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The first article of Alan Gibson's thesis
The first article of Alan Gibson's thesis
Dual-Pathway Mechanism and Nonlinear Dynamics in the Electrooxidation of Methanol on Platinum
ACS Catal. 2025, 15, 12598-12609
Elucidating the mechanism of the electro-oxidation of alcohols on Pt is critical for applications ranging from energy conversion and storage to the chemicals industry and catalyst development. In the work reported here, time-resolved ATR-SEIRA spectra were recorded during the oscillatory electrooxidation of methanol on Pt electrodes, under galvanostatic conditions. Correlations between the coverages of adsorbed CO and bidentate adsorbed formate observed during the potential oscillations confirm that adsorbed CO is the main intermediate in the complete oxidation of methanol to CO2, while adsorbed formate mediates partial oxidation of methanol to formic acid and methyl formate. UV−vis reflectance measurements revealed a shift in the oxidation of the Pt surface to more positive potentials in the presence of methanol, as a consequence of methanol and Pt oxidation reactions competing for adsorbed OH. Combined with the ATR-SEIRAS results, this work provides spectroscopic evidence for the involvement of surface oxides in the oscillatory behavior. In particular, we show how chaotic oscillations emerge due to, and are mediated by, the competition between methanol and surface oxidation reactions for adsorbed OH.
The first results of a fruitful collaboration with Victor Yiukuhiro and Pablo Sebastian Fernandez from Universidade Estadual de Campinas
The first results of a fruitful collaboration with Victor Yiukuhiro and Pablo Sebastian Fernandez from Universidade Estadual de Campinas
Alkaline-Metal Cations Affect Pt Deactivation for the Electrooxidation of Small Organic Molecules by Affecting the Formation of Inactive Pt Oxide
J. Am. Chem. Soc. 2025, 146, 27745-27754
The activity of Pt for the electro-oxidation of several organic molecules changes with the cation of the electrolyte. It has been proposed that the underlying reason behind that effect is the so-called noncovalent interactions between the hydrated cations and adsorbed OH (OHad). However, there is a lack of spectroscopic evidence for this phenomenon, resulting in an incomplete understanding at the microscopic level of these electrochemical processes. Herein, we explore the electro-oxidation of glycerol (EOG) on platinum (Pt) in LiOH, NaOH and KOH using in situ surface-enhanced infrared absorption spectroscopy in the attenuated total reflectance mode (ATR-SEIRAS) and in situ X-ray absorption spectroscopy (XAS). Our results show that the electrolyte cation influences the rate and potential at which adsorbed CO (COad), a catalytic poison, is formed and oxidized. We attribute this to the cation-dependent stability of oxygenated species on the metallic Pt surface and the different intensities of the electric field at the electrode/electrolyte interface. We also demonstrate that the formation of an inactive Pt oxide layer is indirectly also cation-dependent: the formation of this layer is triggered by the cation-dependent oxidative removal of reaction intermediates (for instance, CO). This phenomenon explains the well-known cation-induced differences in the voltammetric profiles, of not just glycerol, but generally of alcohols and polyols.
The first article of Jani Shibuya's thesis. The seed of his spin-off Hychor and of two patent applications.
The first article of Jani Shibuya's thesis. The seed of his spin-off Hychor and of two patent applications.
Putting stored hydrogen to work without consuming it: A flexible system for energy conversion and water desalination
J. Power Sources 2024, 613, 234906
We report a flow battery that utilises hydrogen as a charge carrier in both the cathode and anode and makes use of the energy released in acid-base neutralisation to desalinate seawater and generate electricity, based on cheap and relatively safe electrolytes stored externally. We demonstrate desalination of simulated seawater from 0.6 to 0.009 ± 0.005 M NaCl and successful removal of Na+, K+, Mg2+, and Ca2+ from real seawater to potable levels. The battery can also be used for osmotic energy conversion through reverse electrodialysis (RED) if the acid and base are substituted by neutral diluted aqueous solution (e.g., freshwater), reaching power densities similar to state-of-the-art systems while using a much more environmentally friendly redox charge carrier, namely hydrogen, than those common in RED systems. The most important characteristics of the reported system are (i) its flexibility, which allows easy tuning to favour either energy generation or degree of desalination by changing the flow rates and volumes of each individual channel and/or the discharge current and (ii) the possibility of putting hydrogen to work without consuming it while stored for later shipment, thereby producing a profit that can contribute to decreasing the cost of green hydrogen.
