M , Bell Alexis T. , Weber Adam Z.
Published: February 2020

Gas-diffusion electrodes (GDEs) for electrochemical CO2 reduction allow for an order-of-magnitude increase in obtainable limiting current densities (~100 mA/cm2) compared to planar systems (~10 mA/cm2) due to the increase in CO2 flux, catalyst surface area, and reduction in diffusion length. Despite this improvement, aqueous GDE systems suffer from extensive catalyst dissolution/delamination and membrane degradation under operating conditions, as well as exhibit significant ohmic resistances stemming from their electrolyte layers. These characteristics limit the current densities that can be achieved at applied overpotentials and render them impractical for industrial implementation.

Membrane-electrode assemblies (MEAs), consisting of humidified gaseous feeds at one or both electrodes and no aqueous electrolyte between the electrodes (i.e. only using a solid ion-conducting polymer or ionomer as an electrolyte), can overcome the limitations of the aqueous GDE. In this poster, two MEA cell designs will be addressed: Full-MEA (humidified gaseous feeds at both the anode and cathode) and Exchange-MEA (humidified gaseous feed at the cathode and an adjoining water or salt solution, e.g. KHCO3 or KOH, at the anode to provide hydration and a source of ions). The experimental performance results obtained from the near-optimized vapor-fed Full-MEA and H2O Exchange-MEA systems for CO2RR at ambient temperature and pressure conditions and the details of our ongoing work in building a fully integrated, tandem/cascade catalysis device are described. This poster also details plans for future investigations in exploring critical fabrication, operating conditions, and MEA properties.

Acknowledgements

This material is based upon work performed by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under Award Number DE-SC0004993. We would also like to thank Nemanja Danilovic, Kun Jiang, Julie Fornaciari, Yagya Regmi, Douglas Kushner, and Christianna Lininger for their help, discussions, and guidance in the course of this research project.
Towards Efficient Electrocatalytic Conversion of CO2 to Formate Via Novel Electrolyzer Configurations
Authors: Klein Walter Ellis , Chen Yingying , Vise Ashlee , Mooney Mason , Deutsch Todd G , Neyerlin K C
Published: February 2020

Formate (HCOO-) has been proposed as an intermediate compound to store energy and carbon for microbial conversion to fuels and chemicals1. Formate can be generated by electrochemical reduction of CO2 and subsequently assimilated by microbes that are able to use it as a sole source of energy and carbon for growth and, as recently demonstrated, to produce higher-value chemicals like higher alcohols2. Using formate as an intermediate molecule could provide several advantages over direct conversion from gaseous feeds, such as utilizing renewable energy sources by uncoupling the power availability from the fluctuations inherent to renewable energy sources such as wind, solar, or tidal1. To enable formate as a foundation for the storage of carbon and energy and subsequent conversion to value-added fuels and chemicals, CO2 mass transport limitation issues need to be overcome.

High current densities are required for CO2 electrolyzers to be relevant for industrial applications. Due to the solubility limit of CO2, current densities are restricted to about 30 mA/cm2 in a liquid/planar electrode configuration3. Proof of principle results have shown the mass transport issues can be overcome through utilization of gas diffusion electrodes (GDE) with high interphase (gas/liquid/solid) surface area4.

Here we will discuss how higher current densities and faradaic efficiencies for the gas-phase CO2 to formate conversion process can be achieved through the utilization of novel bipolar membrane (BPM) architectures and reactor designs coupled with optimized reaction condition parameters. We will also show an introductory view of developed testing methods and equipment coupled with in-situ product analysis for electrocatalytic conversions not limited to formate production.

References

[1] Yishai, O., Lindner, S. N., Gonzalez de la Cruz, J., Tenenboim, H. & Bar-Even, A. The formate bio-economy. Curr Opin Chem Biol
35, 1–9 (2016).

[2] Li, H. et al. Integrated electromicrobial conversion of CO2 to higher alcohols. Science
335, 1596–1596 (2012).

[3] Salvatore, D. A. et al. Electrolysis of gaseous CO2 to CO in a flow cell with a bipolar membrane. ACS Energy Lett.
3, 149–154 (2017).

[4] Kopljar, D., Inan, A., Vindayer, P., Wagner, N. & Klemm, E. Electrochemical reduction of CO2 to formate at high current density using gas diffusion electrodes. J Appl Electrochem
44, 1107–1116 (2014).

Figure 1
ZnO/CuO Nanocomposite for Gas Phase Electrochemical Conversion of CO2 to CO at Elevated Pressure
Authors: Malik Karan , Verma Anil
Published: February 2020

Over the past few years, electrochemical reduction of CO2 (ERC) has attracted a lot of interest among researchers to convert CO2 into value added products using renewable energy.1 Thermodynamic reduction potential of ERC is close to that of hydrogen reduction potential (HER). Moreover, ERC can lead to many products i.e. CO, CH4, C2H4, C2H6, HCOOH, CH3OH etc. depending upon the catalyst and reaction conditions.2 Hence, catalysts play a crucial role in selective electroreduction of CO2. Therefore, majority of the research has been carried out on developing catalyst for selective ERC and most of the studies were conducted in aqueous phase ERC.3 The main limitation of this approach is the CO2 mass transfer limitations due to the low solubility of CO2 in water. However, sufficient studies relevant to the technological development of the direct gas phase ERC are still needed.

