Reversible Hybrid Aqueous Li?CO2 Batteries with High Energy Density and Formic Acid Production

Article abstract of DOI:10.1002/cssc.201903297

Metal?CO₂ batteries, an attractive technology for both energy storage and CO₂ utilization, are typically classified into organic Li(Na)?CO₂ batteries with a high energy density/output voltage and aqueous Zn?CO₂ batteries with flexible chemical production. However, achieving both high-efficiency energy storage and flexible chemical production is still challenging. In this study, a reversible hybrid aqueous Li?CO₂ battery is developed, integrating Li with an aqueous phase, which exhibits not only a high operating voltage and energy density but also highly selective formic acid production. Based on a Li plate as the anode, NaCl solution as the aqueous electrolyte, solid electrolyte Li_1.5Al_0.5Ge_1.5P₃O₁₂ (LAGP) as a separator and Li⁺ transporter, and a bifunctional Pd-based electrocatalyst as the cathode, the resulting battery shows a high discharge voltage of up to 2.6 V, an outstanding energy conversion efficiency of above 80 %, and remarkable selectivity of CO₂-to-HCOOH conversion of up to 97 %. The related reaction mechanism is proposed as CO₂+2 Li+2 H⁺?HCOOH+2 Li⁺.

Full text of DOI:10.1002/cssc.201903297

Accepted Article
Title: Reversible Hybrid Aqueous Li-CO2 Batteries with High Energy
Density and HCOOH Production
Authors: Rui Yang, Zhen Peng, Jiafang Xie, Yiyin Huang, Rahul Anil
Borse, Xueyuan Wang, Maoxiang Wu, and Yaobing Wang
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Reversible Hybrid Aqueous Li-CO2 Batteries with High Energy
Density and HCOOH Production
Rui Yang, [a], [b]+ Zhen Peng, [a], [b]+ Jiafang Xie, [a] Yiyin Huang, [a] Rahul Anil Borse, [a], [b] Xueyuan Wang,
[a], [b] Maoxiang Wu, [a] and Yaobing Wang*[a]
+These authors contributed equally to this work.
[a]
[b]
R. Yang, Dr. J. Xie, Z. Peng, Dr. Y. Huang, R. A. Borse, X. Wang, Prof. M. Wu, Prof. Y. Wang
CAS Key Laboratory of Design and Assembly of Functional Nanostructures, Fujian Provincial Key Laboratory of Nanomaterials, State Key Laboratory of
Structural Chemistry
Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences
Yang Qiao West Road 155#, Fuzhou 350002, P. R. China
E-mail: wangyb@fjirsm.ac.cn
R. Yang, Z. Peng, R. A. Borse, X. Wang
University of Chinese Academy of Sciences, Beijing 100049, P. R. China
Supporting information for this article is given via a link at the end of the document.
Abstract: Metal-CO2 batteries, an attractive technology for both
energy storage and CO2 utilization, are typically classified into
organic Li(Na)-CO2 batteries with a high energy density/output
voltage and aqueous Zn-CO2 batteries with flexible chemical
production. However, achieving high-efficiency energy storage and
flexible chemical production simultaneously is still challenging.
Herein, we proposed and realized a reversible hybrid aqueous Li-
CO2 battery integrating Li with aqueous phase, exhibiting not only a
high operating voltage and energy density, but also highly selective
HCOOH production simultaneously. Based on a Li plate as the
anode, NaCl solution as aqueous electrolyte, solid electrolyte
Li1.5Al0.5Ge1.5P3O12 (LAGP) as separator and Li+ transporter, and a
bifunctional Pd-based electrocatalyst as the cathode, the resulting
battery possessed the high discharge voltage up to 2.6 V, the
outstanding energy conversion efficiency higher than 80%, and the
remarkable selectivity of CO2-to-HCOOH conversion up to 97%. The
related reaction mechanism was proposed as CO2+2Li+2H+
⇋HCOOH+2Li+.
Al-CO2 electrochemical cells with ionic liquid as electrolyte and
O2 assistance have also been reported for value-added chemical
production.[6]
Primary organic Li-CO2 batteries with pure CO2 as feed gas
were proposed by Archer’s group in 2013, in which CO2 was
converted into Li2CO3 and C at moderate temperatures.[7] The
first rechargeable Li-CO2 battery with high discharge voltage
was realized by Zhou’s group.[8] Since then, organic Li(Na)-CO2
batteries with various advanced cathodes have been
investigated, including graphene [9], Cu nanoparticles dispersed
onto N-doped grapheme (Cu-NG) [10], and Ru/Ni [11], for getting
high energy density, output voltage, and durability. But, the
limited product selectivity of CO2 conversion obstructs its wider
application.