Between 2023 and 2025 we have published several articles focusing on the structure of aqueous and non-aqueous electrode-electrolyte interfaces. This work was funded by the Leverhulme Trust and also involved the collaboration of Nandita Mohandas and Tharangattu N. Narayana from the Tata Institute of Fundamental Research-Hyderabad, India.
Between 2023 and 2025 we have published several articles focusing on the structure of aqueous and non-aqueous electrode-electrolyte interfaces. This work was funded by the Leverhulme Trust and also involved the collaboration of Nandita Mohandas and Tharangattu N. Narayana from the Tata Institute of Fundamental Research-Hyderabad, India.
Double-layer structure and cation-dependent solvent decomposition in acetonitrile-based electrolytes
J. Solid State Electrochem. 2025, 29, 2213-2224
We present an analysis of the microscopic structure of the interface between a gold electrode and acetonitrile-based electrolytes, utilising surface-enhanced infrared absorption spectroscopy in attenuated total reflection mode (ATR-SEIRAS) combined with voltammetric data. The investigation focuses on the potential-induced changes in the interactions between interfacial acetonitrile molecules and on the onset of reductive acetonitrile decomposition in Li+- and Na+-containing electrolytes. The acetonitrile molecules exhibit a potential-dependent reorientation, leading to an increase in the concentration of antiparallel dimers at the interface at negative potentials, as the nitrogen end of the molecule is pushed away from the surface. The initial stages of reductive decomposition of acetonitrile are different in the Li+- and Na+-based electrolytes. Spectral signatures characteristic of amines are seen in LiClO4 acetonitrile solutions, while amide bands are also observed in NaClO4. Because traces of water in acetonitrile must be the proton source for the reduction of interfacial acetonitrile to amines and amides, OH− must also be generated during those processes. In fact, ATR-SEIRA spectra reveal the formation and subsequent precipitation of LiOH. Precipitation of NaOH in NaClO4 seems to be absent, though. With increasingly negative potential, the reductive cleavage of acetonitrile results in the formation of several cyanide species. The corresponding cyanide-characteristic bands show a potential-dependent stretching frequency that suggests they correspond to adsorbed species. These findings highlight the effect of potential-induced solvent reorientation on solvent–solvent interactions at the interface as well as the impact of the electrolyte cation on the products of the reductive decomposition of acetonitrile.
Understanding electrochemical interfaces through comparing experimental and computational charge density-potential curves
Chem. Sci. 2024, 15, 6643-6660
Electrode–electrolyte interfaces play a decisive role in electrochemical charge accumulation and transfer processes. Theoretical modelling of these interfaces is critical to decipher the microscopic details of such phenomena. Different force field-based molecular dynamics protocols are compared here in a view to connect calculated and experimental charge density–potential relationships. Platinum–aqueous electrolyte interfaces are taken as a model. The potential of using experimental charge density–potential curves to transform cell voltage into electrode potential in force-field molecular dynamics simulations, and the need for that purpose of developing simulation protocols that can accurately calculate the double-layer capacitance, are discussed.
