bluuebunny/crossref_metadata_2025 huggingface dataset:
Composition Controllable Synthesis of Highly Opened PtCu Nanodendrites with Efficient Electrocatalytic Activity and Stability for Methanol Oxidation Induced By High-Index Surface and Electronic Interaction
Authors: Lu Linfang
Published: February 2020

Metal nanodendritic structures have attracted a lot of attention because of their high activity toward catalytic reactions. Herein, we present a facile method for the one-pot synthesis of highly branched PtCu alloy nanodendrites. The composition of the PtCu nanodendrites can be easily tuned by changing the molar ratio of the precursors. The PtCu nanodendrites exhibit efficient catalytic activity toward the methanol oxidation reaction (MOR). Particularly, the Pt1Cu1 nanodendrites exert 4.6× increase in the specific activity and 3.8× increase in the mass activity compared to the commercial Pt/C catalyst. The mechanism of the enhancement was comprehensively studied. The enhanced catalytic activities can be ascribed to the high index surface of the branched structure and the electronic effect between the alloy metals. Specifically, the addition of Cu downshifts the binding energy of Pt, increasing the CO-tolerance ability of PtCu nanodendrites and, hence, improves their MOR activities. Moreover, the PtCu nanodendrites display better stability and durability for MOR compared to Pt/C. The approach can be adapted to synthesize desired Pt-based nanodendrites for various catalytic reactions.

Figure 1
Understanding the Role of the PdCu Nanoalloys for the Enhanced Hydrogen Oxidation Reaction
Authors: Xin Le , Qiu Yang , Li Wenzhen , Li Yawei , Janik Michael J. , Guo Fangmin , Liu Qi , Ren Yang
Published: February 2020

Hydroxide membrane fuel cells (HEMFCs) operated in alkaline media enables the use of the non-noble catalyst for oxygen reduction reaction (ORR). Therefore, it seems promising that HEM technology can replace the Pt-metal dependent proton exchange membrane (PEM) technology. However, the sluggish hydrogen oxidation reactions (HORs) on Pt-metal catalysts in the alkaline electrolyte, which are up to two orders of magnitude slower than in the acid electrolyte, requires a higher loading of precious metals on the anode of HEMFCs. This, to a larger extent, offsets the cost gains from employing non-precious metal on the cathode of HEMFCs. In order to tackle this challenge, we prepared Pd50Cu50 alloy nanoparticles (NPs) and characterized them for HOR in 0.1 M potassium hydroxide. The HOR activity exhibited a strong dependence on the annealing temperature. In particular, Pd50Cu50 alloy NPs annealed at intermediate temperature outperforms Pt and Pd. The conventional lab-based XRD shows the annealed Pd50Cu50 alloy features a special crystalline phase. And the synchrotron sources based x-ray further revealed the time-resolved phase change of Pd50Cu50 alloy as the temperature was ramped from 30°C to 950°C. Analysis of STEM and XPS, along with the theoretical modeling based on density functional theory (DFT), provides a new insight into the correlation between the crystalline structure of Pd50Cu50 alloy with HOR activity in alkaline media.
High Performance Anion-Exchange Membranes and Ionomers for Use in Alkaline Membrane Fuel Cells
Authors: Wang Lianqin , Ponce Gonzalez Julia , Bance-Soualhi Rachida , Whelligan Daniel , Varcoe John
Published: February 2020

This presentation will describe the latest research at the University of Surrey on the development of high-performance anion-exchange membranes (AEM) and ionomers (AEI) for use in alkaline membrane fuel cells (AEMFC). These anion-exchange polymer electrolyte matreials are produced using the peroxidation pre-irradiation grafting method (RG).

Recent achievements that will be discussed in this presentation include:

Synthesis of RG-AEMs with new chemistries that are more stable to alkali than those containing the benzyltrimethylammonium benchmark;

The ability to produce RG-AEMs based on low density polyethylene (LDPE) as well as poly(ethylene-co-tetrafluoroethylene) (ETFE);

Synthesis of thinner AEMs (< 30 μm thickness);

Synthesis of an interesting class of RG-based solid-state AEI powders;

AEMs with high hydroxide conductivities and high performances in hydrogen-fuelled AEMFC;

Advanced use of Raman micro-spectroscopy for studying radiation-grafted anion-exchange polymer electrolytes.

We will demonstrate that changes in head-group chemistry can switch off several alkali degradation mechanisms for RG-AEMs. We will also show that 2 W cm-2 peak power densities can be achieved in H2/O2 AEMFCs containing Pt cathodes and > 1 W cm-2 can be achieved with non-platinum-group-metal cathodes. The figure below shows the performance of a thin ETFE-based RG-AEM in H2/O2 and H2/air(CO2-free) AEMFCs when Ag/C cathode is used as a cathode electrocatalyst.

Figure 1
The Impact of Subsurface and Thin Pt Layer in Nafion Membrane on H2/O2 PEM Fuel Cell Performance
Authors: Daniel Lius , Bonakdarpour Arman , Wilkinson David P.
Published: February 2020

Electroless deposition is a simple and scalable method to deposit a thin layer of Pt in the membrane that has been demonstrated in a number of studies [1]–[6]. Recent advancements in the deposition method has enabled deposition of an ultra-thin Pt layer in Nafion (< 200 nm) [5], but no thorough study with respect to the impact of deposition parameters on the physical structures and fuel cell performance has been reported in the literature. For fuel cell applications, it is essential to design an optimum platinized membrane structure which maximizes Pt utilization while minimizing the Pt loading. In this study, the ultra-thin electroless deposited layers with various loadings were studied and characterized physically and electrochemically. Grain size and ECSA characterization from XRD and CV analysis indicate that inter-particle electrical connectivity was improved as the Pt loading increased, until the loading reached a value of about 52 μgPt/cm2 (Figure 1). Fuel cell polarizations and constant current operation under different humidity levels were examined with the additional electroless deposited Pt layers at loadings below 45 μgPt/cm2 than for the standard MEAs. The kinetic performance of the electroless deposited Pt layers in the membrane was also examined and will be presented at the meeting.

