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Enhanced Li2O2 Decomposition in Rechargeable Li-O2 Battery by Incorporating WO3 Nanowire Array Photocatalyst Yaya Feng, Hairong Xue, Tao Wang, Hao Gong, Bin Gao, Wei Xia, Cheng Jiang, Jingjing Li, Xianli Huang, and Jianping He ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b05944 • Publication Date (Web): 21 Feb 2019 Downloaded from http://pubs.acs.org on February 22, 2019

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ACS Sustainable Chemistry & Engineering

Enhanced Li2O2 decomposition in rechargeable Li-O2 battery by incorporating WO3 nanowire array photocatalyst Yaya Feng,† Hairong Xue,† Tao Wang,* Hao Gong, Bin Gao, Wei Xia, Cheng Jiang, Jingjing Li, Xianli Huang, Jianping He* College of Materials Science and Technology, Jiangsu Key Laboratory of Electrochemical Energy Storage Technologies, Nanjing University of Aeronautics and Astronautics, 29 Yudao Street, 210016 Nanjing, P. R. China. * Corresponding authors: [email protected], [email protected] †

These authors contributed equally to this work.

ABSTRACT Reducing the high charging overpotential of non-aqueous Li-O2 batteries is very important for their energy storage ability. Herein, we propose a newly photo-assisted Li-O2 battery system, in which WO3 nanowires array grows on carbon textile serves as a photocatalyst on the cathode. Owing to its abundant holes excited by visible light, the Li2O2 coated on WO3 nanowires can be efficiently oxidized during the charging process, resulting in the reduced charging potential and enhanced Li-O2 battery performance. Notably, the charging potential can still maintain at 3.55 V even after 100 cycles in this photo-assisted battery system, which is much lower than that of the dark state (4.4 V). These positive results indicate that the introduction of WO3 nanowires array photocatalyst provide possibilities in improving the energy conversion efficiency of the Li-O2 battery. Keywords: WO3 nanowire array, Li2O2 oxidation, photocatalyst, low overpotential, photo-assisted LiO2 battery

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INTRODUCTION As the concerns of global energy crisis, the development of new energy conversions and storage systems is highly desired in modern society.1-5 Rechargeable nonaqueous Li-O2 batteries provoke considerable attention as a promising power source for electric vehicles in recent years, due to their much higher theoretical specific energy (~3560 Wh kg-1) relative to traditional Li-ion batteries (387 Wh kg-1).6-9 Unfortunately, several fundamental challenges are still hindering their practical application.10-12 In this battery system, the typical discharge product (Li2O2) shows electrical poor conductivity and adverse insolubility, thus a high charging voltage (4-4.5V) for the decomposition of Li2O2 is unavoidable.13-16 The high charging voltage results in not only the low charge-discharge efficiency, but also the poor cycling life caused by the possible decomposition of organic electrolyte.1721

Therefore, reducing the high charging overpotential is highly desired for non-aqueous Li-O2

batteries. To overcome this critical issue for non-aqueous Li-O2 batteries, intensive research effort has been devoted in the past few years.22-26 At present, the introduction of oxygen evolution reaction (OER) catalysts is a common strategy for reducing charging overpotential. Traditionally, precious metals (i.e., Ru, RuO2 and IrO2) have been considered as a state-of-the-art catalyst towards OER, which can significantly lower charging overpotential due to their high OER activity.27-30 Nevertheless, scarcity and high-cost have hindered their practical application in non-aqueous Li-O2 batteries. Other nonprecious metals also have been widely used as OER catalysts, such as transition metallic oxide/sulfide/phosphide, and perovskite-type materials, whereas the reduction of charging potential (~4.0 V) is still limited.31-38 Recently, adding some redox mediators (i.e., I-) into the electrolyte is an effective method to obtain a low charging potential.39 However, the corrosivity of redox mediators 2