The aqueous Zn-CO2 battery system was proposed by our
group, which could flexibly convert CO2 to kinds of value-added
chemicals with the help of the proton-coupled electron transfer
mechanism in aqueous electrolyte. For example, the
rechargeable aqueous Zn-CO2 batteries with bifunctional Ir@Au
produced CO[12] and the reversible aqueous Zn-CO2 batteries
with Pd-based electrocatalyst produced HCOOH[13]. Furthermore,
non-precious metal-based Ni–N and P–O codoped graphene
(NiPG)[14] and metal-free carbon-based materials Si and N
codoped carbon (SiNC)[15] were also developed as cathode in
aqueous Zn-CO2 batteries. However, aqueous Zn-CO2 batteries
exhibits relatively lower operating voltage and energy density
compared to organic Li(Na)-CO2 batteries.[16]
Both organic Li-CO2 and aqueous Zn-CO2 batteries can
convert CO2 and store intermittent electricity during discharge
and charge processes, though they gain different advantages.
Organic Li-CO2 batteries shows high energy density/output
voltage but limited CO2 conversion products. In contrast,
aqueous Zn-CO2 batteries shows the feasible CO2
electrochemistry for value-added chemicals production but lower
energy density/operating voltage. Thus, neither organic Li-CO2
nor aqueous Zn-CO2 batteries can satisfy the practical
requirements of high energy density/output voltage as well as
value-added chemicals production simultaneously in one battery.
Introduction
The excessive usage of fossil fuels results in soaring carbon
dioxide (CO2) emissions that inhibits the sustainable
development of the society. Renewable energy sources, as
green alternatives but intermittent supply, are explored to
partially substitute for fossil fuels.[1] Therefore, it is necessary to
develop new green energy conversion and storage techniques
with abilities of CO2 fixation/utilization and electricity
production/sustainable supply.[2]
Metal-CO2 batteries can store intermittent electricity from
fossil fuels and renewable power sources during charging, and
convert CO2 to value-add chemicals during discharging.[3] Thus,
It grows into a new and promising technology for energy storage
and CO2 utilization, which mainly sorts into organic Li(Na)-CO2
batteries with highly active Li(Na) anodes and organic
[4]
electrolytes
and aqueous Zn-CO2 batteries with relatively
lower active Zn anode and aqueous electrolytes.[5] Additionally,
1
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Herein, the reversible hybrid aqueous Li-CO2 battery was
proposed and assembled with three-dimensional integrated Pd
(3DI-Pd) electrocatalyst, Li plate, and solid electrolyte
Li1.5Al0.5Ge1.5P3O12 (LAGP) as the cathode, anode, and
separator, respectively. The battery performance, such as high
energy density/output voltage as well as value-added chemicals
production, was investigated. Finally, the battery reaction
mechanism was also proposed.
respectively. The high-resolution transmission electron
microscopy (HRTEM) image (Figure. S4) displayed well
crystallized with well-resolved lattice fringes with the interplanar
space of 0.23 nm, belonging to the metallic Pd (111).[17] The
high-angle annular dark field (HAADF) image and the
corresponding mappings (Figure. S5) showed the existence of
abundant Pd. The X-ray photoelectron spectroscopy (XPS)
showed the Pd peaks without other metals (Figure. S6),
suggesting the pure Pd phase in the prepared material. The
fitting peaks of Pd 3d5/2 (Figure. S7) were located at 335.4 eV,
335.9 eV, and 336.6 eV, corresponding to Pd (0), Pd (II), and Pd
(IV), respectively.[18] The double-layer capacitance (Cdl) of 3DI-
Pd was 19 mF cm-2, indicating the ample electrochemically
active surface of the obtained material (Figure. S8). The
Brunauer–Emmett–Teller (BET) surface area of the 3DI-Pd
obtained from nitrogen adsorption–desorption measurement was
estimated to describe specific surface area (Figure. S9). These
results demonstrated that we successfully synthesized 3DI-Pd
with massive and uniformly distributed pores and high
electrochemically active surface, indicating the potential
employment as the cathode in the battery.