Figure 1
(Invited) In Situ Measurement of Mechanical Properties of Solid Electrolyte Interphase (SEI) Layers
Authors: Yoon Insun , Jurng Sunhyung , Abraham Daniel P , Lucht Brett , Guduru Pradeep R.
Published: February 2020

With increasing demand for light-weight, high energy density energy storage, lithium metal electrodes are being actively revisited decades after its abandonment in the 1970s. Metallic lithium can play the role of host-free electrode, and thus has much higher charge capacity compared to traditional graphite-based electrodes. The major challenge with the lithium electrode is the generation of dendrites, resulting in internal short-circuits and poor cell cyclability. Several approaches, including electrolyte engineering and artificial solid electrolyte interphase (SEI) formation, are being pursued to resolve lithium dendrite formation. Recent theoretical studies of lithium metal electrodes suggest that surface films with high elastic modulus suppress dendrite growth. Inhibition of lithium dendrite with ionic liquid electrolytes, which are known to form inorganic SEI, support this theoretical suggestion. This background provides the motivation to develop an experimental method to measure elastic moduli, stress-strain curve and fracture toughness of SEI formed with various electrolytes. In this work, we report results of two experimental methods to measure mechanical properties of SEI: (i) micro-scale membrane bulge tests and (ii) strain induced elastic buckling instability (SIEBI). Lithium thin film electrodes (~50 nm) were prepared on a polydimethylsiloxane (PDMS) substrate by thermal evaporation and converted to SEI through chemical and electrochemical reactions. Various organic and ionic liquid electrolytes were used to understand compositional influence on the mechanical properties of SEI. SEI layers either remain flat or buckle depending on the elastic modulus and the residual stress state, which are governed by the electrolyte composition. For the flat SEI layer case, rectangular free-standing PDMS/SEI membrane were fabricated and subjected to bulge testing in inert atmosphere. The maximum deflection at each pressure was measured by an atomic force microscope (AFM) to get the pressure-deflection curve, which was analyzed to obtain the elastic modulus and stress-strain curve of the SEI layers. For the buckled SEI layer case, the elastic modulus of SEI layer was calculated from the wavelength of the buckling pattern. These two approaches allow us to study the role of electrolyte composition on the mechanical properties of SEI layers. It is be possible to extend these methods to study the inelastic behavior and fracture properties of SEI as well.
Aramid Nanofiber/Graphene/Carbon Nanotube Composite Electrodes for Structural Energy and Power
Authors: Patel Anish , Harris John , Lutkenhaus Jodie
Published: February 2020

Multifunctional energy storage devices could prevent catastrophic failure in batteries or act as structural elements in vehicles, such electric cars and unmanned aerial vehicles, by simultaneously dissipating energy and bearing a load. Graphene is particularly interesting for multifunctional energy storage devices. Graphene paper has exhibited high stiffness (41.8 GPa) and graphene based supercapacitors have shown high capacity (205 F/g). However, mechano-electro-chemical coupling in multifunctional materials is largely unexplored. Herein we report on multifunctional composite electrodes consisting of graphene, aramid nanofibers (ANFs), and carbon nanotubes (CNTs) using vacuum-assisted self-assembly. CNTs were used to prevent graphene agglomeration and improve through plane conductivity. ANFs are nanoscale building blocks created from Kevlar thread, which is well known for its extremely high stiffness and strength. We hypothesize that the ANFs reinforce the composite and improve mechanical properties. The effects of CNTs and ANFs are explored by varying the amount of each component present in the composite. Electrochemical performance is evaluated using cyclic voltammetry and galvanostatic charge/discharge while mechanical performance is evaluated using tensile testing. Finally, plans for testing mechano-electro-chemical coupling are discussed.
(Organic and Biological Electrochemistry Division Manuel M. Baizer Award Address) Molecular Electrochemistry of Fragile and Soft Molecular Systems
Authors: Maran Flavio
Published: February 2020

I am deeply honored of being the 2018 winner of the Manuel M. Baizer Award, which celebrates achievements in electroorganic chemistry in a broad sense. Personally, I have always been fascinated by the challenges associated with the understanding of mechanisms and properties of molecular systems, especially organic molecules. In this context, I followed the steps of my mentor, the late Professor Elio Vianello, as well as those of others I had the privilege to work or discuss with. In other words, I have always been an advocate of the molecular approach to address scientific problems and thus of the importance of explaining the fine details of electrochemical reactions on a true molecular basis. Molecular electrochemistry is known to embrace a number of topics, such as electron-transfer (ET) induced transformation of molecules, associated chemical reactions, control of long-range and mediated ET reactions, and electrochemistry on electrodes and modified electrodes. Molecules can be seen in different ways. Generally, molecules are hard objects, characterized by well-defined shapes and minor structural variations upon ET. Sometimes, however, they are fragile in the sense that ET causes cleavage of a σ-bond, resulting in the formation of two molecular fragments. More complex molecular systems, on the other hand, can be seen as soft or hard-soft. This is especially true in ligand-protected gold nanoclusters, i.e., molecules in which a hard gold core is protected by a soft interface of flexible ligands that form a nanoenvironment through which the core interacts with the outside medium and thus, ultimately, redox partners. In this presentation, I will describe how molecular electrochemistry concepts can be applied to understand the ET behavior and properties of both fragile and soft molecular systems. Examples of how electrochemical results can be nicely integrated with data from other techniques or methods will also be described.
The Micro-Optical Ring Electrode: A Sensor for Multiple Actinide Ions Monitoring
Authors: Linnett Gary
Published: February 2020

