Papers by Andrea E Russell
Physical Chemistry Chemical Physics, 2019
Iridium and ruthenium oxide are active electrocatalysts for oxygen evolution. The relation betwee... more Iridium and ruthenium oxide are active electrocatalysts for oxygen evolution. The relation between preparation method, structure, and behavior of mixed oxides of iridium and ruthenium are of interest in order to obtain active and stable catalysts. In this work the structure of mixed Ru-Ir oxides synthesized by the polymeric precursor method, which involves the formation of a gel containing the metal precursors and subsequent heat-treatment in air, was studied for the Ir x Ru 1−x O 2 system. An in-depth analysis of X-ray diffraction (XRD) and X-ray absorption (XAS) data, including EXAFS and linear combination of XANES, shows that the polymeric precursor synthesis method is capable of providing an intimate mixing of Ir and Ru in the catalyst. In addition to the oxide phase, metal phases, i.e. with Ru or Ir or both in oxidation state zero (Ir(fcc) and Ru(hcp)), were also found in the product materials. Facing complex structures such as some of those synthesized here, we have shown that a representation of shells with more than one atom type are efficiently represented using mixed sites, i.e. including scattering contributions from several elements in a site corresponding to a partial occupancy of the site by these elements, this method forming a very efficient basis for analyzing EXAFS data.
Faraday Discussions, 2018
Comprehensive identification of the phases and atomic configurations of bimetallic nanoparticle c... more Comprehensive identification of the phases and atomic configurations of bimetallic nanoparticle catalysts are critical in understanding structure-property relationships in catalysis. However, control of the structure, whilst retaining the same composition, is challenging. Here, the same carbon supported Pt 3 Sn catalyst is annealed under air, Ar and H 2 resulting in variation of the extent of alloying of the two components. The atmosphere-induced extent of alloying is characterised using a variety of methods including TEM, XRD, XPS, XANES and EXAFS and is defined as the fraction of Sn present as Sn 0 (XPS and XANES) or the ratio of the calculated composition of the bimetallic particle to the nominal composition according to the stoichiometric ratio of the preparation (TEM, XRD and EXAFS). The values obtained depend on the structural method used, but the trend air < Ar < H 2 annealed samples is consistent. These results are then used to provide insights regarding the electrocatalytic activity of Pt 3 Sn catalysts for CO, methanol, ethanol and 1-butanol oxidation and the roles of alloyed Sn and SnO 2 .
Journal of materials chemistry. A, Materials for energy and sustainability, 2020
Low cost, high-efficiency catalysts towards water splitting are urgently required to fulfil the i... more Low cost, high-efficiency catalysts towards water splitting are urgently required to fulfil the increasing demand for energy. In this work, low-loading (<20 wt%) Ni-confined in layered metal oxide anode catalysts (birnessite and lepidocrocite titanate) have been synthesized by facile ion exchange methodology and subjected to systematic electrochemical studies. It was found that Ni-intercalated on K-rich birnessite (Ni-KMO) presents an onset overpotential (h onset) as low as 100 mV and overpotential at 10 mA cm À2 (h 10) of 206 mV in pH ¼ 14 electrolyte. By combining electrochemical methods and X-ray absorption and emission spectroscopies (XAS and XES), we demonstrate Ni sites are the active sites for OER catalysis and that the Mn 3+ sites facilitate Ni intercalation during the ion-exchange process, but display no observable contribution towards OER activity. The effect of the pH and the nature of the supporting electrolyte on the electrochemical performance was also evaluated.
Chemical Communications, 2015
Pt and PtSn catalysts were studied for n-butanol electro-oxidation at various temperatures. PtSn ... more Pt and PtSn catalysts were studied for n-butanol electro-oxidation at various temperatures. PtSn showed a higher activity towards butanol electro-oxidation compared to Pt in acidic media. The onset potential for n-butanol oxidation on PtSn is B520 mV lower than that found on Pt, and significantly lower activation energy was found for PtSn compared with that for Pt.
