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Journal articleJackson C, Smith GT, Mpofu N, et al., 2020,
A quick and versatile one step metal–organic chemical deposition method for supported Pt and Pt-alloy catalysts
, RSC Advances: an international journal to further the chemical sciences, Vol: 10, Pages: 19982-19996, ISSN: 2046-2069A simple, modified Metal–Organic Chemical Deposition (MOCD) method for Pt, PtRu and PtCo nanoparticle deposition onto a variety of support materials, including C, SiC, B4C, LaB6, TiB2, TiN and a ceramic/carbon nanofiber, is described. Pt deposition using Pt(acac)2 as a precursor is shown to occur via a mixed solid/liquid/vapour precursor phase which results in a high Pt yield of 90–92% on the support material. Pt and Pt alloy nanoparticles range 1.5–6.2 nm, and are well dispersed on all support materials, in a one-step method, with a total catalyst preparation time of ∼10 hours (2.4–4× quicker than conventional methods). The MOCD preparation method includes moderate temperatures of 350 °C in a tubular furnace with an inert gas supply at 2 bar, a high pressure (2–4 bar) compared to typical MOCVD methods (∼0.02–10 mbar). Pt/C catalysts with Pt loadings of 20, 40 and 60 wt% were synthesised, physically characterised, electrochemically characterised and compared to commercial Pt/C catalysts. TEM, XRD and ex situ EXAFS show similar Pt particle sizes and Pt particle shape identifiers, namely the ratio of the third to first Pt coordination numbers modelled from ex situ EXAFS, between the MOCD prepared catalysts and commercial catalysts. Moreover, electrochemical characterisation of the Pt/C MOCD catalysts obtained ORR mass activities with a maximum of 428 A gPt−1 at 0.9 V, which has similar mass activities to the commercial catalysts (80–160% compared to the commercial Pt/C catalysts).
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Journal articleHakola L, Puerto AP, Vaari A, et al., 2020,
Anode ink formulation for a fully printed flexible fuel cell stack
, Flexible and Printed Electronics, Vol: 5, Pages: 1-12, ISSN: 2058-8585In fuel cells the underlying reactions take place at the catalyst layers composed of materials favoring the desired electrochemical reactions. This paper introduces a formulation process for a catalyst inkjet ink used as an anode for a fully printed flexible fuel cell stack. The optimal ink formulation was 2.5 wt% of carbon–platinum–ruthenium mixture with 0.5% Nafion concentration in a diacetone alcohol solvent vehicle. The best jetting performance was achieved when 1 wt% binder was included in the ink formulation. Anodes with resistivity of approximately 0.1 Ω cm were inkjet printed, which is close to the commercial anode resistivity of 0.05 Ω cm. The anodes were used in fuel cell stacks that were prepared by utilizing only printing methods. The best five-cell-air-breathing stack showed an open circuit potential under H2/air conditions of 3.4 V. The peak power of this stack was 120 µW cm−2 at 1.75 V, with a resistance obtained from potentiostatic impedance analysis of 295 Ohm cm2. The printed electrodes showed a performance suitable for low-performance solutions, such as powering single-use sensors.
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Journal articleZalitis C, Kucernak A, Lin X, et al., 2020,
Electrochemical measurement of intrinsic oxygen reduction reaction activity at high current densities as a function of particle size for Pt4–xCox/C (x = 0, 1, 3) catalysts
, ACS Catalysis, Vol: 10, Pages: 4361-4376, ISSN: 2155-5435While extensive literature shows Pt alloy catalysts are a more active substitute for pure Pt catalysts at 0.9 V, high activity is also needed at high current densities if they are to be adopted for fuel cell application. We use a newly developed electrochemical technique to compare the performance of a range of catalysts with initial composition Pt4–xCox/C of different particle sizes at high current densities (∼0.65 V vs RHE) as well as the typical ∼0.9 V vs RHE. Moving from 0.9 to 0.65 V, the current densities were found to increase by up to 80-fold for the Pt/C catalysts, with this factor decreasing as the amount of Co in the PtCo alloy increases. A kinetic model incorporating site blocking species at both high and low potentials has been used to explain this change. While the dealloyed catalysts were found to have a greater mass activity at low current densities (∼0.9 V vs RHE), they were no longer as active as 2.1 nm Pt particle catalyst at high current densities (∼0.65 V vs RHE). However, for equivalent particle sizes, the mass activity of the dealloyed Co-containing catalysts remains higher across the normal operating potentials of a fuel cell. Using this insight, we predict that at 0.65 V a catalyst composed of 3.8 nm CoPt@Pt1ML particles would give optimum mass activity performance. In addition, two peaks were observed during the cyclic voltammetry (CV) of the oxygen reduction reaction (ORR) on pure Pt nanoparticles in the hydrogen adsorption region (0–0.4 V vs RHE). These peaks are associated with surface sites with different reactivities toward the ORR.
