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. 

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).

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.

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.

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