We present on the development of the Micro-Optical Ring Electrode (MORE) for the analysis of trans-uranium elements in aqueous mixtures. The MORE is a photo-electrochemical device based on a ring microelectrode that uses the insulator interior to the ring as a light guide. This single device exploits the unique photophysical and electrochemical properties of multiple analytes present in mixtures to quantify them. Our study aims to develop a protocol for the analysis of ions of uranium, neptunium and plutonium, which are most relevant to the nuclear industry, especially in the areas of decommissioning and fuel reprocessing, where speedy and safe identification of radioactive contaminants is essential.

The technique offers a number of advantages over traditional methods in the area of radiochemical analysis such as real time monitoring in-situ, reduced radiation dose impact to the analyst as a result of greatly reduced sample handling and preparation, improved analysis times allowing quick decision making, at a much reduced cost (e.g. compared to ICP-MS and Scintillation counting).
Luminescence Studies of Single Molecule Electron Transfer Events
Authors: Han Donghoon , Fu Kaiyu , Crouch Garrison , Kwon Seung-Ryong , Bohn Paul W.
Published: February 2020

Single electron transfer events in both immobilized and freely diffusing redox-active molecules can now be studied with some facility using a special kind of bimodal nanoelectrochemical-nanophotonic architecture – the electrochemical zero-mode waveguide (E-ZMW). The E-ZMW consists of a high density array of recessed dual-ring electrode nanopores that can moderate the interaction between single electron-transfer events and fluorescence emission, in the zeptoliter optical confinement volume of a zero-mode waveguide. The dual optical-electrochemical functionality makes it possible to perform single molecule spectroelectrochemical measurements under redox cycling conditions – both when the upper electrode is potential-controlled and using self-induced redox cycling. These have been performed with flavin mononucleotide, FMN, whose isoalloxazine chromophore is fluorescent in the oxidized state and dark in the reduced state, FMNH2. This property permits the redox state of single FMN molecules to be followed by fluorescence, with each high/low luminescence transition signaling single molecule cycling. Capture efficiencies are characterized as a function of the potential applied to the upper ring electrode, and single molecule electrochemical-spectroscopic cross-correlation measurements are performed as a function of nanopore occupancy down to  ~0.001.
Optimizing Surface Modifications for Quantum Dot Labelled DNA SAMs Using Electrochemistry Coupled Fluorescence Imaging
Authors: Sundar Rochita , Bizzotto Dan
Published: February 2020

Electrochemical biosensors are being developed for detecting specific sequences of nucleic acids using DNA modified gold surfaces[1]. A single crystal gold bead electrode was used to study the arrangement on DNA on different gold surfaces[2]. The gold surface was prepared with a mercaptoundecanol (MUDOL) self-assembled monolayer (SAM). Using a specific desorption potential of -0.850 V/SCE, the MUDOL was reductively desorbed from the Au(111) facet. The defects in the SAM were passivated with a shorter alkylthiol, mercaptohexanol. Thiol modified DNA which is also labeled with a fluorophore was allowed to populate the 111 facet specifically. This was studied using fluorescence microscopy coupled with electrochemical control. A fluorescence image of the gold bead (Figure a) showed that only the 111 facets were modified. The density of the DNA modification was also evaluated using the reorientation of DNA based on the electrode charge density. At positive potentials the DNA was positioned close to the electrode and the fluorescence was quenched. At negative potentials the DNA was repelled and the fluorescence increased. This change in fluorescence is indicative of the density of DNA on the surface. The same approach will be used to assemble DNA modified Quantum Dots (QDs) onto the Au(111) facets. A complementary ssDNA was attached to a glutathione capped quantum dot vis a his-tag peptide. The QD labelled ssDNA was allowed to hybridize with the ssDNA on the gold electrode. Figure (b) is the cartoon depiction of such a layer. Recent research results will be described on the characterization of QD labelled DNA SAMs. The QDs due to their broad absorption and narrow emission spectrum also offer the advantage of building more complicated multiplexed systems in future.

(1) Hsieh, K.; Ferguson, B. S.; Eisenstein, M.; Plaxco, K. W.; Soh, H. T. Integrated Electrochemical Microsystems for Genetic Detection of Pathogens at the Point of Care. Acc. Chem. Res.
2015, 48, 911–920.

(2) Yu, Z. L.; Casanova-Moreno, J.; Guryanov, I.; Maran, F.; Bizzotto, D. Influence of Surface Structure on Single or Mixed Component Self-Assembled Monolayers via in Situ Spectroelectrochemical Fluorescence Imaging of the Complete Stereographic Triangle on a Single Crystal Au Bead Electrode. J. Am. Chem. Soc
2015, 137, 276–288.

