Publications
137 results found
Murawski J, Yin S, Zalitis C, et al., 2022, Oxygen Evolution Reaction Catalyst Development: Benchmarking IrO<sub>x</sub> Catalyst Activity and Stability, ECS Meeting Abstracts, Vol: MA2022-01, Pages: 1367-1367
<jats:p> While PEM electrolyser catalyst cost may not be a significant portion of system costs<jats:sup>1</jats:sup> it does represent a bottleneck for the ability to generate TW level of H<jats:sub>2</jats:sub>. This is primarily because of the reliance on IrO<jats:sub>x</jats:sub> as a stable oxygen evolution catalyst in order to meet future green H<jats:sub>2</jats:sub> needs either replacement or reduction of iridium loading of at least 50 times is needed while maintaining a high level of stability<jats:sup>2</jats:sup>. IrO<jats:sub>x</jats:sub> based materials are the only oxygen evolution catalysts combining activity and stability under PEM electrolysis conditions; even so, they are insufficiently stable.</jats:p> <jats:p>In the current work, we tailored the activity of IrOx catalysts synthesised by a variant of the Adams fusion reaction<jats:sup>3</jats:sup> using decomposition of Iridium nitrate and varying temperature of synthesis to generate a series of catalysts with differing crystallinity and surface area. We benchmarked their stability using both accelerated degradation electrochemical measurements (30k cycles 1.2-1.7V<jats:sub>RHE</jats:sub> @ 500 mV s<jats:sup>-1</jats:sup>) and inductively coupled plasma-mass spectrometry(ICP-MS), both in rotating disk electrode(RDE) measurements and in a single cell PEM electrolyser.</jats:p> <jats:p>We have compared several different methods for probing electrochemical surface area, including BET, double layer capacitance from cyclic voltammetry, adsorption capacitance using impedance spectroscopy and CO stripping using ultrasensitive on chip electrochemical mass spectrometry.</jats:p> <jats:p>The results from the RDE measurements are shown in figure 1; they show that while the high surface area amorphous IrO<jats:sub&g
Mukadam Z, Liu S, Scott S, et al., 2022, Electrocatalytic Reduction of Furfural Using Single-Atom Molecular Catalysts, ECS Meeting Abstracts, Vol: MA2022-01, Pages: 961-961
<jats:p> The electrochemical conversion of bio-based platform chemicals is an effective way of moving away from a crude oil reliant chemical source. Lignocellulosic biomass such as hemicellulose provides a sustainable chemicals source which can yield important platform chemicals including furfural, which can be upgraded into higher valued chemicals for biofuels, renewable polymers, and pharmaceuticals. In this study, we investigate the electrochemical reduction of furfural using Cu and Co single-atom molecular catalysts on carbon electrodes in a mild basic electrolyte (pH 10) for selective production of hydrofuroin, a promising precursor to sustainable drop-in jet fuels. Using density functional theory, we show that the selectivity of furfural reduction products on transition metals could be generally described by the adsorption energies of furfural and hydrogen (Fig 1a). In particular, we predict that the weak-binding molecular catalysts could give rise to a facile reaction path towards coupling product. Based on theoretical calculations, we synthesized Cu and Co-doped phthalocyanines and show that those single-atom molecular catalysts display up to 92% Faradaic efficiency for hydrofuroin production with suppressed hydrogen evolution in pH 10 at -0.50 V vs. the reversible hydrogen electrode (RHE). Combining experiment and theory, we show that the rate-determining step for hydrofuroin formation on single-atom molecular catalysts is the first proton-coupled electron transfer rather than the chemical coupling step. Furthermore, a single-atom molecular design principle is briefly proposed by tuning the adsorption strength of furfural.</jats:p> <jats:p> <jats:inline-formula> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="961fig1.JPG" xlink:type="simple" /> </jats:inline-formula> </jats:p>
Favero S, Stephens IEL, Titirici M, 2022, Deconvoluting Transport and Kinetics on Ionic Liquid-Modified Fe Catalysts for Oxygen Reduction, ECS Meeting Abstracts, Vol: MA2022-01, Pages: 1471-1471