Water at electrode-electrolyte interfaces: combining HOD vibrational spectra with ab initio-molecular dynamics simulations
Chem. Sci. 2024, 15, 17469-17480
We have undertaken a vibrational study of the structure of interfacial water and its potential dependence using H2O:D2O mixtures to explore the O–H and O–D stretching modes of HOD as well as the bending modes of HOD and H2O. Due to the symmetry reduction, some of the complexity characteristic of the vibrational spectrum of water is removed in HOD. Coupled with potential-dependent ab initio simulations of the gold–water interface, this has enabled a deeper insight into the hydrogen-bond network of interfacial water and into how it is affected by the applied potential. Possibly the most important conclusions of our work are (i) the absence of any ice-like first layer of interfacial water at any potential and (ii) that interfacial water reorients around a stable backbone of hydrogen bonds roughly parallel to the electrode surface. At E > pzc, interfacial water molecules are oriented with the oxygen lone pairs towards the surface and form exclusively or nearly exclusively hydrogen-donating hydrogen bonds with other water molecules. At E < pzc, the oxygen lone pairs instead point away from the surface, but the population of hydrogen-donating water molecules does not vanish. In fact, the population of hydrogen-accepting water molecules only dominates at considerably negative charge densities, due to the weak interaction of the hydrogen atoms of interfacial water molecules with the Au surface.
Tailoring the Interfacial Water Structure by Electrolyte Engineering for Selective Electrocatalytic Reduction of Carbon Dioxide
ACS Catal. 2023, 13, 8384-8393
Engineering aqueous electrolytes with low amounts of additives to achieve a tunable CO2 reduction product is an underexplored territory in electrocatalysis. Here, we show the enhancement of the Faradaic efficiency (FE) of CO2 reduction to CO on unmodified polycrystalline gold from ∼67 to ∼94% by the addition of up to 15 mol % of N,N-dimethylformamide (DMF) to an aqueous electrolyte. The role of electrolyte structure modification near the electrode−electrolyte interface was studied using in situ surface-enhanced infrared absorption spectroscopy in attenuated total reflection mode (ATR-SEIRAS). In addition to the expected detection of the adsorbed CO (COad) intermediate present on the Au surface, in both the linearly bonded and bridge-bonded forms, we observed changes in the structure of interfacial water induced by the addition of DMF. The changes in the water stretching band and the DMF carbonyl band indicate an increase in the strongly hydrogen-bonded DMF−water pairs with increasingly negative potential near the interface in the presence of DMF. We hold this interfacial water structure modification by DMF responsible for increasing the CO2RR FE and decreasing the the competing hydrogen evolution reaction (HER). Furthermore, the suppression of the HER is observed in other electrolytes and also when platinum was used as an electrode and hence can be a potential method for increasing the product selectivity of complex electrocatalytic reactions.
20-22 March 2023
We've been visiting Victor Climent's Group at the University of Alicante learning how to perform laser-induced T-jump experiments. Ready now to couple the technique with infrared spectroscopy in our ongoing collaboration. Thank you very much to Natalia, Pepe and Victor for being so wellcoming and teaching us so much!
The last of the articles belonging to Laura Perez-Martinez's, published in the Journal of Chemical Physics (J. Phys. Chem. 2023, 158, 094705)
Kinetics of formic acid dehydration on Pt electrodes by time-resolved ATR-SEIRAS
The potential dependence of the rate of dehydration of formic acid to adsorbed CO (COad) on Pt at pH 1 has been studied on a polycrystalline Pt surface by time-resolved surface-enhanced infrared absorption spectroscopy in the attenuated total reflection mode (ATR-SEIRAS) with simultaneous recording of current transients after a potential step. A range of formic acid concentrations has been used to obtain a deeper insight into the mechanism of the reaction. The experiments have allowed us to confirm that the potential dependence of the rate of dehydration has a bell shape, going through a maximum around the potential of zero total charge (pztc) of the most active site. The analysis of the integrated intensity and frequency of the bands corresponding to COL and COB/M shows a progressive population of the active sites on the surface. The observed potential dependence of the rate of formation of COad is consistent with a mechanism in which the reversible electroadsorption of HCOOad is followed by its rate-determining reduction to COad.