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cannot be neglected, which could result in the poor cycle performance. Therefore, it is necessary to develop a new, low-cost, and effective strategy to reduce the charging overpotential of non-aqueous Li-O2 batteries. Recently, a new photo-assisted Li-O2 battery has been developed to further reduce its charging overpotential.39-41 In this system of battery, the solar energy can convert into the electrical energy and then directly store in the battery. As a matter of fact, the semiconductor is most important part for this photo-assisted Li-O2 battery, which should possess high photoelectric conversion efficiencies.39, 41, 42 A great deal of the long-life photo-generated holes favor the decomposition of the Li2O2, leading to the low charging potential. Simultaneously, the long-life photo-generated electrons ensure the high rate performance.41, 43-46 Lately, a few researches for photo-assisted Li-O2 battery have been reported, which mainly focus on TiO2-based semiconductor materials.47-49 For example, introducing a dyesensitized TiO2 photoelectrode into Li-O2 battery can distinctly reduce their charging potential.40 However, TiO2 as a common semiconductor only can absorb ultraviolet light, which results in the very low utilization of the sunlight. Zhou group reported that the high overpotential of the traditional Li-O2 battery can be reduced by the incorporation of g-C3N4 photocatalyst for Li-O2 battery, in which g-C3N4 photocatalyst can absorb visible light.39 In general, the photo-generated electrons and holes on g-C3N4 photocatalyst easily recombine due to its low crystallinity, which against the long-life cycling stability. Among the various semiconductor photoelectrodes, WO3 with satisfying visible light response shows the advantageous hole diffusion length and electron mobility.50 Therefore, WO3 has a great potential for being a prospective candidate for the photo-assisted Li-O2 battery. Herein, monoclinic WO3 nanowire (NW) array is in situ grown on carbon textile (CT) by the simple hydrothermal method combined with heat treatment. The binder-free WO3 NW/CT can be used as both 3



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photoelectrode and air cathode for the photo-assisted Li-O2 battery, which exhibits a lower charging potential, high cycling stability, and good rate capability under visible light. This new-type Li-O2 battery realizes the conversion and storage of solar energy, and offers an effective method to reduce the overpotential of Li-O2 battery. EXPERIMENTAL SECTION In-situ growth of WO3 nanowires on carbon textiles The carbon textiles (Shanghai Hesen Electric Corporation) are cut in pieces of 2 3 cm2 and then treated by ultrasonic in acetone, deionized water, and anhydrous ethanol, respectively. The Na2WO4·2H2O is dissolved in deionized water with a magnetic stirrer at room temperature for 20 min. Subsequently, 3M HCl aqueous solution is slowly dropped into the above solution to adjust the pH (1.2). After forming a yellowish solution, 35 mmol H2C2O4·2H2O is added to the mixture, stirring to complete dissolution and diluted to 250 ml. For the next procedure, the as-prepared precursor was transferred into a Teflon-lined steel autoclave. Meanwhile, 2g (NH4)2SO4 is added into the reactor, and a piece of carbon textile is put into the autoclave and sealed at 180 oC for 4-20 h. After cooling to room temperature, the carbon textile is taken out and rinsed with deionized water several times, followed by drying in air at 60 oC. The as-prepared samples are calcination at 450 oC in air for 2 h or in N2 at 550 oC

for 2 h, or at 450 oC in air for 2 h and then at 550 oC in N2 for 2 h to obtain WO3-A, WO3-N,

WO3-AN, respectively. Characterization The morphology and structure of all samples are observed by the scanning electron microscope (SEM; Hitachi S-4800) and transmission electron microscopy (TEM; JEOL JEM-2100F). X-ray diffraction 4


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(XRD) patterns are recorded on a D8 Advance Diffractometer with monochromatic Cu Kα radiation. The diffuse reflectance spectra are recorded on a UV-visible spectrophotometer (DR UV-vis; Shimadzu UV-3600) and then converted into absorption spectra based on Kubelka-Munk transformations. X-ray photoelectron spectroscopy (XPS; ESCALab220i-XL spectrometer) is used to analyze the elemental chemical analysis and oxygen vacancy. Weight change is analyzed via a TG instrument (Shimadzu DTG-60HDTA-TG) in air at a heating rate of 10 oC min-1. Photoelectrochemical and electrochemical measurements The photoelectrochemical properties of the WO3 photoanodes are conducted in a three-electrode mode by using the Pt foil as a counter electrode, and saturated calomel electrode as a reference electrode, meanwhile, and the WO3 grown on the carbon textiles as working electrode. A 300 W Xe arc lamp is employed for the light source and the light beam was passed a set of glass filters (400 nm < λ < 800 nm) to filter the ultraviolet light and infrared light. Linear sweep voltammetry (LSV) under a scan rate of 10 mV s-1 and i-t curves at 1.23 V (vs. RHE) are obtained by the CHI660A electrochemical workstation. Zahner IM6 workstation Electrochemical impedance spectra (EIS) are evaluated by the Mott-Schottky (M-S) plots are measured by the Zahner IM6. The Li-O2 batteries are assembled in the glove box contained with dry Ar. It is made up of four parts: Li plate as the anode, ceramic membrane as a separator, and the WO3 NW array/CT as a cathode, 0.5 M LiClO4 disolved in TEGDME as electrolyte. LAND CT2001A battery test system is used to record the galvanostatic discharge/charge curves. The charging of Li-O2 battery was conduct with or without the light (400 nm < λ < 800 nm). RESULTS AND DISCUSSION

