- Email: [email protected]
Fabrication of large size nanoporous BiVO4 photoanode by a printing-like method for efficient solar water splitting application
Catalysis Today xxx (xxxx) xxx–xxx
Contents lists available at ScienceDirect
Catalysis Today journal homepage: www.elsevier.com/locate/cattod
Fabrication of large size nanoporous BiVO4 photoanode by a printing-like method for efficient solar water splitting application ⁎
⁎
Xianglin Zhu1, Xizhuang Liang1, Peng Wang , Baibiao Huang , Qianqian Zhang, Xiaoyan Qin, Xiaoyang Zhang State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Large size photoanode Nanoporous BiVO4 Electrodeposition Photoelectrochemical water splitting
Large size and high efficient nanoporous BiVO4 photoelectrode was prepared through a simple printing-like electrochemical synthesis method. The prepared BiVO4 electrode was applied to split water to produce O2 and H2 in a three-electrode system under the irradiation of simulated solar light. NiOOH as cocatalyst was deposited by photo-electrodeposition method to improve the photoelectrochemical (PEC) performance of BiVO4 photoanode. Results reveal that NiOOH can enhance the photocurrent density and lower the over potential of water oxidation reaction. IPCE measurements were used to evaluate solar energy conversion efficiencies of BiVO4 photoanode and BiVO4/NiOOH photoanode. These two kind electrodes showed 17% and 24% IPCE in water splitting reaction. Furthermore, the prepared large size photoanode was proved to have good stability for water splitting. Our study raises the feasibility of fabrication of large size photoelectrode with high efficiency for practical application.
1. Introduction The development of modern society is built on energy consumption, and large amounts of fossil energies including coal, oil and natural gas etc. have been burned to keep the high development rate of world economy for last hundred years. However, these fossil fuels are unrenewable and unfriendly to environment. The environmental problem caused by burning of fossil fuel has attracted attention of the whole world in recent years. Most effective way to solve the energy and environment problems is looking for an ideal energy to replace fossil fuel. The abundant and clean solar energy makes it to be one of the best candidates. The conversion and utilization of solar energy has become hot topic in recent years [1–14]. Storing solar energy in hydrogen energy by photoelectrochemical (PEC) water splitting technology has been considered as a brilliant solution to provide enough clean energy satisfying the increasing energy demands of modern society [15–20]. To harness solar energy to split water with wanted efficiency, the most momentous factor is providing enough photo-voltage to overcome kinetic limitations and other losses mainly coming from oxygen evolution reaction (OER). So preparing appropriate photoanode with high efficiency and low over potential is vital for designing of PEC cells. Some n-type semiconductor photoanodes have shown ability to spilt
water at low over-potential like TiO2, ZnO, WO3, Ag2ZnSnS4 etc. and their application for water oxidation have attracted great attention [21–28]. Limited by self-defects, these materials only absorb pure UV light or have poor stability under sunlight irradiation. In view of this, developing stable photoanodes with narrow band gaps which can absorb and use visible light is still essential to enhance PEC water splitting efficiency. Among numerous visible light response photoanodes, BiVO4 is found to be an ideal candidate with appropriate bandgap (∼2.4 eV) and high stability [29–32]. Much attention has been devoted on preparing and improving of BiVO4 photoanode in recent years. Great progresses have been got, but some problems still need to be solved before practical application, such as the fabrication of large size photoanode with high efficiency in water splitting. As we all know, the photoelectric conversion efficiency of BiVO4 photoanode is mainly limited by low separation of photo-generated electrons and holes. Many methods including doping, fabricating heterojunction, preparing special structure and loading cocatalyst etc. have been developed to enhance the separation efficiency of photoinduced carriers [33–36]. Among all these methods, nanoporous structure and loading cocatalyst were proved as feasible and effective methods. The existing of nanoporous structure provides more activity sites for transporting photo-generated carriers, while the loading of
⁎
Corresponding authors. E-mail addresses: [email protected] (P. Wang), [email protected] (B. Huang). 1 These authors contributed equally to this work. https://doi.org/10.1016/j.cattod.2019.02.024 Received 30 September 2018; Received in revised form 2 January 2019; Accepted 12 February 2019 0920-5861/ © 2019 Elsevier B.V. All rights reserved.
Please cite this article as: Xianglin Zhu, et al., Catalysis Today, https://doi.org/10.1016/j.cattod.2019.02.024
Catalysis Today xxx (xxxx) xxx–xxx
X. Zhu, et al.
was used as the light source. Photo-electrodeposition of NiOOH on BiVO4 photoanode was carried out at an external bias of 0.11 V vs. Ag/ AgCl in a 0.1 M Ni(NO3)2 solution (pH: ∼7 by adding NaOH). The photocurrent was about 50 ∼ 80 μA/cm2 and different deposition amounts of NiOOH were deposited by adjusting the deposition charge quantities (10 mC/cm2, 20 mC/cm2 and 30 mC/cm2). Finally, the optimal amount (20 mC/cm2) deposited on the film shows the best performance than others, and will be referred to as BiVO4/NiOOH in the following.
cocatalyst can enhance the activity and lower over potential of water oxidation reaction. For the preparing of electrodes, precursor spin coating and electrochemical synthesis methods have been proved two main feasible method to fabricate film photoelectrodes [37–39], but there are flaws still existing with these methods. For the preparation of small size BiVO4 photoanode, the most used method is spin coating because of its commonality in fabrication of film electrode [39–41]. But limited by nature defect of spinning, it is very hard to keep uniform for the central part and the peripheral part of the substrates. So it is difficult to obtain large size and uniform film. In this work, a printing-like electrochemical synthesis method was used to prepare large size nanoporous BiVO4 photoanode. Different from the normal methods (spin coating and anodization), in this method, metal bismuth film as Bi precursor is electroplated onto the FTO substrate directly through progressive electrodeposition which can overcome the ununiform of the electric field on the FTO surface and it is easy to get large size electrode. NiOOH as cocatalyst was loaded to enhance activity of BiVO4 and the results showed that NiOOH promoted the separation efficiency of charge carriers and reduced 0.34 V over potential of water oxidation reaction. BiVO4 and BiVO4/NiOOH photoanode exhibited 17% and 24% IPCE respectively and showed good stability in oxidizing pure water.
2.4. Materials characterization XRD pattern of the photoanode was recorded on a Bruker AXS D8 advance powder diffractometer with Cu-Kα X-ray radiation. The morphology was investigated by a scanning electron microscopy (G300 FESEM System). XPS measurement was carried out on a VG MicroTech ESCA 3000 X-ray photoelectron spectroscope with amonochromatic AlKα source to explore the elements on the surface. The amount of O2 generation was determined by gas chromatography (GC-7806, Shiweipx, Beijing) equipped with a thermal conductivity detector (Ar as a carrier gas). 2.5. Photoelectrochemical (PEC) measurements
2. Experimental Photoelectrochemical properties of as prepared BiVO4 photoanode were carried out using the same three-electrode system. The prepared photoelectrode was used as working electrode, a Pt plate and a commercially available Ag/AgCl electrode were used as counter electrode and reference electrode, respectively. A 300 W Xe arc lamp with an AM 1.5 G filter (100 mW/cm2) was used as the light source and 0.5 M Na2SO4 solution (pH ∼5.5) was used as the electrolyte. The scan rate for the linear sweep voltammetry was 10 mV/s. Electrochemical impedance spectroscopy (EIS) was carried out in potentiostatic mode from 100 kHz to 0.1 Hz at 1.23 V vs. RHE under AM 1.5 G illumination. Before experiment, Ar was bubbled for half an hour to remove the dissolved O2. All measurements were carried out with Ag/AgCl as reference electrode, but final potentials in this work were converted to a reversible hydrogen electrode (RHE) scale according to the Eq. (1):
2.1. Materials and reagents All the reagents used in the experiment, including Bi(NO3)3·5H2O, Ni(NO3)2·6H2O, HNO3, NaOH, ethanol, acetone, vanadyl acetylacetonate and dimethyl sulphoxide were purchased from Sinopharm Chemical Reagent and without further purification. 2.2. Preparation of large size nanoporous BiVO4 photoanode Fluorine-doped tin oxide (FTO) glasses were cut to 7.5 cm × 10.0 cm and then ultrasonic cleaned with deionized water, acetone and absolute alcohol. BiVO4 photoanodes were prepared through an electrodeposition method. A typical three-electrode cell was used for electrodeposition. Metal Bi was first deposited on FTO glasses through electrodeposition progress in 20 mM Bi(NO3)3 solution at E = −1.0 V vs. Ag/AgCl. Bi(NO3)3 solution was prepared by dissolving Bi (NO3)3∙5H2O in 1 M HNO3 aqueous solution. Metal Bi was deposited through two different ways. In the first method, the FTO glasses were immerged into electrolyte directly for electrodeposition. In another way, the FTO glasses were gradually immerged into electrolyte starting from the bottom side with controlled speeds. These Bi deposited FTO glasses were then washed with absolute alcohol carefully and dried at 80 °C. Finally, a 7.5 cm × 7.5 cm Bi film on FTO glasses was got. For further preparing BiVO4, Bi was first oxidized to Bi2O3 by annealing in a muffle furnace at 450 °C (ramping rate was 5 °C/min) for 1 h. Then 0.2 M vanadyl acetylacetonate (VO(acac)2) solution in dimethyl sulphoxide (DMSO) was dripped onto Bi2O3 (30–50 μL/cm2) and was reheated at 450 °C (ramping rate was 5 °C/min) for 2 h in air to convert Bi2O3 to BiVO4. After cooling to air temperature, the photoanode was immersed in 1 M NaOH solution for 1 h to remove the excess V2O5.