The last results of Marco Papasizza's and Xiaohui Yang's PhD theses, published in ACS Catalysis (ACS Catal. 2022, 12, 6770 - 6780)
The last results of Marco Papasizza's and Xiaohui Yang's PhD theses, published in ACS Catalysis (ACS Catal. 2022, 12, 6770 - 6780)
Water-In-Salt Environment Reduces the Overpotential for Reduction of CO2 to CO2– in Ionic Liquid/Water Mixtures
Water-In-Salt Environment Reduces the Overpotential for Reduction of CO2 to CO2– in Ionic Liquid/Water Mixtures
We report a combined computational and experimental work aimed at estimating the equilibrium potential for the electroreduction of CO2 to CO2– (widely accepted to be a crucial and overpotential-determining step) and at providing an alternative view on the reason behind the lower overpotential for CO2 reduction in imidazolium-based ionic liquid/water mixtures. To begin with, we obtained an 80 ps ab-initio molecular dynamics trajectory of the CO2– solvation structures in an 18% EMIM–BF4/water mixture, which delivered no evidence of interaction between EMIM+ and CO2–. Next, using the Fc+/Fc couple as the non-aqueous reference, we calculated the equilibrium potential of the CO2/CO2– couple in the mixture and aligned it with the aqueous SHE scale, proving that the equilibrium potential of CO2/CO2– in the mixture is about 0.3 V less negative than in the aqueous medium. We then looked for the origin of this catalytic effect by comparing the computed vibrational spectra with experimental Fourier transform infrared spectra. This revealed the presence of two water populations in the mixture, namely, bulk-like water and water in the vicinity of EMIM–BF4. Finally, we compared the hydrogen bonding interactions between the CO2– radical and H2O molecules in water and in the mixture, which showed that stabilization of CO2– by water molecules in the EMIM–BF4/water mixture is stronger than in the aqueous medium. This suggests that water in EMIM–BF4/water mixtures could be responsible for the low overpotential reported in these kinds of electrolytes.
Our work in collaboration with colleagues from Brazil and Chile in which we used imaged-based STS to map the electronic structure of electropolymerised polypyrrole films made it to the cover page.
Our work in collaboration with colleagues from Brazil and Chile in which we used imaged-based STS to map the electronic structure of electropolymerised polypyrrole films made it to the cover page.
Mapping the electronic structure of polypyrrole with image-based electrochemical scanning tunnelling spectroscopy
Mapping the electronic structure of polypyrrole with image-based electrochemical scanning tunnelling spectroscopy
https://chemistry-europe.onlinelibrary.wiley.com/share/NEGPNQQJ9HRVFNDPPXXS?target=10.1002/elsa.202280201
Methanol Dehydrogenation on Pt Electrodes: Active Sites and Role of Adsorbed Spectators Revealed through Time-Resolved ATR-SEIRAS
Methanol Dehydrogenation on Pt Electrodes: Active Sites and Role of Adsorbed Spectators Revealed through Time-Resolved ATR-SEIRAS
Laura Pérez-Martínez, Laura M. Machado de los Toyos, Jani J. T. Shibuya, and Angel Cuesta*
Cite this: ACS Catal. 2021, 11, 21, 13483–13495
Publication Date:October 22, 2021
Laura Perez-Martinez's detailed work on the dehydrogenation of methanol to adsorbed carbon monoxide on Pt electrodes, containing contributions from their undergraduate projects by Laura Machado and Jani Shibuya was published in ACS Catalysis.
Our experiments reveal that the electrooxidation of methanol to COad is possible at potentials at least as negative as 0.01 V versus reversible hydrogen electrode and occurs nearly exclusively at (111)- and (100)-oriented defect sites, whereby (111)-oriented defects show higher activity unless blocked by spectator species. Under conditions in which, due to a combination of low methanol concentration and sufficiently negative potential, the formation of COad is very slow, we have been able to determine the singleton frequency of linearly bonded COad (COL) on Pt (2002 cm–1 ± 2 between 0.01 and 0.06 V). We could observe the progressive population of terraces by COad diffusing from the defect sites where it has been formed. We also detected a band at 1677 cm–1, which we attribute to adsorbed formyl (HCOad) and which we suggest is the last intermediate in the oxidation leading from methanol to COad. Our experiments also allow the direct spectroscopic determination of Tafel plots revealing the potential dependence of the reaction rate. These plots, together with the potential dependence of the time elapsed between the first observation in spectra of COB/COM and that of COL, provide evidence of the important role played by adsorbed spectators in determining the reaction rate.