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Journal articleMa Y, Sikdar D, Fedosyuk A, et al., 2020,
Electrotunable nanoplasmonics for amplified surface enhanced Raman spectroscopy
, ACS Nano, Vol: 14, Pages: 328-336, ISSN: 1936-0851Tuning the properties of optical metamaterials in real time is one of the grand challenges of photonics. Being able to do so will enable a new class of photonic materials for use in applications such as surface enhanced Raman spectroscopy and reflectors/absorbers. One strategy to achieving this goal is based on the electrovariable self-assembly and disassembly of two-dimensional nanoparticle arrays at a metal liquid interface. As expected the structure results in plasmonic coupling between NPs in the array but perhaps as importantly between the array and the metal surface. In such a system the density of the nanoparticle array can be controlled by the variation of electrode potential. Due to the additive effect, we show that less than 1 V variation of electrode potential can give rise to a dramatic simultaneous change in optical reflectivity from ~93 % to ~1 % and the amplification of the SERS signal by up to 5 orders of magnitude. The process allows for reversible tunability. These concepts are demonstrated in this manuscript, using a platform based on the voltage-controlled assembly of 40 nm Au-nanoparticle arrays at a TiN/Ag electrode in contact with an aqueous electrolyte. We show that all the physics underpinning the behaviour of this platform works precisely as suggested by the proposed theory, setting the electrochemical nanoplasmonics as a promising new direction in photonics research.
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Journal articleJavier R-G, Kucernak A, Liu R, et al., 2020,
Hydrogen/functionalized benzoquinone for a high-performance regenerative fuel cell as a potential large-scale energy storage platform
, Journal of Materials Chemistry A, Vol: 8, Pages: 3933-3941, ISSN: 2050-7488The redox flow battery (RFB) is a suitable option for electricity storage due to its high energy efficiency, scalability and relative safety. However, the limited metallic resources for redox materials and the high cost in systems such as the all-vanadium RFB are major challenges for wider application. Organics may be sourced more abundantly and have lower prices than metal based redox couples. In this work a regenerative fuel cell involving relatively inexpensive organic redox couples is demonstrated. The electrochemical properties of 1,2-dihydrobenzoquinone-3,5-disulfonic acid (BQDS) are characterised by cyclic voltammetry and linear-sweep voltammetry under hydrodynamic conditions. A regenerative fuel cell using 0.65 M BQDS in 1 M H2SO4 as positive electrolyte and gaseous hydrogen (1 bar) as negative redox-material results in an open circuit cell voltage of 0.86 V, a power density of 122 mW/cm2, and an energy density of 10.90 Wh L-1 without considering the volume occupied by the hydrogen. Very promising performance with an energy efficiency >60% at 100 mA cm-2 for 200 cycles is reported. New organic redox species resistant to side reactions could facilitate the use of this new system in practical applications. The use of hydrogen may also contribute to reduced side reactions of the organic redox associated with degradation in the presence of oxygen.