ERHE = EAg / AgCl + 0.197 + 0.059pH
(1)
3. Results and discussion 3.1. Schematic diagram of preparing photoanode We used two different ways to deposit metal Bi onto FTO glass in electrodeposition experiment. For the first kind method, large size FTO glass was directly put into electrolyte for electrodeposition experiment. The result showed that Bi couldn’t be deposited onto the FTO glass and Bi was more inclined to locate at the top part and the bottom part of FTO glass. There was little Bi on the whole FTO surface. The deposition of Bi was inhomogeneous in vertical dimension (Fig. S1a). This indicated that it wasn’t suitable for large size FTO electrode to depositing metal with a direct deposition method. FTO electrode covered with homogenous Bi were got through dipping the glass into electrolyte gradually from the bottom side at a controlled speed during the electrodeposition progress (Fig. S1b). The deposition amount was controlled by adjusting the dipping speed carefully. With this approach, large size BiVO4 photoanode could be easily got. Fig. 1 is a detailed scheme used to prepare large size BiVO4 photoanode.
2.3. Preparation of nanoporous BiVO4/ NiOOH photoanode BiVO4/NiOOH photoanode was prepared through a simple photoelectrodeposition method, which was carried out using the three-electrode system with the CHI660E electrochemical workstation. The asprepared BiVO4 photoanode was used as working electrode, a Pt plate and a commercially available Ag/AgCl electrode were used as counter electrode and reference electrode, respectively. A 300 W Xe lamp (Perfectlight, Beijing) coupled with an AM 1.5 G filter (100 mW/cm2)
3.2. Crystal structures and morphology of photoanode The crystalline phases and composition of BiVO4 and BiVO4/NiOOH were characterized by XRD measurement as shown in Fig. 2. The characteristic diffraction peaks (diamond mark) appeared at about 2
Catalysis Today xxx (xxxx) xxx–xxx
X. Zhu, et al.
Fig. 1. Electrodeposition diagrammatic sketch and as-prepared large size BiVO4 photoanode.
Fig. 3(f–i) are the element distribution results of Bi, V, O and Ni. As demonstrated in Fig. 3i, Ni element is distributed on the film uniformly, which is benefit to water oxidation reaction. In order to confirm the nanoporosity of the samples, the BET surface area and a pore diameter distribution of BiVO4 and BiVO4/NiOOH are characterized, as shown in Fig. 4. According to the Barret-Joyner-Halenda (BJH) model analysis, the BiVO4 film shows a wide pore size distribution of 2–20 nm calculated from the adsorption branch of the isotherm, which verifies the mesoporous structure of BiVO4 nanoparticles. From the Table S1, the BET surface area and average pore diameter of BiVO4 nanoparticles are 6.34 m2/g and 18.5 nm, and those of BiVO4/NiOOH are 5.41 m2/g and 18.4 nm. These results (Fig.3(a, d), Fig. 4 and Table S1) prove that BiVO4 and BiVO4/NiOOH have nanoporous structures with big BET surface areas. 3.3. XPS analysis of photoanode Fig. 2. XRD patterns of BiVO4 and BiVO4/NiOOH photoanode.
More details about metal valence and oxidation state of photoelectrodes were further characterized using XPS technology. Fig. 5 shows the XPS results of BiVO4 and BiVO4/NiOOH photoanode. Fig. 5(a–c) respond to pristine BiVO4 and Fig. 5(d–h) are the spectra of BiVO4/NiOOH. Peaks around 158.9 eV and 164.2 eV respond to Bi 4f7/2 and Bi 4f5/2 [42]. Peaks located around 516.2 eV and 523.5 eV come from V 2p3/2 and V 2p1/2 [43]. XPS spectra of Bi and V elements have no obvious change before and after the NiOOH deposited. For the O 1 s region, two peaks at 529.3 eV and 531.5 eV are signals of lattice oxygen and surface absorbed oxygen. The additional new peak at 532.8 eV is associated with OH group [44]. Four peaks appeared at the Ni region. The fitting peaks at 856.0 eV and 873.7 eV can be assigned to Ni3+, while peaks at 861.7 eV and 879.5 eV are two shake-up type peaks of nickel at the high binding energy side of the Ni 2p3/2 and Ni 2p1/2 edge [45–48]. The peaks at 532.8 eV, 856.0 eV and 873.7 eV indicate that NiOOH was synthesized and deposited on the surface of BiVO4 through the photo-electrodeposition progress.
26.5°, 33.7°, 37.8°, 51.5° and 61.6° are attributed to the FTO substrate. In addition to the five peaks of FTO substrate, we can see that all peaks are in good agreement with the values given in the standard Joint Committee on Powder Diffraction Standards (JCPDS) Card No. 14-688, which implied that Bi2O3 was all turned into BiVO4, excess V2O5 was all removed in 1 M NaOH solution and pure monoclinic BiVO4 was got. Compared with the XRD of pristine BiVO4 photoanode, there is no significant change in the peak position and intensity of the XRD patterns of the BiVO4/NiOOH photoanode, and the diffraction peaks of NiOOH are not detected, which can be ascribed to the fact that photoelectrodeposition of NiOOH is amorphous. The morphology and elements distribution of BiVO4 and BiVO4/ NiOOH were investigated using a Scanning Electron Microscopy. Fig. 3a and Fig. 3d are the top-view SEM images of BiVO4 and BiVO4/NiOOH, respectively. As seen from the Fig. 3(a, b), BiVO4 film is composed of nanoparticles with diameter of about 150–200 nm. A high-resolution TEM (HRTEM) image (Fig. 3c) demonstrates that the distinct lattice fringe of d = 0.309 nm matches with the (-121) crystallographic plane of BiVO4, which is in good agreement with the XRD patterns (Fig. 2). Compared with the pristine BiVO4 photoanode, Fig. 3(d, e) show the porosity of BiVO4 after photo-electrodeposition of NiOOH is significantly reduced and the surface is more compact and rougher. The thicknesses of as prepared BiVO4 photoanodes with different deposition charge densities are shown in Fig. S3. Seen from the results, the thickness of as prepared BiVO4 film increases as the deposition charge density of the deposited metal Bi increases. Furthermore, EDS element mapping results of BiVO4 and BiVO4/NiOOH are shown in Fig. S4 and Fig. 3(f–i), respectively. NiOOH as cocatalyst was loaded on the surface of BiVO4 electrode through a photo-electrodeposition method.
