Poly(dihydroxybenzoquinone): Its high-density and robust charge storage capability in rechargeable acidic polymer-air batteries

Article abstract of DOI:10.1039/d0cc00660b

A rechargeable acidic polymer-air battery was firstly fabricated with poly(2,5-dihydroxy-1,4-benzoquinone-3,6-methylene) (PDBM) as the anode, the conventional Pt/C cathode catalyst, and acidic aqueous electrolyte (pH 1). This battery yielded a high discharging capacity of 349 mA h g_polymer^-1 with a long-lifetime of >500 cycles and high rate capabilities (up to 10C).

Full text of DOI:10.1039/d0cc00660b

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Poly(dihydroxybenzoquinone): Its High-density and Robust Charge
Storage Capability in Rechargeable Acidic Polymer-air Batteries
Received 00th January 20xx,
Accepted 00th January 20xx
Kouki Oka,a Shuhei Furukawa,a Saki Murao,a Tatsuya Oka,a Hiroyuki Nishide a,b and Kenichi Oyaizu
a,b
DOI: 10.1039/x0xx00000x
*
A rechargeable acidic polymer-air battery was firstly fabricated their densely populated redox sites16-19. These redox polymers
with
poly(2,5-dihydroxy-1,4-benzoquinone-3,6-methylene) have been applied in sensors20, electrochromic displays21, solar
(PDBM) as the anode, the conventional Pt/C cathode catalyst, and cells22-24, and also in rechargeable devices as anode- and
acidic aqueous electrolyte (pH 1). This battery yielded a high cathode-active materials6, 25-33. They are light-weight, flexible,
discharging capacity of 349 mAh/gpolymer with a long-lifetime of moldable, and are easily processed by wet-fabrication.
>500 cycles and high rate capabilities (up to 10 C).
Previously, we reported anthraquinone polymers as an anode-
active material for rechargeable air batteries30, 31. The use of
redox polymers, instead of metals, released the rechargeable
air batteries from the dendrite problem and reduced the
environmental impact by virtue of the heavy atom-free
process. However, the carbonate clogging problem still
remains due to the use of the strongly basic 10 M NaOH
aqueous solution as the electrolyte. It is desirable that the
rechargeable air batteries are composed of organic redox
polymers and neutral or acidic electrolyte. Fortunately,
bifunctional air electrodes for acidic aqueous electrolyte have
been aggressively investigated for unitized regenerative
Recently, electrochemical energy storage devices have been
intensively pursued for the future renewable energy-based
society, to buffer the unpredictable energy generation, to
facilitate the efficient use of the renewable energy sources,
and to reduce the environmental impact of device materials1-7
In spite of the great success of lithium-ion batteries8,
.
,
9
aqueous metal-air batteries have gained revived interest to
achieve much larger energy density for the increasing demand
of electricity consumption and lower environmental burden4,
10, 11. Aqueous metal-air batteries combine the design features
of both conventional batteries and fuel cells 10, and are
fabricated with a metal anode and an air-breathing cathode in
a proper aqueous electrolyte. While primary Zn-air batteries
are commercialized, the rechargeable air batteries are still
under development due to the low cycle performance as a
proton exchange membrane fuel cells34, 35
.
In the current work, we focused on 2,5-dihydroxy-1,4-
benzoquinone (DHBQ), which is the major survivor of the
bleaching treatment of cellulose products36. DHBQ is readily
formed from the breakdown of cellulose products and exhibits
high resistance toward oxidants such as hydrogen peroxide,
ozone, and oxygen by virtue of resonance stabilization36.
DHBQ undergoes redox reaction in basic aqueous electrolyte
and organic electrolyte, and thus DHBQ and its polymer have
been investigated as the electrode-active material for alkaline
result of the formation of dendrites on the metal anodes4, 10, 12
.
In addition, a very basic aqueous solution (e.g., 6－7 M KOH
aqueous solution) is usually used as an electrolyte to achieve
the optimum ionic conductivity13. The batteries often suffer
from the carbonate clogging problem, which arises from the
reaction of CO2 in the air4.
aqueous redox-flow, lithium, and sodium-ion batteries37-40
.
Organic materials, with their inexpensive, abundant and
readily available building blocks and tunable or designable
properties, have been proposed as replacements for inorganic
Aziz and coworkers revealed a two-electron, two-proton redox
process of DHBQ in acidic aqueous solution37. However, there
have been no reports on the detailed electrochemical
characteristics in acidic aqueous solution and performance in
rechargeable air batteries. The polymeric extension of DHBQ
and its electrochemical properties in acidic aqueous solution
are described herein along with the molecular design of the
anode-active redox polymer toward the fabrication of a
rechargeable acidic polymer-air battery.
The cyclic voltammogram of DHBQ in acidic aqueous
electrolyte (pH 1), shown in Figure 1, is dominated by the