<jats:p> <jats:bold>Introduction</jats:bold> </jats:p> <jats:p>Hydrogen fuel cells could play a key role in the decarbonization of the energy sector. However, their commercialization is hindered by the sluggish kinetics of the oxygen reduction reaction (ORR) and by the requirement of platinum, which is expensive and unsustainable. Alternative catalysts based on transition metals have proven promising, but their activity and durability is still far from that of platinum.</jats:p> <jats:p>Recently, thin layers of ionic liquids have been successfully used to improve both the durability and activity of noble-metal free ORR catalysts<jats:uri xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#_ftn1" xlink:type="simple">[1]</jats:uri>. As shown in Figure 1, the presence of the ionic liquid layer can influence the reaction kinetics through multiple effects: (i) O<jats:sub>2</jats:sub> transport, (ii) water transport (iii) proton transport and (iv) binding to the reaction intermediate.</jats:p> <jats:p>These competing effects are generally convoluted. To that end, we have recently developed models to quantify the effect of the ionic liquid on both oxygen transport and reaction kinetics.</jats:p> <jats:p> <jats:bold>Effect of Ionic liquids on reaction kinetics</jats:bold> </jats:p> <jats:p>The ionic liquids tested for oxygen reduction are hydrophobic and their degree of water uptake is largely controlled by the cation. By decreasing the concentration of water at the active sites, they can cause the dehydration of the *OH intermediate, ultimately weakening the *OH bond<jats:uri xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#_ftn2" xlink:type="simple">[2
Titirici M, Baird SG, Sparks TD, et al., 2022, The sustainable materials roadmap, Journal of Physics: Materials, Vol: 5, Pages: 1-98, ISSN: 2515-7639
Over the past 150 years, our ability to produce and transform engineered materials has been responsible for our current high standards of living, especially in developed economies. However, we must carefully think of the effects our addiction to creating and using materials at this fast rate will have on the future generations. The way we currently make and use materials detrimentally affects the planet Earth, creating many severe environmental problems. It affects the next generations by putting in danger the future of the economy, energy, and climate. We are at the point where something must drastically change, and it must change now. We must create more sustainable materials alternatives using natural raw materials and inspiration from nature while making sure not to deplete important resources, i.e. in competition with the food chain supply. We must use less materials, eliminate the use of toxic materials and create a circular materials economy where reuse and recycle are priorities. We must develop sustainable methods for materials recycling and encourage design for disassembly. We must look across the whole materials life cycle from raw resources till end of life and apply thorough life cycle assessments (LCAs) based on reliable and relevant data to quantify sustainability. We need to seriously start thinking of where our future materials will come from and how could we track them, given that we are confronted with resource scarcity and geographical constrains. This is particularly important for the development of new and sustainable energy technologies, key to our transition to net zero. Currently 'critical materials' are central components of sustainable energy systems because they are the best performing. A few examples include the permanent magnets based on rare earth metals (Dy, Nd, Pr) used in wind turbines, Li and Co in Li-ion batteries, Pt and Ir in fuel cells and electrolysers, Si in solar cells just to mention a few. These materials are classified as
Bozal-Ginesta C, Rao RR, Mesa CA, et al., 2022, Spectroelectrochemistry of Water Oxidation Kinetics in Molecularversus Heterogeneous Oxide Iridium Electrocatalysts, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, Vol: 144, Pages: 8454-8459, ISSN: 0002-7863
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- Citations: 12
Rao RR, Corby S, Bucci A, et al., 2022, Spectroelectrochemical analysis of the water oxidation mechanism on doped nickel oxides, Journal of the American Chemical Society, Vol: 144, Pages: 7622-7633, ISSN: 0002-7863
