Palladium Hydride as a Reference Electrode in Aprotic Solutions

Abstract

The results of a variety of electrochemical tests indicate palladium hydride (β-PdH) functions as a thermodynamic reference electrode in three aprotic solutions containing H 2(g) and solvents of dichloromethane, dimethylsulfoxide, and acetonitrile. For enhanced electrical conductivity all solutions contained 0.2 M of an ionic liquid, 1-methyl-3-butyl imidazolium tetrafluoroborate. As is required of all thermodynamic reference electrodes (i) the potential of β-PdH was stable, (ii) its small amplitude anodic and cathodic polarization were reversible, and (iii) it exhibited Nernstian behavior assuming that the hydrogen cation activity is controlled by the concentration of adsorbed hydrogen, which is set by the partial pressure of H 2(g) . © The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0421603jes] All rights reserved.Manuscript submitted October 30, 2015; revised manuscript received December 8, 2015. Published December 17, 2015 Palladium hydride (PdH) has long been used as a redox system for measurement of pH, and as a titration electrode in nonaqueous solvents.1 The present investigation of PdH as a reference electrode in aprotic solutions arose from an interest in applying electrochemical techniques to assess the corrosivity of crude oil. Specifically, the current study was an offshoot of our efforts to use cyclic voltammetry of platinum in crude oil as a means for identifying the presence and concentrations of redox active corrosive species, such as naphthenic acids, which contribute significantly to the corrosion of steels in crude oil.At present, TAN (Total Acid Number) is employed to estimate the corrosiveness of a crude oil. TAN is the number of mg of potassium hydroxide required to neutralize the acids present in a 1 g sample of crude.2 However, it has been known for some time that there is considerable scatter in plots of low and intermediate values of TAN versus crudes' corrosiveness.3,4 For this reason, we have investigated the possibility of employing electrochemical techniques to characterize the corrosivity of an unknown crude.There are two major obstacles preventing the use of electrochemical techniques to assess the corrosivity of crudes. The first is the high electrical resistivity of crude oil. In a separate study we have addressed the resistivity issue by a combination of the use of ultramicroelectrodes (UME) and the addition of a supporting electrolyte, which does not itself affect the solution's corrosivity. 5 Many virgin crude oils have electrical resistivities on the order of 1 × 10 8 ohm•cm, which, although it is a high value, is nevertheless sufficiently low to permit electrochemical testing by employing UMEs without the need for a supporting electrolyte. However, the main concern over a crude's corrosivity relates to co...

Design of a flexible but robust setup for temperature‐dependent electrochemistry down to cryogenic temperatures

“…However, this conflicts with the Nernst equation (see eqn. S7), which essentially demands the opposite [39]. Interestingly, we are not the first to discover "anti-Nernst" behavior, as similar observations have recently been reported by Patrick et al for a PdH RE in aprotic solventbased electrolytes upon increasing the hydrogen pressure, i. e., from ~0.04 to ~1.01 bar.…”

“…As described above, the Mini Hydro-Flex ® RE is also comprised of Pd [35], which exhibits a strong solubility towards H 2 , that is up to ~1000 times its volume of dissolved hydrogen within the crystal structure [39][40][41][42]. Such formed palladium hydride (PdH) is capable of providing hydrogen cations and thus establishing a reversible hydrogen electrode even in aprotic solution [39,43]. Meanwhile, the applicability of PdH and the Mini HydroFlex ® as reference electrode in aprotic organic solvents has been demonstrated by Patrick et al [39].…”

“…The GDE consists of a (platinized) Pt mesh incorporated with palladium (Pd) and PTFE, which is immersed in the electrolyte solution [35]. While this satisfies the principles of a (reversible) hydrogen reference electrode (RHE) in aqueous electrolyte solutions, that is the hydrogen redox reaction (H + (aq) + 1e À * * 0.5H 2(g) ) on Pt eventually establishing the equilibrium potential (i. e., 0.000 V vs. RHE) for measurements at given pH [36][37][38], this is not valid in aprotic organic solvents [39]. As described above, the Mini Hydro-Flex ® RE is also comprised of Pd [35], which exhibits a strong solubility towards H 2 , that is up to ~1000 times its volume of dissolved hydrogen within the crystal structure [39][40][41][42].…”

“…Such formed palladium hydride (PdH) is capable of providing hydrogen cations and thus establishing a reversible hydrogen electrode even in aprotic solution [39,43]. Meanwhile, the applicability of PdH and the Mini HydroFlex ® as reference electrode in aprotic organic solvents has been demonstrated by Patrick et al [39]. and Gaskatel [44], respectively.…”

“…RHE) for measurements at given pH [36–38], this is not valid in aprotic organic solvents [39]. As described above, the Mini HydroFlex® RE is also comprised of Pd [35], which exhibits a strong solubility towards H 2 , that is up to ~1000 times its volume of dissolved hydrogen within the crystal structure [39–42]. Such formed palladium hydride (PdH) is capable of providing hydrogen cations and thus establishing a reversible hydrogen electrode even in aprotic solution [39, 43].…”