134 results found
Tort R, Bagger A, Westhead O, et al., 2023, Searching for the Rules of Electrochemical Nitrogen Fixation., ACS Catal, Vol: 13, Pages: 14513-14522, ISSN: 2155-5435
Li-mediated ammonia synthesis is, thus far, the only electrochemical method for heterogeneous decentralized ammonia production. The unique selectivity of the solid electrode provides an alternative to one of the largest heterogeneous thermal catalytic processes. However, it is burdened with intrinsic energy losses, operating at a Li plating potential. In this work, we survey the periodic table to understand the fundamental features that make Li stand out. Through density functional theory calculations and experimentation on chemistries analogous to lithium (e.g., Na, Mg, Ca), we find that lithium is unique in several ways. It combines a stable nitride that readily decomposes to ammonia with an ideal solid electrolyte interphase, balancing reagents at the reactive interface. We propose descriptors based on simulated formation and binding energies of key intermediates and further on hard and soft acids and bases (HSAB principle) to generalize such features. The survey will help the community toward electrochemical systems beyond Li for nitrogen fixation.
Pedersen A, Bagger A, Barrio J, et al., 2023, Atomic metal coordinated to nitrogen-doped carbon electrocatalysts for proton exchange membrane fuel cells: a perspective on progress, pitfalls and prospectives., J Mater Chem A Mater, Vol: 11, Pages: 23211-23222, ISSN: 2050-7488
Proton exchange membrane fuel cells require reduced construction costs to improve commercial viability, which can be fueled by elimination of platinum as the O2 reduction electrocatalyst. The past 10 years has seen significant developments in synthesis, characterisation, and electrocatalytic performance of the most promising alternative electrocatalyst; single metal atoms coordinated to nitrogen-doped carbon (M-N-C). In this Perspective we recap some of the important achievements of M-N-Cs in the last decade, as well as discussing current knowledge gaps and future research directions for the community. We provide a new outlook on M-N-C stability and atomistic understanding with a set of original density functional theory simulations.
Páez Fajardo GJ, Fiamegkou E, Gott JA, et al., 2023, Synergistic Degradation Mechanism in Single Crystal Ni-Rich NMC//Graphite Cells, ACS Energy Letters, Pages: 5025-5031, ISSN: 2380-8195
Sarma SC, Barrio J, Bagger A, et al., 2023, Reaching the fundamental limitation in CO2 reduction to CO with single atom catalysts, Advanced Functional Materials, Vol: 33, ISSN: 1616-301X
The electrochemical CO2 reduction reaction (CO2RR) to value-added chemicals with renewable electricity is a promising method to decarbonize parts of the chemical industry. Recently, single metal atoms in nitrogen-doped carbon (MNC) have emerged as potential electrocatalysts for CO2RR to CO with high activity and faradaic efficiency, although the reaction limitation for CO2RR to CO is unclear. To understand the comparison of intrinsic activity of different MNCs, two catalysts are synthesized through a decoupled two-step synthesis approach of high temperature pyrolysis and low temperature metalation (Fe or Ni). The highly meso-porous structure results in the highest reported electrochemical active site utilization based on in situ nitrite stripping; up to 59±6% for NiNC. Ex situ X-ray absorption spectroscopy (XAS) confirms the penta-coordinated nature of the active sites. The catalysts are amongst the most active in the literature for CO2 reduction to CO. The density functional theory calculations (DFT) show that their binding to the reaction intermediates approximates to that of Au surfaces. However, it is found that the turnover frequencies (TOFs) of the most active catalysts for CO evolution converge, suggesting a fundamental ceiling to the catalytic rates.
Favero S, Stephens IEL, Titirici M-M, 2023, Deconvoluting kinetics and transport effects of ionic liquid layers on FeN4-based oxygen reduction catalysts, EES Catalysis, Vol: 1, Pages: 742-754, ISSN: 2753-801X
The use of ionic liquid layers has been reported to improve both the activity and durability of several oxygen reduction catalysts. However, the development of this technology has been hindered by the lack of understanding of the mechanism behind this performance enhancement. In this work, we use a library of ionic liquids to modify a model FeN4 catalyst (iron phthalocyanine), to decouple the effects of ionic liquid layers on oxygen reduction kinetics and oxygen transport. Our results show that oxygen reduction activity at low overpotentials it determined by the ionic liquids’ influence on the *OH binding energy on the active sites, while oxygen solubility and diffusivity controls transport at high overpotentials. Finally, using nitrogen physisorption, we have demonstrated that the distribution of the ionic liquids on the catalyst is inhomogeneous, and depends on the nature of the ionic liquid used.