Physical Chemistry Chemical Physics, 2018
Pt nanoparticles dispersed over carbonaceous supports are widely used as catalysts for different ... more Pt nanoparticles dispersed over carbonaceous supports are widely used as catalysts for different applications, making studies on the interplay between size and support effects indispensable for rational catalyst design. Here, we use DFT calculations to simulate the interaction between O, CO, and ethanol with free platinum cuboctahedral nanoparticles with up to 147 atoms and with the same Pt nanoparticles supported on a single layer of graphene with up to 720 carbon atoms. We compute adsorption energies for each adsorbate on different adsorption sites for supported and unsupported Pt nanoparticles. We show that as the Pt nanoparticle grows the adsorption energy decreases, and that the size effect is more important for O and CO adsorption than for ethanol. We observe that the generalized coordination number of each adsorption site controls the interaction strength for O and CO to a much larger extent than for ethanol. Electronic charge redistributions and density of states projected on the d band of the interacting Pt facets are used to obtain a better understanding of the differences between the electronic interactions for each adsorbate. For Pt nanoparticles supported on graphene, the support effects weaken the adsorption energies for all the adsorbates, but this effect rapidly decreases with larger nanoparticles, and it is only significant for our smallest nanoparticle Pt 13. By demonstrating that the effects of nanoparticle size and support are different for ethanol as compared with O and CO, we conclude that it should be possible to modify different parameters in the catalyst design in order to tune the Pt nanoparticle to interact with specific adsorbates.
Physical Chemistry Chemical Physics, 2016
State-of-the-art catalysts are often created via deposition of monolayers, sub-monolayers or nano... more State-of-the-art catalysts are often created via deposition of monolayers, sub-monolayers or nanoparticles of the catalytic material over supports, aiming to increase the surface area and decrease the loading of the catalytic material and therefore the overall cost. Here, we employ large-scale DFT calculations to simulate platinum clusters with up to 309 atoms interacting with single layer graphene supports with up to 880 carbon atoms. We compute the adsorption, cohesion and formation energies of two and three-dimensional Pt clusters interacting with the support, including dispersion interactions via a semi-empirical dispersion correction and a vdW functional. We find that three-dimensional Pt clusters are more stable than the two-dimensional when interacting with the support, and that the difference between their stabilities increases with the system size. Also, the dispersion interactions are more pronounced as we increase the nanoparticle size, being essential to a reliable description of larger systems. We observe inter-atomic expansion (contraction) on the closest (farthest) Pt facets from the graphene sheet and charge redistribution with overall charge being transferred from the platinum clusters to the support. The Pt-Pt expansion, which is related to the charge transfer in the system, correlates with the adsorption energy per Pt atom in contact with the graphene. These, and other electronic and structural observations show that the effect of the support cannot be neglected. Our study provides for the first time, to the best of our knowledge, quantitative results on the non-trivial combination of size and support effects for nanoparticles sizes which are relevant to catalyst design.
Pure and Applied Chemistry, Nov 1, 2020
This glossary provides a formal vocabulary of terms for concepts in surface analysis and gives cl... more This glossary provides a formal vocabulary of terms for concepts in surface analysis and gives clear definitions to those who utilize surface chemical analysis or need to interpret surface chemical analysis results but are not themselves surface chemists or surface spectroscopists.
ACS Applied Materials & Interfaces, Jan 4, 2022
The electrochemical conversion of carbon dioxide (CO 2) to useful chemical fuels is a promising r... more The electrochemical conversion of carbon dioxide (CO 2) to useful chemical fuels is a promising route toward the achievement of carbon neutral and carbon negative energy technologies. Copper (Cu)-and Cu oxide-derived surfaces are known to electrochemically convert CO 2 to high-value and energy-dense products. However, the nature and stability of oxidized Cu species under reaction conditions are the subject of much debate in the literature. Herein, we present the synthesis and characterization of copper-titanate nanocatalysts, with discrete Cu−O coordination environments, for the electrochemical CO 2 reduction reaction (CO 2 RR). We employ real-time in situ X-ray absorption spectroscopy (XAS) to monitor Cu species under neutral-pH CO 2 RR conditions. Combination of voltammetry and on-line electrochemical mass spectrometry with XAS results demonstrates that the titanate motif promotes the retention of oxidized Cu species under reducing conditions for extended periods, without itself possessing any CO 2 RR activity. Additionally, we demonstrate that the specific nature of the Cu−O environment and the size of the catalyst dictate the long-term stability of the oxidized Cu species and, subsequently, the product selectivity.