Mapping the electronic structure of polypyrrole with image-based electrochemical scanning tunnelling spectroscopy
Mapping the electronic structure of polypyrrole with image-based electrochemical scanning tunnelling spectroscopy
R. Gonçalves, R.S. Paiva, A.M.R. Ramírez, J.A. Mwanda, E.C. Pereira, A. Cuesta
Electrochem. Sci. Adv. 2022, 2, e2100028. https://doi.org/10.1002/elsa.202100028
Wiley's new Open Access journal Electrochemical Science Advances has just published our work in collaboration with colleagues from Brazil and Chile in which we used imaged-based STS to map the electronic structure of electropolymerised polypyrrole films.
IB-EC-STS located the band edge of the polymer’s valence band (VB) at 0.95 V vs. RHE (-5.33 eV in the absolute potential scale) and the intragap polaron states formed when the polymer is doped, at 0.46 V vs. RHE (-4.84 eV). The IB-EC-STS data were cross checked with electrochemical impedance spectroscopy (EIS) and Mott-Schottky analysis of the interfacial capacitance. The DOS spectrum obtained from EIS data is consistent with the STS-deduced location of the VB and the polarons.
Reactive and inhibiting species in the electrocatalytic oxidation of glycerol on gold. A study combining in-situ visible reflectance and ATR-SEIRAS.
Reactive and inhibiting species in the electrocatalytic oxidation of glycerol on gold. A study combining in-situ visible reflectance and ATR-SEIRAS.
L. Pérez-Martínez, L. Balke, A. Cuesta,
J. Catal. 394 (2021) 1-7
Our recent work published in the Special Issue of Journal of Catalysis dedicated to Electrocatalysis combines ATR-SEIRAS and visible reflectance measurements to improve our understanding of the inhibiting effect of adsorbed reaction products as of the role of the role of surface oxygenated species. The work belongs to Laura Perez-Martinez's PhD thesis who was assisted by undergraduate student Lisa Balke.
Building on Marco's and Xiaohui's PhD Theses, we have published a brief review on the electrocatalytic reduction of carbon dioxide in neat and water-containing nimidazolium-based ionic liquids. Curr. Op. Electrochem. 2020, 23, 80-88; https://www.sciencedirect.com/science/article/pii/S2451910320300843.
Alex Betts' excellent work during his final year MChem project abroad has been published in ACS Catalysis (ACS Catal. 2020, 10, 8120-8130; https://pubs.acs.org/doi/10.1021/acscatal.0c00791). The article is the result of a collaboration with Prof. Enrique Herrero's group in Alicante. and reports a study using Pt(111) and Pt(100) electrodes of the role of adsorbed formate in both the direct and indirect pathways of the electrocatalytic oxidation of formic acid. Cyclic voltammetry at different concentrations of formic acid and different scan rates and pulsed voltammetry were used to obtain a deeper insight into the effect of formate coverage on the rate of the direct pathway. Pulsed voltammetry also provided information on the effect of the concentration of formic acid on the rate of the formation of adsorbed CO on Pt(100). At low to medium coverage, increasing formate coverage increases the rate of its direct oxidation, suggesting that decreasing the distance between neighboring bidentate-adsorbed formate favors its interconversion to and/or stabilizes monodentate formate (the reactive species). However, increasing the formate coverage beyond approximately 50% results in a decrease of the rate of the direct oxidation, probably because bidentate formate is too closely packed for its conversion to monodentate formate to be possible. Cyclic voltammetry at very high scan rates reveals the presence of an order–disorder phase transition within the bidentate formate adlayer on Pt(111) when the coverage approaches saturation. The dependence of the potential of the maximum rate of dehydration to adsorbed CO, and of the rate at the maximum, on the concentration of formic acid is in good agreement with predictions made for a mechanism, in which adsorbed CO is formed through the adsorption of formate followed by its reduction to adsorbed CO, thus confirming that monodentate-adsorbed formate is the last intermediate common to both the direct and indirect pathways.