Stephens IEL, 2023, (Invited) Correlative Spectroscopy to Elucidate the Factors Controlling the Kinetics of Oxygen Evolution, ECS Meeting Abstracts, Vol: MA2023-01, Pages: 2513-2513
<jats:p> It is particularly challenging to catalyse oxygen evolution under the acidic conditions of polymer electrolyte membrane (PEM) electrolysers. All compounds, apart from IrO<jats:sub>x</jats:sub> and RuO<jats:italic> <jats:sub>x</jats:sub> </jats:italic>, are catalytically inactive or unstable. In alkaline electrolysers, a wider range of materials are available, including non precious metal oxides based on Co and Ni.</jats:p> <jats:p>Herein, I will discuss our recent mechanistic studies on model oxygen evolution catalysts, including RuOx, IrOx, doped CoO<jats:sub>x</jats:sub>H<jats:sub>y</jats:sub> and NiO<jats:sub>x</jats:sub>H<jats:sub>y</jats:sub>.<jats:sup>1-6</jats:sup> I will correlate operando spectroscopy to X-ray absorption spectroscopy, to reveal the factors controlling the factors controlling the kinetics for water oxidation. Density functional theory measurements provide a molecular scale explanation for the observed phenomena.</jats:p> <jats:p>1 Rao, R. R., Corby, S., Bucci, A., Garcia-Tecedor, M., Mesa, C. A., Rossmeisl, J., Gimenez, S., Lloret-Fillol, J., Stephens, I. E. L. & Durrant, J. R. <jats:bold> <jats:italic>J. Am. Chem. Soc.</jats:italic> </jats:bold> 144, 7622, (2022).</jats:p> <jats:p>2 Bozal-Ginesta, C., Rao, R. R., Mesa, C. A., Wang, Y. X., Zhao, Y. Y., Hu, G. F., Anton-Garcia, D., Stephens, I. E. L., Reisner, E., Brudvig, G. W., Wang, D. W. & Durrant, J. R. <jats:bold> <jats:italic>J. Am. Chem. Soc.</jats:italic> </jats:bold> 144, 8454, (2022).</jats:p> <jats:p>3 Rao, R. R., Stephens, I. E. L. & Durrant, J. R. <jats:bold> &
Westhead O, Tort R, Spry M, et al., 2023, The origin of overpotential in lithium-mediated nitrogen reduction, FARADAY DISCUSSIONS, Vol: 243, Pages: 321-338, ISSN: 1359-6640
Mukadam Z, Liu S, Pedersen A, et al., 2023, Furfural electrovalorisation using single-atom molecular catalysts, ENERGY & ENVIRONMENTAL SCIENCE, Vol: 16, Pages: 2934-2944, ISSN: 1754-5692
Liu S, Mukadam Z, Scott SB, et al., 2023, Unraveling the reaction mechanisms for furfural electroreduction on copper., EES Catal, Vol: 1, Pages: 539-551
Electrochemical routes for the valorization of biomass-derived feedstock molecules offer sustainable pathways to produce chemicals and fuels. However, the underlying reaction mechanisms for their electrochemical conversion remain elusive. In particular, the exact role of proton-electron coupled transfer and electrocatalytic hydrogenation in the reaction mechanisms for biomass electroreduction are disputed. In this work, we study the reaction mechanism underlying the electroreduction of furfural, an important biomass-derived platform chemical, combining grand-canonical (constant-potential) density functional theory-based microkinetic simulations and pH dependent experiments on Cu under acidic conditions. Our simulations indicate the second PCET step in the reaction pathway to be the rate- and selectivity-determining step for the production of the two main products of furfural electroreduction on Cu, i.e., furfuryl alcohol and 2-methyl furan, at moderate overpotentials. We further identify the source of Cu's ability to produce both products with comparable activity in their nearly equal activation energies. Furthermore, our microkinetic simulations suggest that surface hydrogenation steps play a minor role in determining the overall activity of furfural electroreduction compared to PCET steps due to the low steady-state hydrogen coverage predicted under reaction conditions, the high activation barriers for surface hydrogenation and the observed pH dependence of the reaction. As a theoretical guideline, low pH (<1.5) and moderate potential (ca. -0.5 V vs. SHE) conditions are suggested for selective 2-MF production.