Physical Chemistry Chemical Physics, 2020
Please note that technical editing may introduce minor changes to the text and/or graphics, which... more Please note that technical editing may introduce minor changes to the text and/or graphics, which may alter content. The journal's standard Terms & Conditions and the Ethical guidelines still apply. In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains.
Faraday Discussions, 2018
Catalysts made of Pt nanoparticles and Pt alloys are considered state-of-the-art catalysts for th... more Catalysts made of Pt nanoparticles and Pt alloys are considered state-of-the-art catalysts for the anodic and cathodic reactions involved in hydrogen fuel cells. The optimal size of such nanoparticles for each chemical reaction is an unsolved problem, which depends on environmental variables, such as reactant concentration, solvent, temperature, etc 1,2. From a theoretical point of view, this problem has been tackled mainly by observing how single key adsorbates react with different nanoparticles in controlled conditions. In this work, we use large-scale DFT calculations to examine the interplay between the Pt nanoparticle size and O coverage effects. We examine single O adsorptions for three adsorption sites on cuboctahedral platinum nanoparticles with different sizes. As we grow the nanoparticle size, the binding strength decreases and we observed a quick convergence of the adsorption energies with increasing nanoparticle size, which correlates with the calculated d-band centre for (111) Pt facets on such nanoparticles. We also carried out a detailed study of the effect of oxygen coverage with varying fractions of O monolayer coverage, computing adsorption energies per O atom for Pt 55 , Pt 147 , and Pt 309 nanoparticles with several O coverages. In general, the increase of O coverage led to weaker adsorption energies per O atom, and when analysing the results in terms of oxygen monolayers, this effect is more pronounced for larger nanoparticles. The O coverage dependency of the adsorption energy per O atom is analysed in terms of the O distribution for each nanoparticle size and electronic changes that the adsorbed oxygen causes to the Pt nanoparticle. In studying nanoparticle size and oxygen coverage effects simultaneously, we offer insights with DFT accuracy to help on heterogeneous catalyst design.
Topics in Catalysis, Jan 19, 2018
Electrochemical oxidation of four different alcohol molecules (methanol, ethanol, n-butanol and 2... more Electrochemical oxidation of four different alcohol molecules (methanol, ethanol, n-butanol and 2-butanol) at electrodeposited Pt film and carbon-supported Pt catalyst film electrodes, as well as the effect of mass transport on the oxidation reaction, has been studied systematically using the rotating disk electrode (RDE) technique. It was shown that oxidation current decreased with an increase in the rotation rate (ω) for all alcohols studied over electrodeposited Pt film electrodes. In contrast, the oxidation current was found to increase with an increase in the ω for Pt/C in ethanol and n-butanol-containing solutions. The decrease was found to be nearly reversible for ethanol and n-butanol at the electrodeposited Pt film electrode ruling out the possibility of intermediate CO ads poisoning being the sole cause of the decrease and was attributed to the formation of soluble intermediate species which diffuse away from the electrode at higher ω. In contrast, an increase in the current with an increase in ω for the carbon supported catalyst may suggest that the increase in residence time of the soluble species within the catalyst layer, results in further oxidation of these species. Furthermore, the reversibility of the peak current on decreasing the ω could indicate that the surface state has not significantly changed due to the sluggish reaction kinetics of ethanol and n-butanol.
