CuI as Hole-Transport Channel for Enhancing Photoelectrocatalytic

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CuI as Hole Transport Channel for Enhancing Photoelectrocatalytic Activity by Constructing BiOI/CuI Heterojunction Mingjuan Sun, Jiayue Hu, Chunyang Zhai, Mingshan Zhu, and Jianguo Pan ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b01840 • Publication Date (Web): 03 Apr 2017 Downloaded from http://pubs.acs.org on April 4, 2017

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ACS Applied Materials & Interfaces

CuI as Hole Transport Channel for Enhancing Photoelectrocatalytic Activity by Constructing BiOI/CuI Heterojunction Mingjuan Sun, Jiayue Hu, Chunyang Zhai, Mingshan Zhu,* and Jianguo Pan* School of Materials Science and Chemical Engineering, Ningbo University, Ningbo 315211, China ABSTRACT In this paper, CuI, as a typical hole transport channel, was used to construct high performance visible-light-driven CuI/BiOI heterostructure for photoelectrocatalytic applications. The heterostructure combines the broad visible absorption of BiOI and high hole mobility of CuI. Compared to pure BiOI, the CuI/BiOI heterostructure exhibited distinctly enhanced photoelectrocatalytic performances for the oxidation of methanol and organic pollutant under visible light irradiation. The photogenerated electron-hole pairs of the excited BiOI can be separated efficiently through CuI, in which the CuI acts as superior holes transport channel for the improvement of photoelectrocatalytic oxidization of methanol and organic pollutants. The outstanding photoelectrocatalytic activities show that the p-type CuI works as promising hole transport channel for improving the photocatalytic performance of the traditional semiconductors. Keywords: bismuth oxyiodide; copper iodide; hole transport; photoelectrocatalyst; visible light

INTRODUCTION 1

ACS Paragon Plus Environment


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Bismuth oxyhalides (BiOX, X = Cl, Br, and I), a class of promising layered inorganic semiconductor materials, receive great research interest in solar energy conversion owing to their suitable band gaps, chemically stabilized, nontoxic, and corrosion resistant.1-9 Because of its narrow band gap, BiOI is the most efficient visible-light harvesting photocatalyst among the BiOX.3 Despite the above excellent advantages, the practical applications of BiOI are still limited owing to their low photocatalytic efficiency. Generally, in application to solar energy conversion, the efficiency relies on the separation rate of photoexcited electrons-holes pairs of photocatalysts. Actually, rapid recombination of these photoexcited carriers occurs and only few electrons and holes can move to the surface and to participate in following redox reaction, respectively.10 This is because of the valence band Bi 6s and O 2p orbitals hybridize, resulting in rapid charge carrier recombination.3 Hence, many strategies involve the combination pristine BiOI with other semiconductors to construct heterostructure for achieving higher carrier mobility and reducing recombination rate. As a p-type wide energy band gap (ca. 3.1 eV) material, copper (I) iodide (CuI) has received great attention to be a versatile candidate in photovoltaic devices.11-14 Usually, in these photovoltaic devices, the layer of CuI is served as a hole transport layer (HTL).11-14 This is owing to its wide energy band gap with work function of 5.1 eV, which provides a suitable energy level alignment at the interface between substrate such as indium-tin-oxide (ITO) and active layers for hole transport.11 Considering the fascinating optical properties of BiOI in the combination with ideal 2


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HTL materials of CuI, efficient charger separation might be achieved in the constructed CuI/BiOI heterostructure. Herein, the p-type CuI was chose to be a hole transport channel for constructing CuI/BiOI heterostructure. After that, Pt nanoparticles were deposited as cocatalysts for photoelectrocatalytic oxidation of methanol and organic pollutants. Compared to pure BiOI, the heterostructure of CuI/BiOI displayed 4.3 and 1.8 times for the oxidation of methanol and methylene blue (MB), respectively. The efficient charger separation contributes the improvement of the photoelectrocatalytic activities. The present works show that the p-type CuI not only can be worked as promising hole transport channel for improving the photocatalytic performance of the traditional semiconductors but also provided more insight into developing highly efficient visible light photo-responsive catalysts in the fields of solar and chemical energy conversion. EXPERIMENTAL SECTION

Materials

and

Characterization.