Westhead O, Spry M, Bagger A, et al., 2023, The role of ion solvation in lithium mediated nitrogen reduction, Journal of Materials Chemistry A, Vol: 11, Pages: 12746-12758, ISSN: 2050-7488
Since its verification in 2019, there have been numerous high-profile papers reporting improved efficiency of lithium-mediated electrochemical nitrogen reduction to make ammonia. However, the literature lacks any coherent investigation systematically linking bulk electrolyte properties to electrochemical performance and Solid Electrolyte Interphase (SEI) properties. In this study, we discover that the salt concentration has a remarkable effect on electrolyte stability: at concentrations of 0.6 M LiClO4 and above the electrode potential is stable for at least 12 hours at an applied current density of −2 mA cm−2 at ambient temperature and pressure. Conversely, at the lower concentrations explored in prior studies, the potential required to maintain a given N2 reduction current increased by 8 V within a period of 1 hour under the same conditions. The behaviour is linked more coordination of the salt anion and cation with increasing salt concentration in the electrolyte observed via Raman spectroscopy. Time of flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy reveal a more inorganic, and therefore more stable, SEI layer is formed with increasing salt concentration. A drop in faradaic efficiency for nitrogen reduction is seen at concentrations higher than 0.6 M LiClO4, which is attributed to a combination of a decrease in nitrogen solubility and diffusivity as well as increased SEI conductivity as measured by electrochemical impedance spectroscopy.
Barrio J, Pedersen A, Sarma SC, et al., 2023, FeNC Oxygen Reduction Electrocatalyst with High Utilization Penta-Coordinated Sites, ADVANCED MATERIALS, Vol: 35, ISSN: 0935-9648
Becker H, Murawski J, Shinde DV, et al., 2023, Impact of impurities on water electrolysis: a review, SUSTAINABLE ENERGY & FUELS, Vol: 7, Pages: 1565-1603, ISSN: 2398-4902
Westhead O, Barrio J, Bagger A, et al., 2023, Near ambient N<sub>2</sub> fixation on solid electrodes versus enzymes and homogeneous catalysts (vol 7, pg 184, 2023), NATURE REVIEWS CHEMISTRY, Vol: 7, Pages: 225-225
Westhead O, Barrio J, Bagger A, et al., 2023, Near ambient N2 fixation on solid electrodes versus enzymes and homogeneous catalysts, Nature Reviews Chemistry, Vol: 7, Pages: 184-201, ISSN: 2397-3358
The Mo/Fe nitrogenase enzyme is unique in its ability to efficiently reduce dinitrogen to ammonia at atmospheric pressures and room temperature. Should an artificial electrolytic device achieve the same feat, it would revolutionise fertilizers and even provide an energy dense, truly carbon-free fuel. This Review provides a coherent comparison of recent progress made in dinitrogen fixation on (i) solid electrodes, (ii) homogeneous catalysts and (iii) nitrogenases. Specific emphasis is placed on systems for which there is unequivocal evidence that dinitrogen reduction has taken place. By establishing the cross-cutting themes and synergies between these systems, we identify viable avenues for future research.
Spry M, Westhead O, Tort R, et al., 2023, Water increases the Faradaic selectivity of Li-mediated nitrogen reduction, ACS ENERGY LETTERS, Vol: 8, Pages: 1230-1235, ISSN: 2380-8195
The lithium-mediated system catalyzes nitrogen to ammonia under ambient conditions. Herein we discover that trace amount of water as an electrolyte additive─in contrast to prior reports from the literature–can effect a dramatic improvement in the Faradaic selectivity of N2 reduction to NH3. We report that an optimal water concentration of 35.9 mM and LiClO4 salt concentration of 0.8 M allows a Faradaic efficiency up to 27.9 ± 2.5% at ambient pressure. We attribute the increase in Faradaic efficiency to the incorporation of Li2O in the solid electrolyte interphase, as suggested by our X-ray photoelectron spectroscopy measurements. Our results highlight the extreme sensitivity of lithium-mediated N2 reduction to small changes in the experimental conditions.
