Direct Measurement of the Differential Capacitance of Solvent-Free and Dilute Ionic Liquids

Abstract

Differential capacitance is a key quantity in the understanding of electrical double-layer charging of electrolytes. However, experimental observations of ionic liquid systems are controversial, inconsistent, and often unable of confirming or refuting existing theories as well as highlighting discrepancies between the measurement techniques. We study the differential capacitance in both pure and dilute ionic liquids at room temperature. Using chronoamperometry to measure the differential capacitance of the liquids at a polycrystalline platinum electrode, we find good agreement between the measured capacitance curves and the extended mean-field model of Goodwin–Kornyshev [Goodwin, Z. A.; et al. Electrochim. Acta.2017, 225, 190–197]. A crossover is found from the pure to the dilute regime, as shown by a transition from a camel-shape capacitance curve to a U-like one, together with a nonmonotonic dependence of capacitance with electrolyte concentration.

Stabilizing lithium metal anode by octaphenyl polyoxyethylene-lithium complexation

“…The observed electrochemical stability could be due to the adsorption of the PEObased additives onto the metal Li surface, allowing these complexes to regulate the deposition of lithium during the charge-discharge process. The capacitance of PEO-based additives was significantly lower than that of the unmodified electrolyte, and a capacitance peak appears at −0.56 V for both OP-10 and PEGDME, showing the adsorption of additive to the electrode surface and formation of a thick double layer (SEI membrane) 40,41 . This adsorption is the driving force for the increase in interfacial charge resistance, which is consistent with the EIS results described above ( Supplementary Fig.…”

Potential Screening at Electrode/Ionic Liquid Interfaces from In Situ X‐ray Photoelectron Spectroscopy

“…Recently, the reliability of experimental observations of charged IL interfaces by EIS and CV has been discussed. These techniques can yield inconsistent/irreproducible results, due to impurities, neglect of the slow kinetic response, and questionable data analysis in EIS …”

“…(2) we measure under ultra‐high vacuum conditions with very clean ILs, as was carefully checked by XPS . (3) XPS gives direct access to the potential screening, without having to assume an equivalent circuit in EIS, which has been questioned in literature . The properties of the EDLs can be directly studied by comparing the potential screening on anode and cathode via binding energy shifts of IL signals in XPS.…”

Porous g‐C3N4 and MXene Dual‐Confined FeOOH Quantum Dots for Superior Energy Storage in an Ionic Liquid

“…According to Kornyshev theory, for camel-shaped curves, the potential of zero charge (PZC) is the potential corresponding to the minimum capacitance between the two peaks. [53,54] When the electrode potential negatively moves away from the PZC, the cations move towards the stern layer to shield the negative charge on the electrode surface (more details are provided in Figure S17, Supporting Information). For the EMIMBF 4 IL electrolyte ( Figure S18, Supporting Information), movement of the larger-sized EMIM + cations in the diffuse layer and accumulation in the stern layer are more difficult compared with the smaller BF 4 − anions.…”

“…For the EMIMBF 4 IL electrolyte ( Figure S18, Supporting Information), movement of the larger-sized EMIM + cations in the diffuse layer and accumulation in the stern layer are more difficult compared with the smaller BF 4 − anions. [53,55] As a result, the differential capacitance of the FQDs/ACNF electrode is lower under negative polarization than positive polarization, indicating its inefficient EMIM + accumulation in the stern layer. However, EMIM + is the working ion triggering the pseudocapacitive reaction with FQDs in the electrode, so the unsatisfactory pseudocapacitive storage of the FQDs/ ACNF electrode is due to the lack of EMIM + for sufficient redox reaction with FQDs in the FQDs/ACNF electrode (the left model in Figure 3c).…”