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Journal articleParra-Puerto A, Ng KL, Fahy K, et al., 2019,
Supported transition metal phosphides: Activity survey for HER, ORR, OER and corrosion resistance in acid and alkaline electrolytes
, ACS Catalysis, Vol: 9, Pages: 11515-11529, ISSN: 2155-5435Carbon supported MxPy (M = Ni, Co, W, Cr and Mo) were prepared via pyrolysis using a very simple and scalable method utilizing non-toxic metal and phosphorous precursors. The electrochemical hydrogen evolution (HER), oxygen reduction (ORR), and oxygen evolution (OER) reactions and corrosion resistance under both acid and alkaline conditions were examined for all these catalysts and compared to the benchmark catalysts Pt/C (HER/ORR) and IrO2(OER). The highest activities were found in alkaline solutions for Co2P for HER and ORR and Ni2P for OER. Good activity for these was also found in acid for some of these reactions, although the catalysts suffered from susceptibility to corrosion. Co2P was further studied in an alkaline environment as it shows high catalytic activity towards the oxygen reduction reaction (ORR) without significant hysteresis. The onset potential (at 0.5 mA cm-2) obtained was 0.8 V and a Tafel slope value of 38 mV dec-1 with a maximum kinetic mass activity of 2870 A gCo-1 at 0.7 V (RHE). Utilising high resolution transmission electron microscopy (HRTEM) it is possible to observe high-surface area needle-like single crystal cobalt oxide structures on the surfaces of the Co2P particles at the beginning of the ORR. Hence the high rates of initial corrosion of the Co2P identified appear to be associated with the dissolution and precipitation of Cobalt oxide on the particle surface. The as-synthesised Co2P/C also shows good performance in an 8-hour stability test for the Oxygen Evolution Reaction (OER), carried out at 1.6 V vs. RHE in alkaline conditions, with negligible drop in current density over time. Interestingly, in an acidic environment the catalyst is very active towards 2-electron- oxygen reduction leading to H2O2 with high selectivity (85%). It is intriguing that the pH dependence on this catalyst towards the ORR is similar to that seen for gold.
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Journal articleLopes T, Beruski O, Manthanwar A, et al., 2019,
Spatially resolved oxygen reaction, water, and temperature distribution: Experimental results as a function of flow field and implications for polymer electrolyte fuel cell operation
, Applied Energy, Vol: 252, ISSN: 0306-2619In situ and ex situ spatially-resolved techniques are employed to investigate reactant distribution and its impacts in a polymer electrolyte fuel cell. Temperature distribution data provides further evidence for secondary flows inferred from reactant imaging data, highlighting the contribution of convection in heat as well as reactant distribution. Water build-up from neutron tomography is linked to component degradation, matching the pattern seen in the reactant distribution and thus suggesting that high, non-uniform local current densities shape degradation patterns in fuel cells. The correlations shown between different techniques confirm the use of the versatile reactant imaging technique, which is used to compare commonly used flow field designs. Among serpentine-type designs, the single serpentine is superior in both equivalent current density and reactant distribution, showing large contributions from convective flow. On the other hand, the interdigitated design is shown to produce larger equivalent current densities, while showing a somewhat poorer reactant distribution. Considering the correlations drawn between the techniques, this suggests that the interdigitated design compromises durability in favour of power output. The results highlight how established techniques provide a robust background for the use of a new and flexible imaging technique toward designing advanced flow fields for practical fuel cell applications.
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Conference paperAnthony D, Nguyen S, Senokos E, et al., 2019,
Hierarchical carbon aerogel modified carbon fiber composites for structural power applications
, 22nd International Conference on Composite Materials 2019 (ICCM22), Publisher: Engineers Australia, Pages: 1-7The desire to reduce overall weight in devices is a key driver for perpetual material development; the ability to combine composites with energy storage functions/capabilities which simultaneously provide structural integrity has the potential to supersede monofunctional components. To achieve this ambition, the multifunctional structure must perform both mechanical and energy storage functions sufficiently, but often there is a trade off in performance which is a significant challenge to overcome. Carbon aerogels have been shown to contribute positively to (electro-chemical double layer) capacitive performance due to an increased surface area in multifunctional carbon fiber based composite electrodes, but have also been shown to reduce mechanical properties; the addition of nanoscale reinforcers, such as carbon nanotubes, graphene or alike, with their superlative electrical and mechanical properties are proposed to address these concerns and create a truly hierarchical structure suitable for structural power applications.