In this presentation we will discuss our work on role of pressure in improving gas phase ERC carried out in zero gap cell. We have synthesised ZnO/CuO nanocomposite and ZnO nanoparticles by two methods (wet chemical method and hydrothermal method). We have also synthesised a polyethyleneimine (PEI) based anion exchange membrane. Setup was systematically tested at various operating conditions. Results show that CO2 adsorption on the catalyst aided by the amine functional groups on membrane can be further enhanced by increasing the pressure. As the pressure slightly elevated to 0.5 bar from ambient pressure, HER was supressed and CO faradaic efficiency (FECO) of ~30% was reached. Moreover, current density was increased to ~50mA/cm2 from 4 mA/cm2. In this presentation we will compare the FECO, conversion and current densities of the synthesised electrocatalyst and seek to describe how elevating pressure increases rate of ERC on particular catalyst.

References

D. Raciti and C. Wang, ACS Energy Lett., 3, 1545-1556 (2018).

L.M. Aeshala, R. U. and A. Verma, Phys. Chem. Chem. Phys., 16,17588 (2014).

B. Kim, F. Hillman, M. Ariyoshi, S. Fujikawa and P.J.A. Kenis, J. Power Sources, 312, 192 – 198 (2016).
(Invited) Molecular Dynamics Analysis on the Behavior of Water and Alcohol Liquids on a OH-Terminated SiO2 Surface
Authors: Yamaguchi Yasutaka , Nakaoka Satoshi , Hayashi Takuya , Kawakami Masayuki , Yano Daisaku
Published: February 2020

Cleaning process to remove impurities is one of the essential processes for the fabrication of semiconductor device, where cleaning of trenches with water, replacement with IPA (isopropyl-alcohol) and its removal are iteratively carried out, and this process is still required upon recent reduction of the line width under 10 nm. This size is already at the border of the continuum limit where the theories of fluid mechanics can be applied. Hence, the authors adopted molecular dynamics (MD) simulations to examine the liquid behavior, especially wetting behavior and solid-liquid friction at the nanoscale with respect to simple Lennard-Jones fluid, water, methanol as well as IPA as the liquids, whereas simple non-polar crystal and silica as the solids [1-8]. In these studies, we have shown that surprisingly the liquid behavior even around this continuum border was qualitatively not remarkably different from that expected from a macroscopic point of view. On the other hand, the physical properties of liquids in the so-called adsorption layers formed in the vicinity of the solid typically of a few molecular diameters, are different from those in bulk, and their effects should be extracted and properly connected to the macroscopic scale, e.g. as a boundary condition to predict the liquid behavior.

In the presentation, we will discuss about the MD simulation results of liquid infiltration into a nanoscale slit, effects of gas molecules in the slit as well the diffusion of water and alcohol molecules on OH-terminated silica surfaces. In addition, the replacement procedure of adsorbed water/alcohol by bulk alcohol/water liquid will be discussed.

[1] Y. Yamaguchi, H. Kusudo, D. Surblys, T. Omori and G. Kikugawa, J. Chem. Phys. 150 (2019), 044701.

[2] D. Surblys, F. Leroy, Y. Yamaguchi, F. Mueller-Plathe, J. Chem. Phys. 148 (2018), 134707.

[3] S. Nakaoka, Y. Yamaguchi, T. Omori, L. Joly, Mechanical Engineering Lett. 3 (2017), 17-00422.

[4] S. Nakaoka, Y. Yamaguchi, T. Omori, L. Joly, J. Chem. Phys. 146 (2017), 174702.

[5] S. Nakaoka, Y. Yamaguchi, T. Omori, M. Kagawa, T. Nakajima, H. Fujimura, Phys. Rev. E 92 (2015), 022402.

[6] S. Nishida, D. Surblys, Y. Yamaguchi , K. Kuroda, M. Kagawa, T. Nakajima and H. Fujimura, J. Chem. Phys. 140 (2014), 074707.

[7] D. Surblys, Y. Yamaguchi , K. Kuroda, T. Nakajima and H. Fujimura, J. Chem. Phys. 140 (2014), 034505.