3.4. Photoelectrochemical (PEC) measurements For preparing of BiVO4 film photoelectrode, it’s important to control the thickness of films. As shown in the Fig. S2, as the deposition amount of Bi increased, the color of prepared electrode got darker, which means the BiVO4 film got thickened. If the film is too thin, more light will transit through the film and this is not conductive to making full use of light. But too thick film is also not benefit to photoelectric conversion efficiency, and the separation of photoelectrons and holes will be limited, because thicker thickness (larger deposited amounts of 1.0 C/cm2) is difficult for the transport of holes to the photoanode surface, and is good for the recombination of electrons and holes in the body. So we first prepared BiVO4 photoanodes with different thickness, as shown in 3
Catalysis Today xxx (xxxx) xxx–xxx
X. Zhu, et al.
Fig. 3. SEM (a), TEM (b) and HRTEM (c) images of BiVO4 film. SEM (d, e) images and EDS element mapping results (f) Bi, (g) V, (h) O and (i) Ni in BiVO4/NiOOH film.
reported an efficient cocatalyst during the water oxidation reaction was deposited through a photo-electrodeposition method. It can not only enhance the PEC performance but also can decrease the over potential. Fig. 7a is LSV comparison curves of pristine BiVO4 and BiVO4/NiOOH photoanodes and from the result we can see the photocurrent density greatly enhances and the initial potential decreases after depositing NiOOH. Insert graph in Fig. 7a shows the change of water oxidation over potential before and after cocatalyst deposition. For pristine BiVO4, the initial potential of water oxidation is about 0.54 V, and when NiOOH deposited, the initial potential is reduced to 0.2 V. Electrochemical impedance spectra (EIS) plots of pure BiVO4 and BiVO4/
Fig. S3. Fig. 6 is the LSV curves of BiVO4 photoelectrodes with different deposition amount of metal Bi. The PEC performance first increased with the increasing of Bi deposition charge density and the BiVO4 photoelectrode showed best photocurrent density when the deposition charge density was about 0.75 C/cm2. Hence, we choose BiVO4 photoanode with deposition charge density of 0.75 C/cm2 for further testing and characterization. For the reaction of water splitting: 2H2 O → 2H2 + O2 (ΔE = 1.23 eV ) , the key progress is to reduce the over potential of oxidizing water to O2. To further improve the water oxidation activity of BiVO4 photoanode, NiOOH which has been
Fig. 4. (a) Nitrogen adsorption/desorption isotherm curves and (b) a pore diameter distribution of BiVO4 and BiVO4/NiOOH powders scraped from the FTO substrate. 4
Catalysis Today xxx (xxxx) xxx–xxx
X. Zhu, et al.
Fig. 5. High-resolution XPS spectra of (a–c) BiVO4 photoanode with deposition charge density of 0.75 C/cm2 and (d–h) BiVO4/NiOOH photoanode.
absorption but improved the separation of photon-generated carriers. To confirm the faradaic efficiency of the photoanode, the amount of O2 evolved in the PEC cell during irradiation with simulated sunlight (AM 1.5 G) is analyzed using a gas chromatograph, as shown in Fig. S6. From the results we can see that O2 generation curve is good and linear in one hour, which is almost consistent with the expected value calculated from the photocurrent (red line). The comparative analysis of the oxygen yield determines the faradaic efficiency up to 97.4%. In general, the BiVO4 photoanode after photo-electrodepositing NiOOH shows high faradaic efficiency and good stability in the PEC water splitting experiment. 3.5. Photocurrent stability test of large size photoanode The stability of as prepared BiVO4 photoanode was studied through continuous water splitting at 1.23 V vs. RHE for an hour, as showed in Fig. 7d. From the result we can see that both pure BiVO4 and BiVO4/ NiOOH photoanode displayed good stability in one hour. Especially for BiVO4, the photocurrent almost didn’t change after 10 min later. In addition, as demonstrated in Fig. 8, the PEC stability test of large size BiVO4 photoanode was also tested. Limit by the irradiation area (inset in Fig. 8), only about 10 mA photocurrent produced. The decreasing of the photocurrent at about 50–60 min was because of too much O2 bubbles absorbing on the BiVO4 surface, which influenced the interface contact of electrode and electrolyte. After removing the O2, the photocurrent retuned to 10 mA again. On the whole, the large size BiVO4 photoanode showed high efficiency and good stability in the photoelectrochemical water splitting experiment.
Fig. 6. LSV curves of BiVO4 photoanodes with different Bi deposition charge densities.
NiOOH under simulated sunlight radiation are demonstrated in Fig. 7b. After loading the cocatalyst, the BiVO4 has a smaller charge transfer resistance (Rct). These results indicate that NiOOH can improve the PEC performance of BiVO4 photoanode obviously due to reducing charge transfer resistance and promoting the separation of holes and electrons [31,48]. To make a more systematic comparison, the PEC performance of BiVO4 photoanodes decorated with varying amount of oxidized Ni species measured in neutral Na2SO4 (0.5 M) solution have been provided in Fig. S5. When the deposition charge density of oxidized Ni species is 20 mC/cm2, the BiVO4/NiOOH photoanode has higher photocurrent density, smaller charge transfer resistance and higher incident monochromatic photon-to-current conversion efficiency (IPCE). The IPCE as an important index to evaluate solar energy utilization efficiency was characterized, which was then calculated following the Eq. (2) [40,41,49]:
IPCE =
1239.8(V × nm) × |Iph (mA/ cm2)| Pmono (mW / cm2) × λ (nm)
4. Conclusions We report a facile printing-like method to construct large size nanoporous BiVO4 photoanode. The prepared BiVO4 photoanode showed high efficiency and stability in splitting pure water. The stability photocurrent was about 1.2 mA/cm2 and IPCE was over 17% for pure BiVO4 at 1.23 V vs. RHE. Cocatalyst NiOOH was deposited through photo-electrodeposition method to further improve the PEC performance by promoting the separation of holes and electrons, and then higher photocurrent (∼1.7 mA/cm2) and IPCE (24%) were got. Besides, the onset potential of water oxidation reaction was reduced from 0.54 V to 0.2 V. In summary, we provided an efficient method to fabricate large size nanoporous BiVO4 photoanode on FTO glass. These large size photoanodes had good performance and stability on splitting pure water and showed potential application values in solar energy
× 100% Eq. (2)
Where Iph is photocurrent density, Pmono is incident light density and λ is the wavelength of the incident light. We got IPCE results of BiVO4 and BiVO4/NiOOH photoelectrodes in reaction of water splitting at 1.23 V vs. RHE, as showed in Fig. 7c. For pure BiVO4 photoanode, the IPCE at 440 nm is about 17%, and for BiVO4/NiOOH photoanode it is about 24%. The PEC activity obviously enhanced after deposited NiOOH. IPCE measurements also prove that NiOOH didn’t expand light 5
Catalysis Today xxx (xxxx) xxx–xxx
X. Zhu, et al.
Fig. 7. (a) Photocurrent density-applied potential curves and (b) electrochemical impedance spectra (EIS) plots of BiVO4 photoanode with deposition charge density of 0.75 C/cm2 and BiVO4/NiOOH photoanode under simulated sunlight radiation. Rs: solution resistance; Rct: charge transfer resistance; CPE: constant phase element. (c) IPCE spectra and (d) the PEC durability tests of BiVO4 with deposition charge density of 0.75 C/cm2 and BiVO4/NiOOH photoanode measured at 1.23 V vs. RHE.