Figure 1
Electrowetting of Liquid Drops Revisited By XPS
Authors: Aydogan-Gokturk Pinar , Ulgut Burak , Suzer Sefik
Published: February 2020

Electrowetting behavior of liquid drops has been followed in-situ and in-vacuum using XPS in a chemically resolved fashion, under both D.C. and A.C. excitations. Various liquid drops, compatible with the UHV conditions, consisting of an Ionic Liquid, DEME-TFSI, [N,N-Diethyl-N-methyl-N-(2-methoxyethyl) ammonium bis (trifluoromethanesulfonyl) imide]), or Poly-Ethylene-Glycol (PEG, M.W. ~600 amu) and their mixtures. For the dielectric substrate, a ~300 nm thick silicon oxide (SiO2/Si) without and with a thin (~20 nm) hydrophobic amorphous fluoropolymer coating, CYTOP (Bellex International Co.), has been employed. XPS data have been recorded both in the conventional scan and also in the fast (<1s) snap-shot modes. Intensity and position of the peaks, representing the liquid drops (F1s in the case of the IL, or C1s/O1s of the PEG) as well as those of the substrates (Si2p for the oxide only and F1s for the hydrophobic coated one) have been recorded under various electrical excitations. Under AC excitation at a fixed frequency, intensity modulations in the XPS peaks reveal geometrical changes of the drops, while the peak position modulations reveal electrical potentials developed. Monitoring binding energy modulations as a function of the changes in the AC frequency (10-2 – 104 Hz) allows us tap into ionic, dipolar and electronic contributions of the dielectric susceptibility of both the liquid drops and the substrates. Experimental details and various applications will be presented and discussed.

This work is partially supported by TUBITAK through Grant No. 215Z534
(Invited) Controlling the ORR with Proton Kinetics and Non-Precious Metal Catalysts
Authors: Gewirth Andrew A
Published: February 2020

This talk addresses the Oxygen Reduction Reaction (ORR) a reaction important in fuel cells. We use a kinetic isotope effect analysis to more fully elucidate both the ORR and OER mechanisms for both precious metal and non-precious metal systems. We develop a new platform based on a hybrid bilayer membrane (HBM) to more generally address proton-coupled electron transfer (PCET) reactions, of which the ORR is one, and show that ORR speciation can be controlled by tuning the kinetics of proton transfer. The HBM is shown to illuminate other electrochemical processes, such as anion transport, and quinone reduction speciation. We develop new non-precious metal catalysts for the ORR based on carbon encapsulated superparamagetic Fe nanoparticles. We use surface chemistry to develop new insight into the origin of activity on these constructs.
Transport & Charge Transfer Near Electrochemical Interfaces: A Quasi-Fermi Perspective
Authors: Grew Kyle N.
Published: February 2020

Theories describing the electrochemical double layer have long presented challenges to researchers, yet remain important understanding electrochemical processes. Many of these challenges stem from the multiscale nature of electrochemical interfaces where excess carrier concentrations, whether ions in electrolytes or electrons/holes in semiconductors, can extend 10s of nanometers into the bulk. It is expensive and difficult to capture the full interface with atomistic methods whereas continuum-level mean field approaches often face issues with adequately capturing steric and other physiochemical aspects of the carriers. In both cases, there are issues with the definition of potentials which are experimentally relevant and self-consistent with the associated effects on the participating media [1].

Nevertheless, numerous physiochemical effects that include but are not limited to specific adsorption, dielectric decrement, specific adsorption, osmotic pressures, solvent mixing, and ionic correlations have been identified and described [1-3]. And corrections to mean field theories, such as through the perturbation for finite sized ions, have been put forth to improve predictability [4-6].

In this talk, a quasi-Fermi perspective on transport and space charge near interfaces will be presented. The approach put forward simplifies analysis for electrolytic solutions including for transport at dissimilar interfaces. A perspective on the potential scale and ties to absolute electrode potentials will be presented. The approach will be demonstrated with bipolar membrane electrolyte and photoelectrochemical conversion interfaces.

References

[1.] A. Baskin and D. Prendergast, Improving Continuum Models to Define Practical Limits for Molecular Models of Electrified Interfaces, J Electrochem Soc
164 (2017), E3438-E3447.

[2.] D. Ben-Yaakov, D. Andelman, D. Harries and R. Podgornik, Beyond standard Poisson-Boltzmann theory: ion-specific interactions in aqueous solutions, J Phys-Condens Mat
21 (2009).

[3.] D. Ben-Yaakov, D. Andelman and R. Podgornik, Dielectric decrement as a source of ion-specific effects, J Chem Phys
134 (2011).

[4.] M. S. Kilic, M. Z. Bazant and A. Ajdari, Steric effects in the dynamics of electrolytes at large applied voltages. II. Modified Poisson-Nernst-Planck equations, Phys Rev E
75 (2007).

[5.] M. S. Kilic, M. Z. Bazant and A. Ajdari, Steric effects in the dynamics of electrolytes at large applied voltages. I. Double-layer charging, Phys Rev E
75 (2007).

[6.] M. Z. Bazant, Theory of Chemical Kinetics and Charge Transfer based on Nonequilibrium Thermodynamics, Accounts Chem Res
46 (2013), 1144-1160.
(Invited) Recent Advances in Electrocatalysis of Oxygen Reduction Using Metallo-Corroles
Authors: Friedman Ariel , Levy Naomi , Elbaz Lior
Published: February 2020

In recent years we have been exploring a relatively new and exciting family of transition metal complexes as catalysts for oxygen reduction. We used advanced synthesis techniques in order to change the parameters that may influence their catalytic activity: the metal center, the substituents in their meso-position and the substituents in their beta-position, as well as the effect of their interaction with different carbonaceous supports. In this talk we will summarize this work and give a clear direction and insight into the design and utilization of this class of catalysts, and will show some of the best performing, non-pyrolyzed, molecular catalysts for oxygen reduction to-date. We will show that the metal center has great affect over the ORR electrocatlysis, and that it changes in the order of Co > Fe > Ni > Mn > Cu, this effect will be rationalized using molecular modeling performed by us. In addition, we studied the effect of electron-withdrawing substituents on different position and we will show that although there is some effect on glassy carbon electrodes, once the corroles are incorporated in high surface area carbon (BP2000), this effect vanishes. We will also share some of our latest results on 3D structures of these molecular complexes and the cooperative effect, which raises their electrocatalytic performance when compared to a single molecule.
Reduced-Graphene-Oxide-Based Hybrid Supports for Platinum Catalysts Active at Low Loadings during Oxygen Reduction
Authors: Kulesza Pawel J , Dembinska Beata , Zoladek Sylwia , Rutkowska Iwona Agnieszka , Miecznikowski Krzysztof , Jablonska Anna , Stobinski Leszek , Zak Jerzy , Negro Enrico , Di Noto Vito
Published: February 2020