Results and Discussion
Scheme 1. Schematic representation of the proposed reversible hybrid
aqueous Li-CO2 battery.
The proposed reversible hybrid aqueous Li-CO2 battery was
shown in Scheme 1. It consists with 3DI-Pd, Li plate, and solid
electrolyte LAGP as the cathode, the anode, and the separator,
respectively. During discharge process, CO2 was converted into
HCOOH on 3DI-Pd cathode, driven by Li dissolution on the
anode. During charge process, HCOOH-to-CO2 conversion
occurred on Pd cathode, accompanied by the migration of Li+
through the LAGP and its deposition on the anode. By taking
advantage of the LAGP as the Li+ transporter and the
bifunctional electrocatalyst cathode, the proposed Li-CO2 battery
could be reversible. The theoretical operating voltage and
energy density were calculated as +2.73 V and 2528 Wh kg-1,
respectively (details in Experimental Section). Thus, the
designed Li-CO2 battery theoretically presents high output
voltage/energy density and HCOOH production simultaneously,
comparable to organic Li-CO2 batteries and aqueous Zn-CO2
batteries, respectively.
To realize such a reversible hybrid aqueous Li-CO2 battery,
the bifunctional electrocatalyst cathode for electrochemical
carbon oxide reduction reaction (CDRR) and formic acid
oxidation (FAO) is required. We prepared an integrated Pd
nanoparticles @ carbon paper electrode, namely 3DI Pd, by
potentiostatic deposition method, as shown Figure. S1 and
Figure. S2. Scanning electron microscopy (SEM) reveals that
the abundant and uniformly distributed pores consisted of
nanoparticles on carbon paper. (Figure. 1a and Figure. S3).
Figure 1b proclaimed the powder X-ray diffraction (PXRD)
pattern of the prepared material. with four peaks at 40.2°, 46.8°,
68.3°, and 82.4°, which were indexed to the (111), (200), (220),
and (311) facets of the metallic Pd (JCPDS 87-0638),
Figure 1. Characterization and electrocatalytic performances of 3DI-Pd
catalyst. a) SEM image. b) XRD spectrum. c) LSV curves with bare carbon
paper (CP) as comparison in CO2 and Ar atmosphere with 10 mV s-1. d) Partial
current densities and e) Faradaic efficiencies (FEs) of HCOOH and H2. f) Total
current density generated on 3DI-Pd during long-term electrolysis. The
electrocatalyst CO2 reduction reaction was witnessed in CO2-purged 0.1 M
NaCl and 0.1 M LiCl solution. The scale bar is 40 μm in a.
The CDRR activity on 3DI-Pd catalyst was assessed by
linear sweep voltammetry (LSV) and potentiostatic electrolysis in
a three-electrode system and CO2-saturated neutral electrolyte.
3DI-Pd showed the current density (j) of 5 mA cm-2 in CO2 at
only -0.22 V, which rapidly increased to 10 mA cm-2 at -0.33 V.
2
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The much lower current density in Ar, exemplifying 2.3 mA cm-2
at -0.33 V, suggested the high electrocatalytic properties of 3DI-
Pd to CDRR (Figure. 1c). The negligible response of bare
carbon paper (CP) in both CO2 and Ar demonstrated the high
electrocatalytic activity was originated from 3DI-Pd, which was
consistent with rich pores and high electrochemically active
surface. To further verify the CDRR activity and the related
products on prepared 3DI-Pd, potentiostatic electrolysis was
tested in CO2-saturated 0.1 M NaCl and 0.1 M LiCl solution. At -
0.17 V, the partial current density of HCOOH was around 5 mA
cm-2, which raised up to 16 mA cm-2 at -0.37 V. In contrast, H2
production showed the largest current density of 0.65 mA cm-2 at
-0.17 V (Figure. 1d). Furthermore, the Faradaic efficiency (FE) of
HCOOH was 61% at 140 mV overpotential and rapidly
increased to higher than 90% at 190 mV overpotential (Figure.