Metal oxides and oxyhydroxides exhibit state-of-the-art activity for the oxygen evolution reaction (OER); however, their reaction mechanism, particularly the relationship between charging of the oxide and OER kinetics, remains elusive. Here, we investigate a series of Mn-, Co-, Fe-, and Zn-doped nickel oxides using operando UV–vis spectroscopy coupled with time-resolved stepped potential spectroelectrochemistry. The Ni2+/Ni3+ redox peak potential is found to shift anodically from Mn- < Co- < Fe- < Zn-doped samples, suggesting a decrease in oxygen binding energetics from Mn- to Zn-doped samples. At OER-relevant potentials, using optical absorption spectroscopy, we quantitatively detect the subsequent oxidation of these redox centers. The OER kinetics was found to have a second-order dependence on the density of these oxidized species, suggesting a chemical rate-determining step involving coupling of two oxo species. The intrinsic turnover frequency per oxidized species exhibits a volcano trend with the binding energy of oxygen on the Ni site, having a maximum activity of ∼0.05 s–1 at 300 mV overpotential for the Fe-doped sample. Consequently, we propose that for Ni centers that bind oxygen too strongly (Mn- and Co-doped oxides), OER kinetics is limited by O–O coupling and oxygen desorption, while for Ni centers that bind oxygen too weakly (Zn-doped oxides), OER kinetics is limited by the formation of oxo groups. This study not only experimentally demonstrates the relation between electroadsorption free energy and intrinsic kinetics for OER on this class of materials but also highlights the critical role of oxidized species in facilitating OER kinetics.
Oates RP, Murawski J, Hor C, et al., 2022, How to Minimise Hydrogen Evolution on Carbon Based Materials?, JOURNAL OF THE ELECTROCHEMICAL SOCIETY, Vol: 169, ISSN: 0013-4651
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- Citations: 4
Barrio Hermida J, Pedersen A, Feng J, et al., 2022, Metal coordination in C2N-like materials towards dual atom catalysts for oxygen reduction, Journal of Materials Chemistry A, ISSN: 2050-7488
Pedersen A, Barrio J, Li A, et al., 2022, Dual-Metal Atom Electrocatalysts: Theory, Synthesis, Characterization, and Applications, ADVANCED ENERGY MATERIALS, Vol: 12, ISSN: 1614-6832
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- Citations: 56
Bozal-Ginesta C, Rao RR, Mesa CA, et al., 2021, Redox-state kinetics in water-oxidation IrOx electrocatalysts measured by operando spectroelectrochemistry, ACS Catalysis, Vol: 11, Pages: 15013-15025, ISSN: 2155-5435
Hydrous iridium oxides (IrOx) are the best oxygen evolution electrocatalysts available for operation in acidic environments. In this study, we employ time-resolved operando spectroelectrochemistry to investigate the redox-state kinetics of IrOx electrocatalyst films for both water and hydrogen peroxide oxidation. Three different redox species involving Ir3+, Ir3.x+, Ir4+, and Ir4.y+ are identified spectroscopically, and their concentrations are quantified as a function of applied potential. The generation of Ir4.y+ states is found to be the potential-determining step for catalytic water oxidation, while H2O2 oxidation is observed to be driven by the generation of Ir4+ states. The reaction kinetics for water oxidation, determined from the optical signal decays at open circuit, accelerates from ∼20 to <0.5 s with increasing applied potential above 1.3 V versus reversible hydrogen electrode [i.e., turnover frequencies (TOFs) per active Ir state increasing from 0.05 to 2 s–1]. In contrast, the reaction kinetics for H2O2 is found to be almost independent of the applied potential (increasing from 0.1 to 0.3 s–1 over a wider potential window), indicative of a first-order reaction mechanism. These spectroelectrochemical data quantify the increase of both the density of active Ir4.y+ states and the TOFs of these states with applied positive potential, resulting in the observed sharp turn on of catalytic water oxidation current. We reconcile these data with the broader literature while providing a unique kinetic insight into IrOx electrocatalytic reaction mechanisms, indicating a first-order reaction mechanism for H2O2 oxidation driven by Ir4+ states and a higher-order reaction mechanism involving the cooperative interaction of multiple Ir4.y+ states for water oxidation.