Hybrid systems composed of the reduced-graphene-oxide supported gold, iridium or bimetallic (AuIr) nanoparticles (at loadings typically below 5 µg cm-2) have been considered as active matrices for platinum catalysts utilized at low loadings (<20 µg cm-2) during the reduction of oxygen in mostly acid but also alkaline media. Comparison is made to the analogous systems based on conventional Vulcan carbon carriers. Gold nanoparticles are prepared both by the electrochemical and chemical reductionapproaches in which the pre-reduced Keggin-type phosphomolybdate heteropolyblue species act as the reducing agent for the HAuCl4 precursor. Polyoxmetallate (PMo12O40
3-) adsorbates or “capping ligands” tend to stabilize gold (iridium or bimetallic) nanoparticle deposits, facilitate their dispersion and attachment to carbon supports. Indeed, it is apparent from the independent diagnostic voltammetric experiments (in 0.5 mol dm-3 H2SO4) that heteropolymolybdates form readily stable adsorbates on nanostructures of gold, irridium and carbon (reduced graphene oxide and Vulcan). It is reasonable to expect that the polyoxometallate-assisted nucleation of gold has occurred in the proximity of oxygenated defects existing on carbon substrates. Under conditions of the electrochemical experiments performed in 0.1 mol dm-3 KOH) the phosphomolybdate adsorbates are removed from the interface because they undergo dissolution and decomposition in alkaline medium. High electrocatalytic activity of the reduced-graphene oxide-supported catalytic systems toward the reduction of oxygen is demonstrated using chronoamperometry and gas-diffusion electrode, in addition to the conventional and rotating ring-disk electrode (RDE) voltammetry. Among important issues is the presence of structural defects existing on poorly organized graphitic structure of reduced graphene oxide (as evident from Raman spectroscopy). When using the reduced graphene oxide carriers for Au (Ir or AuIr) nanostructures together with Pt nanoparticles, the resulting catalytic systems have exhibited typically higher (certainly not lower) O2-reduction currents (relative to those recorded at conventional Vulcan-supported Pt at the same loading) in acid medium (0.5 M H2SO4). The RDE data are consistent with the lower formation of the hydrogen peroxide intermediate (<1% at potentials 0.6 V, or lower, vs RHE). Furthermore, the long-term durability of this family of catalysts should be appreciated.
(Invited) Structural and Mechanistic Basis for the Oxygen Reduction Activity of Pyrolyzed Fe-N-C Electrocatalysts
Authors: Mukerjee Sanjeev , Jia Qingying
Published: February 2020

Oxygen reduction reaction (ORR) constitutes a critical element in the commercialization of electrochemical energy conversion and storage devices. Consequently, the replacement of unsustainable noble metal catalysts with earth-abundant materials constitutes a vital technological strategy towards fixing the twin challenge of energy security and climate change. The success in this regard requires the development of scalable non-precious metal (non-PGM) catalysts with high performance in practical devices. The major bottleneck in developing Fe-N-C materials as the leading non-PGM catalysts lies in the poor understanding of the nature of active sites and reaction mechanisms. Herein, we systematically characterized a series of Fe-N-C catalysts under both ex situ and in situ conditions using combined microscopic and spectroscopic techniques. We show that the structures of active sites under ex situ and working conditions are drastically different. Resultantly, the active site structure proposed here, a non-planar ferrous Fe-N4 moiety embedded in distorted carbon matrix characterized by a high Fe2+/3+ redox potential, is in contrast with those proposed hitherto derived from ex situ characterizations. This site reversibly switches to an in-plane ferric Fe-N4 moiety poisoned by oxygen adsorbates during the redox transition, with the population of active sites controlled by the Fe2+/3+ redox potential. The high inherent activity of the active site is correlated to its near-optimal Fe2+/3+ redox potential, which essentially originates from its favorable biomimetic dynamic nature that balances the site-blocking effect and O2 dissociation. The porous and disordered carbon matrix of the catalyst plays pivotal roles for its measured high ORR activity by hosting high population of reactant-accessible active sites.

Acknowledgement:

The authors deeply appreciate financial assistance from the U.S. Department of Energy, EERE (DE-EE-0000459). Use of the National Synchrotron Light Source (beamline X3B), Brookhaven National Laboratory (BNL), was supported by the U.S. Department of Energy, Office of Basic Energy Sciences. This publication was made possible by the Center for Synchrotron Biosciences grant, P30-EB-009998, from the National Institute of Biomedical Imaging and Bioengineering (NBIB). Support from beamline personnel Dr. Erik Farquhar and Mark Chance (X3B) are gratefully acknowledged. MRCAT operations are supported by the Department of Energy and the MRCAT member institutions. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.
Long-Term Oxygen Reduction Reaction Activity of Surface Modified Cathode Materials for Solid Oxide Fuel Cells
Authors: Lin Ye , Lee Shiwoo , Abernathy Harry , Yang Tao , Hackett Gregory A
Published: February 2020