1e and Figure. S10), demonstrating the superior CO2-to-HCOOH
Based on the bifunctional 3DI-Pd electrocatalyst as the
cathode, the reversible hybrid aqueous Li-CO2 battery was
assembled. The polarization and power density curves of the
battery suggested the feasibility of the reversible hybrid aqueous
Li-CO2 battery (Figure. S14). The discharge capacity achieved
as high as 2825 μAh cm-2 at 2.0 V. Moreover, the max power
density of reversible hybrid aqueous Li-CO2 battery was
determined to 7.22 mW cm-2. With the discharge current
increasing, the tendency of discharge voltage of the battery was
obtained in Figure 2a. At discharge current of 0.01 mA (0.056
mA cm-2), the voltage was stable at around 2.6 V, which
remained 2.23 V and 1.67 V as the discharge current increased
to 0.1 mA (0.56 mA cm-2) and 1 mA (5.56 mA cm-2), respectively.
The resulting energy density of the battery was 2408 Wh Kg-1,
2065 Wh Kg-1, and 1546 Wh Kg-1 at 0.01 mA, 0.1 mA, and 1 mA,
respectively. The charge voltage of the battery was only 2.86 V
at 0.1 mA (0.56 mA cm-2), which increased slowly to 3.17 V at
0.5 mA (2.78 mA cm-2) (Figure. S15). CO2 was the charge
product from the GC signals (Figure. S16). Moreover, the
corresponding HCOOH product obtained 70% FE at 0.5 mA
(2.78 mA cm-2) and 97% at 1.0 mA (5.56 mA cm-2) (Figure. 2b
and Figure. S17). In Li-CO2 batteries with hybrid electrolytes, the
discharge products depend on the cathode materials (Figure
S18).
Furthermore, at the discharge-charge cyclic current of 1.0
mA (5.56 mA cm-2), the discharge voltage rapidly reached the
stable value of 1.7 V, which very slowly deceased to 1.49 V at
240 min (Figure. 2c). Meanwhile, the corresponding selectivity of
HCOOH product was always higher than 90% during long-term
test. When the current increased to 0.1 mA (0.56 mA cm-2), the
discharge and charge voltages were 2.87 V and 2.35 V,
respectively, which slightly changed to 1.67 V and 2.67 V after
400 min (Figure. 2d). The voltage gap between discharge and
charge was 0.52 V and slowly decreased to 1 V after 30 cycles.
The discharge and charge voltage were stable at 1.75 V and
3.72 V separately, when cycled for 400 min at 0.5 mA (2.78 mA
cm-2). The cycle performance at 2.78 mA cm-2 was kept stable
even after 10h (Figure S19).
conversion selectivity comparing with H2 generation on 3DI-Pd
[19]
catalyst (Figure. 1d and 1e)
The FE sum of HCOOH and H2
products was always near 100%, suggesting no other products
of CDRR on 3DI-Pd. The GC signals also demonstrate it (Figure
S11). The electrochemical impedance spectroscopy (EIS)
analysis (Figure. S12) showed the good conductivity and small
charge transfer resistance of 3DI-Pd. Besides, 3DI-Pd also
showed stable current densities during potentiostatic electrolysis
(Figure. 1f), confirming the excellent catalytic stability of 3DI-Pd
towards CDRR. Electrocatalyst FAO was characterized by cyclic
voltammetry (CV) (Figure. S13) in the solution of 0.1 M NaCl,
0.1 M LiCl and 0.1 M HCOONa. A obvious peak at 0.54 V was
obtained with current density of 25 mA cm-2, showing the
[20]
superior catalyst activity of FAO.
The above results
manifested the 3DI-Pd as a bifunctional electrocatalyst towards
CDRR (CO2 reduction to HCOOH) and FAO (HCOOH oxidation
to CO2) possessing high electrochemical activity and selectivity,
which could be applied as the bifunctional cathode in the
reversible hybrid aqueous Li-CO2 battery.
Figure 2. The discharge voltage and HCOOH production of the reversible
hybrid aqueous Li-CO2 battery. a) Galvanostatic discharge voltages, and b)
the corresponding FEs of HCOOH and H2 at different currents. c)
Galvanostatic long-time discharge curve at 5.56 mA cm-2 and corresponding
products selectivity. d) Galvanostatic discharge–charge cycling curves at 0.56
mA cm-2 and 2.78 mA cm-2. The area of cathode is 0.18 cm2.
Figure 3. Deep discharge and charge profiles of the reversible hybrid aqueous
Li-CO2 battery. a) Galvanostatic discharge and charge curves at curtailing
capacity 1130 μAh cm-2. b) Cycling behavior at a current density of 0.56 mA
3
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cm-2. c) The energy efficiency and voltage gap between charge and discharge
at 0.56 mA cm-2 cycling.