Luo H, Barrio J, Sunny N, et al., 2021, Progress and Perspectives in Photo- and Electrochemical-Oxidation of Biomass for Sustainable Chemicals and Hydrogen Production, ADVANCED ENERGY MATERIALS, Vol: 11, ISSN: 1614-6832
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- Citations: 130
Stephens IEL, Westhead O, Bagger A, et al., 2021, (Keynote) Why Is Lithium Uniquely Able to Reduce Nitrogen to Ammonia Under Ambient Conditions?, ECS Meeting Abstracts, Vol: MA2021-02, Pages: 1542-1542
Iriawan H, Andersen SZ, Zhang X, et al., 2021, (Invited) Nitrogen Activation by Reduction and Oxidation: A Primer for Rigorous and Reproducible Measurements, ECS Meeting Abstracts, Vol: MA2021-02, Pages: 1552-1552
Iriawan H, Zamany S, Zhang X, et al., 2021, Methods for nitrogen activation by reduction and oxidation, Nature Reviews Methods Primers, Vol: 1, ISSN: 2662-8449
The industrial Haber-Bosch process to produce ammonia (NH3) from dinitrogen (N2) is crucial for modern society. However, N2 activation is inherently challenging and the Haber-Bosch process has significant drawbacks, as it is highly energy intensive, not sustainable due to substantial CO2 emissions primarily from the generation of H2 and requires large-centralized facilities. New strategies of sustainable N2 activation, such as low-temperature thermochemical catalysis and (photo)electrocatalysis, have been pursued, but progress has been hindered by the lack of rigor and reproducibility in the collection and analysis of results. In this Primer, we provide a holistic step-by-step protocol, applicable to all nitrogen-transformation reactions, focused on verifying genuine N2 activation by accounting for all contamination sources. We compare state-of-the-art results from different catalytic reactions following the protocol’s framework, and discuss necessary reporting metrics and ways to interpret both experimental and density functional theory results. This Primer covers various common pitfalls in the field, best practices to improve reproducibility and cost-efficient methods to carry out rigorous experimentation. The future of nitrogen catalysis will require an increase in rigorous experimentation and standardization to prevent false positives from appearing in the literature, which can enable advancing towards practical technologies for the activation of N2.
Guo L, Thornton DB, Koronfel MA, et al., 2021, Degradation in lithium ion battery current collectors, JPhys Energy, Vol: 3, ISSN: 2515-7655
Lithium ion battery (LIB) technology is the state-of-the-art rechargeable energy storage technology for electric vehicles, stationary energy storage and personal electronics. However, a wide variety of degradation effects still contribute to performance limitations. The metallic copper and aluminium current collectors in an LIB can be subject to dissolution or other reactions with the electrolytes. Corrosion of these metal foils is significantly detrimental to the overall performance of an LIB, however the mechanisms of this degradation are poorly understood. This review summarises the key effects contributing to metal current collector degradation in LIBs as well as introduces relevant corrosion and LIB principles. By developing the understanding of these complex chemistries, LIB degradation can be mitigated, enabling safer operation and longer lifetimes.
Westhead O, Jervis R, Stephens IEL, 2021, Is lithium the key for nitrogen electroreduction?, Science, Vol: 372, Pages: 1149-1150, ISSN: 0036-8075
Bagger A, Wan H, Stephens IEL, et al., 2021, Role of catalyst in controlling N-2 reduction selectivity: a unified view of nitrogenase and solid electrodes, ACS Catalysis, Vol: 11, Pages: 6596-6601, ISSN: 2155-5435
The Haber–Bosch process conventionally reduces N2 to ammonia at 200 bar and 500 °C. Under ambient conditions, i.e., room temperature and ambient pressure, N2 can be converted into ammonia by the nitrogenase molecule and lithium-containing solid electrodes in nonaqueous media. In this work, we explore the catalyst space for the N2 reduction reaction under ambient conditions. We describe N2 reduction on the basis of the *N2 binding energy versus the *H binding energy; we find that under standard conditions, no catalyst can bind and reduce *N2 without producing H2. We show why a selective catalyst for N2 reduction will also likely be selective for CO2 reduction, but N2 reduction is intrinsically more challenging than CO2 reduction. Only by modulating the reaction pathway, like nitrogenase, or by tuning chemical potentials, like the Haber–Bosch and the Li-mediated process, N2 can be reduced.
