Charge- and Proton-Storage Capability of Naphthoquinone-Substituted Poly(allylamine) as Electrode-Active Material for Polymer–Air Secondary Batteries

Abstract

1,4-Naphthoquinone (NQ) undergoes a two electron and two proton redox process in one step at a potential of −0.05 V (vs Ag/ AgCl) in 0.05 M H 2 SO 4 aqueous solution. Its heterogeneous electron transfer rate constant is comparable to those of electrochemically reversible redox-active molecules. Therefore, NQ is a potential electrode-active material candidate in acidic aqueous electrolyte. Simple nucleophilic substitution of 2-bromo-1,4-naphthoquinone and poly-(allylamine) yields NQ-substituted poly(allylamine) (PNQ), enabling us to adjust the hydrophilicity of the redox polymer according to the NQ introduction rate. A polymer−air secondary battery composed of the PNQ anode, the Pt/C cathode, and 0.05 M H 2 SO 4 aqueous electrolyte displayed high cyclability (>100 cycles) and C-rate capability (∼15 C) with a moderate voltage of 0.8 V during discharging.

Structure-Property Relationship in Selected Naphtho- and Anthra-Quinone Derivatives on the Basis of Density Functional Theory and Car–Parrinello Molecular Dynamics

“…They are also interesting classes of compounds from the materials science point of view. Their derivatives have been mentioned as, e.g., potential electrode-active material candidates in an acidic aqueous electrolyte [14]. They are able to improve the performance of flow batteries [15], and also, long-life lithium-organic batteries were developed based on the core structure of naphthoquinone [16].…”

Hydrophilic Anthraquinone-Substituted Polymer: Its Environmentally Friendly Preparation and Efficient Charge/Proton-Storage Capability for Polymer–Air Secondary Batteries

“…The diffusion coefficient of electrons and protons in the polymer layer was estimated from the chronoamperometry measurement of the polymer thin film in 0.5 M H 2 SO 4 aqueous solution using the method described in our previous reports. 6,8,10 The diffusion coefficient was 1.4 × 10 −11 cm 2 s −1 (Figure 1a; the rate constant for the electron self-exchange reaction was 4.7 × 10 3 M −1 s −1 ), which is an order of magnitude higher than that of conventional organic redox Scheme 1. Synthesis of Anthraquinone-Substituted Poly(allylamine) polymers that have a redox capability involving two electrons in one step.…”

“…For a first trial, we aimed to synthesize an anthraquinone-substituted poly-(allylamine) with sufficient hydrophilicity to be swollen by water. 6 In our previous report, poly(allylamine) substituted with naphthoquinone, which has a higher hydrophilicity than anthraquinone, achieved its full capacity by reducing the introduction degree of naphthoquinone to about 20%. We therefore aimed for an anthraquinone introduction degree of ≤20%.…”

“…We very recently proposed a relatively facile synthesis of hydrophilic redox polymers using commercially available poly(allylamine), which is easy to purify and whose hydrophilicity is easily adjusted by changing the redox molecule's introduction degree. 6 In addition, a higher hydrophilicity is expected in an acidic aqueous electrolyte as a result of cationization of the unreacted amine sites in the poly(allylamine) (pK a 9.5 31 ). For a first trial, we aimed to synthesize an anthraquinone-substituted poly-(allylamine) with sufficient hydrophilicity to be swollen by water.…”

“…Synthesis of Anthraquinone-Substituted Poly(allylamine) polymers that have a redox capability involving two electrons in one step. 6,8,[18][19][20]28 This rapid electron (and proton) transport capacity in the polymer layer (Figure 1b) is presumably ascribed to its high hydrophilicity and the inhibition of π−π stacking of the side-chain redox units and suggests that the polymer/carbon composite electrode would be expected to operate at an unprecedentedly high rate capability.…”