On the other hand, from the view of value-added CO2
conversion, reported organic Li-CO2 batteries produce carbon or
oxalate, while the reversible hybrid aqueous Li-CO2 battery
generates HCOOH, a widely used feedstock and promising fuel,
which was also reported in aqueous Zn-CO2 batteries. Moreover,
the reversible hybrid aqueous Li-CO2 battery exhibits great
potential to produce more valuable products, such as ethylene,
alcohols, and aldehyde, because of its higher driving force than
aqueous Zn-CO2 batteries. Therefore, compared with aqueous
Zn-CO2 batteries and organic Li-CO2 batteries, the reversible
hybrid aqueous Li-CO2 battery has not only both advantages of
high energy density, discharge voltage, as well as selective
HCOOH production, but also higher energy density and more
value-add chemicals, such as ethylene and ethanol, which
require higher overpotentials.
The galvanostatic discharge and charge at different currents
was implemented (Figure. 3a) to better depict the characteristic
of the reversible hybrid aqueous Li-CO2 battery. With the
curtailing high capacity of 1130 μAh cm-2, as the current density
increased from 0.56 mA cm-2 to 2.78 mA cm-2 and further to 5.56
mA cm-2, the battery displayed low flat charge plateaus at 2.86 V,
3.15 V and 3.8 V, with stable discharge plateaus at 2.38 V, 2.06
V, and 1.71 V, respectively. The voltages of discharge and
charge were slightly changed when cycled at a current density of
0.56 mA cm-2 and a curtailing capacity of 48 μAh cm-2 (Figure.
3b). And the voltage of discharge and charge kept stable even
after 60 cycles at higher 2.78 mA cm-2 with a curtailing capacity
of 240 μAh cm-2 (Figure. S20). As the cycle current was at 0.56
mA cm-2, the energy efficiency was higher than 80% at
beginning and kept around 70% even after 30 cycles (Figure.
3c). Meantime, the battery delivered a stable voltage gap during
30 cycles. Thus, the energy density of the battery reached 2180
Wh Kg-1, which slightly decreased to 1502 Wh Kg-1 after 30
cycles.
On one hand, from the view of energy conversion and
storage, the reversible hybrid aqueous Li-CO2 battery possesses
the output voltage that is far higher than aqueous Zn-CO2
batteries and comparable to organic Li-CO2 batteries, and
moreover the charge voltage that is much lower than organic Li-
CO2 batteries. Meantime, the reversible hybrid aqueous Li-CO2
battery showed the superb rate performance even at high
current densities. These advantages of the reversible hybrid
aqueous Li-CO2 battery could be owing to the new reaction
mechanism derived from the integration of Li anode and
aqueous catholyte in the battery.
Conclusion
In summary, we realized the first reversible hybrid aqueous Li-
CO2 battery integrated Li/aqueous phase with solid electrolyte
LAGP as Li+ transporter and separator, 3DI-Pd electrocatalyst as
cathode, and the Li plate as anode. The reversible hybrid
aqueous Li-CO2 battery revealed high discharge voltage up to
2.6 V, energy conversion efficiency higher than 80%, as well as
selective CO2-to-HCOOH conversion with 97% FE. The related
battery mechanism was proposed as CO2+2Li+2H+
⇋HCOOH+2Li+. This work provides the possibilities for metal-
CO2 batteries with high energy density/output voltages and
value-added chemicals product simultanueously, encouraging
the further research for more practical applications and usages.
Experimental Section
In reported organic Li-CO2 batteries, the battery reaction
mostly occurred as described in Equation 1 [21]
:
3CO2+4Li++4e- →2Li2CO3+C
Eθ=2.80 V vs Li+/Li (1)
Chemicals and reagents: Carbon paper (HCP 020N, HeSen),
PdCl2 (59-60%, MACKLIN), nafion membrane (nafion 211,
DuPont), KHCO3 (99.7% Sigma-Aldrich), DI water was used in
this work. All other reagents were purchased from Sinopharm
Chemical Reagent Co., Ltd. without further purification.
Synthesis of 3DI-Pd: In a typical experiment, the 3DI-Pd was
obtained in three electrode system by electrodeposition, which
was carried out in 0.09 M PdCl2, 0.1 M HCl, 0.5 M H2SO4 and
0.1 M CH3COOH at -1V vs Ag/AgCl for 40s with Pt mesh as
counter electrode and carbon papers as substrates. The
resulting sample was washed using DI water and dried under N2
flow. Carbon papers with the working size of 0.18 cm2 were used
as substrates without any pre-treatment.