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The needle-like WO3 NW array is in-situ grown on carbon textiles through a hydrothermal reaction combined with heat treatment (Figure 1a). During the hydrothermal reaction, the reaction time plays an important role on the formation of the WO3 NW array. Figure 1b shows the feature of carbon textiles, which are woven from carbon fibers with smooth surface. In the initial reaction period, some W-precursor NWs begin to grow on the carbon fiber surface (Figure 1c). With the increase of hydrothermal time, more and more W-precursor NWs cover on the carbon fibers (Figure 1d, e). After hydrothermal reaction for 16 h, the carbon fibers are uniformly and completely coated with Wprecursor NWs (Figure 1f). Further increasing hydrothermal time to 20 h, too thick W-precursor NW array can be found on the carbon textiles (Figure 1g), which leads to the unfavorable electrolyte permeation and electronic transmission. The above results indicate the optimum hydrothermal time is 16 h. It is worth noting that the as-prepared W-precursor NWs grown on the carbon textiles are tungstic acid (Figure S1). Normally, monoclinic WO3 absorbs more visible light than hexagonal WO3, which are suitable for serving as photocatalysis or photoelectrocatalysis.51,

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Therefore, for purpose of

control the crystalline phase and improve the crystallinity of WO3, it is necessary to further heat treatment after the hydrothermal process. To explore the key factors for controlling the crystal form and crystallinity of WO3, several heat treatment methods are performed. After calcining at 450 °C in air for 2 h, the obtained WO3-A shows four broad peaks at 13.8, 22.8, 28.1 and 36.6°, corresponding to (100), (001), (200), (201) of hexagonal WO3 (JCPDS card no. 33-1387) (Figure 2a). With the increase in heat treatment temperature, the monoclinic WO3 are formed. Simultaneously, the carbon fibers start to be oxidized and cannot stably maintain their consecutive structure, evidenced by thermogravimetry of carbon textiles (Figure S2). The higher heat treatment temperature (450 °C) in air could destroy the structure of carbon textiles. 6


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For the WO3-N prepared by heating at 550 °C for 2 h in N2, the peaks appearing in 23.1, 23.5, 24.2 and 34.1° are well indexed to monoclinic phase (JCPDS card no. 20-1324). However, the color of WO3-N is navy blue (Figure S3), we speculate that this phenomenon is due to the existence of more defects in WO3-N. To gain more insight, we will discuss later. Taking the above observations into account, in order to obtain WO3 with fewer defects and monoclinic phase, the calcination process is performed at 450 °C for 2 h in air and then at 550 °C for 2 h in N2 atmosphere. The obtained sample (WO3-AN) shows typically monoclinic phase (JCPDS card no. 20-1324). The optical properties of the prepared samples were characterized by the UV-vis absorption spectra. As shown in Fig. 2b, the absorption edges of W-precursor NWs and the hexagonal WO3 (WO3-A) were about 425 nm. Whereas the absorption edge of monoclinic WO3 (WO3-N, WO3-AN) shows distinctly red shift (450 nm). According to these results, it can be concluded that the monoclinic WO3 could absorb more visible light relative to hexagonal WO3. Figure 2c shows the tauc plot of all samples, and the band gap can be obtained by the formula, αhν=A (hν-Eg)n, where h value is Planck's constant, ν value is the frequency of light, A is a material related constant, Eg is band gap energy, and n value is 2 for an indirect semiconductor WO3. Then, the band gaps of W-precursor NWs, WO3-A, WO3-N, WO3-AN can be fitted to be 3.01, 2.90, 2.65 and 2.63 eV, respectively. The similarly smaller values of WO3-N and WO3-AN confirm their monoclinic phase. The above results indicate the monoclinic WO3 can be prepared by heating at 550 °C under N2 atmosphere, nevertheless, it may have more defects. Interestingly, it can be found that all of the samples have a certain absorption of visible light in the range of 500-800 nm, which is commonly induced by the oxygen vacancy (Figure 2b).53, 54 It is frustrating that the oxygen vacancy is not conducive to the separation of electron-holes. It is generally believed that, the oxygen vacancy content could be effectively reduced through the calcination in air. 7