[8] Y. Yamaguchi, M. Kawakami, D. Yano, Jpn. J. Multiphase Flow 32-2 (2018), 218 (in Japanese).
Probing the Atomic-Scale Structure of Thin Films Grown By Atomic Layer Deposition
Authors: Young Matthias J , Bedford Nicholas , Elam Jeffrey W. , Yanguas-Gil Angel , Letourneau Steven , Coile Matthew , Mandia David , George Steven M. , Cavanagh Andrew S. , He Xiaoqing , Jasim Ahmed , Wyatt Quinton , White Tommi , Kaiser Helmut , Heitmann Thomas W
Published: February 2020

The ability to grow conformal films with Ångstrom resolution makes atomic layer deposition (ALD) an attractive means of protecting and/or chemically functionalizing surfaces for catalysis, energy storage, photoelectrochemistry, and other applications. However, the performance of ALD coatings frequently falls short of expectations, largely because the atomic-scale structure (and therefore the chemical and physical properties) of ALD films deviate from idealized preconceptions. Single-crystal materials are only rarely achieved by ALD. More often, ALD films form amorphous, polycrystalline, or defective structures. ALD process conditions such as precursor selection(s), precursor exposure(s), and reactor temperature are known to impact the properties of resulting films. The substrate also affects the properties of ALD films, especially for ultrathin film thicknesses. To date, the ALD community has had difficulty connecting the atomic-scale structure of ALD films with their performance, largely because of limited availability of techniques to determine the atomic-scale structure of the ALD films. In this work, we demonstrate the ability to probe the structure of ALD films (e.g. Al2O3) using various advanced characterization techniques including both ex situ and in situ high-energy X-ray diffraction (HE-XRD) coupled with pair distribution function (PDF) analysis, electron diffraction (ED), and neutron scattering (NS). We evaluate the effect of ALD process variables (e.g. growth temperature and substrate) on atomic-scale structure, and connect the measured ALD structural features to observed electrochemical properties. The techniques we demonstrate can be applied broadly to probe the local structure of ALD films, while the fundamental understanding gained from this work will help tailor ALD for electrochemical applications.

Figure 1
(Invited) Sputter Beam Epitaxy for Atomic Ordering in Complex Epitaxial Thin Films
Authors: Hauser Adam J
Published: February 2020

Innovation is driven by the materials mankind has mastered to advance society. Our information age traces back to wartime invention of methods to fabricate silicon and germanium crystals with defects lower than 1 part in 100, a threshold at which the intrinsic properties could then be applied. Today, complex materials (>2 elements with atomic ordering) are at a similar inflection point. Unfortunately, improvement beyond 1 defect in 4 has proven challenging: energetic defects abound and many elements are not compatible with current low-defect growth techniques. Despite significant external funding for the materials themselves, a lack of funding for new synthetic technologies has left us with methods unable to reach the inflection point.

Our goal is to transform materials discovery by developing a complex material thin film system that can attain 99% atomic ordering in today’s “too-complex” materials. This talk will highlight our progress in thin film growth via Sputter Beam Epitaxy, an approach combining the fabrication strengths of off-axis magnetron sputtering and molecular beam epitaxy.
A Modeling Study of Dislocation Behavior in InGaAs/GaAs (001) and InAlGaAs/GaAs (001) Heterostructures Utilizing Strained-Layer Superlattices
Authors: Islam Md Tanvirul , Kujofsa Tedi , Ayers John E
Published: February 2020

There have been a number of studies of dislocation filtering by strained-layer superlattices incorporated into semiconductor heterostructures. Despite the extensive nature of this body of work, a general understanding of the phenomenon has proved elusive, preventing wide application of SLS dislocation filters in practical devices. However, recent advances in the understanding of dislocation dynamics and the consequent development of detailed plastic flow models allow the prediction of threading dislocation density profiles in general semiconductor heterostructures. In this work, we have applied such a plastic flow model to InGaAs/GaAs (001) heterostructures containing an InGaAs-based SLS, and we have studied the dependence of the surface and average threading dislocation densities on the placement and design of the SLS.
Accelerated Stress Tests on Fuel Cell Cathode Catalysts: Thin Film (Ex-situ) Vs. Catalyst Layer (In-situ)
Authors: Rice Cynthia A.
Published: February 2020

For proton exchange membrane fuel cells (PEMFC), cathode catalyst durability is presently a key limiting factor to commercialization for automotive applications. The oxygen reduction reaction takes place on the cathode – transforming O2 + 4H+ + 4e- to 2H2O. Degradation occurs during normal operational load profiles for idle-to-peak power transients (rapid stop-go drive cycles), as the cathode voltage quickly switches from 0.9-1.2V (idle) to ~0.6V (peak). Cathode catalyst durability is dependent upon multiple operational factors, including; potential limits, temperature, and pH. As a result of the transient potentials, the electrochemical surface area (ECSA) of the carbon supported platinum catalyst (Pt/C) is reduced, due to a combination of Pt dissolution, Pt particle growth (migration and/or redeposition), and carbon corrosion (Pt detachment). Typically, accelerated stress tests (AST) are performed on thin films to evaluate catalyst durability and decouple contributions from ancillary fuel cell materials and structures. The thin films consists of catalyst deposited on a conductive rotating disk electrode and analyzed in liquid electrolyte (HClO4 or H2SO4) vs. a separate counter and reference electrode – ex-situ to the actual PEMFC environment. This removes the additional complexity of the catalyst layers 3-deminsional structure (containing both Pt/C and proton conducting ionomer), diffusion media and membrane – in-situ.