Oxygen chemical surface exchange coefficient (k) and bulk diffusion coefficient (D) obtained by electrical conductivity relaxation (ECR) are useful indices to characterize and compare oxygen reduction reaction (ORR) activity of solid oxide fuel cell (SOFC) cathodes. While ECR is an often-used method to characterize a new material’s performance, there has been limited reports on how k and D values change for extended period under fuel cell operating conditions. As performance degradation of the cathode is closely related with changes in surface activity and/or bulk diffusivity, long-term ECR tests and post-mortem microstructural analyses were performed on La-Sr-Co-Fe-O based cathodes to understand the degradation behavior at cathode. In this work, we chose La-Sr-Co-Fe-O based cathodes with different composition (stoichiometric La0.6Sr0.4Co0.2Fe0.8O3-δ
(LSCF) vs. A-site deficient (La0.6Sr0.4)0.95Co0.2Fe0.8O3-δ (LSCF-A)) and with different configurations (unmodified LSCF-A vs. LSCF-A surface modified with Pr0.6Sr0.4CoO3-δ (PSC-LSCF-A)), and monitored variations of k and D values up to 1000 hours. The initial apparent k values followed the trend as PSC-LSCF-A > LSCF-A > LSCF, indicating that A-site deficiency in LSCF improves surface activity. The k values decreased gradually for all the samples over ~1000 hour ECR tests, while the D values were more constant. Oxygen partial pressure dependency of k of the PSC-LSCF-A sample also changed after the long-term tests, indicating a change in oxygen reduction behavior. The samples’ surface chemistry and element ratios before and after the long-term tests showed evidence of Sr-segregation and Co-depletion compared with the original bulk materials. The degradation behavior of k is compared with the degradation behavior from symmetrical cell and single cell performance data. The results imply that controlled ECR measurements can be used to identify surface modification electrocatalysts that can improve surface exchange behavior and mitigate surface degradation.
(Invited) Magnetoelectrocatalysis of Oxygen Reduction Reaction (ORR) By Lanthanide Triflates in Acetonitrile
Authors: Knoche Krysti L. , Parr Daniel , Leddy Johna
Published: February 2020

Lanthanides have sufficiently similar chemical and physical properties that lanthanides are difficult to separate. Among the common properties are standard potentials that fall within 100 mV for Ln3|0. The standard potentials are sufficiently extreme that lanthanide electrochemistry is commonly undertaken in ionic liquids and molten salts. Recently, it was demonstrated that cyclic voltammetry of lanthanide triflates is accessible in acetonitrile at Nafion modified electrodes. Because at least four different oxidation states of the lanthanides are accessible, the voltammetric response is complex, as demonstrated by fitting the mechanism.

Interest in benchtop electrochemistry of lanthanides arose from investigations of magnetoelectrocatalysis, where magnetic properties and spin impact rates of electron transfer at electrodes and electrocatalysts. Despite largely similar properties, lanthanide magnetic properties are diverse because the number of unpaired electrons in the d orbitals ranges from 0 to 7. The presence of lanthanides at the electrode surface mediates rates of important reactions that include the oxygen reduction reaction (ORR).

Ytterbium triflate extracted into Nafion on electrode in acetonitrile increase oxygen reduction currents by 15%. On introduction of electrochemically inert hematite microparticles into Nafion, oxygen reduction currents are enhanced 35%. Other measures of catalysis that include decreased overpotential are also observed.

Reference

Johna Leddy and Krysti L. Knoche, Lanthanide Electrochemistry, published 12 November 2015 as US Patent Application, 20150322581-A1
Reduced-Graphene-Oxide with Transition Metal Hexacyanometallates As Active Support for Traces of Platinum Catalyst at Low Loading during Oxygen Electroreduction
Authors: Zakrzewska Barbara , Miecznikowski Krzysztof , Dembinska Beata , Stobinski Leszek , Zoladek Sylwia , Rutkowska Iwona Agnieszka , Zlotorowicz Agnieszka , Zak Jerzy , Negro Enrico , Kulesza Pawel J , Di Noto Vito
Published: February 2020

Reduced graphene-oxide-supported the various metals analogue of polynuclear Prussian Blue are considered here together with traces of platinum as well as low loadings of platinum (10-15 mg cm-2) as catalytic materials for reduction of oxygen in acid media. Comparison is made to the analogous systems based on conventional Vulcan carbon carriers. Electrocatalysts based on graphene and graphene-oxide (GO) are more homogeneous and possess properties such as excellent conductivity, good chemical stability and can be functionalized in a controlled manner. Following the heat-treatment step at higher temperatures, some thermal decomposition of the cyanometallate network occurs and, consequently, metallic sites are generated. The resulting material has occurred to show highly potent electrocatalytic properties toward electroreductions of oxygen in acid solution (the highest currents and the most positive electroreduction potentials) using cyclic and rotating ring-disk electrode (RDE) voltammetric experiments. Among important issues are possible activating interactions between analogue of Prussian Blue, platinum nanoparticles and the support, as well as presence of structural defects existing on poorly organized graphitic structure of reduced graphene oxide (as evident from Raman spectroscopy). An electrocatalytic system, that utilizes metal hexacyanometallates nanoparticles with trace amount of Pt modified reduced graphene-oxide-supported is also characterized here by additional diagnostic experiments, namely galvanodynamic measurements with use of so called gas diffusion electrode (GDE) operating under conditions resembling those characteristic of the cathode in a real fuel cell.
Active Non-Precious Metal Based Nitride Catalysts for the Oxygen Reduction Reaction
Authors: King Laurie Ann , Kreider Melissa , Siahrostami Samira , Back Seoin , Jaramillo Thomas F
Published: February 2020

Proton-exchange membrane fuel cells (PEMFC) that convert chemical energy from a fuel into electricity offer a promising route for decarbonisation of both the electricity and transportation sector. Today, platinum-based catalysts are the most active and widely implemented catalyst for both the oxidation and reduction reactions in a PEMFC. However, concerns regarding the scarcity and high costs associated with platinum motivate the search for alternative active and stable catalysts.1 In particular at the cathode, the sluggish oxygen reduction reaction (ORR) kinetics requires a high loading of platinum. Thus, new non-platinum group metal based catalysts are necessary to reduce the cost of PEMFC technologies.