Petersen AS, Jensen KD, Wan H, et al., 2023, Modeling Anion Poisoning during Oxygen Reduction on Pt Near-Surface Alloys, ACS CATALYSIS, ISSN: 2155-5435
Tort R, Westhead O, Spry M, et al., 2023, Nonaqueous Li-mediated nitrogen reduction: taking control of potentials, ACS Energy Letters, Vol: 8, Pages: 1003-1009, ISSN: 2380-8195
The performance of the Li-mediated ammonia synthesis has progressed dramatically since its recent reintroduction. However, fundamental understanding of this reaction is slower paced, due to the many uncontrolled variables influencing it. To address this, we developed a true nonaqueous LiFePO4 reference electrode, providing both a redox anchor from which to measure potentials against and estimates of sources of energy efficiency loss. We demonstrate its stable electrochemical potential in operation using different N2- and H2-saturated electrolytes. Using this reference, we uncover the relation between partial current density and potentials. While the counter electrode potential increases linearly with current, the working electrode remains stable at lithium plating, suggesting it to be the only electrochemical step involved in this process. We also use the LiFePO4/Li+ equilibrium as a tool to probe Li-ion activity changes in situ. We hope to drive the field toward more defined systems to allow a holistic understanding of this reaction.
Westhead O, Spry M, Bagger A, et al., 2023, Correction: The role of ion solvation in lithium mediated nitrogen reduction, Journal of Materials Chemistry A, Vol: 11, Pages: 13039-13039, ISSN: 2050-7488
Correction for ‘The role of ion solvation in lithium mediated nitrogen reduction’ by O. Westhead et al., J. Mater. Chem. A, 2023, https://doi.org/10.1039/D2TA07686A.
Pedersen A, Pandya J, Leonzio G, et al., 2023, Comparative techno-economic and life-cycle analysis of precious <i>versus</i> non-precious metal electrocatalysts: the case of PEM fuel cell cathodes, Green Chemistry, ISSN: 1463-9262
<jats:p>Fe–N–C catalyst production outperforms Pt/C from an enviro-economic viewpoint, but further Fe–N–C activity development is required before deployment in PEMFCs.</jats:p>
Luo H, Yukuhiro VY, Fernandez PS, et al., 2022, Role of Ni in PtNi Bimetallic Electrocatalysts for Hydrogen and Value-Added Chemicals Coproduction via Glycerol Electrooxidation, ACS CATALYSIS, Vol: 12, Pages: 14492-14506, ISSN: 2155-5435
Eder S, Ding B, Thornton DB, et al., 2022, Squarephaneic tetraanhydride: a conjugated square‐shaped cyclophane for the synthesis of porous organic materials, Angewandte Chemie International Edition, Vol: 61, Pages: 1-8, ISSN: 1433-7851
Aromatic carboxylic anhydrides are ubiquitous building blocks in organic materials chemistry and have received considerable attention in the synthesis of organic semiconductors, pigments, and battery electrode materials. Here we extend the family of aromatic carboxylic anhydrides with a unique new member, a conjugated cyclophane with four anhydride groups. The cyclophane is obtained in a three-step synthesis and can be functionalised efficiently, as shown by the conversion into tetraimides and an octacarboxylate. Crystal structures reveal the high degree of porosity achievable with the new building block. Excellent electrochemical properties and reversible reduction to the tetraanions are shown for the imides; NMR and EPR measurements confirm the global aromaticity of the dianions and evidence the global Baird aromaticity of the tetraanions. Considering the short synthesis and unique properties, we expect widespread use of the new building block in the development of organic materials.
