Tetraoctylphosphonium Tetrakis(pentafluorophenyl)borate Room Temperature Ionic Liquid toward Enhanced Physicochemical Properties for Electrochemistry

Abstract

Presented herein is the facile preparation of a new room temperature ionic liquid (RTIL), tetraoctylphosphonium tetrakis(pentafluorophenyl)borate (P(8888)TB). Subsequently, its physicochemical properties such as density, viscosity, and conductivity were characterized relative to temperature, demonstrating values of 1.22 g·cm(-3), 727 mPa·s, and 180 μS·cm(-1), respectively, at 60 °C. The electrochemistry of P(8888)TB was also investigated using cyclic voltammetry at a Pt-disk ultramicroelectrode and at a microinterface between water and the RTIL; this analysis revealed a wide metal-electrolyte potential window, ∼3.5 V, and a large liquid|liquid polarizable potential window, ∼0.9 V, at a temperature of 60 °C. Additionally, electron transfer (ET) reactions at a metal electrode|RTIL interface along with ion transfer (IT) reactions at the water|P(8888)TB interface were examined; the kinetics of these reactions were explored using finite element analysis. Increased ET and IT kinetics combined with enhancements of physicochemical properties versus RTILs we made previously seemingly suggest modest improvements. However, taken as a whole, they demonstrate significant progress toward a hydrophobic RTIL that can be used in conventional electrochemistry and biphasic metal ion extractions.

Single LiBH4 nanocrystal stochastic impacts at a micro water|ionic liquid interface

“…1A). The PPW is 400mV wide and in good agreement with previous results [60][61][62], but is small compared to ILs incorporating fluorinated phenyl borate anions [18,56,58,63,64]. The lower viscosity of P66614NTf2, however, makes it easier to manipulate at ambient temperature (~330mPa s, [65,66]) versus more hydrophobic ILs [18,54,56,58,63,64].…”

“…In this case, using common conventions for ion transfer (IT) currents [56], either Li + transfers from w→IL or NTf2from IL→w, at positive potentials, while either SO4 2-, from w→IL, or P66614 + , from IL→w transfers at the negative end. However, the formal Li + transfer potential, ∆ + ′ , is probably well beyond the positive limit [57,58], and since P66614 + is quite hydrophobic [59], the PPW is predominately limited by NTf2and SO4 2transfer (see inset in Fig. 1A).…”

Preparation and crystal structure of tetraoctylphosphonium tetrakis(pentafluorophenyl)borate ionic liquid for electrochemistry at its interface with water

“…All electrochemical experiments were conducted using a Modulab workstation (Ametek Advanced Measurement Technology, Farnborough, UK) and using a modified micropipette holder (HEKA Electronics, Mahone Bay, NS), 2.0 mm inner diameter, as has been described recently [10,29]. Micropipettes, with a 25 µm diameter, 250-500 µm long, micro-channel situated at the tip, were fabricated as has been detailed previously [10,29]. The micropipette as installed into the holder, which has an integrated silver wire connecting to the working electrode (WE) lead of the workstation, and then back filled with the aqueous solution using a syringe.…”

“…low diffusion coefficient, in the IL phase for the IL to w transfer wave. For the former, the small volume of solutionrelative to the interfacial sizemeans 9 that N(CH3)4 + ions in the vicinity of the interface are consumed faster than they can diffuse from higher up in the micro-channel; this is also called 'linear diffusion', and gives rise to a peak-shaped signal rather than a steady-state voltammogram typical of solid microelectrodes [29,33]. The low diffusion coefficient generates a similar linear diffusion-based response in the IL to w transfer.…”

“…P8888(C6F5)4 was recrystallized twice at -20°C in ethanol. After each step, the IL was structurally confirmed through 1 H-, 31 P-, and19 F-NMR, as has been detailed elsewhere[3,24,29].…”