The AST used in this study includes 25,000 potential cycles from idle to peak potential limits using either square or triangular waveforms (SW or TW, respectively) at 10 sec intervals, for both Pt/C thin films and catalyst layers. ECSA was measured periodically during the cycles, either by integration of the hydrogen desorption area or by CO stripping analysis. The following operational limits were used with a lower potential limit of 0.6V – several upper potential limits (UPL) from 0.9 to 1.2V, multiple temperature ranges between 25°C and 70°C, and different electrolyte pH ranges 0 to 1.

Ex-situ AST results in 0.1 M HClO4 at 70°C show that the loss in ECSA was affected by both the UPL and the potential wave profile. For the 0.9V UPL dominated by Pt dissolution, the SW was more aggressive than the TW, resulting in a 45.6% and 36.8% ECSA loss, respectively. While the higher UPL of 1.2V had nearly identical ECSA losses for both potential wave profiles of 89%, due to the dominance of carbon corrosion. Figure 1A shows the effects of pH on AST induced ECSA losses at room temperature for the UPL of 1.2V using a TW. The pH values correspond to different concentrations of HClO4 (0.1 M HClO4 = pH of 1). As the pH is lowered there is an increase in ECSA loss. In Figure 1B the TW was found to cause more catalyst degradation at lower pH values. This potentially could be related to in-situ relative humidity dependent degradation – to be further studied in-situ on a catalyst layer.

Figure 1
Pt-Based Intermetallic Nanostructures: Activity Origin and Multifunctionality for Efficient Electrocatalysis
Authors: Kim Ho Young , Kim Jong Min , Ha Yoonhoo , Woo Jinwoo , Kim Hyungjun , Kim Jin Young , Joo Sang Hoon
Published: February 2020

Pt-based intermetallic nanostructures have demonstrated superior electrocatalytic performances compared to random alloy structures. However, the origin of their enhanced catalytic properties remains elusive. Furthermore, a robust synthetic strategy for well-defined intermetallic nanostructures represents a challenge. In this work, we reveal by combining theoretical and experimental results that the activity enhancement in intermetallic structures for oxygen reduction reaction (ORR) originates from the intensified ligand effect. We prepared well-defined model nanocatalysts via confined nanospace-directed synthesis using mesoporous silica templates, which allows precise control over the size and shape of nanostructures. Importantly, this method can transform disordered alloy nanostructures into intermetallic analogues without agglomeration, enabling decoupling of an atomic ordering effect in catalysis. The prepared ordered intermetallic Pt3Co nanowires (O-PtCo NWs) can benefit from the intensified ligand effect, Pt-skin layer, and aggregation-tolerant contiguous structure, which lead to their superior ORR activity and durability to disordered alloy Pt3Co nanowires (D-PtCo NWs) and Pt/C catalysts. The multifunctionality of O-PtCo NWs is demonstrated with their higher activity and durability in alkaline hydrogen evolution reaction and acidic methanol oxidation reaction than D-PtCo NWs and Pt/C catalysts. Furthermore, the O-PtCo NWs-based cathode in proton exchange membrane fuel cell (PEMFC) shows much better durability than a Pt/C-based PEMFC.

Figure 1
Low Pt Loaded Nitrogen Doped Carbon As Efficient Catalyst Support for Proton Exchange Membrane Fuel Cells
Authors: Ramaprabhu Sundara , Ramanujam Kothandaraman , Ganguly Dipsikha
Published: February 2020

Proton exchange membrane fuel cells are one of the promising renewable energy technologies, which generate electricity by utilizing hydrogen and oxygen as fuel and oxidant respectively. Platinum is so far the best catalyst for fuel cells. But for cost effective as well as efficient fuel cells, synthesizing low loading of platinum without hampering the performance has become the necessity of research. Roadmap for the development of PEMFC electrocatalyst by achieving DOE’s 2020 target of low Pt-loading 0.125 mgPt cm-2 with a deliverable power density of 0.9-1 Wcm-2. In order to achieve that target, catalytically active, highly conducting stable support materials are needed to decorate Platinum. In this work, nitrogen doped high surface area conducting carbon has been used as the support for the ultra small platinum nanoparticles. Nitrogen doping has been done using a bio-waste precursor whereas ultra small platinum nanoparticles (2-3 nm) has been decorated using polyol reduction method. ORR performance and stability of the catalysts were investigated using half-cell study (RDE, RRDE, and cyclic voltammetry) to fully understand the catalytic activity, which also shows the 4-electron transfer for the catalyst in 0.5 M H2SO4 solution. Full cell studies has been carried out using Pt/NC catalyst at the cathode and Pt/C at anode maintaining Pt-loading of 0.1 mgPt cm-2 on both the sides which resulted in a maximum power density of ~710 mW/ cm2 and 904 mW cm-2 at 60 C without and with iR correction which is comparatively higher than conventional catalysts. Mass activity of the catalyst has been found to be 686 A/g for 0.84 V, where as the maximum current density obtained was 2.3 A/ cm2 at 0.25 V. Power density of ~500 mW cm-2 was obtained at 0.6 V (without any iR correction) which complies to the DOE standards. Further modifications were done in order to reduce the iR losses at high current density and are discussed.
Effect of the Catalyst Metal Content on PEMFC Durability
Authors: Li Dongguo , Pan Yung-Tin , Wang Xiaojing , Wang Chenyu , Kim Yu Seung , Spendelow Jacob S
Published: February 2020