Spry M, Westhead O, Barrio J, et al., 2022, An in-Situ FTIR Study of Lithium-Mediated Electrochemical Nitrogen Reduction, ECS Meeting Abstracts, Vol: MA2022-02, Pages: 1928-1928
<jats:p> Electrochemical ammonia synthesis under ambient conditions is a promising sustainable alternative to the highly carbon-intensive Haber-Bosch process. The lithium-mediated system<jats:sup>1</jats:sup> is to date the only rigorously verified method of reducing dinitrogen that has been reproduced by several laboratories; nonetheless, its mechanism is not yet understood. It is generally accepted that lithium is key to the success of this system. Metallic lithium binds strongly to dinitrogen and can directly reduce it under ambient conditions. However, it is possible that the apparently unique ability of this system to reduce dinitrogen under ambient conditions lies in its formation of a Solid Electrolyte Interphase (SEI)<jats:sup>2</jats:sup> on the working electrode, like those formed in lithium-ion batteries. This likely provides a kinetic barrier to the competing hydrogen evolution reaction by moderating, but not blocking, proton mobility, thus favouring nitrogen reduction.</jats:p> <jats:p>While some post-mortem characterisation of the SEI for this system has been published<jats:sup>3</jats:sup>, specific SEI forming reactions and the roles of SEI species in the success of the lithium-mediated system are not yet understood. Optimising this system requires optimisation of the properties of the SEI. It is therefore highly desirable to identify key components which govern its properties and develop a mechanistic understanding of their formation. Just as lithium-ion battery electrolytes are tailored to optimise SEI properties, a deeper understanding of the formation of SEI species from bulk electrolyte components in this system would then inform specific tailoring of the electrolyte to optimise selectivity towards nitrogen reduction. Some reports thus far<jats:sup>1,4,5</jats:sup> have proposed that electrodeposited metallic lithium reduces dinitrogen<jats:sup>1</jats:sup
Stephens IEL, Chan K, Bagger A, et al., 2022, 2022 roadmap on low temperature electrochemical CO<sub>2</sub> reduction, JOURNAL OF PHYSICS-ENERGY, Vol: 4, ISSN: 2515-7655
Sarma SC, Barrio J, Titirici M, et al., 2022, Tuning CO<sub>2</sub> to CO Conversion on Metal-Doped Carbon Catalysts, ECS Meeting Abstracts, Vol: MA2022-01, Pages: 1613-1613
<jats:p> One of the significant challenges faced during electrochemical CO<jats:sub>2</jats:sub> reduction (ECO<jats:sub>2</jats:sub>RR) is the low selectivity of the products obtained. The best example is polycrystalline Cu, which can electrochemically produce hydrocarbons and alcohols but with poor selectivity.<jats:sup>1, 2</jats:sup> To date, high selectivity has been achieved only towards CO and formate on Au and Sn surface, respectively but scalability and commercialization are limited owing to their cost and stability. Metal-nitrogen-carbon (MNC) materials are comparable to Au or Ag catalysts, albeit with their lower overpotentials, higher mass activity and high selectivity toward CO.<jats:sup>3</jats:sup> <jats:sup>,</jats:sup> <jats:sup>4</jats:sup> During the pyrolysis of N-containing carbon molecules, different chemical functionalities such as pyridinic, pyrrolic and graphitic N atoms can be formed, each behaving as a product-specific active site. <jats:sup>5</jats:sup> It is still debatable whether pyrdinic or pyrrolic N is responsible for CO<jats:sub>2</jats:sub>RR activity; thus, it remains unclear how to favor CO<jats:sub>2</jats:sub> reduction over hydrogen evolution.</jats:p> <jats:p>In this work, we aimed to synthesize C<jats:sub>2</jats:sub>N-like covalent organic frameworks, with 8-10 Å pore size, tailored to host dual atoms coordinated to nitrogen. Such sites are expected to favor C-C coupling and produce multi-carbon products during ECO<jats:sub>2</jats:sub>RR. A step-by-step synthetic approach was employed to optimize the CO<jats:sub>2</jats:sub>RR:HER ratio through: <jats:list list-type="bullet"> <jats:list-item> <jats:p>Tuning carbon:nitrogen ratio using two
Thornton DB, Davies B, Scott S, et al., 2022, Probing Crossover Degradation Effects in Nickel-Rich LiNi<sub>x</sub>Mn<sub>y</sub>Co<sub>z</sub>O<sub>2</sub> Lithium-Ion Battery Cathodes with Ultrasensitive on-Chip Electrochemistry Mass Spectrometry, ECS Meeting Abstracts, Vol: MA2022-01, Pages: 350-350