Kalium

iodidum

(KI),

bismuth

nitrate

(Bi(NO3)3•5H2O), copper sulfate (CuSO4·5H2O), chloroplatinic acid hexahydrate (H2PtCl6·6H2O), methylene blue (MB), sodium sulfate(Na2SO4), potassium hydroxide (KOH), sulphuric acid (H2SO4), methanol (CH3OH), etc. were purchased from Sinopharm Chemical Reagent Co., Ltd. All of above materials were used directly without further purification. The morphology, phase structure and surface chemical states of the as-prepared samples were characterized by scanning electron microscope (SEM, JEOL, JSM-6330FT), transmission electron microscopy (TEM, JEOL, 2100, operated at 100 3



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KV), X-ray diffraction (XRD, Bruker D8 Focus, X-ray diffractometer with Cu Kα radiation of wavelength λ=1.5418Å), and X-ray photoelectron spectroscopy (XPS, JEOL JPS-9010 MC spectrometer). The adventitious carbon (the C 1s line at 284.8 eV) was used as reference to binding energies for XPS measurements. The optical properties of samples were investigated using a UV-vis-NIR Spectro-photometer (LAMBDA 950 UV/Vis/NIR Spectrophotometer). Synthesis of CuI/BiOI and Pt-CuI/BiOI nanostructures. The CuI/BiOI heterostructures were prepared using a facile hydrothermal method. Basically, 0.24 g of Bi(NO3)3·5H2O and 0.012 g CuSO4·5H2O were added in 20 mL of ethanol-H2O mixture solution (Vethanol:VH2O=1:1) and then with ultrasonication for 30min to obtain homogeneous solution. Then, 0.11 g KI was added into the above solution and with for 1 hour. After that, the mixture was transferred to 25 ml Teflon autoclave and then held at 160 oC for 2 hours. After reaction, the mixture was cooled to room naturally and the products were washed by water and ethanol three times respectively, and then dried in oven at 70 oC, resulting CuI/BiOI heterostructures (the ratio of CuI is around 5%). The pure CuI or BiOI was synthesized by using Cu or Bi ions as precursor, respectively. The different ratio of CuI in CuI/BiOI were prepared by using different amount of CuSO4·5H2O as precursor. The Pt deposited CuI/BiOI nanocomposites were obtained by hydrothermal method. 50 mg CuI/BiOI and 1.7 mL (c=3.86×10-2 mol L-1) H2PtCl6 added into 20 mL ethanol-H2O mixture solution (Vethanol:VH2O=1:1) and with ultrasonication for 2 hours. The above mixture was transferred to 25 mL Teflon autoclave and held at 140 oC for 4 4


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hours and the Teflon autoclave was cooled to room temperature naturally. The powders were washed by water and ethanol three times and dried in oven at 70 oC, resulting in Pt-CuI/BiOI. The amount of Pt accounts for 20% of the total mass in this process. Photoelectrochemical catalysis (PEC) measurements. The working electrode was prepared as follow: 2 mg samples and 10 µL Nafion solution were added into 2 mL ethanol-H2O mixture solution (Vethanol:VH2O=1:1) with ultrasonication for 30 min to make a homogeneous dispersion. Then, 5 µL of the above dispersion was dropped onto the glassy carbon electrode, and dried in air at the room temperature. The PEC experiments were performed in a standard three electrode system (CHI 660E) with platinum wire as the counter electrode and saturated calomel electrode (SCE) as the reference electrode. Prior to each electrochemical measurement, the working electrode was processed by potential cycling in aqueous solution of KOH (1 M) in the range of -0.9 V to 0.2 V that until a stable state was reached. The PEC oxidation of methanol was measured by cyclic voltammograms (CVs) measurements at a scan rate of 50 mV s−1 from -0.9 to 0.2 V in the mixture of 1.0 M CH3OH/KOH. Chronoamperometry (CA) and photocurrent responses of the samples under dark and visible light illumination were measured at −0.2 V at a scan rate of 50 mV s−1. 2.5 mM K3[Fe(CN)6/K4[Fe(CN)6] (1:1) mixture as a redox probe in the aqueous solution of KCl (0.1 M) at 0.15 V was measured for electrochemical impedance spectroscopy (EIS) measurements. Different potentials of EIS were carried out by using 1.0 M CH3OH/KOH solution (AC voltage amplitude is 5.0 mV) over the frequency range 5



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between 0.1 and 105 Hz. For photoelectrocatalytic degradation of MB: 100 mg as-synthesized samples and 50 µl Nafion were added into 1 mL ethanol-H2O mixtures, with ultrasound for 30 min to obtain a homogeneous dispersion. After that, 100 µL of the above dispersion was dropped on the surface of F-doped tin oxide (FTO, 1.5 cm×1.5 cm), and dried at the room temperature. The experiments of photoelectrochemical decomposition of MB were measured in a three electrode system of the modified FTO electrode, SCE, and platinum wire, were acted as working, reference, and counter electrodes, respectively. In a typical run of photoelectrochemical decomposition of MB, the modified FTO electrode dip into 20 mL MB (10 mg L-1) with 0.1 M Na2SO4 aqueous solution in a quartz cell at 0.6 V and the solution was stirred in dark for 1 hour to ensure adsorption equilibrium. The record of concentration of MB solution at 664 nm on UV–vis spectrophotometer was using for emulating photoelectrocatalytic performances. The 300W Xenon lamp with >420 nm filter was used as visible light source for all PEC measurements. RESULTS AND DISCUSSION The pure BiOI nanosheets and CuI particles were synthesized by only using Bi and Cu salt precursor, respectively. The SEM images of above two samples show that the as-synthesized BiOI with sheet-like and CuI with irregular particles morphologies (Figure S1). When both precursors were used, CuI/BiOI heterostructures were obtained. The SEM and TEM images clear show that sheet-like BiOI attached with 6