The sluggish oxygen reduction reaction (ORR) continues to limit proton exchange membrane fuel cell (PEMFC) performance, while degradation of ORR catalysts contributes to poor durability. So far, carbon supported Pt (Pt/C) and Pt based alloy catalysts are the most effective for electrocatalysis of ORR. In addition to the metal particle properties, the metal to carbon ratio and type of carbon support also affect the performance and durability. Therefore, it is necessary to single out these factors and evaluate each of them while keeping other parameters consistent.

In this work, we systematically investigated the effect of cathode catalysts on the PEMFC activity and durability using a single cell membrane electrode assembly (MEA). By screening commercial Pt/C catalysts supplied by Tanaka, we were able to establish that both metal to carbon ratio (from 5% to 50% wt.) and the type of carbon support (Vulcan XC-72 and high surface area) influence the MEA performance and durability. The Vulcan XC-72 carbon catalysts (VC) showed inferior initial mass activity at 0.90 V and lower electrochemically active surface area (ECSA) but similar power density at 0.67 V compared with the high surface area carbon catalyst (HSC). Moreover, the degradation of Pt/VC was more severe than that of Pt/HSC after accelerated stress testing (AST, 30000 cycles between 0.60 V and 0.95 V). This may be related to Pt particles distribution on the surface of carbon as opposed to those in the pores. The Pt particle distribution on the HSC was also probed by the carbon monoxide (CO) stripping under different relative humidity, which further indicated that Pt particles became more accessible after AST. On the other hand, the HSC with lower metal carbon ratio (10%, 20% wt.) demonstrate better durability, which may be attributed to the higher inter-particle distance. All the data will be presented and discussed for implication in practical PEMFC operation.
Novel Pt-Co Catalyst Concept to Boost the Oxygen Reduction Reaction for Acidic and Alkaline Polymer Electrolyte Fuel Cells
Authors: Weber Philipp , Weber Daniel Jochen , Janssen Marek , Oezaslan Mehtap
Published: February 2020

Polymer electrolyte fuel cells (PEFCs) play a critical role in clean and sustainable energy conversion technology in the near future. However, the widespread application of PEFCs is currently limited by their high loadings of costly and rare platinum group metals (PGM) and insufficient long-term durability. In the last 20 years, Pt-M alloys (M = Cu, Co, Ni) have been emerged as one of the promising catalyst materials to accelerate the sluggish kinetics of oxygen reduction reaction (ORR).[1-2] The superior ORR activity originates from ligand effects and geometric effects (lattice mismatch).[3]

In our work, we present a novel catalyst concept to efficiently modify PtxCo1-x (1<x<0) alloy nanoparticles for the ORR in acidic and alkaline media. The chemical composition and structure of the Pt-Co nanoparticles are controlled by variation of the synthetic parameters during the industrial relevant wet impregnation method.

Our catalyst concept is based on the surface rearrangement of the Pt-Co alloy nanoparticles to form core-shell or inverse core-shell structures by tuning the electrochemical parameters. Transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS) and CO chemisorption were used to understand the different stages of the surface rearrangement of Pt-Co alloy nanoparticles. In fact, 12 to 30 – fold increases in Pt surface area-based specific activity and 6 to 11 – fold higher Pt mass-based activities are achieved with our catalyst concept compared to commercial Pt/C. The simple switching between core-shell and inverse core-shell nanoparticles creates an efficient bifunctional catalyst to tune the reactivity and selectivity for the ORR in acidic and alkaline media. The observed activity improvement allows to reduce the Pt loading by a factor of at least 6, thus exceeding the DOE targets from ~0.4 to below 0.1 mg cm-2 of PGM loading for ORR.[4]

Based on our results, we present a novel Pt-Co catalyst concept to boost the electroreduction of oxygen for alkaline and acidic PEFCs.

References:

[1] T. Toda, H. Igarashi and M. Watanabe, Journal of The Electrochemical Society, 1998, 145, 4185-4188.