B.B.H. acknowledges support from the Taishan Scholars Program of Shandong Province. Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.cattod.2019.02.024. References [1] K. Sekizawa, K. Maeda, K. Domen, K. Koike, O. Ishitani, J. Am. Chem. Soc. 135 (2013) 4596–4599. [2] Y. Wu, P. Wang, X. Zhu, Q. Zhang, Z. Wang, Y. Liu, G. Zou, Y. Dai, M.H. Whangbo, B. Huang, Adv. Mater. 30 (2018) 1704342. [3] J. Yu, J. Low, W. Xiao, P. Zhou, M. Jaroniec, J. Am. Chem. Soc. 136 (2014) 8839–8842. [4] X. Liu, X. Liang, P. Wang, B. Huang, X. Qin, X. Zhang, Y. Dai, Appl. Catal. B: Environ. 203 (2017) 282–288. [5] X. Zong, H. Yan, G. Wu, G. Ma, F. Wen, L. Wang, C. Li, J. Am. Chem. Soc. 130 (2008) 7176–7177. [6] Y. Wu, P. Wang, Z. Guan, J. Liu, Z. Wang, Z. Zheng, S. Jin, Y. Dai, M.-H. Whangbo, B. Huang, ACS Catal. 8 (2018) 10349–10357. [7] Y. Zhao, K. Zhu, Chem. Soc. Rev. 45 (2016) 655–689. [8] P. Zhou, Y. Liu, Z. Wang, P. Wang, X. Qin, X. Zhang, B. Huang, Y. Dai, Chemphotochem 1 (2017) 518–523. [9] Z. Lou, M. Fujitsuka, T. Majima, ACS Nano 10 (2016) 6299–6305. [10] X. Zhu, X. Liang, P. Wang, Y. Dai, B. Huang, Appl. Surf. Sci. 456 (2018) 493–500. [11] T. Sun, J. Song, J. Jia, X. Li, X. Sun, Nano Energy 26 (2016) 83–89. [12] X. Liang, P. Wang, M. Li, Q. Zhang, Z. Wang, Y. Dai, X. Zhang, Y. Liu, M.-
Fig. 8. Photocurrent stability test of large size BiVO4 photoanode under prolonged simulated sunlight radiation.
conversion. Acknowledgements This work was financially supported by the National Natural Science Foundation of China (51602179 and 21832005). P. Wang acknowledges support from the Recruitment Program of Global Experts, China. 6
Catalysis Today xxx (xxxx) xxx–xxx
X. Zhu, et al.
[33] X. Chang, T. Wang, P. Zhang, J. Zhang, A. Li, J. Gong, J. Am. Chem. Soc. 137 (2015) 8356–8359. [34] T.W. Kim, Y. Ping, G.A. Galli, K.-S. Choi, Nat. Commun. 6 (2015) 8769. [35] B.J. Trześniewski, W.A. Smith, J. Mater. Chem. A Mater. Energy Sustain. 4 (2016) 2919–2926. [36] V. Nair, C.L. Perkins, Q.Y. Lin, M. Law, Energy Environ. Sci. 9 (2016) 1412–1429. [37] M. Zhong, T. Hisatomi, T. Minegishi, H. Nishiyama, M. Katayama, T. Yamada, K. Domen, J. Mater. Chem. A Mater. Energy Sustain. 4 (2016) 9858–9864. [38] D. Kang, T.W. Kim, S.R. Kubota, A.C. Cardiel, H.G. Cha, K.-S. Choi, Chem. Rev. 115 (2015) 12839–12887. [39] D. Guevarra, A. Shinde, S.K. Suram, I.D. Sharp, F.M. Toma, J.A. Haber, J.M. Gregoire, Energy Environ. Sci. 9 (2016) 565–580. [40] B. Zhang, H. Zhang, Z. Wang, X. Zhang, X. Qin, Y. Dai, Y. Liu, P. Wang, Y. Li, B. Huang, Appl. Catal. B: Environ. 211 (2017) 258–265. [41] H. Zhang, H. Li, Z. Wang, Z. Zheng, P. Wang, Y. Liu, X. Zhang, X. Qin, Y. Dai, B. Huang, Appl. Catal. B: Environ. 238 (2018) 586–591. [42] Y. Liu, G. Zhu, J. Gao, M. Hojamberdiev, R. Zhu, X. Wei, Q. Guo, P. Liu, Appl. Catal. B: Environ. 200 (2017) 72–82. [43] M. Ou, Q. Zhong, S. Zhang, H. Nie, Z. Lv, W. Cai, Appl. Catal. B: Environ 193 (2016) 160–169. [44] G. Wang, B. Huang, Z. Lou, Z. Wang, X. Qin, X. Zhang, Y. Dai, Appl. Catal. B: Environ. 180 (2016) 6–12. [45] Y.-H. Chang, N.Y. Hau, C. Liu, Y.-T. Huang, C.-C. Li, K. Shih, S.-P. Feng, Nanoscale 6 (2014) 15309–15315. [46] X. Qin, X. Li, L. Yang, Z. Wang, B. Zheng, H. Yuan, D. Xiao, J. Alloy. Comp. 610 (2014) 549–554. [47] M. Schulze, R. Reissner, M. Lorenz, U. Radke, W. Schnurnberger, Electrochim. Acta 44 (1999) 3969–3976. [48] X. Shi, I.Y. Choi, K. Zhang, J. Kwon, D.Y. Kim, J.K. Lee, J.H. Park, Nat. Commun. 5 (2014) 4775. [49] A.B. Murphy, P.R.F. Barnes, L.K. Randeniya, I.C. Plumb, I.E. Grey, M.D. Horne, J.A. Glasscock, Int. J. Hydrogen Energ. 31 (2006) 1999–2017.
H. Whangbo, B. Huang, Appl. Catal. B: Environ. 220 (2018) 356–361. [13] Z. Zheng, T. Tachikawa, T. Majima, J. Am. Chem. Soc. 136 (2014) 6870–6873. [14] X. Liang, P. Wang, B. Huang, Q. Zhang, Z. Wang, Y. Liu, Z. Zheng, X. Qin, X. Zhang, Y. Dai, ChemPhotoChem 2 (2018) 811–817. [15] A. Fujishima, K. Honda, Nature 238 (1972) 37–38. [16] R. Lv, T. Wang, F. Su, P. Zhang, C. Li, J. Gong, Nano Energy 7 (2014) 143–150. [17] Q. Wang, T. Hisatomi, Q. Jia, H. Tokudome, M. Zhong, C. Wang, Z. Pan, T. Takata, M. Nakabayashi, N. Shibata, Y. Li, I.D. Sharp, A. Kudo, T. Yamada, K. Domen, Nature Mater. 15 (2016) 611–615. [18] T. Hisatomi, J. Kubota, K. Domen, Chem. Soc. Rev. 43 (2014) 7520–7535. [19] Z. Liu, J. Zhang, W. Yan, ACS Sustainable Chem. Eng 6 (2018) 3565–3574. [20] D. Chen, Z. Liu, M. Zhou, P. Wu, J. Wei, J. Alloy. Comp. 742 (2018) 918–927. [21] A. Chatzitakis, A. Papaderakis, N. Karanasios, J. Georgieva, E. Pavlidou, G. Litsardakis, I. Poulios, S. Sotiropoulos, Catal. Today 280 (2017) 14–20. [22] G. Wang, H. Wang, Y. Ling, Y. Tang, X. Yang, R.C. Fitzmorris, C. Wang, J. Zhang, Y. Li, Nano Lett. 11 (2011) 3026–3033. [23] B. Zhang, Z. Wang, B. Huang, X. Zhang, X. Qin, H. Li, Y. Dai, Y. Li, Chem. Mater. 28 (2016) 6613–6620. [24] C. Fàbrega, S. Murcia-López, D. Monllor-Satoca, J.D. Prades, M.D. HernándezAlonso, G. Penelas, J.R. Morante, T. Andreu, Appl. Catal. B: Environ 189 (2016) 133–140. [25] S. Wang, H. Chen, G. Gao, T. Butburee, M.Q. Lyu, S. Thaweesak, J.-H. Yun, A. Du, G. Liu, L. Wang, Nano Energy 24 (2016) 94–102. [26] X. Liang, P. Wang, B. Huang, Q. Zhang, Z. Wang, Y. Liu, Z. Zheng, X. Qin, X. Zhang, Y. Dai, J. Mater. Chem. A Mater. Energy Sustain. 7 (2019) 1647–1657. [27] J. Zhang, Z. Liu, Z. Liu, ACS appl, Mater. Interfaces 8 (2016) 9684–9691. [28] J. Han, Z. Liu, K. Guo, B. Wang, X. Zhang, T. Hong, Appl. Catal. B: Environ. 163 (2015) 179–188. [29] A. Kudo, K. Omori, H. Kato, J. Am. Chem. Soc. 121 (1999) 11459–11467. [30] S. Tokunaga, H. Kato, A. Kudo, Chem. Mater. 13 (2001) 4624–4628. [31] T.W. Kim, K.-S. Choi, Science 343 (2014) 990–994. [32] D.K. Lee, K.-S. Choi, Nat. Energy 3 (2018) 53–60.
