Correlation between the interfacial ion dynamics and charge storage properties of poly(ortho-phenylenediamine) electrodes exhibiting high cycling stability

Abstract

An integrated electrogravimetric study based on electrochemical quartz crystal microbalance (EQCM) unravels the interfacial ion transfer phenomena of the poly(orthophenylenediamine) (PoPD) thin film electrodes. Through a methodology coupling QCM with electrochemical impedance spectroscopy (ac-electrogravimetry), our work indicates that charge compensation process of PoPD in aqueous electrolytes (in acidified NaCl) occurs with the participation of multiple species, each playing a role at different temporal scales. The PoPD films are tested in a 2 electrode Swagelok cell in which Zn is used as both reference and counter electrodes and exhibit excellent stability over 8000 cycles with a relatively high specific capacitance of about 110 F•g-1 at 30 C (0.63 mA•cm-2) current density. The high rate capability and the excellent cycling stability of the PoPD electrodes are correlated to the electrolyte composition and the significant role of H + to the charge compensation process is unravelled, which is made possible with coupled electrogravimetric methods of our study. By determining the interfacial flux dynamics and as well as the relative proportions of species transferred at the electrode/electrolyte interface, our results contribute to the understanding of the charge-discharge process of PoPD polymer, yet underexplored but emerging as a pseudo-capacitive electrode material.

Poly(ortho-phenylenediamine) overlaid fibrous carbon networks exhibiting a synergistic effect for enhanced performance in hybrid micro energy storage devices

“…poly(orthophenylenediamine) and adopted a strategy that PoPD layer envelops a previously formed carbon network, leading to a carbon/PoPD nanofibrous composite electrode. The rationale behind this strategy is that the PoPD layer alone shows a relatively high cycling stability, 43 but with a modest specific capacitance value. The latter is attributed to a relatively low electronic conductivity and it has been expected to be enhanced with a subjacent carbon network.…”

“…For comparison purposes, the electrochemical polymerization of oPD without SWCNT addition has been pursued in a similar manner as described above. 43…”

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“…An anodic current increase starting at ≈0.47 and ≈0.54 V during the first and the subsequent scans is observed, reflecting the oxidation of oPD monomer. [ 31 ] Correspondingly, the Δ m of the electrode with a significant increase of ≈0.14 µg cm –2 is observed during the first anodic scan, and ≈0.41 µg cm –2 is deposited on the quartz resonator after the initial five cycles. The subsequent cycles show a progressively decreased current intensity (Figure S3a, Supporting Information), leading to a decreased mass ingress from cycle to cycle.…”

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“…EQCM measurements were carried out using AT-cut 9 MHz quartz resonators (AWS, Valencia, Spain) modified with gold electrodes as substrates. Electrochemical polymerization of the oPD monomer was carried out according to previously reported literature. , Briefly, 5 mM oPD was dissolved in 0.1 M H 2 SO 4 and cycled 200 times within the potential range of −0.4 and 0.8 V vs Ag/AgCl at a scan rate of 50 mV s –1 . In order to keep the gravimetric regime of the microbalance, the number of cycles were restricted to 200 (unlike the graphite surface), giving sufficient coverage of the PoPD film on the gold electrode (0.2 cm 2 ) of the quartz resonator.…”

“…42,45 Likewise, electropolymerization of oPD using CV in previous studies has also exhibited analogous redox behavior. 40,46 The molecular structure of PoPD electrode was investigated by FTIR (Figure 1b). The representative peaks at 3324 and 3180 cm −1 are ascribed to −NH− and −NH 2 , respectively.…”