Plot of the potential for the maximum rate of formation of adsorbed CO and of its value vs the concentration of formic acid.
If you are interested in applying infrared spectroscopy to the study of the electrocatalytic reduction of carbon dioxide, you might find our recent review in collaboration with the group in Delft useful: ChemPhysChem 2019, 20, 2904-2925; https://onlinelibrary.wiley.com/doi/abs/10.1002/cphc.201900533.
Building on Jonathan's PhD Thesis, we have published a brief review on the electrochemical metallization of molecular adlayers. Curr. Op. Electrochem. 2019, 17, 72-78; https://www.sciencedirect.com/science/article/pii/S2451910319300067.
Our publication in Electrochim. Acta 2019, 327, 135055 (https://www.sciencedirect.com/science/article/pii/S0013468619319267) describes, combining data from vibrational spectroscopy, double layer capacitance measurements and ab-initio molecular dynamics simulations, how cations determine the interfacial potential profile, and discusses the relevance of this effect for the carbon dioxide reduction reaction (CO2RR). We show that the cation size determines the location of the outer Helmholtz plane, whereby smaller cations increase not just the polarisation but, most importantly, the polarizability of adsorbed CO (COad) and the accumulation of electronic density on the oxygen atom of COad. This strongly affects its adsorption energy, the degree of hydrogen bonding of interfacial water to COad and the degree of polarisation of water molecules in the cation’s solvation shell, all of which can deeply affect the subsequent steps of the CO2RR. Laura, Ghulam and Marco contributed with this work, which continued the collaboration between those of us who remain in Aberden and those who have relocated to Xiamen (Jiabo and Jun).
a) Schematic illustration of the surface sensitivity of surface-enhanced infrared absorption spectroscopy in the attenuated total reflection mode (ATR-SEIRAS), due to thecombination of the thin layer of electrolyte probed by the evanescent wave (typical of the ATR configuration) and to the short rage of the SEIRA effect generated by surface plasmon excitation within the rough metal film deposited on the Si prismatic window. (b) Model of the Pt(111)-CO/water interface used for AIMD simulations. Pt, C, O, H and cation are coloured by grey, brown, red, white and blue, respectively. The Pt(111) surface is covered by the (2 x 2)-3CO structure (coverage = 0.75 ML) known to exist on this surface in CO-saturated solutions at E 0.45 V vs. RHE [32]. (c) ATR-SEIRA spectra of a Pt electrode in CO-saturated 0.1 M Rb2SO4 in the spectral region corresponding to the C-O stretching of adsorbed CO. The spectra are shown at potential intervals of 0.20 V for the sake of clarity and were calculated using the spectrum of the CO-free Pt surface at the open-circuit potential as background. (d) ATR-SEIRA spectra of a Pt electrode in CO-saturated 0.1 M Rb2SO4 in the spectral region corresponding to the O-H stretching of H2O. The spectra are show at potential intervals of 100 mV for the sake of clarity and were calculated using the spectrum of CO-covered Pt surface at +0.4 V as background.