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Journal articleMontelongo Y, Sikdar D, Ma Y, et al., 2019,
Author Correction: Electrotunable nanoplasmonic liquid mirror.
, Nat Mater, ISSN: 1476-1122In the version of this Article originally published, the last sentence of the acknowledgements incorrectly read 'L.V. acknowledges the support of a Marie Skodowska-Curie fellowship (N-SHEAD)'; it should have read 'L.V. and D.S. acknowledge the support of Marie Skłodowska-Curie fellowships, N-SHEAD and S-OMMs, respectively'.
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Conference paperSikdar D, Ma Y, Kucernak AR, et al., 2019,
Nanoplasmonic metamaterial devices as electrically switchable perfect mirrors and perfect absorbers
, Conference on Lasers and Electro-Optics (CLEO), Publisher: IEEE, Pages: 1-2, ISSN: 2160-9020We introduce nanoplasmonic metamaterial devices — electrically-switchable between perfect- mirror/absorber states — based on voltage-controlled assembly/disassembly of gold nanoparticles on silver films. These are investigated using effective-medium-theory, verified with simulations and experiments.
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Journal articleCastanheira L, Bedouet M, Kucernak A, et al., 2019,
Influence of microporous layer on corrosion of metallic bipolar plates in fuel cells
, Journal of Power Sources, Vol: 418, Pages: 147-151, ISSN: 0378-7753The effect of the presence of a microporous layer on the propensity for corrosion of metallic bipolar plates in an operating polymer electrolyte membrane fuel cell is investigated using an in situ reference electrode array. The local potential at the surface of the cathode bipolar plate is significantly more negative in the presence of the microporous layer, which is attributed to the higher ionic resistance of the aqueous phase in the reactant transport layer associated with more effective removal of water from the catalyst layer/reactant transport layer interface. As a result the bipolar plate is effectively shielded from elevated potentials that may be present at the cathode electrode, even during start-up and shutdown of the cell. Revision of ex situ test protocols for candidate bipolar plate materials, surface treatments and coatings is recommended to reduce unnecessary conservatism in testing.
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Journal articleMalko D, Guo Y, Jones P, et al., 2019,
Heterogeneous iron containing carbon catalyst (Fe-N/C) for epoxidation with molecular oxygen
, Journal of Catalysis, Vol: 370, Pages: 357-363, ISSN: 0021-9517Pyrolized transition metal and nitrogen containing carbon materials (M-N/C) have shown promising activities as electrocatalysts for oxygen reduction reactions (ORR) in fuel cell cathodes. Similar materials have recently gained interest as heterogeneous catalysts. We report that ORR-active heterogeneous M-N/C materials can catalyze the chemical epoxidation of olefins with molecular oxygen and two equivalents of aldehyde at room temperature and ambient pressure. The observed yield and selectivity is higher than that for homogeneous analogues and the catalysts achieve TOF > 2700 h−1 and TON > 16,000. The ability to recycle the catalyst several times is also demonstrated.
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Conference paperEdel JB, Kornyshev AA, Kucernak AR, et al., 2019,
Electrochemical plasmonics for dynamic control of optical properties of self-assembling metamaterials
, Pages: 1364-1365This talk will overview a new direction of research based on self-assembly of plasmonic nanoparticles at electrochemical liquid-liquid or solid-liquid interfaces. Optical properties of such systems can be varied in real time via voltage-control over the structure and density of the nanoparticle assemblies. Potential applications involve switchable mirror-windows, tunable color mirrors, optical cavities, and pixels.