[2] M. Oezaslan, F. Hasché and P. Strasser, The Journal of Physical Chemistry Letters, 2013, 4, 3273-3291.

[3] B. Hammer and J. K. Norskov, Advances in Catalysis, 2000, 45, 71-129.

[4] https://www.energy.gov/eere/fuelcells/downloads/fuel-cell-technologies-office-multi-year-research-development-and-22.
Observation of Thermal Formation of FeN4 Sites during Pyrolysis
Authors: Li Jingkun , Jiao Li , Sougrati Moulay-Tahar , Mukerjee Sanjeev , Wegener Even Charles , Kropf A. Jeremy , Myers Deborah J. , Jaouen Frederic , Jia Qingying
Published: February 2020

It is unclear by far how the FeN4 site, which is responsible for the high activity toward the oxygen reduction reaction (ORR) of Fe-N-C catalysts, forms during pyrolysis, which limits further advancement of Fe-N-C catalysts for the ORR. Herein by conducting operando in-temperature x-ray absorption spectroscopy on Fe compounds mixed with a variety of species during pyrolysis, we observed the formation of in-plane FeN4 moieties starting around 600 ℃, accompanied with an ORR activity jump in acid in a rotating disk electrode. By varying the N and C precursors, as well as pyrolysis temperature, we showed that inorganic Fe species such as Fe nanoparticles, oxides, carbides et al. will form if Fe cannot be effectively incorporated into N-doped micropores during pyrolysis. The formation mechanism of in-plane FeN4 moieties during pyrolysis will be discussed.

Acknowledgement

This work was supported by the US Department of Energy under award number DE-EE0008416. The authors declare no competing financial interests. MRCAT operations are supported by the Department of Energy and the MRCAT member institution. This research used resources of the Advanced Photon Source, a DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.
Preparation of Various Platinum Rare Earth Metal Alloy Nanoparticles and Their ORR Performance
Authors: Brandes Benedikt Axel , Hu Yang , Cleemann Lars Nilausen , Li Qingfeng , Jensen Jens Oluf
Published: February 2020

Polymer electrolyte hydrogen fuel cells and their application can contribute to a sustainable future energy landscape. A significant contribution to their costs originates from the platinum-based catalyst. To this date platinum cobalt alloy nanoparticles are the industry standard catalysts to facilitate the sluggish Oxygen reduction reaction (ORR). It has been demonstrated that platinum rare earth metal alloy nanoparticles have high ORR activities which is retained during accelerated stress tests (AST) [1].

The very negative reduction potential of the rare earth metals (-2.0 V to -2.5 V) pose great challenges on the synthesis of its respective platinum alloys with the right properties such as alloy phase and particle size distribution [2].

Last year we showed the successful synthesis of small Pt3Y alloy nanoparticles using potassium vapor as the reducing agent at mild temperatures around 400 °C. Herein we demonstrate the synthesis of platinum alloy nanoparticles of gadolinium, cerium and lanthanum using the same method. Furthermore, we investigated the phase stability of different alloys towards acid leaching and the ORR performance before and after AST.

The Pt3Y alloy phase appears to be stable against acid leaching, in contrast to Pt2Y and all of the synthesized alloy phases of Gd, Ce and La. However, a lattice strain (shown by XRD) and traces of the respective rare earth element in the catalyst surface (shown by XPS) in combination with promising ORR results justify further investigation into these catalysts.

[1] Hernandez-Fernandez, P., Masini, F., McCarthy, D. N., Strebel, C. E., Friebel, D., Deiana, D., ... Chorkendorff, I. (2014). Mass-selected nanoparticles of PtxY as model catalysts for oxygen electroreduction. Nature Chemistry, 6(8), 732–738. https://doi.org/10.1038/nchem.2001

[2] Knudsen, B. P. (2016). Synthesis of Platinum Rare Earth Alloy Catalysts for Fuel Cells.
Study of Alkaline Durability and Anion Conductivity Using New Expanded Pyridinium Polymer with Self-Assembly Ability
Authors: Motoishi Yuki , Fujigaya Tsuyohiko
Published: February 2020

Polymer electrolyte fuel cells (PEFCs) are promising for practical use as the next generation clean power source. Since the anion exchange membrane fuel cell (AEMFC) operates in a basic environment, cost reduction is possible because non-platinum catalysts such as iron can be used. In addition, since the activation overpotential of oxygen reduction is smaller than that of a proton exchange membrane fuel cell (PEMFC), it is attracting attention as an alternative to PEMFC [1]. However, for practical use, further improvement of the anion conductivity and alkaline durability of the anion exchange membrane (AEM), in which a hydroxide ion (OH-) acts as an anion conductor is required. General strategy to promote anion conduction has been to move cation side chain freely, however problem is that the decomposition reaction occurs due to the attack from the OH-.