<jats:p> Performance improvements in electric vehicle batteries are needed in order to reduce their cost and encourage greater use.<jats:sup>1</jats:sup> This improvement is dependent on the properties (e.g. specific capacity and stability) of the cathode active material in the electric vehicle’s lithium ion battery.<jats:sup>1</jats:sup> Lithium Nickel Cobalt Manganese Oxide (NMC) is a layered transition metal oxide that shows great promise as an electrode in lithium ion batteries for electric vehicles, with a high theoretical specific capacity and good stability in the layered structure.<jats:sup>2</jats:sup> As the nickel content of the cathode material increases, so does the discharge capacity, however this increase comes at the cost of significantly decreased capacity retention.<jats:sup>1</jats:sup> The mechanisms that contribute to this degradation are complex and interlinking and many of them are accompanied by some form of gas evolution. For example, the solid electrolyte interphase (SEI) formation at the cathode evolves CO<jats:sub>2</jats:sub>, which is able to crossover and contribute to solid electrolyte interphase formation at the anode.<jats:sup>1</jats:sup> Similarly, upon electrochemical cycling a reactive form of oxygen can be evolved from the NMC lattice, resulting in a cascade of parasitic reactions within a lithium-ion battery.<jats:sup>2</jats:sup> </jats:p> <jats:p>Herein, we probe these gas evolving degradation mechanisms through the development and use of a novel type of electrochemistry mass spectrometry (EC-MS) with unprecedented time resolution and sensitivity.<jats:sup>3,4</jats:sup> The new technique, known as on-chip EC-MS, employs a microfabricated membrane chip to precisely control the transfer of volatile species from an electrochemical cell to a mass spectrometer. Its design also allo
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"></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
Barrio J, Pedersen A, Feng J, et al., 2022, Targeted Synthesis of Metal Dual Atom Electrocatalysts, ECS Meeting Abstracts, Vol: MA2022-01, Pages: 629-629
<jats:p> Natural enzymes present within their structure active centres composed of earth-abundant metals in atomic proximity. Such active sites, dual atom catalysts, display a unique efficiency in catalytic processes such as the nitrogen conversion to ammonia, the production of ethylene through C-C coupling, or the oxygen reduction reaction in fuel cells amongst others.<jats:sup>1,2</jats:sup> Theoretical calculations suggest that the high catalytic activity of dual atom catalysts arises from the different binding mode of reactant molecules to that of metal foils and single atom catalysts, which allows to break transition scaling relationships.<jats:sup>3</jats:sup> Nevertheless, the experimental synthesis and characterisation of this class of materials is highly challenging.<jats:sup>4</jats:sup> It is particularly difficult to avoid the formation of single atom catalysts or nanoparticles. In this work we show a general approach to fabricate bioinspired Fe dual atom catalysts in a nitrogen doped carbon support; we test the catalyst for the oxygen reduction reaction under acidic conditions. The catalyst exhibited an activity of 2.4 ± 0.3 A g<jats:sup>-1</jats:sup> <jats:sub>carbon</jats:sub> at 0.8 V versus a reversible hydrogen electrode in acidic media, comparable to the most active in the literature. The two-step procedure leads to well defined Fe-based dimers. We characterised these materials by means of X-ray absorption spectroscopy (XAS) and scanning transmission electron microscopy. Our general approach providing a new towards targeted synthesis of dual atom electrocatalysts for energy-critical reactions.</jats:p> <jats:p>References</jats:p> <jats:p>(1) Chen, J. G.; Crooks, R. M.; Seefeldt, L. C.; Bren, K. L.; Bullock, R. M.; Darensbourg, M. Y.; Holland, P. L.; Hoffman, B.; Janik, M. J.; Jones, A. K.; Kanatzidis, M. G
Oates RP, Murawski J, Hor C, et al., 2022, How to Impede Hydrogen Evolution on Carbon Based Materials?, ECS Meeting Abstracts, Vol: MA2022-01, Pages: 1481-1481
<jats:p> Hydrogen is a highly attractive zero-emission energy sector. However, in many electrochemical systems, such as carbon dioxide reduction, batteries and supercapacitors hydrogen evolution reaction (HER) is an undesired competing reaction. It is therefore important to tailor these electrochemical systems in order to minimise hydrogen production. Carbon black materials are often added to the catalyst layers as they are low cost, abundant, inert, and have a high conductivity and surface area. This work has investigated HER activities for seven different commercial carbon materials to identify the required structural properties of carbon for minimizing the hydrogen evolution reaction.</jats:p> <jats:p>Rotating disk electrode, X-ray diffraction, and nitrogen adsorption/ desorption were used to determine the electrochemical and physical characteristics of the carbon materials. An on-chip electrochemical mass spectrometer was used to further probe the gaseous products being produced at the electrode <jats:italic>insitu; </jats:italic>we established that the exact onset of the HER at -0.4 V vs RHE, as shown in Figure 1. Furthermore, we have correlated our electrochemical experiments to earlier characterization data on the same carbon materials, including: X-ray photoelectron spectroscopy, elemental analysis (e.g. Fe, H, S, C) using neutron activation analysis.<jats:sup>1</jats:sup> Our results indicate that the most graphitic carbons with low amount of metal impurities are the best for inhibiting H<jats:sub>2 </jats:sub>evolution.</jats:p> <jats:p> <jats:list list-type="roman-lower"> <jats:list-item> <jats:p>V Čolić, S. Yang, Z Révay, I E L Stephens & I Chorkendorff, <jats:italic>Electrochim</jats:italic> <jats:italic>Acta, &l
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