ORALS

SESSION: MoltenSatPM1-R1	Angell International Symposium on Molten Salt, Ionic & Glass-forming Liquids: Processing and Sustainability (7th Intl. Symp. on Molten Salt, Ionic & Glass-forming Liquids: Processing and Sustainability).
Sat Oct, 26 2019 / Room: Ambrosia A (77/RF)
Session Chairs: Vasily Lutsyk; Pierre Lucas; Session Monitor: TBA

14:25: [MoltenSatPM106]
Proton shuttling in protic ionic liquid fuel cells
Darren Walsh¹ ; Daniel Smith¹ ; ¹University of Nottingham, Nottingham, United Kingdom;
Paper Id: 254 [Abstract]

The conventional polymer-electrolyte membranes used in low-temperature fuel cells are limited to operating temperatures below about 120 celsius, as they must be fully hydrated to facilitate proton transport. Protic ionic liquids (PILs) are ionic liquids formed by transferring protons from Brønsted acids to Brønsted bases, and it has recently been shown that some ammonium-based PILs inherently exhibit high proton conductivities. Consequently, PILs have been proposed for use as electrolytes in non-humidified fuel cells that can operate above 120 celsius (at intermediate temperatures).^1-3 While they nominally consist entirely of ions, however, PILs can often contain a significant quantity of neutral species (either molecules or ion clusters) that can affect the physicochemical properties of the liquids.<br />In this contribution, we first describe an electroanalytical method for detecting and quantifying residual Brønsted acids in a series of ammonium-based PILs. Ultramicroelectrode voltammetry reveals that some of the accepted methods for synthesizing PILs can readily result in the formation of nonstoichiometric PILs containing up to 230 mmol/L residual acid. We will then show that residual acids in PILs can have a drastic effect on the electrocatalytic oxygen reduction reaction (ORR) in the PILs. For example, the potential at which the ORR occurs at Pt in the PIL diethylmethylammonium trifluoromethanesulfonate, [dema][TfO], decreases linearly as the strength of the proton donor in the liquid decreases. In pure [dema][TfO], in which the proton donors during the ORR are the cations of the PIL (p<i>K</i>_a = 10), the onset potential of the ORR is the same as that of the hydrogen oxidation reaction (HOR) in the PIL. These observations have significant implications for the use of PILs as electrolytes in fuel cells and indicate that the best PILs are highly "acidic" liquids that can support oxygen reduction at high potentials.

References:
1. M. Watanabe, M. L. Thomas, S. Zhang, K. Ueno, T. Yasuda, K. Dokko, Chem. Rev. 2017, 117, 7190-7239.\n2. J. Thomson, P. Dunn, L. Holmes, J.-P. Belieres, C. A. Angell, D. Gervasio, ECS Trans.\n2008, 13, 21-29.\n3. D. R. MacFarlane, N. Tachikawa, M. Forsyth, J. M. Pringle, P. C. Howlett, G. D. Elliott,\nJ. H. Davis Jr., M. Watanabe, P. Simon, C. A. Angell, Energy Environ. Sci. 2014, 7, 232-250.

SESSION: AdvancedMaterialsFriAM-R2	5th Intl. Symp. on New and Advanced Materials and Technologies for Energy, Environment and Sustainable Development
Fri Oct, 25 2019 / Room: Leda (99/Mezz. F)
Session Chairs: Nikoloz Chikhradze; Ivanka Netinger Grubesa; Session Monitor: TBA

11:20: [AdvancedMaterialsFriAM01]
Polyoxometalate Chemistry in Carbon Nanotubes
Graham Newton¹ ; Jack Jordan¹ ; Andrei Khlobystov¹ ; Darren Walsh¹ ; ¹University of Nottingham, Nottingham, United Kingdom;
Paper Id: 253 [Abstract]

Polyoxometalates (POMs) have received considerable attention in recent years due to their rich redox properties and potential applications in energy storage.[1] Due to their discrete nature, the use of POMs as components in energy storage devices relies on their stable combination with conductive supports.[2] Carbon nanotubes (CNTs) are stable, hollow cylinders made entirely of carbon. These nanostructured carbons are highly conductive, mechanically strong and can be functionalized.[3] By encapsulating molecular materials within CNTs, their properties can be enhanced. This work describes the first report of the encapsulation of the Keggin [PW₁₂O₄₀]^3- and Wells-Dawson [P₂W₁₈O₆₂]^6- heteropolyanions within carbon nanotubes (CNTs), along with detailed structural, chemical and electronic characterizations. Transmission electron microscopy (TEM) confirms the presence of encapsulated POMs, as well as provides the necessary energy to perform observable chemical transformations within the CNTs. Access to POM redox properties from within the CNT upon encapsulation is described. The POM electrochemistry is shown to be stabilized across a greater range of conditions and cycles than typically possible. Using Raman spectroscopy, investigations probe the electronic coupling between the host and guest, showing electron transfer between the two.

References:
1. Sadakane, M.; Steckhan, E., Electrochemical Properties of Polyoxometalates as Electrocatalysts. Chem. Rev. 1998, 98 (1), 219-238.
2. Song, Y.-F.; Tsunashima, R., Recent advances on polyoxometalate-based molecular and composite materials. Chem. Soc. Rev. 2012, 41 (22), 7384-7402.
3. Miners, S. A.; Rance, G. A.; Khlobystov, A. N., Chemical reactions confined within carbon nanotubes. Chem. Soc. Rev. 2016, 45 (17), 4727-4746.