(a) Model illustrating the potential profile across the electrode-electrolyte interface, and the effect of the cation size on the interfacial properties and on the polarizability of the CO adlayer. The red cation is divalent, and therefore the situation depicted corresponds to twice the charge density than in the case of the monovalent blue and green cations. Deltaxa and Deltaxg correspond to the thickness of the CO adlayer and the vacuum gap, respectively, and rH is the radius of the hydrated cation. The dashed lines illustrate the potential drops across the CO adlayer and the vacuum gap had εa remained constant. (b) Distribution of excess electronic density along the surface normal direction, as calculated from AIMD simulation and averaged in the XY plane. The excess electronic density is defined as Dre ¼ rinterface rPt rwater rNa. (c) Potential distribution across the interface. The zero z-coordinate corresponds to the Pt(111) surface. Blue, red and green curves correspond to the interface at the pzc (+1.1), 0.1 V and 1.2 V, respectively.
(a) and (b): Plots of the Stark tuning rate and the interfacial capacitance, respectively, as a function of the ratio between the charge number of the cation and the cation’s hydrodynamic radius, z/rH, as obtained from the corresponding limiting ionic conductivityl. The dashed horizontal lines in a and b correspond to the interfacial capacitance and the Stark tuning rate, respectively, when H+ is the electrolyte cation, and the vertical dashed lines correspond to the resulting estimated effective radius of hydrated H+ at the electrical double layer. (c)Plot of the Stark tuning rate vs. the interfacial capacitance for all 14 cations used in this study. The dashed red line is the best linear fit to the data corresponding to the three largest cations (TBA+, TPA+ and TEA+). The dashed blue line is a linear fit to the rest of the data.
Xiao-Hui's computational Ag/AgCl reference electrode was published in the Journal of Physical Chemistry B (J. Phys. Chem. B 2019, 123, 10224-10232; https://pubs.acs.org/doi/abs/10.1021/acs.jpcb.9b06650). We developed a scheme to compute the standard potential of the Ag/AgCl reference electrode using density functional theory-based molecular dynamics, similar to the computational standard hydrogen electrode (SHE) developed by Cheng, Sulpizi, and Sprik [J. Chem. Phys. 2009, 131, 154504], with which our new computational reference electrode was compared. We have obtained a similar value of the potential of the Ag/AgCl electrode versus SHE to the experiment. The newly developed computational reference electrode will be extended to nonaqueous solvents in the future, where it will be used to predict standard equilibrium potentials to be compared with experimental data.
Marco's last work has just appeared in ACS Caltalysis (ACS Catal. 2018, 8, 6345-6352; https://pubs.acs.org/articlesonrequest/AOR-TvgFMCxjWYpjdvCrHTII). There, we report a study of CO2 electroreduction on Au in a [EMIM]BF4 / H2O mixture (18% mol / mol) combining cyclic voltammetry and surface-enhanced infrared absorption spectroscopy in the attenuated total reflection mode (ATR-SEIRAS). The onset of the reduction current in the CV coincides with a decrease of the interfacial CO2 concentration, but the appearance of adsorbed CO (COad) is slightly delayed, as CO must probably first reach a minimum concentration at the interface. Comparisons with spectra collected in the absence of CO2 and in CO-saturated electrolyte reveal that the structure of the double layer at negative potentials is different when CO2 is present (probably due to the formation of COad) and allow us to assign the main band in the spectra to CO adsorbed linearly on Au (COL), with a smaller band corresponding to bridge-bonded CO (COB). The CO bands show a large inhomogeneous broadening and are considerably broader than those typically observed in aqueous electrolytes. While both COL and COB can be observed in the CO adlayer generated by the electroreduction of CO2, only a single, even broader band, at a frequency characteristic of COL is seen in CO-saturated solutions. We attribute this to the lower coverage of the adlayer formed upon reduction of CO2, which leads to a lower degree of dipole-dipole coupling. Upon reversing the direction of the sweep in the CV, the intensity of the CO bands continues increasing for as long as a reduction current flows, but starts decreasing at more positive potentials due to CO desorption from the surface.