In this research, a new strategy of “self-organizing cation units to form channel structure” is studied to improve alkaline durability and anion conductivity at the same time. It is considered that this self-assembly strategy can achieve both the low mobility of cation to suppress from OH- attack and the anion conduction path. To realize this concept, an extended pyridinium monomer was newly designed with reference to extended pyridinium, one of the heteropolycyclic aromatic cation. Since strong π-π interactions have been reported between extended pyridiniums, introducing an extended pyridinium into the polymer will suppress the molecular motion of the anion conduction site and will induce the formation of self-assembled channels.

A new extended pyridinium monomer (TVP) was synthesized according to the synthesis method of the extended pyridinium salt of Katrizky et al [2]. Synthesized TVP was obtained as a pale yellow powder. From the 1H-NMR spectrum, vinyl group and aromatic peaks were observed, and it was confirmed that the monomer possessed high purity. The homopolymer (PTVP) was synthesized by free radical solution polymerization of TVP. Synthesized PTVP was obtained as a yellow solid. In 1H-NMR measurement, vinyl peaks were disappeared and the broadening of aromatic ring peaks were observed, suggesting that the free radical polymerization was taken place. Since PTVP is brittle and difficult to use as a film probably due to its rigid molecular structure, the introduction of a copolymer monomer was examined. When styrene and isoprene reported as an anion exchange membrane were examined as a copolymerization monomer, copolymer of PTVP-styrene and PTVP-isoprene were obtained, respectively. Although a PTVP-styrene copolymer film was brittle, a PTVP-isoprene copolymer film was obtained as a free standing film. Alkaline stability and anion conductivity of the films will be discussed.

[1] G. Merle; M. Wessling; K. Nijmeijer, J. Membr. Sci, 2011, 377, 1-35.

[2] A. R. Katritzky; Z. Zakarial; E. Lunt; P. G. Jones; O. Kennard, J. Chem. Soc., Chem. Commun., 1979, 6, 268-269.
Comparison of Direct Sodium Borohydride Fuel Cells with Cation and Anion Exchange Membranes
Authors: Swider-Lyons Karen , Garsany Y , Hjelm R. M. E.
Published: February 2020

Direct sodium borohydride fuel cells (DBFCs) present challenging electrochemistry due to the complexity of the electrocatalytic reactions at the cathode and anode plus the lack of a suitable membrane. The complex 8-electron oxidation reaction for sodium borohydride (NaBH4) to borate (BO2) at the anode is most efficient in alkaline electrolyte. However, the reduction of peroxide (H2O2) at the cathode is best carried out in acid electrolyte. The selection of whether to use an acidic or alkaline membrane has not been clear. Most researchers have used a perfluorosulfonic acid proton exchange membrane (PEM) as the membrane separator in the cells, but this becomes highly resistive when it becomes exchanged with sodium ions from the NaBH4, serving as a cation exchange membrane (CEM). The standard membrane for DBFCs has been Nafion 117, which is 7-mils thick. This relatively thick membrane has been chosen by DBFC researchers to improve the separation between the acidic cathode electrolyte and the alkaline anode electrolyte. We determine herein how H2O2-DBFCs performance is improved when made with a commercial 0.8-mil-thick anion exchange membrane (AEM) or a 0.8-.mil-thick CEM, in comparison to cells with 7-mil-thick CEMs.

The H2O2-DBFCs design is based on a well-characterized flow-cell design (1). Both the anode and cathode catalyst layers are prepared with carbon-black supported Pt electrocatalyst (Pt/CB, 50 wt. % Pt). The compartments are separated by either a Na-exchanged CEM (Nafion® 117 or Nafion HP) or AEM (Fumasep FAA-3-20). The electrochemical performance of the cell and its impedance are measured at an operating cell temperatures of 25 and 60 ° C.

H2O2-DBFCs with the 0.8-mil-thick AEM have a marked improvement of the current density of the standard cells with the 7-mil-thick Nafion 117 membrane below 0.8 V at 25 ° C (Figure 1a). There is also a performance gain over the cell with the Nafion 117 membrane when the0.8-mil-thick Nafion HP is used, suggesting that the standard cells are highly limited by the resistance of the membranes. The trend changes at the more relevant operation condition of 60 ° C (Figure 1b). The H2O2-DBFCs with the Nafion HP membrane are the best performers with a maximum power density of ~600 mW cm-2, followed by the cells with the AEM (~500 mW cm-2), and then the Nafion 117 (~360 mW cm-2).

The presentation will discuss these results, in combination with electrochemical impedance spectroscopy results, to reconcile how the thinner membranes improve cell performance and also affect the charge-transfer reactions at the electrodes.

References:

M. E. Hjelm, Y. Garsany, R. W. Atkinson III, R. O. Stroman, K. E. Swider-Lyons, C. Lafforgue and M. Chatenet, ECS Trans, 80, 1033 (2017).