7
Contents lists available at ScienceDirect
Catalysis Today journal homepage: www.elsevier.com/locate/cattod
Fabrication of large size nanoporous BiVO4 photoanode by a printing-like method for efficient solar water splitting application ⁎
⁎
Xianglin Zhu1, Xizhuang Liang1, Peng Wang , Baibiao Huang , Qianqian Zhang, Xiaoyan Qin, Xiaoyang Zhang State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Large size photoanode Nanoporous BiVO4 Electrodeposition Photoelectrochemical water splitting
Large size and high efficient nanoporous BiVO4 photoelectrode was prepared through a simple printing-like electrochemical synthesis method. The prepared BiVO4 electrode was applied to split water to produce O2 and H2 in a three-electrode system under the irradiation of simulated solar light. NiOOH as cocatalyst was deposited by photo-electrodeposition method to improve the photoelectrochemical (PEC) performance of BiVO4 photoanode. Results reveal that NiOOH can enhance the photocurrent density and lower the over potential of water oxidation reaction. IPCE measurements were used to evaluate solar energy conversion efficiencies of BiVO4 photoanode and BiVO4/NiOOH photoanode. These two kind electrodes showed 17% and 24% IPCE in water splitting reaction. Furthermore, the prepared large size photoanode was proved to have good stability for water splitting. Our study raises the feasibility of fabrication of large size photoelectrode with high efficiency for practical application.
1. Introduction The development of modern society is built on energy consumption, and large amounts of fossil energies including coal, oil and natural gas etc. have been burned to keep the high development rate of world economy for last hundred years. However, these fossil fuels are unrenewable and unfriendly to environment. The environmental problem caused by burning of fossil fuel has attracted attention of the whole world in recent years. Most effective way to solve the energy and environment problems is looking for an ideal energy to replace fossil fuel. The abundant and clean solar energy makes it to be one of the best candidates. The conversion and utilization of solar energy has become hot topic in recent years [1–14]. Storing solar energy in hydrogen energy by photoelectrochemical (PEC) water splitting technology has been considered as a brilliant solution to provide enough clean energy satisfying the increasing energy demands of modern society [15–20]. To harness solar energy to split water with wanted efficiency, the most momentous factor is providing enough photo-voltage to overcome kinetic limitations and other losses mainly coming from oxygen evolution reaction (OER). So preparing appropriate photoanode with high efficiency and low over potential is vital for designing of PEC cells. Some n-type semiconductor photoanodes have shown ability to spilt
water at low over-potential like TiO2, ZnO, WO3, Ag2ZnSnS4 etc. and their application for water oxidation have attracted great attention [21–28]. Limited by self-defects, these materials only absorb pure UV light or have poor stability under sunlight irradiation. In view of this, developing stable photoanodes with narrow band gaps which can absorb and use visible light is still essential to enhance PEC water splitting efficiency. Among numerous visible light response photoanodes, BiVO4 is found to be an ideal candidate with appropriate bandgap (∼2.4 eV) and high stability [29–32]. Much attention has been devoted on preparing and improving of BiVO4 photoanode in recent years. Great progresses have been got, but some problems still need to be solved before practical application, such as the fabrication of large size photoanode with high efficiency in water splitting. As we all know, the photoelectric conversion efficiency of BiVO4 photoanode is mainly limited by low separation of photo-generated electrons and holes. Many methods including doping, fabricating heterojunction, preparing special structure and loading cocatalyst etc. have been developed to enhance the separation efficiency of photoinduced carriers [33–36]. Among all these methods, nanoporous structure and loading cocatalyst were proved as feasible and effective methods. The existing of nanoporous structure provides more activity sites for transporting photo-generated carriers, while the loading of
⁎
Corresponding authors. E-mail addresses: [email protected] (P. Wang), [email protected] (B. Huang). 1 These authors contributed equally to this work. https://doi.org/10.1016/j.cattod.2019.02.024 Received 30 September 2018; Received in revised form 2 January 2019; Accepted 12 February 2019 0920-5861/ © 2019 Elsevier B.V. All rights reserved.
Please cite this article as: Xianglin Zhu, et al., Catalysis Today, https://doi.org/10.1016/j.cattod.2019.02.024
Catalysis Today xxx (xxxx) xxx–xxx
X. Zhu, et al.
was used as the light source. Photo-electrodeposition of NiOOH on BiVO4 photoanode was carried out at an external bias of 0.11 V vs. Ag/ AgCl in a 0.1 M Ni(NO3)2 solution (pH: ∼7 by adding NaOH). The photocurrent was about 50 ∼ 80 μA/cm2 and different deposition amounts of NiOOH were deposited by adjusting the deposition charge quantities (10 mC/cm2, 20 mC/cm2 and 30 mC/cm2). Finally, the optimal amount (20 mC/cm2) deposited on the film shows the best performance than others, and will be referred to as BiVO4/NiOOH in the following.
cocatalyst can enhance the activity and lower over potential of water oxidation reaction. For the preparing of electrodes, precursor spin coating and electrochemical synthesis methods have been proved two main feasible method to fabricate film photoelectrodes [37–39], but there are flaws still existing with these methods. For the preparation of small size BiVO4 photoanode, the most used method is spin coating because of its commonality in fabrication of film electrode [39–41]. But limited by nature defect of spinning, it is very hard to keep uniform for the central part and the peripheral part of the substrates. So it is difficult to obtain large size and uniform film. In this work, a printing-like electrochemical synthesis method was used to prepare large size nanoporous BiVO4 photoanode. Different from the normal methods (spin coating and anodization), in this method, metal bismuth film as Bi precursor is electroplated onto the FTO substrate directly through progressive electrodeposition which can overcome the ununiform of the electric field on the FTO surface and it is easy to get large size electrode. NiOOH as cocatalyst was loaded to enhance activity of BiVO4 and the results showed that NiOOH promoted the separation efficiency of charge carriers and reduced 0.34 V over potential of water oxidation reaction. BiVO4 and BiVO4/NiOOH photoanode exhibited 17% and 24% IPCE respectively and showed good stability in oxidizing pure water.
2.4. Materials characterization XRD pattern of the photoanode was recorded on a Bruker AXS D8 advance powder diffractometer with Cu-Kα X-ray radiation. The morphology was investigated by a scanning electron microscopy (G300 FESEM System). XPS measurement was carried out on a VG MicroTech ESCA 3000 X-ray photoelectron spectroscope with amonochromatic AlKα source to explore the elements on the surface. The amount of O2 generation was determined by gas chromatography (GC-7806, Shiweipx, Beijing) equipped with a thermal conductivity detector (Ar as a carrier gas). 2.5. Photoelectrochemical (PEC) measurements
2. Experimental Photoelectrochemical properties of as prepared BiVO4 photoanode were carried out using the same three-electrode system. The prepared photoelectrode was used as working electrode, a Pt plate and a commercially available Ag/AgCl electrode were used as counter electrode and reference electrode, respectively. A 300 W Xe arc lamp with an AM 1.5 G filter (100 mW/cm2) was used as the light source and 0.5 M Na2SO4 solution (pH ∼5.5) was used as the electrolyte. The scan rate for the linear sweep voltammetry was 10 mV/s. Electrochemical impedance spectroscopy (EIS) was carried out in potentiostatic mode from 100 kHz to 0.1 Hz at 1.23 V vs. RHE under AM 1.5 G illumination. Before experiment, Ar was bubbled for half an hour to remove the dissolved O2. All measurements were carried out with Ag/AgCl as reference electrode, but final potentials in this work were converted to a reversible hydrogen electrode (RHE) scale according to the Eq. (1):
2.1. Materials and reagents All the reagents used in the experiment, including Bi(NO3)3·5H2O, Ni(NO3)2·6H2O, HNO3, NaOH, ethanol, acetone, vanadyl acetylacetonate and dimethyl sulphoxide were purchased from Sinopharm Chemical Reagent and without further purification. 2.2. Preparation of large size nanoporous BiVO4 photoanode Fluorine-doped tin oxide (FTO) glasses were cut to 7.5 cm × 10.0 cm and then ultrasonic cleaned with deionized water, acetone and absolute alcohol. BiVO4 photoanodes were prepared through an electrodeposition method. A typical three-electrode cell was used for electrodeposition. Metal Bi was first deposited on FTO glasses through electrodeposition progress in 20 mM Bi(NO3)3 solution at E = −1.0 V vs. Ag/AgCl. Bi(NO3)3 solution was prepared by dissolving Bi (NO3)3∙5H2O in 1 M HNO3 aqueous solution. Metal Bi was deposited through two different ways. In the first method, the FTO glasses were immerged into electrolyte directly for electrodeposition. In another way, the FTO glasses were gradually immerged into electrolyte starting from the bottom side with controlled speeds. These Bi deposited FTO glasses were then washed with absolute alcohol carefully and dried at 80 °C. Finally, a 7.5 cm × 7.5 cm Bi film on FTO glasses was got. For further preparing BiVO4, Bi was first oxidized to Bi2O3 by annealing in a muffle furnace at 450 °C (ramping rate was 5 °C/min) for 1 h. Then 0.2 M vanadyl acetylacetonate (VO(acac)2) solution in dimethyl sulphoxide (DMSO) was dripped onto Bi2O3 (30–50 μL/cm2) and was reheated at 450 °C (ramping rate was 5 °C/min) for 2 h in air to convert Bi2O3 to BiVO4. After cooling to air temperature, the photoanode was immersed in 1 M NaOH solution for 1 h to remove the excess V2O5.
