Hydrogen Electrooxidation under Conditions of High Mass Transport in Room-Temperature Ionic Liquids and the Role of Underpotential-Deposited Hydrogen

Abstract

. (2016) Hydrogen electrooxidation under conditions of high mass transport in room-temperature ionic liquids and the role of underpotential-deposited hydrogen. Journal of Physical Chemistry C, 120 (21). pp. 11498-11507. ISSN 1932-7455 Access from the University of Nottingham repository: http://eprints.nottingham.ac.uk/33911/1/Article%20jp-2016-01592f.R2.pdf Copyright and reuse:The Nottingham ePrints service makes this work by researchers of the University of Nottingham available open access under the following conditions. This article is made available under the University of Nottingham End User licence and may be reused according to the conditions of the licence. For more details see: http://eprints.nottingham.ac.uk/end_user_agreement.pdf A note on versions:The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription. AbstractThe hydrogen oxidation reaction (HOR), an electrocatalytic reaction of fundamental and applied interest, was studied in the protic ionic liquid (PIL) diethylmethylammonium trifluoromethanesulfonate, [dema][TfO], at Pt electrodes using rotating disk electrode (RDE) and ultramicroelectrode (UME) voltammetry. A steady-state HOR current is observed during RDE voltammetry at overpotentials > 50 mV but an additional plateau is observed in the overpotential region 50-200 mV when using UMEs. The difference in voltammetric responses is attributed to higher rate of mass transport to the UME than to the RDE. Three models have been used to fit the experimental data. The first is a dual-pathway model, which assumes that the Tafel-Volmer and Heyrovsky-Volmer pathways are both active over the potential range of interest and no blockage of catalytic sites occurs during the reaction. The second is a dual-pathway model, which assumes that reaction intermediates block access of H 2 to catalytic sites. The third is based on the premise that underpotential-deposited hydrogen atoms (H upd ) can block adsorption and electrooxidation of H 2 at the Pt surface. While each model fits the polarisation curves reasonably well, detailed analysis suggests that the H updblocking model describes the responses better. To the best of our knowledge, this work is the first to demonstrate the advantages of UME voltammetry over RDE voltammetry for studying electrocatalytic reactions in PILs, and the first to show that H upd can inhibit an electrocatalytic reactions in an ionic liquid, a factor that may become important as the technological applications of these liquids increase.3

Macroporous platinum electrodes for hydrogen oxidation in ionic liquids

“…Less has been published on the mechanism in aprotic solvents such as room temperature ionic liquids (RTILs). The oxidation of hydrogen on Pt in RTILs has been reported by various groups [9][10][11][12][13][14][15][16][17][18][19], with pre-anodization ("activation") of the electrode giving rise to higher currents and more reversible voltammetry [9,12,15,16]. A detailed four-step mechanism involving the radical of the RTIL anion ([NTf2] -) was recently proposed [17]:…”

The contrasting effects of diethylmethylamine during reduction of protons and oxidation of formic acid in diethylmethylammonium-based protic ionic liquids

“…Ionic liquids are formally defined as materials that are composed entirely of ions and which are liquid below 100 °C [1]. Due to their inherent conductivities and thermal and electrochemical stabilities, ionic liquids are being used in an increasing number of electrochemical applications, including fundamental studies of the electrical double layer [2], investigations into mass and charge transport [3][4], electrochemical sensing [5], batteries [6], supercapacitors [7], and fuel cells [8]. While a large number of ionic liquids can potentially be synthesised, they can be broadly divided into two classes.…”

Electrochemical Oxidation of Hydrogen in Bis(trifluoromethylsulfonyl)imide Ionic Liquids under Anaerobic and Aerobic Conditions

“…This was explained based on the difference in the energy for proton extraction from the anion (acid with the form HA: HA + e – ↔ A – + 1 / 2 H 2 ) and from the cation (acid with the form BH + : BH + + e – ↔ B + 1 / 2 H 2 ) . In another study of protic ionic liquid diethylmethyl­ammonium tri­fluo­ro­meth­ane­sulfonate, [dema]­[TfO], at Pt electrodes, the hydrogen oxidation mechanisms were proposed to follow the Tafel–Volmer and Heyrovsky–Volmer pathways, and the underpotential-deposited hydrogen atoms (H upd ) can block adsorption and electrooxidation of hydrogen at the Pt surface. It is widely accepted that hydrogen oxidation involves intermediate adsorption during the hydrogen redox processes and the electrode–electrolyte double layer structure is very important for its kinetics. , For example, in aqueous electrolytes, the weakly solvated spherical ions, such as SO 4 2– , Br – , and I – were known to form ordered layers at the electrolyte/electrode interface .…”