Kluge RM, Haid RW, Stephens IEL, et al., 2021, Monitoring the active sites for the hydrogen evolution reaction at model carbon surfaces, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 23, Pages: 10051-10058, ISSN: 1463-9076
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- Citations: 20
Yadegari H, Koronfel MA, Wang K, et al., 2021, Operando measurement of layer breathing modes in lithiated graphite, ACS Energy Letters, Vol: 6, Pages: 1633-1638, ISSN: 2380-8195
Despite their ubiquitous usage and increasing societal dependence on Li-ion batteries, there remains a lack of detailed empirical evidence of Li intercalation/deintercalation into graphite even though this process dictates the performance, longevity, and safety of the system. Here, we report direct detection and dissociation of specific crystallographic phases in the lithiated graphite, which form through a stepwise staging process. Using operando measurements, LiC18, LiC12, and LiC6 phases are observed via distinct low-frequency Raman features, which are the result of displacement of the graphite lattice by induced local strain. Density functional theory calculations confirm the nature of the Raman-active vibrational modes, to the layer breathing modes (LBMs) of the lithiated graphite. The new findings indicate graphene-like characteristics in the lithiated graphite under the deep charged condition due to the imposed strain by the inserted Li. Moreover, our approach also provides a simple experimental tool to measure induced strain in the graphite structure under full intercalation conditions.
Rao RR, Stephens IEL, Durrant JR, 2021, Understanding What Controls the Rate of Electrochemical Oxygen Evolution, JOULE, Vol: 5, Pages: 16-18, ISSN: 2542-4351
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- Citations: 14
Favero S, Stephens IEL, Titirici MM, 2021, Engineering the Electrochemical Interface of Oxygen Reduction Electrocatalysts with Ionic Liquids: A Review, ADVANCED ENERGY AND SUSTAINABILITY RESEARCH, Vol: 2, ISSN: 2699-9412
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- Citations: 9
Duarte R, Rao R, Durrant J, et al., 2020, Towards Active and Stable Bifunctional NiCo<sub>2</sub>O<sub>4</sub> Catalysts for O<sub>2</sub> Evolution and Reduction in Alkaline Media, ECS Meeting Abstracts, Vol: MA2020-02, Pages: 3860-3860
<jats:p> It is particularly challenging to find a bifunctional catalyst capable of accelerating both the O<jats:sub>2</jats:sub> evolution reaction (OER) and O<jats:sub>2</jats:sub> reduction reaction (ORR) in aqueous solutions. The discovery of such a material would bring reversible fuel cells and metal air batteries much closer to technological fruition. However, in a real device, such a catalyst will need to retain its activity across an enormous potential window of at least 1 V over several years. To the best of our knowledge, little is known about the factors controlling the stability of bifunctional catalysts.</jats:p> <jats:p>In this contribution, we investigate the electrochemical activity and stability of a NiCo<jats:sub>2</jats:sub>O<jats:sub>4 </jats:sub>catalyst, synthesized at Johnson Matthey as part of EU funded project FLOWCAMP. Using post-mortem techniques, such as inductively coupled plasma mass spectrometry (ICP-MS), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS), we provide experimental evidence about catalyst deactivation mechanisms. Results will also include a spectroelectrochemical in-situ UV-Vis study, that provides insights to the reaction mechanism for the OER. Lastly, the activity and stability of NiCo<jats:sub>2</jats:sub>O<jats:sub>4</jats:sub> catalysts is also evaluated in oxygen-electrode prototypes and characterized in a half-cell configuration.</jats:p> <jats:p>In figure 1 is shown the ORR and OER activity of NiCo<jats:sub>2</jats:sub>O<jats:sub>4</jats:sub> before and after accelerated degradation tests (ADT), in rotating disk electrode (RDE) configuration, employing three different electrochemical potential windows: <jats:italic>i)</jats:italic> 0.6 V<jats:sub>RHE</jats:sub> - 1 V<jats:sub>RHE</jats:sub>; &l