ERHE = EAg / AgCl + 0.197 + 0.059pH
(1)
3. Results and discussion 3.1. Schematic diagram of preparing photoanode We used two different ways to deposit metal Bi onto FTO glass in electrodeposition experiment. For the first kind method, large size FTO glass was directly put into electrolyte for electrodeposition experiment. The result showed that Bi couldn’t be deposited onto the FTO glass and Bi was more inclined to locate at the top part and the bottom part of FTO glass. There was little Bi on the whole FTO surface. The deposition of Bi was inhomogeneous in vertical dimension (Fig. S1a). This indicated that it wasn’t suitable for large size FTO electrode to depositing metal with a direct deposition method. FTO electrode covered with homogenous Bi were got through dipping the glass into electrolyte gradually from the bottom side at a controlled speed during the electrodeposition progress (Fig. S1b). The deposition amount was controlled by adjusting the dipping speed carefully. With this approach, large size BiVO4 photoanode could be easily got. Fig. 1 is a detailed scheme used to prepare large size BiVO4 photoanode.
2.3. Preparation of nanoporous BiVO4/ NiOOH photoanode BiVO4/NiOOH photoanode was prepared through a simple photoelectrodeposition method, which was carried out using the three-electrode system with the CHI660E electrochemical workstation. The asprepared BiVO4 photoanode was used as working electrode, a Pt plate and a commercially available Ag/AgCl electrode were used as counter electrode and reference electrode, respectively. A 300 W Xe lamp (Perfectlight, Beijing) coupled with an AM 1.5 G filter (100 mW/cm2)
3.2. Crystal structures and morphology of photoanode The crystalline phases and composition of BiVO4 and BiVO4/NiOOH were characterized by XRD measurement as shown in Fig. 2. The characteristic diffraction peaks (diamond mark) appeared at about 2
Catalysis Today xxx (xxxx) xxx–xxx
X. Zhu, et al.
Fig. 1. Electrodeposition diagrammatic sketch and as-prepared large size BiVO4 photoanode.
Fig. 3(f–i) are the element distribution results of Bi, V, O and Ni. As demonstrated in Fig. 3i, Ni element is distributed on the film uniformly, which is benefit to water oxidation reaction. In order to confirm the nanoporosity of the samples, the BET surface area and a pore diameter distribution of BiVO4 and BiVO4/NiOOH are characterized, as shown in Fig. 4. According to the Barret-Joyner-Halenda (BJH) model analysis, the BiVO4 film shows a wide pore size distribution of 2–20 nm calculated from the adsorption branch of the isotherm, which verifies the mesoporous structure of BiVO4 nanoparticles. From the Table S1, the BET surface area and average pore diameter of BiVO4 nanoparticles are 6.34 m2/g and 18.5 nm, and those of BiVO4/NiOOH are 5.41 m2/g and 18.4 nm. These results (Fig.3(a, d), Fig. 4 and Table S1) prove that BiVO4 and BiVO4/NiOOH have nanoporous structures with big BET surface areas. 3.3. XPS analysis of photoanode Fig. 2. XRD patterns of BiVO4 and BiVO4/NiOOH photoanode.
More details about metal valence and oxidation state of photoelectrodes were further characterized using XPS technology. Fig. 5 shows the XPS results of BiVO4 and BiVO4/NiOOH photoanode. Fig. 5(a–c) respond to pristine BiVO4 and Fig. 5(d–h) are the spectra of BiVO4/NiOOH. Peaks around 158.9 eV and 164.2 eV respond to Bi 4f7/2 and Bi 4f5/2 [42]. Peaks located around 516.2 eV and 523.5 eV come from V 2p3/2 and V 2p1/2 [43]. XPS spectra of Bi and V elements have no obvious change before and after the NiOOH deposited. For the O 1 s region, two peaks at 529.3 eV and 531.5 eV are signals of lattice oxygen and surface absorbed oxygen. The additional new peak at 532.8 eV is associated with OH group [44]. Four peaks appeared at the Ni region. The fitting peaks at 856.0 eV and 873.7 eV can be assigned to Ni3+, while peaks at 861.7 eV and 879.5 eV are two shake-up type peaks of nickel at the high binding energy side of the Ni 2p3/2 and Ni 2p1/2 edge [45–48]. The peaks at 532.8 eV, 856.0 eV and 873.7 eV indicate that NiOOH was synthesized and deposited on the surface of BiVO4 through the photo-electrodeposition progress.
26.5°, 33.7°, 37.8°, 51.5° and 61.6° are attributed to the FTO substrate. In addition to the five peaks of FTO substrate, we can see that all peaks are in good agreement with the values given in the standard Joint Committee on Powder Diffraction Standards (JCPDS) Card No. 14-688, which implied that Bi2O3 was all turned into BiVO4, excess V2O5 was all removed in 1 M NaOH solution and pure monoclinic BiVO4 was got. Compared with the XRD of pristine BiVO4 photoanode, there is no significant change in the peak position and intensity of the XRD patterns of the BiVO4/NiOOH photoanode, and the diffraction peaks of NiOOH are not detected, which can be ascribed to the fact that photoelectrodeposition of NiOOH is amorphous. The morphology and elements distribution of BiVO4 and BiVO4/ NiOOH were investigated using a Scanning Electron Microscopy. Fig. 3a and Fig. 3d are the top-view SEM images of BiVO4 and BiVO4/NiOOH, respectively. As seen from the Fig. 3(a, b), BiVO4 film is composed of nanoparticles with diameter of about 150–200 nm. A high-resolution TEM (HRTEM) image (Fig. 3c) demonstrates that the distinct lattice fringe of d = 0.309 nm matches with the (-121) crystallographic plane of BiVO4, which is in good agreement with the XRD patterns (Fig. 2). Compared with the pristine BiVO4 photoanode, Fig. 3(d, e) show the porosity of BiVO4 after photo-electrodeposition of NiOOH is significantly reduced and the surface is more compact and rougher. The thicknesses of as prepared BiVO4 photoanodes with different deposition charge densities are shown in Fig. S3. Seen from the results, the thickness of as prepared BiVO4 film increases as the deposition charge density of the deposited metal Bi increases. Furthermore, EDS element mapping results of BiVO4 and BiVO4/NiOOH are shown in Fig. S4 and Fig. 3(f–i), respectively. NiOOH as cocatalyst was loaded on the surface of BiVO4 electrode through a photo-electrodeposition method.