chemically reversible hydroquinone/quinone redox conversion
peak centered at 0.2 V vs. Ag/AgCl. This peak has previously
been assigned to the 2e-/2H+ redox conversion (see Figure 1
electrode-active materials14-17
. Especially, organic redox
polymers have progressed significantly, which are composed
of redox-active groups as repeating units and are characterized
by high charge transport and storage capabilities based on
a. Department of Applied Chemistry, Waseda University, Tokyo 169-8555, Japan.
*oyaizu@waseda.jp
b. Research Institute for Science and Engineering, Waseda University, Tokyo 169-
8555, Japan. *oyaizu@waseda.jp
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
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Inset), and as expected the peak shows a linear negative shift Simple addition condensation of DHBQ yielded PDBM (Figure
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39, 40
of the formal potential with increasing pH 37
.
2a)
.
Cottrell plots were obtained from the
DOI: 10.1039/D0CC00660B
chronoamperogram of the PDBM layer over the potential
range of 0.9 to 0.1 V (Figure 2b). In the region of pH around 1
－2, the electron exchange reactions tended to occur rather
than the disproportionation because of the low concentration
and instability of the semiquinone 49. Since the reduction of
DHBQ groups in the polymer layer was accompanied by the
incorporation of protons that diffuse through the layer to
restore electrical neutrality, the current observed in the
experiment is likely limited by proton diffusion, or the proton
10 A
0
O
O
OH
OH
OH
OH
+2H+ +2e-
-2H+ -2e-
HO
HO
0
0.2
0.4
0.6
0.8
Potential (V vs. Ag/AgCl)
Figure 1. Cyclic voltammogram of 1 mM DHBQ in acidic diffusion should be of the same order of magnitude as the
aqueous electrolyte (pH 1) at a scan rate of 10 mV/s. Inset: estimated electron exchange rates49. From the linearity of the
Redox reaction of DHBQ.
Cottrell plots (current density vs t–1/2), at the early stage of the
electrolysis, diffusion-limited behavior was observed and the
The redox interconversion between quinone (Q) and diffusion coefficient for the diffusion of charge within the
hydroquinone (H2Q) utilizes proton coupled electron transfer polymer layer by the electron self exchange was determined
(PCET) in transferring redox equivalents with the transfer of from the slope of the plots. The density of the original polymer
both electrons and protons, to avoid high-energy was estimated to be 1 g/cm3 and the swelling degree for water
intermediates 41-45. From the previous literature 41, 44, 45, the was estimated to be 1.26 (See Supporting Information). The
mechanical details of the electrochemical reduction from Q to diffusion coefficient of D = 3.9 × 10–12 cm2 s−1 was used to
H2Q at pH 1 could be estimated: 1. The reduction from Q to calculate the rate constant for the
semiquinone (HQ.) occurs by electron transfer followed by
proton transfer. 2. HQ. is highly unstable towards
disproportionation to be Q and H2Q. It should be noted that
the interpretation of the Q/H2Q interconversion is typically
complicated by adsorption and mass-transfer effects.
The heterogeneous electron-transfer rate constant (k0) of
DHBQ was estimated using plots of the peak current and the
46
square root of the sweep rate (the Nicholson method
)
(Figure S1). The diffusion coefficient (D) of the reactant was
determined from the diffusion-limited current using a rotating
disc electrode (Figure S2). The k0 and D values of DHBQ were
1.2 ×10−2 cm s−1 and 4.1 ×10−5 cm2 s−1, respectively, which
were similar to those of other typical redox molecules, such as Figure 2. a) Synthesis of PDBM. b) Chronoamperometric
anthraquinones and viologens 6, 37, 47, 48. These kinetic results Cottrell plots for the cast layer of PDBM with the thickness of
indicate that the charge-transfer from a current collector to 10 nm in acidic aqueous solution (pH 1). Inset: Current decay
DHBQ is sufficiently rapid.
of PFBM after application of potential (0 V vs. Ag/AgCl). c)
We anticipated that the DHBQ unit with a one-step two- Schematic image of proton exchange reaction in the polymer
electron reduction and fast electrode kinetics could be used as layer.
an electrode-active organic material with a high capacity and
plateau output voltage. We designed a compact polymer via a
simple polymerization method.
2 | J. Name., 2012, 00, 1-3
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Figure 3. a) Cyclic voltammogram of the PDBM/SWNT composite electrode in acidic aqueous solution (pH 1) at a scan rate of 1
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mV/s. b) The charging (black) and discharging (red) curves of the battery at 10 C. c) Discharging curves ofDtOhIe: 1b0.a10tt3e9r/yD0aCtCv0a0r6io60uBs
discharging rates of 10, 15, 20, 25, 30, and 60 C.
Figure 4. a) Schematic image of the polymer-air secondary battery (charging). b) Schematic image of the battery (discharging). c)
The charging (black) and discharging (red) curves of PDBM/air battery at 5 C. Inset: Capacity retention for 100 cycles upon