Jensen KD, Pedersen AF, Zamburlini E, et al., 2020, X-ray Absorption Spectroscopy Investigation of Platinum-Gadolinium Thin Films with Different Stoichiometry for the Oxygen Reduction Reaction, CATALYSTS, Vol: 10
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- Citations: 2
Rao RR, Kolb MJ, Giordano L, et al., 2020, Operando identification of site-dependent water oxidation activity on ruthenium dioxide single-crystal surfaces, NATURE CATALYSIS, Vol: 3, Pages: 516-525, ISSN: 2520-1158
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- Citations: 137
Francas L, Corby S, Selim S, et al., 2020, Spectroelectrochemical study of water oxidation on nickel and iron oxyhydroxide electrocatalysts (vol 10, 5208, 2019), NATURE COMMUNICATIONS, Vol: 11, ISSN: 2041-1723
O'Mullane AP, Escudero-Escribano M, Stephens IEL, et al., 2019, The Role of Electrocatalysis in a Sustainable Future: From Renewable Energy Conversion and Storage to Emerging Reactions, CHEMPHYSCHEM, Vol: 20, Pages: 2900-2903, ISSN: 1439-4235
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- Citations: 14
Francàs L, Corby S, Selim S, et al., 2019, Spectroelectrochemical study of water oxidation on nickel and iron oxyhydroxide electrocatalysts, Nature Communications, Vol: 10, ISSN: 2041-1723
Ni/Fe oxyhydroxides are the best performing Earth-abundant electrocatalysts for water oxidation. However, the origin of their remarkable performance is not well understood. Herein, we employ spectroelectrochemical techniques to analyse the kinetics of water oxidation on a series of Ni/Fe oxyhydroxide films: FeOOH, FeOOHNiOOH, and Ni(Fe)OOH (5% Fe). The concentrations and reaction rates of the oxidised states accumulated during catalysis are determined. Ni(Fe)OOH is found to exhibit the fastest reaction kinetics but accumulates fewer states, resulting in a similar performance to FeOOHNiOOH. The later catalytic onset in FeOOH is attributed to an anodic shift in the accumulation of oxidised states. Rate law analyses reveal that the rate limiting step for each catalyst involves the accumulation of four oxidised states, Ni-centred for Ni(Fe)OOH but Fe-centred for FeOOH and FeOOHNiOOH. We conclude by highlighting the importance of equilibria between these accumulated species and reactive intermediates in determining the activity of these materials.
Andersen SZ, Colic V, Yang S, et al., 2019, A rigorous electrochemical ammonia synthesis protocol with quantitative isotope measurements (vol 570, pg 504, 2019), NATURE, Vol: 574, Pages: E5-E5, ISSN: 0028-0836
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- Citations: 4
Sebastian-Pascual P, Mezzavilla S, Stephens IEL, et al., 2019, Structure-sensitivity and Electrolyte Effects in CO<sub>2</sub> Electroreduction: From Model Studies to Applications, CHEMCATCHEM, Vol: 11, Pages: 3624-3643, ISSN: 1867-3880
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- Citations: 54
Mezzavilla S, Katayama Y, Rao R, et al., 2019, Activity-or Lack Thereof-of RuO2-Based Electrodes in the Electrocatalytic Reduction of CO2, JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 123, Pages: 17765-17773, ISSN: 1932-7447
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