3.4. Photoelectrochemical (PEC) measurements For preparing of BiVO4 film photoelectrode, it’s important to control the thickness of films. As shown in the Fig. S2, as the deposition amount of Bi increased, the color of prepared electrode got darker, which means the BiVO4 film got thickened. If the film is too thin, more light will transit through the film and this is not conductive to making full use of light. But too thick film is also not benefit to photoelectric conversion efficiency, and the separation of photoelectrons and holes will be limited, because thicker thickness (larger deposited amounts of 1.0 C/cm2) is difficult for the transport of holes to the photoanode surface, and is good for the recombination of electrons and holes in the body. So we first prepared BiVO4 photoanodes with different thickness, as shown in 3
Catalysis Today xxx (xxxx) xxx–xxx
X. Zhu, et al.
Fig. 3. SEM (a), TEM (b) and HRTEM (c) images of BiVO4 film. SEM (d, e) images and EDS element mapping results (f) Bi, (g) V, (h) O and (i) Ni in BiVO4/NiOOH film.
reported an efficient cocatalyst during the water oxidation reaction was deposited through a photo-electrodeposition method. It can not only enhance the PEC performance but also can decrease the over potential. Fig. 7a is LSV comparison curves of pristine BiVO4 and BiVO4/NiOOH photoanodes and from the result we can see the photocurrent density greatly enhances and the initial potential decreases after depositing NiOOH. Insert graph in Fig. 7a shows the change of water oxidation over potential before and after cocatalyst deposition. For pristine BiVO4, the initial potential of water oxidation is about 0.54 V, and when NiOOH deposited, the initial potential is reduced to 0.2 V. Electrochemical impedance spectra (EIS) plots of pure BiVO4 and BiVO4/
Fig. S3. Fig. 6 is the LSV curves of BiVO4 photoelectrodes with different deposition amount of metal Bi. The PEC performance first increased with the increasing of Bi deposition charge density and the BiVO4 photoelectrode showed best photocurrent density when the deposition charge density was about 0.75 C/cm2. Hence, we choose BiVO4 photoanode with deposition charge density of 0.75 C/cm2 for further testing and characterization. For the reaction of water splitting: 2H2 O → 2H2 + O2 (ΔE = 1.23 eV ) , the key progress is to reduce the over potential of oxidizing water to O2. To further improve the water oxidation activity of BiVO4 photoanode, NiOOH which has been
Fig. 4. (a) Nitrogen adsorption/desorption isotherm curves and (b) a pore diameter distribution of BiVO4 and BiVO4/NiOOH powders scraped from the FTO substrate. 4
Catalysis Today xxx (xxxx) xxx–xxx
X. Zhu, et al.
Fig. 5. High-resolution XPS spectra of (a–c) BiVO4 photoanode with deposition charge density of 0.75 C/cm2 and (d–h) BiVO4/NiOOH photoanode.
absorption but improved the separation of photon-generated carriers. To confirm the faradaic efficiency of the photoanode, the amount of O2 evolved in the PEC cell during irradiation with simulated sunlight (AM 1.5 G) is analyzed using a gas chromatograph, as shown in Fig. S6. From the results we can see that O2 generation curve is good and linear in one hour, which is almost consistent with the expected value calculated from the photocurrent (red line). The comparative analysis of the oxygen yield determines the faradaic efficiency up to 97.4%. In general, the BiVO4 photoanode after photo-electrodepositing NiOOH shows high faradaic efficiency and good stability in the PEC water splitting experiment. 3.5. Photocurrent stability test of large size photoanode The stability of as prepared BiVO4 photoanode was studied through continuous water splitting at 1.23 V vs. RHE for an hour, as showed in Fig. 7d. From the result we can see that both pure BiVO4 and BiVO4/ NiOOH photoanode displayed good stability in one hour. Especially for BiVO4, the photocurrent almost didn’t change after 10 min later. In addition, as demonstrated in Fig. 8, the PEC stability test of large size BiVO4 photoanode was also tested. Limit by the irradiation area (inset in Fig. 8), only about 10 mA photocurrent produced. The decreasing of the photocurrent at about 50–60 min was because of too much O2 bubbles absorbing on the BiVO4 surface, which influenced the interface contact of electrode and electrolyte. After removing the O2, the photocurrent retuned to 10 mA again. On the whole, the large size BiVO4 photoanode showed high efficiency and good stability in the photoelectrochemical water splitting experiment.
Fig. 6. LSV curves of BiVO4 photoanodes with different Bi deposition charge densities.
NiOOH under simulated sunlight radiation are demonstrated in Fig. 7b. After loading the cocatalyst, the BiVO4 has a smaller charge transfer resistance (Rct). These results indicate that NiOOH can improve the PEC performance of BiVO4 photoanode obviously due to reducing charge transfer resistance and promoting the separation of holes and electrons [31,48]. To make a more systematic comparison, the PEC performance of BiVO4 photoanodes decorated with varying amount of oxidized Ni species measured in neutral Na2SO4 (0.5 M) solution have been provided in Fig. S5. When the deposition charge density of oxidized Ni species is 20 mC/cm2, the BiVO4/NiOOH photoanode has higher photocurrent density, smaller charge transfer resistance and higher incident monochromatic photon-to-current conversion efficiency (IPCE). The IPCE as an important index to evaluate solar energy utilization efficiency was characterized, which was then calculated following the Eq. (2) [40,41,49]:
IPCE =
1239.8(V × nm) × |Iph (mA/ cm2)| Pmono (mW / cm2) × λ (nm)
4. Conclusions We report a facile printing-like method to construct large size nanoporous BiVO4 photoanode. The prepared BiVO4 photoanode showed high efficiency and stability in splitting pure water. The stability photocurrent was about 1.2 mA/cm2 and IPCE was over 17% for pure BiVO4 at 1.23 V vs. RHE. Cocatalyst NiOOH was deposited through photo-electrodeposition method to further improve the PEC performance by promoting the separation of holes and electrons, and then higher photocurrent (∼1.7 mA/cm2) and IPCE (24%) were got. Besides, the onset potential of water oxidation reaction was reduced from 0.54 V to 0.2 V. In summary, we provided an efficient method to fabricate large size nanoporous BiVO4 photoanode on FTO glass. These large size photoanodes had good performance and stability on splitting pure water and showed potential application values in solar energy
× 100% Eq. (2)
Where Iph is photocurrent density, Pmono is incident light density and λ is the wavelength of the incident light. We got IPCE results of BiVO4 and BiVO4/NiOOH photoelectrodes in reaction of water splitting at 1.23 V vs. RHE, as showed in Fig. 7c. For pure BiVO4 photoanode, the IPCE at 440 nm is about 17%, and for BiVO4/NiOOH photoanode it is about 24%. The PEC activity obviously enhanced after deposited NiOOH. IPCE measurements also prove that NiOOH didn’t expand light 5
Catalysis Today xxx (xxxx) xxx–xxx
X. Zhu, et al.
Fig. 7. (a) Photocurrent density-applied potential curves and (b) electrochemical impedance spectra (EIS) plots of BiVO4 photoanode with deposition charge density of 0.75 C/cm2 and BiVO4/NiOOH photoanode under simulated sunlight radiation. Rs: solution resistance; Rct: charge transfer resistance; CPE: constant phase element. (c) IPCE spectra and (d) the PEC durability tests of BiVO4 with deposition charge density of 0.75 C/cm2 and BiVO4/NiOOH photoanode measured at 1.23 V vs. RHE.