Journal of materials chemistry. A, Materials for energy and sustainability, 2023
Lithium metal anodes could be a key component of high energy density rechargeable batteries, but ... more Lithium metal anodes could be a key component of high energy density rechargeable batteries, but uncontrolled growth of Li dendrites, large volume expansion, and unstable solid electrolyte interface films seriously hinder the practical applications of Li metal batteries. In this work, a self-standing threedimensional TiC-modified carbon fibre (TiC@C) network has been fabricated by carbothermal reduction. Binding energy calculations reveal that Li is preferentially plated on TiC rather than the bare C skeleton. The lithiophilic TiC not only serves as a Li nucleation site to assist homogeneous Li deposition, but it also enables rapid Li deposition due to its high electronic conductivity. The 3D conductive structures with high surface area play an important role in reducing the local current density, and also accommodate Li volume changes during repeated cycling. As a result, the TiC@C electrode achieves a nearly zero Li nucleation overpotential and low voltage hysteresis of 150 mV at 2 mA cm −2. Passing 1 mA h cm −2 charge, the coulombic efficiency (CE) was found to be 99.6% over more than 200 cycles. Furthermore, full cells assembled with a LiFePO 4 cathode in a conventional carbonate electrolyte achieve an impressive capacity retention of 87% over 250 cycles. This work demonstrates a novel design of a 3D lithiophilic host for dendrite-free lithium metal anodes.
ChemElectroChem, Jul 1, 2021
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Journal of combinatorial chemistry, Dec 9, 2003
Electrochemical methods Electrochemical methods F 6000 Combinatorial Electrochemical Screening of... more Electrochemical methods Electrochemical methods F 6000 Combinatorial Electrochemical Screening of Fuel Cell Electrocatalysts.-Hardware and software developed for fast sequential measurements of cyclic voltammetric and steady-state currents in a high-surface-area catalyst screening array is used to establish trends in CO electro-oxidation, oxygen reduction, and methanol oxidation on a series of supported Pt/C catalysts as a function of Pt loading and, hence, particle size. Clear trends in characteristics and activities are revealed.
Current Opinion in Electrochemistry, Oct 1, 2019
In situ vibrational spectroscopy can provide molecular level mechanistic insights missing from pu... more In situ vibrational spectroscopy can provide molecular level mechanistic insights missing from purely electrochemical measurements. Surface enhanced Raman spectroscopy (SERS) is a particularly promising method and is employed in aqueous and non-aqueous studies of a variety of electrode reactions. Enhancement of the weak Raman signal is achieved by structuring the electrode surface or by use of SERS probes. This review article highlights the recent use of SERS to study several important electrode reactions; oxygen reduction and evolution, carbon monoxide oxidation and carbon dioxide reduction, and the electrocatalytic oxidation of small organic molecules such as formic acid. Figure 1: A schematic diagram of the study of electrochemical reaction mechanisms using SERS depicting the reactions covered in this review. The SERS substrate electrode must be structured in a manner to provide the SERS enhancement (see Figure 2) and the reactants, intermediates, and products detected must be located in the region in which the enhancement of the Raman signal is strong for effective detection.
Journal of Catalysis, Apr 1, 2021
Low cost, high-efficient catalysts for water splitting can be potentially fulfilled by developing... more Low cost, high-efficient catalysts for water splitting can be potentially fulfilled by developing earth abundant metal oxides. In this work, surface galvanic formation of Co-OH on K0.45MnO2 (KMO) was achieved via the redox reaction of hydrated Co 2+ with crystalline Mn 4+. The synthesis method takes place at ambient temperature without using any surfactant agent or organic solvent, providing a clean, green route for the design of highly efficient catalysts. The redox reaction resulted in the formation of ultrathin Co-OH nanoflakes with high electrochemical surface area. X-ray adsorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) analysis confirmed the changes in the oxidation state of the bulk and surface species on the Co-OH nanoflakes supported on the KMO. The effect of the anions, chloride, nitrate and sulfate, on the preparation of the catalyst was evaluated by electrochemical and spectrochemical means. XPS and Time of flight secondary ion mass spectrometry (ToF-SIMS) analysis demonstrated that the layer of CoOxHy deposited on the KMO and its electronic structure strongly depends on the anion of the precursor used during the synthesis of the catalyst. In particular, it was found that Cl favors the formation of Co-OH, changing the rate determining step of the reaction, which enhances the catalytic activity towards the OER, producing the most active OER catalyst in alkaline media.