ATR-SEIRA spectra of an Au electrode in CO2-saturated [EMIM]BF4 / water (18% mol / mol) acquired during the negative-going (a) and positive-going (b) sweeps of a cyclic voltammogram at 5x10-4 V s-1. The reference spectrum was taken at −0.60 V just before starting the potential sweep in the negative direction. The highlighted bands correspond to νasym(CO2) ; ν(COL) and ν(COB) . The red lines correspond to the ATR infrared spectrum of the [EMIM]BF4 / H2O mixture (18% mol / mol), and are included for the sake of comparison.
Dr Cuesta's short review on the electrocatalytic oxidation of C1 molecules has been published in Current Opinion in Electrochemistry (Curr. Opin. Electrochem. 2017, 4, 32-38). The link below allows free access to the article until January 24, 2018. No sign up, registration or fees are required – simply click and read.
https://authors.elsevier.com/a/1WAMH8jV-RUzhF
After 24th January 2018, the article can be accessed at https://www.sciencedirect.com/science/article/pii/S2451910317300431.
Onagie's last work has just appeared in ACS Applied Materials and Interfaces (ACS Appl. Mater. Interfaces 2017, 9, 27377-27382; http://pubs.acs.org/doi/pdf/10.1021/acsami.7b07351). We were able to measure the interfacial pH during the electroreduction of CO2 in CO2/bicarbonate buffers with different alkaline metal cations. Onagie's results offer experimental support to a recent hypothesis (Singh et al., J. Am. Chem. Soc. 2016, 138, 13006–13012) according to which the effect of the electrolyte cation on the Faradaic efficiency and selectivity of CO2 electroreduction is due to the buffering ability of cation hydrolysis at the electrical double layer. According to that hypothesis, the pKa of hydrolysis decreases close to the cathode due to the polarization of the solvation water molecules sandwiched between the cation’s positive charge and the negative charge on the electrode surface. We have tested this hypothesis experimentally, by probing the pH at the gold-electrolyte interface in situ using ATR-SEIRAS. The ratio between the integrated intensity of the CO2 and HCO3- bands, which has to be inversely proportional to the concentration of H+, provided a means to determining the pH change at the electrode-electrolyte interface in-situ during the electroreduction of CO2. Our results confirm that the magnitude of the pH increase at the interface follows the trend Li+ > Na+ > K+ > Cs+, adding strong experimental support to Singh’s et al.’s hypothesis. We show, however, that the pH buffering effect was overestimated by Singh et al., their overestimation being larger the larger the cation. Moreover, our results show that the activity trend of the alkali-metal cations can be inverted in the presence of impurities that alter the buffering effect of the electrolyte, although the electrolyte with maximum activity is always that for which the increase of the interfacial pH is smaller.
LSVs at 1 mV s-1 (top panel) of a thin-film Au electrode on Si in CO2-saturated 0.05 M M2CO3 solutions (M = Li (blue), Na (green), K (red), Cs (black)) in D2O, potential dependence of the ratio (mid panel) as obtained from simultaneously recorded ATR-SEIRA spectra, and potential dependence of the interfacial pH (bottom panel).
Steady-state pH at the metal-electrolyte interface during the electroreduction of CO2 at -1 V vs. RHE in CO2-saturated 0.05 M M2CO3 solutions (M = Li, Na, K, Cs). pH values for Ag and Cu correspond to those resulting from Singh’s et al.’s calculations (J. Am. Chem. Soc. 2016, 138, 13006–13012), while in the case of Au they correspond to our experimental determination using ATR-SEIRAS.
Jiabo's work on calculating the pzc of metal electrodes (namely Ag, Au, Pt and Pd) using DFT-based molecular dynamics has just been published in Physical Review Letters. The pzc's were calculated with very good accuracy, and the work reveals that the change in the interface dipole potentials (as compared with the situation in vacuum) is largely due to charge transfer from interfacial water to the metal surface (i.e., there is some degree of chemical bonding between interfacial water and the metal surface). Water orientation barely contributes to the potential drop across the interface at the pzc.
For more information see J. Le, M. Iannuzzi, A. Cuesta, J. Cheng, Phys. Rev. Lett. 2017, 119, 016801. https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.016801
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