One class of materials that has attracted recent attention for ORR in acidic media are the nitrides. In particular, hexagonal boron nitride (h-BN),2 and transition metal nitrides have shown excellent activity and promising stability ORR catalysts.3 In this work we investigate the ORR activity and stability of non-precious metal nitride catalysts as a function of synthesis technique, morphology and chemical composition. Alloying and doping the nitride catalysts, as well as probing the role of substrate identity are investigated. We compare our electrochemical data with computationally investigated ORR activity using density functional theory (DFT) calculations.

References

(1) Seh, Z. W.; Kibsgaard, J.; Dickens, C. F.; Chorkendorff, I.; Nørskov, J. K.; Jaramillo, T. F. Science (80-. ).
2017, 355 (6321), eaad4998.

(2) Uosaki, K.; Elumalai, G.; Noguchi, H.; Masuda, T.; Lyalin, A.; Nakayama, A.; Taketsugu, T. 2014, 136 (111), 6542.

(3) Cao, B.; Neuefeind, J. C.; Adzic, R. R.; Khalifah, P. G. Inorg. Chem.
2015, 54 (5), 2128.
Melamine-Sponge-Derived Fe-N/C Electrocatalyst with Tunable Pore Structure and Nitrogen Chemical State for Exceptional Oxygen Reduction Reaction
Authors: Xia Dongsheng , Gan Lin
Published: February 2020

Developing economic and highly active non-precious metal electrocatalysts for oxygen reduction reaction (ORR) is critical for the development of hydrogen fuel cells. While several nitrogen-carbon precursors have been explored, only limited systems such as phenanthroline-based catalyst after pyrolysis in NH3, polyaniline- and/or cyanimide-derived catalysts, Zn-based metal-organic frameworks (MOF), or a combination of the above precursors were reported to derive highly active Fe-N/C catalysts. It is still challenging to concurrently achieve high density Fe-N4 active sites with optimized local Fe-N/C environment, high microporous surface area, and rational macro-/meso-pore structures at an economic cost. For instance, although MOF-derived Fe-N/C catalysts have shown exclusive high density single Fe atoms confined in the N-doped microporous carbon, the lack of mesopores may limit their ORR performance. In addition, MOF-derived catalysts also suffered from its relatively high cost, hindering their large-scale applications.

We report here a novel melamine-sponge-derived Fe-N/C catalyst with exceptional ORR electrocatalysis by virtue of their simultaneously tunable hierarchical micro-/meso-/macro-porous structure and nitrogen chemical state. The melamine sponge serves as a promising and low cost carbon precursor for hosting Fe-N active sites upon NH3 pyrolysis, showing (i) increasing mesopores for favorable mass transport while keeping a high microporous surface area and (ii) increasing pyridinic nitrogen surrounding the Fe center with increasing pyrolysis time. The optimum Fe-N/C catalyst shows high ORR activity particularly in alkaline media with a half-wave potential of 0.902 V/RHE and mass activity of 15.0 A/g at 0.9 V/RHE, markedly outperforming commercial Pt/C and most non-precious metal catalysts to date. Considering the low cost and industrial scalability of the MS precurosr, the MS-derived Fe-N/C catalysts are expected to be a promising candidate as non-precious fuel cell electrocatalyts.
Durability of Pt/C with Different Nitrogen for Contents for Oxygen Reduction Reaction in PEMFC
Authors: Ham Kahyun , Lee Jae Kwang , Lee Jaeyoung
Published: February 2020

To meet a worldwide demand about the supply of sustainable energy and solve the environmental problems, Polymer electrolyte membrane fuel cell (PEMFC) is one of the promising energy conversion technologies which can be utilized in various industrial fields. Among the components of PEMFC, Pt nanoparticle on carbon (Pt/C) have been intensively studied as a catalyst for oxygen reduction reaction. However, the state-of-art Pt/C cannot meet the requirement for the long-term operation in PEMFC system owing to both Pt dissolution and sintering/particle growth on carbon support. In a view of strengthening interaction between Pt and catalyst support, the use of highly graphitic carbon and S, N-doped carbon could be reasonable approach.

In this study, we investigate the effect of nitrogen contents of carbon support for Pt catalyst in terms of MEA durability. N-doped carbon is provided by ball-milling with pristine carbon and melamine. To designate N contents and investigate surface structure, transmission electron microscopy, X-ray diffraction and Raman spectroscopy are carried out. To understand electron transfer between Pt and N, we conduct X-ray absorption fine spectroscopy and X-ray photoelectron spectroscopy. The synthesized Pt/N-C via polyol process shows improved performance toward oxygen reduction reaction in acidic media than commercial Pt/C.
Introducing a New Functionality on Pt Alloy Nanocrystals for Boosted Electrochemical Activities in Oxygen Reduction Reaction
Authors: Yoo Ji Mun , Chung Dong Young , Ahn Chi-Yeong , Sung Yung-Eun
Published: February 2020