galvanostatic charge and discharge of the battery at 10 C. d) Discharging curves of the battery at various discharging rates of 5,
10, 15, 20, and 30 C.
electron self-exchange reaction kex = 1.1 × 103 M–1 s–1 cathode catalyst, and acidic aqueous electrolyte (pH 1). (Figure
according to the relation D = kexδ2C/6, where C and δ are the 4a and 4b). The charging-discharging curves of the battery at 5
redox site concentration in the layer and the distance at the C exhibited a plateau voltage at 0.5 V and their coulombic
time of the electron (or proton) transfer approximated by efficiencies were ˃99%. (Figure 4c), demonstrating the
(NAC)−1/3, respectively33. These values were similar to those reversible charge storage property of the cell. The capacity for
previously determined for redox polymers developed for facile the anode used in the battery was 349 mAh/gpolymer, suggesting
30, 31
charge storage such as anthraquinone polymers
,
that almost all of the DHBQ moieties contributed to charge
indicating the fast electron (or proton) transport storage. The rate performance of the discharging process is
characteristics of the PDBM layer (Figure 2b). This result shown in Figure 4d. The battery kept the almost full
revealed the applicability of the PDBM anode to the thin-film discharging capacity of 348 mAh/gpolymer even at a rapid
rechargeable devices, using only a small amount of the current discharging of 10 C which corresponded to the full discharging
collector material.
within 360 s. Furthermore, the battery kept the discharging
PDBM was coated on a glassy carbon plate with a thickness of capacity of 209 mAh/gpolymer (60% of the theoretical capacity)
ca. 10 µm in the presence of a small amount (20 wt%) of even at a rapid discharging of 30 C. The high capacities of 93%
single-walled carbon nanotube (SWNT)50 as the conductive after 100 charging-discharging cycles and 88% after 500 cycles
additive. The PDBM electrode displayed a reversible redox were still maintained (Figure 4d), which demonstrated the
response at 0.2 V vs. Ag/AgCl (Figure 3a). Reducing-oxidizing or long-life ability of the rechargeable acidic polymer-air battery.
charging-discharging curves of the PDBM electrode exhibited a
plateau voltage at 0.2 V, and their coulombic efficiencies (the
Conclusions
ratio of discharging vs. charging capacity) were nearly 100%
PDBM was prepared via simple addition condensation, and
(Figure 3b). The capacity of the PDBM electrode was 352
was characterized as an anode-active material in acidic
mAh/gpolymer, suggesting that almost all of the DHBQ moieties
aqueous electrolyte (pH 1). The polymer displayed a reversible
contributed to charge storage (the theoretical capacity of
redox response at 0.2 V vs. Ag/AgCl, and showed remarkably
PDBM was calculated to be 352 mAh/gpolymer). Cycle
high capacity (˃300 mAh/gpolymer) and good cycle performance
performance of the PDBM electrode (Figure 3b Inset) revealed
(˃500 cycles). For the first time, a rechargeable acidic polymer-
that 96% of the initial capacity was maintained after 100 cycles,
air battery was fabricated with a PDBM anode, an air cathode,
which was robust compared to other n-type redox materials
and acidic aqueous electrolyte (pH 1) displayed reversible
having a similar high density (>200 mAh/gpolymer), such as π-
charging-discharging curves at an output voltage of 0.5 V and
conjugated and nonconjugated redox polymers 19, 51. The rate
the active part of the anode showed a moderate energy
performance of the discharging process is shown in Figure 3c.
density of 172 mWh/ganode. In future studies, by developing
The PDBM electrode exhibited a small voltage drop but kept
polymeric anode-active materials, the fabrication of the
the full discharging capacity of 352 mAh/gpolymer which was
rechargeable acidic polymer-air battery with a high voltage of
almost 100% of the theoretical capacity even at a rapid
~1.5
V
and
a
higher energy density will be pursued.
discharging of 10 C which corresponded to the full discharging
within 360 s. Furthermore, the cell kept the high discharging
capacity of 250 mAh/gpolymer (85% of the theoretical capacity)
even at a rapid discharging of 60 C. These results clearly
demonstrated that PDBM was a high capacity electrode-active
material with the redox potential at 0.2 V vs. Ag/AgCl.
Furthermore, exploring the catalyst for air electrode34,
should enable us to fabricate a rechargeable acidic polymer-air
battery made from abundant sources.
35, 52
Conflicts of interest
A rechargeable acidic polymer-air battery was fabricated with
the PDBM electrode as the anode, the conventional Pt/C
There are no conflicts of interest to declare.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
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A rechargeable acidic polymer-air battery was firstly fabricated, which exhibited a long-lifetime of
>500 cycles and high rate capabilities.

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