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Journal articleRubio-Garcia J, Kucernak A, Zhao D, et al., 2019,
Hydrogen/manganese hybrid redox flow battery
, JPhys Energy, Vol: 1, Pages: 1-9, ISSN: 2515-7655Electrochemical energy storage is a key enabling technology for further integration of renewables sources. Redox flow batteries (RFBs) are promising candidates for such applications as a result of their durability, efficiency and fast response. However, deployment of existing RFBs is hindered by the relatively high cost of the (typically vanadium-based) electrolyte. Manganese is an earth-abundant and inexpensive element that is widely used in disposable alkaline batteries. However it has hitherto been little explored for RFBs due to the instability of Mn(III) leading to precipitation of MnO2 via a disproportionation reaction. Here we show that by combining the facile hydrogen negative electrode reaction with electrolytes that suppress Mn(III) disproportionation, it is possible to construct a hydrogen/manganese hybrid RFB with high round trip energy efficiency (82%), and high power and energy density (1410 mW cm−2, 33 Wh l−1), at an estimated 70% cost reduction compared to vanadium redox flow batteries.
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Journal articleMa Y, Zagar C, Klemme DJ, et al., 2018,
A tunable nanoplasmonic mirror at an electrochemical interface
, ACS Photonics, Vol: 5, Pages: 4604-4616, ISSN: 2330-4022Designing tunable optical metamaterials is one of the great challenges in photonics. Strategies for reversible tuning of nanoengineered devices are currently being sought through electromagnetic or piezo effects. For example, bottom-up self-assembly of nanoparticles at solid | liquid or liquid | liquid interfaces can be used to tune optical responses by varying their structure either chemically or through applied voltage. Here, we report on a fully reversible tunable-color mirror based on a TiN-coated Ag substrate immersed in an aqueous solution of negatively charged Au-nanoparticles (NPs). Switching electrode potential can be used to fully control the assembly/disassembly of NPs at the electrode | electrolyte interface within a 0.6 V wide electrochemical window. The plasmon coupling between the electrode and the adsorbed NP array at high positive potentials produces a dip in the optical reflectance spectrum, creating the "absorber" state. Desorption of NPs at low potentials eliminates the dip, returning the system to the reflective "mirror" state. The intensity and wavelength of the dip can be finely tuned through electrode-potential and electrolyte concentration. The excellent match between the experimental data and the theory of optical response for such system allows us to extract valuable information on equilibrium and kinetic properties of NP-assembly/disassembly. Together with modeling of the latter, this study promotes optimization of such meta-surfaces for building electrotunable reflector devices.
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Journal articleTariq F, Rubio-Garcia J, Yufit V, et al., 2018,
Uncovering the mechanisms of electrolyte permeation in porous electrodes for redox flow batteries through real time in situ 3D imaging
, SUSTAINABLE ENERGY & FUELS, Vol: 2, Pages: 2068-2080, ISSN: 2398-4902 -
Conference paperRiedel R, Malko D, Seel A, et al., 2018,
Ion pairing and stability of alkalides in organic solutions
, 256th National Meeting and Exposition of the American-Chemical-Society (ACS) - Nanoscience, Nanotechnology and Beyond, Publisher: AMER CHEMICAL SOC, ISSN: 0065-7727 -
Journal articleRubio-Garcia J, Kucernak ARJ, Charleson A, 2018,
Direct visualization of reactant transport in forced convection electrochemical cells and its application to Redox Flow Batteries
, Electrochemistry Communications, Vol: 93, Pages: 128-132, ISSN: 1388-2481A novel, simple and low cost electrochemiluminescence imaging method for monitoring mass transport phenomena in a redox flow battery-like system is presented. Luminol solutions were pumped through a flow field (FF) with a given design. At the flowfield/electrode interface light is emitted upon dye oxidation allowing direct visualization of channels, U-bends and regions of poor wetting. Image analysis allows direct visualization of reactant distribution and poor mass transport through tortuous materials. These results were compared with the experimental performance of an all‑vanadium redox flow battery with different FFs as a function of flow and good correlation achieved.