Though the theoretical electromotive voltage is as high as 2.8 V,
organic Li-CO2 batteries produced massive non-conductive
compound Li2CO3, which
require high charge voltage to
decompose (3.8 V). Aqueous Zn-CO2 batteries typically produce
CO and O2 during discharge and charge separately (Equation 2
and 3), which results in relatively low operating voltages,
exampling 0.6 V during discharge and 2.5 V during charge.
Zn+CO2+2H++2OH- → Zn(OH)42-+CO+2H2O E=0.707
V
vs
Zn2+/Zn
(2)
Zn(OH)42-+H2O→Zn+1/2O2+2H++4OH- E=2.041V vs Zn2+/Zn
(3)
In contrast, the reversible hybrid aqueous Li-CO2 battery works
as described in Equation 4:
Characterizations: The structure of 3DI-Pd was characterized
with High-resolutionscanning electron microscope (SEM, JEOL-
6700F) and low-resolution SEM images (SEM, Phenon G2).
Structure and element distribution were obtained by
Transmission electron microscopy (TEM, FEI Tecnai G2F30). X-
ray powder diffraction (XRD) was collected on a Philip Xhilip Pro
MPP diffractometer using a Cu Kα (= 1.54 Å) radiation source at
CO2+2Li+2H+⇋HCOOH+2Li+
Eθ=2.73 V vs Li+/Li
(4)
Thus, the reversible hybrid aqueous Li-CO2 battery achieved the
energy efficiency (EE) that is comparable to reported aqueous
Zn-CO2 batteries (81.2%) and organic Li-CO2 batteries ( ≈
80%).[22] Also, its theoretical energy density is far higher than
aqueous Zn-CO2 batteries and comparable to organic Li(Na)-
CO2 batteries (Table S1). Therefore, the reversible hybrid
aqueous Li-CO2 battery showed high energy conversion and
storage performance that matches and even exceeds organic Li-
CO2 batteries and aqueous Zn-CO2 batteries in some indexes.
o
the scan rate of 5 min-1. X-ray photoelectron spectroscopy
(XPS, VG ESCALAB 250) was used to characterize their
chemical valence of the materials with an Al K X-ray source at
1487 eV. The chamber pressure was kept below 3×10−10 mbar
during analysis and specific correction was done by employing
the C 1s binding energy of 284.8 eV.
4
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Electrochemical CO2 reduction (CDRR) measurements: The
CDRR test was operated at a gastight H-type reactor separated
by a nafion membrane with CO2 saturated 0.1 M NaCl and 0.1 M
Anode (0.5 M LiTFSI in TEGDME solution)
Cathode:CO2 + 2e + 2H
HCOOH
Anode:2Li - 2e
2Li
LiCl solution (PH=6.5).
A three-electrode system with an
Overall reaction:
electrochemical station (CHI 660E) was used in electrochemical
measurements. Ag/AgCl (saturated KCl) and Pt mesh (11 cm2)
were used as reference and counter electrode, respectively. The
products were obtained by galvanostatic electrolysis about 0.5 h
with stirring at 500 rpm. Before the experiment, cathodic
electrolyte was pumped with CO2 (purity of 99.999%) for 30 min,
and during the experiment, CO2 was controlled to flow through
cathode compartment with the rate of 20 mL min-1. EIS was
performed at -0.8 V (vs Ag/AgCl) with the frequency range from
0. 1 Hz to 1 MHz and the voltage amplitude of 5 mV. Potential
values were converted to the RHE scale as following equation:
VRHE = VAg/AgCl + 0.197 + 0.059V × pH.
Reversible aqueous Li-CO2 batteries: The reversible aqueous
Li-CO2 batteries consisted of two chambers, separated by
conductive ceramic electrolyte (Li1.5Al0.5Ge1.5P3O12, LAGP). 3DI-
Pd materials in 0.1 M NaCl and 0.1 M LiCl solution were used as
cathode under CO2 flow at the rate of 20 ml min-1. 0.1 M
HCOONa was added in cathode electrolyte during charge and
cycle process. Li plates were applied as anode in 0.5 M LiTFSI
in TEGDME solution. The batteries were assembled in an Ar-
filled glove box with less than 0.1 ppm of both oxygen and
moisture.
