Pt/Polypyrrole Quasi-References Revisited: Robustness and Application in Electrochemical Energy Storage Research

Abstract

Choosing reference electrodes for nonaqueous electrochemical measurements, especially in energy storage research, is challenging due to lengthy experiments (>1 day), the lack of alternatives to the commonly used Ag/Ag + reference electrode (RE), the introduction of junction potentials, and the possibility of sample contamination. Often, quasi-reference electrodes (QREs) such as Ag wires and Li metal strips are used. However, small changes in electrolyte composition can cause large potential drifts, and their surfaces may be reactive to the solution. Here, we propose an alternative QRE based on polypyrrole electrodeposited on Pt wire (PPyQRE) encased in a glass tube with the open end sealed with commercial frits. While freestanding PPyQRE wires have been reported in the literature, simple encasing of the PPyQRE overcomes the above-mentioned drawbacks of QREs while providing a reliable reference potential that is closer to the performance of an RE. During cyclic voltammetric and bulk electrolysis testing of a redox mediator in solution, the encased PPyQRE exhibited stable reference potentials over multiple charge/discharge cycles with minimal drift (∼5 mV) after ∼2.25 days of operation. We also tested the reliability of our reference during the testing of multilayer graphene Li-ion anodes, which often involve cycling samples at highly reducing potentials (<−3 V vs Fc/Fc + ) over long durations (>1 day). In the same testing conditions, the Ag/Ag + electrode led to observable Ag deposits on the graphene and large potential drifts (∼50 mV), while the PPyQRE exhibited no measurable drift and revealed changes in voltammetric features that were obscured by reference drift when using Ag/Ag + . Minor reference drifts of ∼30 mV over long usage of the PPyQRE (∼2 months) can be addressed by calibration with a ferrocene couple at the end of experiments. These results highlight the advantages of using an encased PPyQRE as a simple and practical reference electrode for electrochemical measurements in the field of nonaqueous energy storage research.

Nonaqueous Li-Mediated Nitrogen Reduction: Taking Control of Potentials

“…(ii) Ag + ions tend to leak through that same frit into the bulk electrolyte and can affect electrochemistry by coplating with lithium for instance. 28 , 30 , 31 (iii) Ag/Ag + references need to be freshly prepared for every experiment since the Ag salts used to make their electrolyte are light-sensitive and degrade rather quickly. 26 (iv) These Ag salts are also hygroscopic: this accelerates degradation and may strongly affect N 2 reduction experiments because of its sensitivity to water content in the electrolyte.…”

“…Previous works on controlling potentials were carried out using Ag/Ag + nonaqueous references for their supposed stability, versatility, and ease of use. , However, these electrodes suffer from several drawbacks that intercalation materials such as LiFePO 4 can address: (i) For Ag/Ag + references it is necessary to enclose the reference electrolyte within a fritted tube, creating a junction potential at the frit interface which can actually be unstable , nonreproducible , and variable between electrolytes , , preventing cross-electrolyte comparison and electrochemical analysis of activity coefficients of the active species in solution (which is possible with LiFePO 4 , see discussion in Figure ). (ii) Ag + ions tend to leak through that same frit into the bulk electrolyte and can affect electrochemistry by coplating with lithium for instance. ,, (iii) Ag/Ag + references need to be freshly prepared for every experiment since the Ag salts used to make their electrolyte are light-sensitive and degrade rather quickly . (iv) These Ag salts are also hygroscopic: this accelerates degradation and may strongly affect N 2 reduction experiments because of its sensitivity to water content in the electrolyte. , Going back to LiFePO 4 , its reported tedious preparationcarried out using an electrolyte that is essentially the same as the one where the electrode will then be usedis not as challenging as it seems and has been swiftly adapted from commonly used Li-ion battery electrolytes (e.g., LiPF 6 in cyclic/linear carbonate). , In an Ar glovebox, a LiFePO 4 disc (Ø 18 mm) was assembled in a coin cell (Figure S1a) at the positive side, against a Li metal negative electrode, separated by a glass fiber separator wetted with 1 M LiNTf 2 (i.e., LiN­(SO 2 CF 3 ) 2 ) in THF (omitting ethanol due to incompatibility of lithium with proton sources).…”

Plasmon Energy Transfer Driven by Electrochemical Tuning of Methylene Blue on Single Gold Nanorods

“…Calibration was performed using a half-wave potential ( E 1/2 0 ) of the potassium ferrocyanide redox reaction (Figure S2). , AuNRs with average dimensions of 67 ± 10 × 28 ± 3 nm were spin-cast onto the ITO electrode (Figure S3), generating individual nanoelectrodes, where the reversible redox reaction between MB and leucomethylene blue (LMB) was driven in the presence of 1 μM MB dissolved in 100 mM NaNO 3 aqueous electrolyte (Figure a and b). The supporting electrolyte solution was replaced through flow tubes for direct comparison of plasmonic responses under different chemical and electrochemical environments without the need for change to the optical geometry (Figure a).…”

“…The three electrodes were inserted into the reaction flask and connected to a three-electrode potentiostat (CH Instruments, 630D). The tip of the working electrode was coated with the polypyrrole under cycling potentials between −0.6 and 1.2 V (vs Ag/AgCl) at a sweep rate of 0.1 V s –1 for 100 segments. , …”

A Surface Modification Strategy Towards Reversible Na-ion Intercalation on Graphitic Carbon Using Fluorinated Few-Layer Graphene

“…To maintain concentration comparisons, we subsequently chose 0.1 M NaPF 6 for investigating Na + intercalation. All measurements were performed with a polypyrrole quasi-reference 35,36 (PPyQRE) given Na-metal references can interfere in electrochemical measurements, 37 and 0.5 mm dia. Pt wire as counter electrode.…”