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Journal articleJackson C, Smith GT, Markiewicz M, et al., 2018,
Support induced charge transfer effects on electrochemical characteristics of Pt nanoparticle electrocatalysts
, Journal of Electroanalytical Chemistry, Vol: 819, Pages: 163-170, ISSN: 1572-6657The electrokinetic properties of Pt nanoparticles supported on Carbon (Pt/C) and Boron Carbide-Graphite composite (Pt/BC) are compared over a wide potential range. The influence of the support on the electronic state of Pt was investigated via in-situ X-ray Absorption Spectroscopy. Pt d-band filling, determined from XANES white line analysis, was lower and nearly constant between 0.4 and 0.95V vs. RHE for Pt/BC, indicating more positively charged particles in the double layer region and a delay in the onset of oxide formation by about 0.2V compared to the Pt/C catalyst, which showed a marked increase in d-band vacancies above 0.8V vs. RHE. Moreover, δμ analysis of the XANES data indicated a lack of sub-surface oxygen for the Pt/BC catalyst compared to the Pt/C catalyst above 0.9V vs. RHE. Additional anion adsorption on the Pt/BC in the double layer region, detected by CO displacement, was also confirmed by XANES analysis of the d-band occupancy. The H 2 oxidation activities of electrodes with low catalyst loadings were assessed under high mass transport conditions using the floating electrode methodology. The metal-support interaction between the Pt and BC support improved the maximum hydrogen oxidation current density by 1.4 times when compared to Pt/C.
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Journal articleJaouen F, Jones D, Coutard N, et al., 2018,
Toward platinum group metal-free catalysts for hydrogen/airproton-exchange membrane fuel cells
, Johnson Matthey Technology Review, Vol: 62, Pages: 231-255, ISSN: 2056-5135The status, concepts and challenges toward catalysts free of platinum group metal (pgm) elements for proton-exchange membrane fuel cells (PEMFC) are reviewed. Due to the limited reserves of noble metals in the Earth’s crust, a major challenge for the worldwide development of PEMFC technology is to replace Pt with pgm-free catalysts with sufficient activity and stability. The priority target is the substitution of cathode catalysts (oxygen reduction) that account for more than 80% of pgms in current PEMFCs. Regarding hydrogen oxidation at the anode, ultralow Pt content electrodes have demonstrated good performance, but alternative non-pgm anode catalysts are desirable to increase fuel cell robustness, decrease the H2 purity requirements and ease the transition from H2 derived from natural gas to H2 produced from water and renewable energy sources.
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Journal articleLee M-R, Lee H-Y, Yim S-D, et al., 2018,
Effects of Ionomer Carbon Ratio and Ionomer Dispersity on the Performance and Durability of MEAs
, FUEL CELLS, Vol: 18, Pages: 129-136, ISSN: 1615-6846 -
Journal articlePark JY, Kwak DH, Ma KB, et al., 2018,
Enhanced oxygen reduction reaction of Pt deposited Fe/N-doped bimodal porous carbon nanostructure catalysts
, Journal of Catalysis, Vol: 359, Pages: 46-54, ISSN: 0021-9517© 2018 Elsevier Inc. For commercialization of proton exchange membrane fuel cells (PEMFCs), the loading amount of Pt-based cathode catalysts for oxygen reduction reaction (ORR) needs be significantly reduced. In this study, we propose Pt catalysts supported by an iron/nitrogen-doped porous carbon (FeNC) nanostructure having a catalytic activity for ORR in order to significantly reduce the utilization of Pt. The FeNC nanostructure was prepared using a template method with 50 and 500 nm SiO 2 beads and phthalocyanine as a dopant and carbon source. The nanosized Pt catalysts with different loading weights (5, 10, 20, 30 wt%) were uniformly deposited on the FeNC with a bimodal porous crystalline doped carbon nanostructure using an electron beam radiation method. In particular, the cathode catalyst having 5 wt% Pt on FeNC (Pt5/FeNC) exhibited enhanced ORR mass activities of 2.19 and 2.58 A mg Pt −1 at 0.9 V measured by electrochemical half cells in acidic and alkaline media, respectively, compared to a commercial Pt(20 wt%)/C (Pt20/C). Furthermore, Pt5/FeNC showed a higher mass activity of 18.76 A mg Pt −1 at 0.6 V as a unit cell performance than that of the commercial catalyst. The improved ORR activity of Pt/FeNC might be synergistically attributed to the homogeneous dispersion of Pt nanoparticles on the bimodal porous doped carbon nanostructure, the interaction (electronic effect) between the metallic catalyst and the doped support, and the dual catalytic effect of both Pt and the doped carbon nanostructure.