Electrochimica Acta, Jul 1, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
CrystEngComm
Ionophore complexes of K(TCNQ˙−)(TCNQ0)n adopt a variety of stacking motifs such as wave-like inf... more Ionophore complexes of K(TCNQ˙−)(TCNQ0)n adopt a variety of stacking motifs such as wave-like infinite TCNQ columns separated by K+-cryptates (left) and K+-π-dimerised cation complexes separated by infinite slipped TCNQ stacks (right).
ACS Applied Materials & Interfaces, 2022
The electrochemical conversion of carbon dioxide (CO 2) to useful chemical fuels is a promising r... more The electrochemical conversion of carbon dioxide (CO 2) to useful chemical fuels is a promising route toward the achievement of carbon neutral and carbon negative energy technologies. Copper (Cu)-and Cu oxide-derived surfaces are known to electrochemically convert CO 2 to high-value and energy-dense products. However, the nature and stability of oxidized Cu species under reaction conditions are the subject of much debate in the literature. Herein, we present the synthesis and characterization of copper-titanate nanocatalysts, with discrete Cu−O coordination environments, for the electrochemical CO 2 reduction reaction (CO 2 RR). We employ real-time in situ X-ray absorption spectroscopy (XAS) to monitor Cu species under neutral-pH CO 2 RR conditions. Combination of voltammetry and on-line electrochemical mass spectrometry with XAS results demonstrates that the titanate motif promotes the retention of oxidized Cu species under reducing conditions for extended periods, without itself possessing any CO 2 RR activity. Additionally, we demonstrate that the specific nature of the Cu−O environment and the size of the catalyst dictate the long-term stability of the oxidized Cu species and, subsequently, the product selectivity.
ACS Applied Energy Materials, 2021
Oxygen electrocatalysis at transition metal oxides is one of the key challenges underpinning elec... more Oxygen electrocatalysis at transition metal oxides is one of the key challenges underpinning electrochemical energy conversion systems, involving a delicate interplay of bulk electronic structure and surface coordination of the active sites. In this work, we investigate for the first time the structure-activity relationship of A2RuMnO7 (A = Dy 3+ , Ho 3+ , Er 3+) nanoparticles, demonstrating how orbital mixing of Ru, Mn, and O promotes high density of states (DOS) at the appropriate energy range for oxygen electrocatalysis. The bulk and surface structure of these multicomponent pyrochlores are investigated by high-resolution transmission electron microscopy, X-ray diffraction, X-ray absorption (XAS), X-ray emission (XES) and X-ray photoemission (XPS) spectroscopies. The materials exhibit high phase purity (cubic fcc with a space group Fd3 � m), in which variations in M-O bonds length are less than 1% upon replacing the A-site lanthanide. XES and XPS show that the mean oxidation state at the Mn-site as well as the nanoparticle surface composition were slightly affected by the lanthanide. The pyrochlore nanoparticles are significantly more active than the binary RuO2 and MnO2 towards the 4-electron oxygen reduction reaction (ORR) in alkaline solutions. Interestingly, normalization of kinetic parameters by the number density of electroactive sites concludes that Dy2RuMnO7 shows twice higher activity than benchmark materials such as LaMnO3. Analysis of the electrochemical profiles supported by DFT calculations reveals that the origin of the enhanced catalytic activity is linked to the mixing of Ru and Mn d-orbitals and O p-orbitals at the conduction band which strongly overlap with the formal redox energy of O2 in solution. The activity enhancement strongly manifests in the case of Dy2RuMnO7 where Ru/Mn ratio is closer to 1 in comparison with the Ho 3+ and Er 3+ analogs. These electronic effects are discussed in the context of the Gerischer formalism for electron transfer at the semiconductor/electrolyte junctions.
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Papers by Andrea E Russell