B.B.H. acknowledges support from the Taishan Scholars Program of Shandong Province. Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.cattod.2019.02.024. References [1] K. Sekizawa, K. Maeda, K. Domen, K. Koike, O. Ishitani, J. Am. Chem. Soc. 135 (2013) 4596–4599. [2] Y. Wu, P. Wang, X. Zhu, Q. Zhang, Z. Wang, Y. Liu, G. Zou, Y. Dai, M.H. Whangbo, B. Huang, Adv. Mater. 30 (2018) 1704342. [3] J. Yu, J. Low, W. Xiao, P. Zhou, M. Jaroniec, J. Am. Chem. Soc. 136 (2014) 8839–8842. [4] X. Liu, X. Liang, P. Wang, B. Huang, X. Qin, X. Zhang, Y. Dai, Appl. Catal. B: Environ. 203 (2017) 282–288. [5] X. Zong, H. Yan, G. Wu, G. Ma, F. Wen, L. Wang, C. Li, J. Am. Chem. Soc. 130 (2008) 7176–7177. [6] Y. Wu, P. Wang, Z. Guan, J. Liu, Z. Wang, Z. Zheng, S. Jin, Y. Dai, M.-H. Whangbo, B. Huang, ACS Catal. 8 (2018) 10349–10357. [7] Y. Zhao, K. Zhu, Chem. Soc. Rev. 45 (2016) 655–689. [8] P. Zhou, Y. Liu, Z. Wang, P. Wang, X. Qin, X. Zhang, B. Huang, Y. Dai, Chemphotochem 1 (2017) 518–523. [9] Z. Lou, M. Fujitsuka, T. Majima, ACS Nano 10 (2016) 6299–6305. [10] X. Zhu, X. Liang, P. Wang, Y. Dai, B. Huang, Appl. Surf. Sci. 456 (2018) 493–500. [11] T. Sun, J. Song, J. Jia, X. Li, X. Sun, Nano Energy 26 (2016) 83–89. [12] X. Liang, P. Wang, M. Li, Q. Zhang, Z. Wang, Y. Dai, X. Zhang, Y. Liu, M.-
Fig. 8. Photocurrent stability test of large size BiVO4 photoanode under prolonged simulated sunlight radiation.
conversion. Acknowledgements This work was financially supported by the National Natural Science Foundation of China (51602179 and 21832005). P. Wang acknowledges support from the Recruitment Program of Global Experts, China. 6
Catalysis Today xxx (xxxx) xxx–xxx
X. Zhu, et al.
[33] X. Chang, T. Wang, P. Zhang, J. Zhang, A. Li, J. Gong, J. Am. Chem. Soc. 137 (2015) 8356–8359. [34] T.W. Kim, Y. Ping, G.A. Galli, K.-S. Choi, Nat. Commun. 6 (2015) 8769. [35] B.J. Trześniewski, W.A. Smith, J. Mater. Chem. A Mater. Energy Sustain. 4 (2016) 2919–2926. [36] V. Nair, C.L. Perkins, Q.Y. Lin, M. Law, Energy Environ. Sci. 9 (2016) 1412–1429. [37] M. Zhong, T. Hisatomi, T. Minegishi, H. Nishiyama, M. Katayama, T. Yamada, K. Domen, J. Mater. Chem. A Mater. Energy Sustain. 4 (2016) 9858–9864. [38] D. Kang, T.W. Kim, S.R. Kubota, A.C. Cardiel, H.G. Cha, K.-S. Choi, Chem. Rev. 115 (2015) 12839–12887. [39] D. Guevarra, A. Shinde, S.K. Suram, I.D. Sharp, F.M. Toma, J.A. Haber, J.M. Gregoire, Energy Environ. Sci. 9 (2016) 565–580. [40] B. Zhang, H. Zhang, Z. Wang, X. Zhang, X. Qin, Y. Dai, Y. Liu, P. Wang, Y. Li, B. Huang, Appl. Catal. B: Environ. 211 (2017) 258–265. [41] H. Zhang, H. Li, Z. Wang, Z. Zheng, P. Wang, Y. Liu, X. Zhang, X. Qin, Y. Dai, B. Huang, Appl. Catal. B: Environ. 238 (2018) 586–591. [42] Y. Liu, G. Zhu, J. Gao, M. Hojamberdiev, R. Zhu, X. Wei, Q. Guo, P. Liu, Appl. Catal. B: Environ. 200 (2017) 72–82. [43] M. Ou, Q. Zhong, S. Zhang, H. Nie, Z. Lv, W. Cai, Appl. Catal. B: Environ 193 (2016) 160–169. [44] G. Wang, B. Huang, Z. Lou, Z. Wang, X. Qin, X. Zhang, Y. Dai, Appl. Catal. B: Environ. 180 (2016) 6–12. [45] Y.-H. Chang, N.Y. Hau, C. Liu, Y.-T. Huang, C.-C. Li, K. Shih, S.-P. Feng, Nanoscale 6 (2014) 15309–15315. [46] X. Qin, X. Li, L. Yang, Z. Wang, B. Zheng, H. Yuan, D. Xiao, J. Alloy. Comp. 610 (2014) 549–554. [47] M. Schulze, R. Reissner, M. Lorenz, U. Radke, W. Schnurnberger, Electrochim. Acta 44 (1999) 3969–3976. [48] X. Shi, I.Y. Choi, K. Zhang, J. Kwon, D.Y. Kim, J.K. Lee, J.H. Park, Nat. Commun. 5 (2014) 4775. [49] A.B. Murphy, P.R.F. Barnes, L.K. Randeniya, I.C. Plumb, I.E. Grey, M.D. Horne, J.A. Glasscock, Int. J. Hydrogen Energ. 31 (2006) 1999–2017.
H. Whangbo, B. Huang, Appl. Catal. B: Environ. 220 (2018) 356–361. [13] Z. Zheng, T. Tachikawa, T. Majima, J. Am. Chem. Soc. 136 (2014) 6870–6873. [14] X. Liang, P. Wang, B. Huang, Q. Zhang, Z. Wang, Y. Liu, Z. Zheng, X. Qin, X. Zhang, Y. Dai, ChemPhotoChem 2 (2018) 811–817. [15] A. Fujishima, K. Honda, Nature 238 (1972) 37–38. [16] R. Lv, T. Wang, F. Su, P. Zhang, C. Li, J. Gong, Nano Energy 7 (2014) 143–150. [17] Q. Wang, T. Hisatomi, Q. Jia, H. Tokudome, M. Zhong, C. Wang, Z. Pan, T. Takata, M. Nakabayashi, N. Shibata, Y. Li, I.D. Sharp, A. Kudo, T. Yamada, K. Domen, Nature Mater. 15 (2016) 611–615. [18] T. Hisatomi, J. Kubota, K. Domen, Chem. Soc. Rev. 43 (2014) 7520–7535. [19] Z. Liu, J. Zhang, W. Yan, ACS Sustainable Chem. Eng 6 (2018) 3565–3574. [20] D. Chen, Z. Liu, M. Zhou, P. Wu, J. Wei, J. Alloy. Comp. 742 (2018) 918–927. [21] A. Chatzitakis, A. Papaderakis, N. Karanasios, J. Georgieva, E. Pavlidou, G. Litsardakis, I. Poulios, S. Sotiropoulos, Catal. Today 280 (2017) 14–20. [22] G. Wang, H. Wang, Y. Ling, Y. Tang, X. Yang, R.C. Fitzmorris, C. Wang, J. Zhang, Y. Li, Nano Lett. 11 (2011) 3026–3033. [23] B. Zhang, Z. Wang, B. Huang, X. Zhang, X. Qin, H. Li, Y. Dai, Y. Li, Chem. Mater. 28 (2016) 6613–6620. [24] C. Fàbrega, S. Murcia-López, D. Monllor-Satoca, J.D. Prades, M.D. HernándezAlonso, G. Penelas, J.R. Morante, T. Andreu, Appl. Catal. B: Environ 189 (2016) 133–140. [25] S. Wang, H. Chen, G. Gao, T. Butburee, M.Q. Lyu, S. Thaweesak, J.-H. Yun, A. Du, G. Liu, L. Wang, Nano Energy 24 (2016) 94–102. [26] X. Liang, P. Wang, B. Huang, Q. Zhang, Z. Wang, Y. Liu, Z. Zheng, X. Qin, X. Zhang, Y. Dai, J. Mater. Chem. A Mater. Energy Sustain. 7 (2019) 1647–1657. [27] J. Zhang, Z. Liu, Z. Liu, ACS appl, Mater. Interfaces 8 (2016) 9684–9691. [28] J. Han, Z. Liu, K. Guo, B. Wang, X. Zhang, T. Hong, Appl. Catal. B: Environ. 163 (2015) 179–188. [29] A. Kudo, K. Omori, H. Kato, J. Am. Chem. Soc. 121 (1999) 11459–11467. [30] S. Tokunaga, H. Kato, A. Kudo, Chem. Mater. 13 (2001) 4624–4628. [31] T.W. Kim, K.-S. Choi, Science 343 (2014) 990–994. [32] D.K. Lee, K.-S. Choi, Nat. Energy 3 (2018) 53–60.
7