Securing high electrochemical activity of nanomaterials is one of the most challenging issues in fuel cell electrocatalysts. Especially, in oxygen reduction reaction (ORR), inspiring breakthroughs have been made in activity enhancement based on fundamental knowledge about functional link between material structure and activity; for instance, Pt-M (transition metal) alloy electrocatalysts have surpassed commercial Pt/C by more than 30 times in mass activity. However, for more advanced electrocatalyst, a new functionality should be introduced on surface of nanomaterials which can open a new possibility of boosting electrochemical performance. Considering urgency for highly active and stable electrocatalyst, it is necessary to develop a new strategy to adopt various functionalities onto nanocrystals by post-treatment, and verify the origin of the boosted electrochemical properties. Here, we report introducing a new functionality on surface of Pt alloy nanocrystals with nitrogen dopants and their highly improved electrochemical activity as ORR electrocatalysts. Rational correlation between modified surface structure and electrochemical properties are discussed with various physicochemical and electrochemical analyses.
Electrochemical Deoxygenation of Aqueous Solutions Using Symmetric Activated Carbon Electrodes in Flow-through Cells
Authors: Holubowitch Nicolas , Landon James , Gao X. , Liu K. , Omosebi A.
Published: February 2020

We present a simple electrochemical flow cell using symmetric, unmodified commercially available carbon cloth electrodes that removes 97+% of incoming aqueous dissolved oxygen (DO). The electro-deoxygenation (EDO) cell achieves net O2 removal by leveraging the high overpotential of the oxygen evolution reaction on activated carbon and its propensity to oxidize under anodic polarization in aqueous solution: oxygen is reduced at the cathode via the oxygen reduction reaction (ORR) while water is oxidized and incorporated into surface oxide functional groups at the anode, effectively sequestering dissolved oxygen. The polarized electrodes promote the two-step reduction of DO resulting in some residual hydrogen peroxide in the effluent, which may be beneficial for certain water treatment applications. We modified a cell with Ni cathodes downstream to reduce all H2O2 to water for particularly sensitive applications; in this cell >99% of incoming DO could be removed to sub-10 ppb levels. EDO cells, which currently employ sacrificial anodes, can deaerate 30 L g-1
anode of water at an energy cost of 1 kWh (~$0.10) per 104 L. The technique is versatile, successfully deoxygenating solutions from dilute to seawater concentrations and at flow rates beyond 50 ml min-1 (O2 flux = 10-4 mol s-1 m-2), more than 50x higher throughput DO removal than similar technologies. We demonstrate the utility of an EDO cell as a component in an electrochemical water desalination process; dissolved oxygen removed upstream of a capacitive deionization cell enhances salt adsorption capacity and cell lifetime.

Figure 1. (a) Dissolved oxygen removal by an electro-deoxygenation cell stack with six pairs of electrodes (up to t = 1.1 h) and subsequently with an additional H2O2 removal stack (six Ni cathodes and two additional anodes electrically connected in parallel downstream, t > 1.1 h). The device is operated by holding the cathodes, connected in parallel, at an oxygen-reducing potential versus an in situ reference electrode to achieve E
c = -0.2 V vs. SHE. The electrolyte is 0.1 M NaCl with an initial flow rate of 50 ml min-1, and the effect of increasing flow to 75 and 100 ml min-1 is shown at t > 4.2 h. (b) Salt removal performance of a capacitive deionization (CDI) cell downstream of our EDO cell; the electrolyte is 10 mM NaCl flowing at 20 ml min-1 and the CDI cell consists of four pairs of carbon cloth electrodes totaling 3.2 g with charging/discharging at V
cell = 1.2/0.0 V in a single-pass mode. At t = 24 h, the EDO cell is turned off to highlight its effect on deionization performance.

Figure 1
Improved Long Term Performance Stability of Sr-Fe-O Infiltrated LSM/YSZ Solid Oxide Fuel Cells Under High Steam and High Temperature
Authors: Fan Yueying , Chen Yun , Abernathy Harry , Pineault Richard , Song Xueyan , Liu Jian , Gerdes Kirk , Lee Shiwoo , Kalapos Thomas , Yang Tao , Hackett Gregory A
Published: February 2020

Commercial LSM/YSZ cells infiltrated with a solution containing salts with strontium and iron cations in a 1:2 ratio were evaluated for their performance and long term stability under high steam, high current and high temperature. Sr-Fe-O-infiltrated cells showed higher performance and lower degradation than the uninfiltrated LSM/YSZ baseline cell, which demonstrates that appropriate nanomaterial infiltration could improve the performance and mitigate the degradation of solid oxide fuel cells under high steam. The degradation rate of an uninfiltrated LSM/YSZ cell was about 5.98% per 1000h including initial voltage drop after 10% steam. The degradation rate of Sr-Fe-O infiltrated LSM/YSZ cell was 2.05% per 1000h. TEM analysis indicated significant reaction between the infiltrated elements and LSM backbone when infiltrating LSM/YSZ cells. EDS analysis showed La-Sr-Mn-Fe-O-containing nanoparticles formed in the pore on both the LSM and YSZ surfaces. After 2500h operation under 10% steam, the Sr-Fe-O infiltrated cell had a more open porous structure with a modified surface structure and composition. TEM and EDS analysis of the infiltrated cell showed (MnFe)Ox particles formed with a size of ~100nm. 10-50 nm Fe-doped LSM particles were still be observed on YSZ grain surface and on the surface of LSM grain, and iron further diffused into the LSM backbone. Nano-voids were also observed in the interior of LSM grains for the cell operated under 800°C, 0.75A/cm2 and 10% steam for 2500h. The performance data and TEM analysis indicate that infiltration can be used to boost cell performance while also decreasing long term degradation by changing the degradation modes present in the cathode.