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Hence, WO3-AN and WO3-A may have fewer defects than WO3-N. Fewer defects in sample offers advantageous hole diffusion length and electron mobility. In a word, WO3-AN shows the smallest band gap and fewer defects, which makes WO3-AN absorb more visible light and be more beneficial for the separation of holes and electrons, thus leading to the reduced polarization together with the enhanced rate capability and cycling stability. X-ray photoelectron spectroscopy is used to further investigate the valence states together with surface compositions of the samples. The full spectra of shows there are three elements of W, O and C within all samples (Figure S4). Thereinto, C element is derived from carbon textiles. For these samples, the XPS spectrum of W exhibits two strong peaks for W 4f5/2and W 4f7/2 at 37.9 and 35.8 eV, respectively. After fitting by using the Gaussian fitting method, the obtained four peaks are assigned to W6+ (35.6 and 37.8 eV) and W5+ (34.8 and 36.9 eV), respectively (Figure 2d, e, f). As observed, the content of W5+ in the WO3-N is greater than that of WO3-A and WO3-AN, in which the changes of W5+ are caused by the presence of oxygen defects.55 To further explore this concept, the XPS spectra of O 1s were fitted into peaks at 530 and 531 eV, respectively, corresponding to bulk oxygen and defective oxygen (Figure 2g, h, i),56 which suggests that the content of oxygen vacancy in WO3-N is the highest among three samples. These results are consistent with the phenomenon obtained by the UV-vis absorption spectra. The morphology and structure of the WO3-AN are observed by SEM and TEM. As can be seen from Figure 3a, the surface of the carbon textiles is uniformly covered by the numerous WO3 NWs. These vertically growing WO3 nanowires forms relatively aligned and large-scale nanowire arrays (Figure 3b, c). The well-established WO3 NWs array offers a self-supporting structure and a larger surface area. The length and diameter of the typically needle-like WO3 NWs are about several micrometers 8


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and 100 nm, respectively (Figure 3c, d). In addition, HR-TEM is recorded to acquire more detailed lattice information on the crystalline structure of WO3-AN. It can be found that the clear lattice fringes over a single WO3 NW, indicating the high degree of crystallinity. As observed, the lattice spacing of WO3-AN is 0.39 nm, which are attributed to the (001) plane of the typically monoclinic WO3 (Figure 3e, f). After heat treatment, WO3-A and WO3-N also can maintain their needle-like NW structure (Figure S5). The photoelectrochemical properties are tested by using a traditional three-electrode system, in which WO3 growth on carbon textiles, saturated calomel electrode and Pt electrode serve as the working electrode, reference electrode and counter electrode, respectively, in the phosphate buffer solution. Figure 4a shows the LSV curves of the samples under visible light and dark with a scanning speed of 10 mV s-1. Three kinds of WO3 NWs can absorb visible light and generate photocurrent. Notably, the WO3-AN exhibits the highest current density, due to its fewer oxygen vacancy. The i-t curves tested at 1.23 V (vs. RHE) also shows that the WO3-AN has a higher visible light response than those of WO3-A and WO3-N, which can be stable at 17.5 μA cm-2. (Figure 4b). The EIS curves of the samples are conducted under dark and visible light irradiation. The inset image in Figure 4c and d is the corresponding equivalent circuit, where RS, Rct, Wo, and CPE stand for the solution resistance, charge-transfer resistance, mass transport component (Warburg impedance) and double-layer capacitance, respectively. In dark state, all of the EIS curves at an intermediate-frequency region exhibit the semicircle portions, which are attributed to transport and recombination of electron at the interface between the electrolyte and electrode, which is assigned to the charge-transfer limiting process (Figure 4c). After visible light radiation, the resistance values of the samples show much lower than those of EIS in dark state (Figure 4d). Notably, the WO3-AN shows the smallest impedance 9