Figure 1
(Invited) Large Scale PEM Electrolysis for Industrial Applications
Authors: Lettenmeier Philipp
Published: February 2020

Polymer electrolyte membrane (PEM) based water electrolysis for hydrogen production is widely considered as a key technology to decarbonize our fossil-based energy system. Due to its highly dynamic behavior PEM electrolyzer systems accomplish the requirements to be operated with renewable energy-based electricity such as wind or PV power. The production of chemical energy carrier such as hydrogen enables the integration of renewable energy into industrial processes and mobility and therefore sector coupling.

Changes need to be made in energy production to achieve the long-term goal of the Paris agreement, to keep global warming below 2°C [1], and to reach the CO2 target by 2050 whereas hydrogen could make up to 20% of the abatement [2]. Reaching this target, a transition of the fossil-based hydrogen production towards green hydrogen produced by electrolysis is an essential factor. Therefore, PEM electrolyzer systems have to reach industrial relevant sizes and significant cost reduction.

Siemens Hydrogen Solution has released its next generation of PEM electrolyzer system Silyzer 300 in 2018. By choosing a highly modular concept, Siemens AG is offering hydrogen generation plants from 10 to 100 MW based on PEM technology. It allows the full utilization of economy of scale effects also for customized solutions. However, in order to achieve the expansion targets that are published in various studies of several hundreds of Megawatts per year, it is essential to achieve further progress in regards to cost reduction, efficiency increase and overall hydrogen production plant optimization.

Together with our partners in H2Future, an FCH JU funded project, a demonstration plant is currently being built and will be operated at the largest steel production site of voestalpine Group in Linz, Austria. In a nutshell, the fundamental goal of H2Future is to demonstrate that an industrially integrated PEM electrolyzer system is able to produce green hydrogen and provides grid services at the same time.

[1] https://ec.europa.eu/clima/policies/international/negotiations/paris_de

[2] Hydrogen Council, Hydrogen Scaling up: A sustainable pathway for the global energy transmission, Nov. 2017

Figure 1
(Amazon Catalyst at ECS Grant Winner)
Carbon Catalysts for Cost-Efficient Hydrogen Production in PEM Electrolyzers
Authors: Das Rajib Kumar , Vasilyeva Svetlana V , Zhao Chong , Rinzler Andrew G.
Published: February 2020

Exposure of single-walled carbon nanotubes (CNTs), as well as other lower cost layered graphitic carbons (LGCs), to acidic intercalants, in combination with low voltage electrochemical cycling, induces in these materials hydrogen evolution activity that initiates at near zero overpotential and is on par with that of platinum catalysts.1 These results encouraged the further development and testing of the CNT catalyst in a PEM water splitting electrolyzer prototype. Once activated, the CNT cathode demonstrated 1 A/cm2 of HER current at 1.64 V, comparable to a similarly tested commercial Pt-loaded cathode. While carbon nanotubes are not intrinsically scarce, the single wall nanotubes used in these electrode tests remain relatively expensive. Commercial significance would benefit from a demonstration of comparable performance from activated lower cost layered graphitic carbons in a PEM electrolyzer prototype.

The following LGC materials, having a combination of high electrical conductivity, large pore volumes, and high specific surface areas, were tested in terms of their ability to achieve low HER overpotential during the activation process: microcrystalline graphitic particles, Vulcan XC-72 carbon, highly graphitized stacked-cup tubular carbon nanofibers (CNFs), and carbon needle felt. CNF electrodes demonstrated slightly higher mass basis activity than that of the other tested LGCs in acid electrolyte in a standard three-terminal electrochemical cell.

Here we report excellent performance from activated CNF cathodes, prepared by a scalable spray-coating method, in our PEM electrolyzer prototype (IrRuOx as anode catalyst). As anticipated, a control MEA, based on the non-activated CNF cathode and tested in PEM electrolyzer under identical conditions, showed poor performance, indicating a low electrocatalytic HER activity of the electrode.

The activated CNF cathode-based PEM electrolyzer achieved 1 A/cm2 at 1.78 V, while a control commercial MEA with Pt-loaded cathode/IrRuOx anode (a high Pt catalyst loading of 3 mg/cm2 cathode, Fuel Cells Etc) tested in the same PEM electrolyzer cell demonstrated 1 A/cm2 at 1.7 V.

Acknowledgements.

This work is supported by Amazon through ECS Amazon Catalyst Program.

References:

R. K. Das, Y. Wang, S. V. Vasilyeva, E. Donoghue, I. Pucher, G. Kamenov, H.-P. Cheng, A. G. Rinzler, ACS Nano, 2014, 8 (8), 8447–8456.
Polymer Hydroxide Exchange Membrane Electrolyzers with Pure Water Feed
Authors: Yan Yushan
Published: February 2020

I will provide an overview of the current status and the challenges of water electrolysis using polymer hydroxide exchange membranes without the use of any salt or base. An technoeconomic analysis will also be presented.