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Journal articlezalitis C, Kucernak ARJ, sharman J, et al., 2017,
Design principles for platinum nanoparticles catalysing electrochemical hydrogen evolution and oxidation reactions: edges are much more active than facets
, Journal of Materials Chemistry A, Vol: 5, Pages: 23328-23338, ISSN: 2050-7496Improving the performance of hydrogen evolution and oxidation reactions using precious metal catalysts is key in reducing the cost of electrolysers and fuel cells. By considering the performance of these reactions as a function of platinum particle size (2.1–15 nm) under high mass transport conditions in acids, we find that the activity is composed of two components which vary in a defined way with the particle size. Geometrical considerations and electrokinetic modelling suggest that these two components correspond to the response of edges/vertices and the response of facets (Pt(100) and Pt(111)). Edges and vertices are much more active towards the hydrogen reaction. This assignment also rationalises the poor performance of platinum in alkaline environments. We predict that “ideal” particles made up of only edges/vertices would allow fuel cells and electrolysers to operate with only 1 μgPt cm−2 – about two to three orders of magnitude lower than what is currently used.
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Journal articleBeruski O, Lopes T, Kucernak ARJ, et al., 2017,
Investigation of convective transport in the so-called “gas diffusion layer” used in polymer electrolyte fuel cell
, Physical Review Fluids, Vol: 2, ISSN: 2469-990XRecent experimental data on a fuel-cell-like system revealed insights into the fluid flow in both free and porous media. A computational model is used to investigate the momentum and species transport in such a system, solved using the finite element method. The model consists of a stationary, isothermal, diluted species transport in free and porous media flow. The momentum transport is treated using different formulations, namely, Stokes-Darcy, Darcy-Brinkman, and hybrid Stokes-Brinkman formulations. The species transport is given by the advection equation for a reactant diluted in air. The formulations are compared to each other and to the available experimental data, where it is concluded that the Darcy-Brinkman formulation reproduces the data appropriately. The validated model is used to investigate the contribution of convection in reactant transport in porous media of fuel cells. Convective transport provides a major contribution to reactant distribution in the so-called diffusion media. For a serpentine channel and flow with Re=260–590, convection accounts for 29–58% of total reactant transport to the catalyst layer.
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Journal articleMontelongo Y, Sikdar D, Ma Y, et al., 2017,
Electrotunable nanoplasmonic liquid mirror
, Nature Materials, Vol: 16, Pages: 1127-1135, ISSN: 1476-1122Recently, there has been a drive to design and develop fully tunable metamaterials for applications ranging from new classes of sensors to superlenses among others. Although advances have been made, tuning and modulating the optical properties in real time remains a challenge. We report on the first realization of a reversible electrotunable liquid mirror based on voltage-controlled self-assembly/disassembly of 16 nm plasmonic nanoparticles at the interface between two immiscible electrolyte solutions. We show that optical properties such as reflectivity and spectral position of the absorption band can be varied in situ within ±0.5 V. This observed effect is in excellent agreement with theoretical calculations corresponding to the change in average interparticle spacing. This electrochemical fully tunable nanoplasmonic platform can be switched from a highly reflective ‘mirror’ to a transmissive ‘window’ and back again. This study opens a route towards realization of such platforms in future micro/nanoscale electrochemical cells, enabling the creation of tunable plasmonic metamaterials.
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Journal articleMalko D, Kucernak ARJ, 2017,
Kinetic isotope effect in the oxygen reduction reaction (ORR) over Fe-N/C catalysts under acidic and alkaline conditions.