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among three samples, declaring the lower charge-transfer resistance (Rct) and enhanced charge transfer. Thus, it can absorb more visible light owing to fewer defects. The traditional non-aqueous Li-O2 batteries are still facing a severe challenge. The high charging voltage results in a lower energy utilization, hampering the commercialization of Li-O2 batteries. In this study, we introduced the photocatalyst into the Li-O2 battery to obtain WO3 NW array grown on carbon textiles as a photo-anode and an oxygen electrode. The schematic diagram of the structure of the photo-assisted Li-O2 battery and the potential of the charging process are shown in Figure 5. Under visible light illumination, WO3 NWs can generate holes and electrons. The photoexcited electrons of WO3 NWs through the external circuit transfer to the anode, which can reduce Li+ to Li. Meanwhile, the generated photovoltage is used to lower the required charging voltage. Moreover, photoexcited holes can promote the decomposition of the discharge product Li2O2. According to the Mott Schottky curves (Figure S6), the WO3-AN has a flat band potential of 0.5 V and shows a positive slope, indicating that WO3-AN is an n-type semiconductor. The theoretical photo-assisted charging voltage of the photo-assisted Li-O2 battery with WO3-AN as photocatalyst can be reduced to 3.53V. The WO3 NW array directly grown on carbon textile is evaluated as an air electrode for the Li-O2 battery, 0.5 M LiClO4 dissolved in TEGDME as electrolyte. Using a light source (300 W xenon lamp with ultraviolet filter and infrared filter) during the charging process, the charging and discharging curves exhibit that the three samples have the similar discharging potentials and the WO3-AN shows the lowest charging potential due to its monoclinic phase and fewer defects (Figure S7). In the dark, the charging and discharging potentials in first cycle are about 4.25 and 2.25 V, respectively. After 35 cycles, the charging potential is about 4.4 V, discharge potential is about 2.5 V (Figure S8). The result suggests that the low electrocatalytic activity of the WO3 for ORR and OER. Under visible light 10


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irradiation, its charging potential shown in Figure 6a, b is much lower than that in the dark state shown in Figure S8. For the first cycle, the charging potential is about 3.63 V, which is much lower than that tested in the dark state (4.25 V) and the previously reported air electrode (Table S1), and the discharging potential is about 2.71 V. In accordance with this condition of cycle to 100 cycles, the charging potential and the discharge potential can still maintain at 3.55 V and 2.89 V, respectively. These results indicate that the WO3 NW array cathode has high cycling stability under visible light irradiation. With the increase of the cycles, the increased charging potential and the decreased discharge potential can be found, which may be caused by the dendritic growth of lithium anode and the side reaction of electrolyte. As a reference, the cycle number of the WO3 cathode in this paper is much better than those of some other previously reported photo-assisted Li-O2 batteries (Table S2). Therefore, the photo-assisted charging potential could decrease to 3.55 V relative to the charging potential in the dark state (4.4 V), which significantly reduces the charging potential and dramatically improves performance of Li-O2 batteries. As shown in Figure 6c, the charging potential of 3.41 V are obtained at 0.02 mA cm−1, and the charging potential can even maintain below 3.84 V when the current density increases to 0.10 mA cm−1. Furthermore, the high discharging potentials (above 2.75 V) can be found at the different current densities during the discharge process (Figure 6d). The results show a good rate capability of Li-O2 batteries with WO3-AN cathode. As the increase of current density, the polarization of Li-O2 battery increases, resulting in the increased charging and discharging overpotentials. These phenomenons are in accord with the most of Li-O2 batteries. To further demonstrate that the decomposition of Li2O2 can be efficiently assisted by the photo-generated holes of WO3 photocatalyst, the recharged and discharged cathodes were observed by XRD and SEM (Figure 7). The Figure 7a shows the XRD pattern of the discharge and charged WO3-AN cathodes. 11