+
+
CO + 2Li + 2H
HCOOH + 2Li
RT
2
aHCOOHa2Li+
Etheory =Ec - Ea =EθCO
- EθLi+
-
ln
2 /HCOOH
nF aCO a2Lia2H+
/Li
2
8.314*298.15
2*96485
0.1*0.52
= + 0.02 V - (- 3.05 V) -
= 2.73 V
ln
1*12*(106.5
)
2
EθCO /HCOOH = + 0.02 V vs. SHE
2
EθLi+ /Li = - 3.05 V vs. SHE
Note: R is 8.314 J K-1 mol-1 (molar gas constant), T is
298.15 K, n is 2 (the number of electrons transferred per mole of
product), F is 96485 C mol-1 (Faradaic constant), a is the
corresponding activity.
The theoretical energy density (ED) of the battery could be:
nFEtheory
1Ah 2964852.73
1
ED=

=

=2528Wh Kg1
LiMLi CO MCO 3600C 26.941144 3.6
2
2
Note: n is 2 (the number of electrons transferred per mole of
product), F is 96485 C mol-1 (Faradaic constant), α is chemical
coefficient, M is the relative molecular mass.
Detection of gas products: All gas products from CDRR
electrocatalysis and discharge process were detected by gas
chromatograph (GC, 9700II, FULI), which equipped with a
column (TDX-01), a thermal conductivity detector, a Ni reformer
and a flame ionization detector. H2 were detected using a TDX-
01 column. The carrier gas was Ar and the quantification for
each gas was determined by external standard method. The
Faradaic efficiency (FE) was calculated based on the number of
products, which was obtained from GC analysis during the
potential controlled electrolysis. The total electric charge was
obtained from the steady-state current recorded during
electrolysis.
Acknowledgements
Funding: This work was supported by the National Natural
Science Foundation of China (No. 21872147, 21501173,
21805277, and 21601190), the Natural Science Foundation of
Fujian Province (No. 2018J05030), the National Key R&D
Program of China (2016YFB0100100), the Key Research
Program of Frontier Sciences, CAS (No. ZDBS-LY-SLH028),
and the Strategic Priority Research Program, CAS (No.
XDB20000000). Author contributions: R. Yang synthesized
the material, assembled the battery and wrote the paper. Z.
Peng participated to design experiment, conduct the
characterization and add the supplement experiments. Y. Wang
was in charge of the manuscript. All authors discussed the
results and commented on the manuscript. R. Yang and Z. Peng
contributed equally to this work. Competing interests: The
authors declare that they have no competing interests. Data and
materials availability: All data needed to evaluate the
conclusions in the paper are present in the paper and/or the
Supplementary Materials. Additional data related to this paper
may be requested from the authors.
The FE calculation of H2 was described as:
iH
XH *vCO *n*96485
2
2
2
FEH =
=
2
itotal
itotal
iH
:
partial current for H2 production;
2
itotal
xH
: total current;
:
the production rate of H2 (measured by GC);
2
vCO : CO2 flow rate;
2
n: the number of transferred electrons during product
formation, which is 2 for H2.
Keywords: hybrid aqueous Li-CO2 • electrocatalyst • reversible •
CO2 utilization
Detection of liquid products
All liquid products were tested by high efficiency liquid
chromatography (HPLC, P230 equal degree and RI 230, Elite)
equipped with a SUGAR SH1101 column, a UV230+, and a RI
detector.
Theoretical Potential of Reversible Hybrid Aqueous Li-CO2
Batteries
When the reversible hybrid aqueous Li-CO2 battery cycles:
Cathode (the solution of 0.1 M NaCl, 0.1 M LiCl, and 0.1 M
HCOONa, pH=6.5)
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6
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Entry for the Table of Contents
FULL PAPER
The first reversible hybrid aqueous
Li-CO2 battery was proposed and
realized with solid electrolyte LAGP
as the separator and Li+ transporter,
achieving high energy density,
Rui Yang+, Zhen Peng +, Jiafang Xie,
Yiyin Huang, Rahul Anil Borse,
Xueyuan Wang, Maoxiang Wu, and
Yaobing Wang*
Page No. – Page No.
output voltage, and highly selective
HCOOH production simultaneously,
which expands the application range
of metal-CO2 batteries with high-
efficiency energy storage and value-
added CO2 conversion.
Reversible Hybrid Aqueous Li-CO2
Batteries with High Energy Density
and HCOOH Production
7
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