, Electrochemistry Communications, Vol: 83, Pages: 67-71, ISSN: 1388-2481Heat treated Fe-N/C materials which are highly effective oxygen reduction catalysts in alkaline and acid, show a significant kinetic isotope effect (KIE). The values in acid (~3.4) and alkaline (~2.5) are much larger than the value for the metal free catalyst in acid (~1.8) suggesting that the rate determining step (RDS) is a proton coupled electron transfer in acid with a significant pathway involving a proton independent step under an alkaline environment
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OtherBazant M, Bennewitz R, Bocquet L, et al., 2017,
Electrotunable wetting, and micro- and nanofluidics: general discussion
, Publisher: ROYAL SOC CHEMISTRY- Author Web Link
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- Citations: 2
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Journal articleSymianakis E, Kucernak A, 2017,
Embedded atom method interatomic potentials fitted upon density functional theory calculations for the simulation of binary Pt-Ni nanoparticles
, Computational Materials Science, Vol: 133, Pages: 185-193, ISSN: 0927-0256Embedded Atom Method (EAM) potentials have been fitted for the atomistic simulation of small, 2–5 nm, binary, PtANi, nanoparticles completely from Density Functional Theory (DFT) total energy calculations.The overall quality of the DFT calculations and the final potential is obtained through the independentcalculation of an array of properties of the pure metals and the stable alloys, which arenormally used for the fitting of interatomic potentials. The ability of the fitted potentials to simulatenanostructures is evaluated by the reproduction of binary nanoslabs with thickness 1 nm, and nanoparticlesin the extreme case of the smallest icosahedrons possible, with diameter 0.6 nm. The usedapproach requires high quality of convergence but otherwise low cost DFT as it is based on static totalenergy calculations. It also provides objective criteria for the evaluation of the fitted potentials during fittingand has been implemented with the open source code GULP
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Journal articleCousens N, Kucernak ARJ, 2017,
Reversible ultralow-voltage liquid-liquid electrowetting without a dielectric layer
, Faraday Discussions, Vol: 199, Pages: 63-73, ISSN: 1364-5498Electrowetting-on-dielectric devices typically have operating voltages of 10-20 V. A reduction in the operating voltage could greatly reduce the energy consumption of these devices. Here, the fully reversible one electrolyte electrowetting of a droplet on a solid metal surface is reported for the first time. A reversible change of 29o for an 800 mV step is achieved. The effect of surface roughness, electrolyte composition, electrolyte concentration and droplet composition is investigated. It is found that there is a dramatic dependence of the reversibility and hysteresis of the system on these parameters, contrary to theoretical predictions. When a 3-chloro-1-propanol droplet is used, a system with no hysteresis and a 40o change in angle is achieved.
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Journal articleVelleman L, Sikdar D, Turek V, et al., 2016,
Tuneable 2D self-assembly of plasmonic nanoparticles at liquid | liquid interfaces
, Nanoscale, Vol: 8, Pages: 19229-19241, ISSN: 2040-3372Understanding the structure and assembly of nanoparticles at liquid | liquid interfaces is paramount to their integration into devices for sensing, catalysis, electronics and optics. However, many difficulties arise when attempting to resolve the structure of such interfacial assemblies. In this article we use a combination of X-ray diffraction and optical reflectance to determine the structural arrangement and plasmon coupling between 12.8 nm diameter gold nanoparticles assembled at a water | 1,2-dichloroethane interface. The liquid | liquid interface provides a molecularly flat and defect-correcting platform for nanoparticles to self-assemble. The amount of nanoparticles assembling at the interface can be controlled via the concentration of electrolyte within either the aqueous or organic phase. At higher electrolyte concentration more nanoparticles can settle at the liquid | liquid interface resulting in a decrease in nanoparticle spacing as observed from X-ray diffraction experiments. The coupling of plasmons between the nanoparticles as they come closer together is observed by a red-shift in the optical reflectance spectra. The optical reflectance and the X-ray diffraction data are combined to introduce a new ‘plasmon ruler’. This allows extraction of structural information from simple optical spectroscopy techniques, with important implications in understanding the structure of nanoparticle films at liquid interfaces and their self-assembly.
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