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There are two apparently diffraction peaks at 32.8 and 34.8° in the discharged cathode, which is the (100) and (101) diffraction of discharging products (Li2O2) [32, 47] When the battery was charged under light, the Li2O2 peaks of all features disappeared, which suggesting that the discharge product of Li2O2 can complete decomposition by the photo-generated holes.[32, 47] The SEM images of WO3-AN cathode can visually show the change of the surface morphology of the discharged and recharged cathodes. As shown in Figure 7c, the WO3 NW array is covered with the closed-packed nanosheets, which is very different the fresh cathode (Figure 7b). The closed-packed nanosheets are certified to be Li2O2 and it is been reported in a lot of literature.57, 58 After photo-assisted charge processes, the closed-packed Li2O2 is reversibly disappeared (Figure 7d), which indicates that the WO3-AN cathode shows an excellent catalytic performance for the Li2O2 decomposition, resulting in the high cycling stability. The needle-like WO3 NW array grown on the carbon textiles shows a lower charging potential, high cycling stability, and good rate capability, owing to its favorable material and structural features. Firstly, the monoclinic WO3 NW array prepared by using two-steps heat treatment shows the small band gap and fewer defects, which results in more visible light absorption and easier separation of holes and electrons. Secondly, because of the WO3 NW nanoarrays in situ grown on carbon textile, the obtained robust adhesion between the each WO3 NW and conductive substrate leads to the highefficiency electron transport. Thirdly, due to the presence of large open spaces formed by the neighboring NWs, more catalytic active material can easily contact with the O2 and electrolyte, transmission pathways for Li+ and O2 is effective, and more void volume offers the Li2O2 deposition. Fourthly, the WO3 NW are strongly grown on carbon textile, which avoids the addition of any polymer binder, ensuring the high electrical conductivity of the entire electrode. The above advantages are beneficial to the acquirement of the enhanced battery performance. 12


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CONCLUSION In summary, we have successfully fabricated WO3 NW array photocatalyst on carbon textiles which serves as both the photoanode and air cathode of the Li-O2 battery. In the photo-assisted charging process, there will generate electron-hole pairs on the WO3 NWs, which can aid the decomposition of the discharge product Li2O2 and reduce Li+ to Li. From the results we have obtained, with illumination the charging potential can be decreased to 3.55 V, much lower than the charging potential of the traditional Li-O2 battery (4.4 V). Notably, the battery can be charged and discharged for 100 cycles with no decay and shows the excellent rate property. Our findings are conducive to the further development and utilization of advanced solar energy storage systems. ASSOCIATED CONTENT Supporting Information Additional characterization data and electrochemical data. AUTHOR INFORMATION Corresponding Authors * Dr. Tao Wang and Prof. Jianping He, E-mails: [email protected], [email protected]. ACKOWLEDGMENTS Financial support from the National Natural Science Foundation of China (51602153, 11575084, and 21703065), the Natural Science Foundation of Jiangsu Province (BK20160795), the Fundamental Research Funds for the Central Universities (No. NE2018104), Zhejiang Provincial Natural Science Foundation of China under Grant No. LQ18B010005, and a project funded by the Priority

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Figures and Figure Captions

Figure 1. (a) The schematic for the growth of WO3 on carbon textiles. (b-g) Growth of WO3 on carbon textiles at different hydrothermal times: (b) 0 h, (c) 4 h, (d) 8 h, (e) 12 h, (f) 16 h, (g) 20 h.

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Figure 2. (a) XRD patterns, (b) UV-visible absorption spectra, (c) tauc plot, and (d-i) high-resolution XPS curves of the samples.

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Figure 3. (a, b, c) SEM images, (d, e) TEM and (f) HRTEM images of WO3-AN. The inset in (f) show the Fourier filtered lattice fringe image of (f).

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Figure 4. (a) LSV curves, (b) i-t curves, (c) EIS in dark state and (d) EIS in illumination of WO3 samples under different heat treatment conditions. The inset is the equivalent circuit.

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Figure 5. (a) The schematic diagram of the structure of the photo-assisted Li-O2 battery. (b) Conventional charging potential, theoretical charging potential and the photo-assisted charging potential.

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Figure 6. (a, b) The charging and discharging curves of photo-assisted rechargeable Li-O2 battery with WO3-AN cathode at 0.06 mA cm-2. (c) The charging curves and (d) the discharging curves of the photo-assisted rechargeable Li-O2 battery with WO3-AN cathode at different current densities.

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Figure 7. (a) XRD patterns of WO3-AN cathode after discharge and after photo-assisted charge processes. SEM images of WO3-AN cathode observed at pristine (b), after discharge (c) and after photo-assisted charge processes (d).

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TOC

The WO3 nanowire array grown on carbon textiles as a photocatalyst distinctly reduces the charging potential of the photo-assisted Li-O2 battery.

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Enhanced Li2O2 Decomposition in Rechargeable Li-O2 Battery by

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