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the CuI particles absolutely (Figures 1 and S2). To confirm the above three as-prepared samples, the compositions of samples were also investigated by EDX experiment (Figure S3). It’s shown that Bi, O, I; Cu, I, and Bi, O, I, Cu elements were easily observed in the BiOI, CuI, and CuI/BiOI samples, respectively, revealing that the generation of BiOI, CuI, and CuI/BiOI composites.

Figure 1. SEM (a) and enlarged SEM (b) images of CuI/BiOI composites. Moreover, XPS analysis was investigated to further indicate the chemical composition of the all samples (Figures 2A-2C). Firstly, two characteristic peaks were detected at around 619.3 eV and 630.8 eV (Figure 2A) in pure BiOI and CuI samples, which are assigned to the doublet of I 3d5/2 and I 3d3/2, respectively.15,16 Moreover, the characteristic peaks corresponding to the binding energies for Cu 2p3/2 and Cu 2p1/2; and for Bi 4f7/2 and Bi 4f5/2 are detected at ca. 932.0 and 952.0 eV; and 160.1 and 165.4 eV (Figure 2B and 2C), respectively.15-17 The above data confirm the formation of BiOI and CuI after hydrothermal process. Interestingly, for heterostructure of CuI/BiOI, the binding energies of the I 3d, Cu 2p and Bi 4f all shifted to higher binding energies compared to those of pure BiOI and CuI. Generally, compare with single component, the binding energy shifts in the composites could be 7



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explained by a strong interaction in the two components, which will in favor of the interfacial charge transfer.18

Figure 2. XPS spectra of I 3d (A), Cu 2p (B), and Bi 4f (C) of the CuI/BiOI (a), CuI (b), and BiOI (c). XRD patterns (D) and UV–vis diffuse reflectance spectra (E) of BiOI (a), CuI (b), and BiOI/CuI (c). To reveal the components and crystallographic structures of samples, XRD patterns of BiOI, CuI, and CuI/BiOI composites were studied, as shown in Figure 2D. The peaks of BiOI and CuI were matched well with the standard PDF card of BiOI (JCPDS 10-0445) and CuI (JCPDS 06-0246), respectively. However, for CuI/BiOI composites, the peaks corresponding to CuI were not obviously owing to the low weight amount of CuI in the composites. Figure S4 shows the different ratio of CuI in the CuI/BiOI composites, clear perks assigned to CuI were observed, suggesting the successful formation of the CuI/BiOI composites. 8


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As shown in Figure 2E, the UV–vis diffuse reflectance spectra were studied to show the optical properties of samples. It can be seen that absorption edges around 407 nm and 653 nm for pure CuI and BiOI were observed. The CuI/BiOI display similar absorption to the pure BiOI. This is might due to the overlap absorption of CuI and BiOI. However, the distinctly visible light absorption (up to 667 nm) indicates that the BiOI-based composites have great potential to utilize visible light in solar spectrum for following photoelectrocatalytic application. The photoelectrocatalytics performances of as-synthesized samples were evaluated by the photoelectro-oxidation of methanol. As known, Pt is the most effective electrocatalyst for methanol oxidation. The above samples were deposited Pt nanoparticles for further evaluating the photoelectro-oxidation of methanol. The corresponding of Pt-CuI/BiOI nanocomposites were characterized by SEM, EDX, TEM, XRD, and XPS, respectively, as shown in Figures S5~S8. From SEM and TEM images, it can be seen that the Pt nanoparticles deposited on the surface of CuI/BiOI composites. The dimater size of Pt nanoparticle is around 10 nm. The results from EDX, XRD, and XPS solidy confirmed the successful formation of metallic Pt in the composites of Pt-CuI/BiOI. Figure 3A shows the cyclic voltammograms (CVs) of the as-prepared Pt-BiOI and Pt-CuI/BiOI modified electrodes as working electrodes for photoelectrocatalytic oxidation of methanol in alkaline condition under dark and visible light irradiation. Firstly, under dark environment, a typical CV profile of the electrocatalytic methanol oxidation during 0.2 V and -0.8 V was detected of the Pt-BiOI. Two strong oxidation 9



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peaks assigned to forward peak and backward peak at -0.25 and -0.35 V, respectively, were detected. The forward peak current density was around 705 mA mg–1. When this electrode was under visible light irradiation, the peak current density was distinctly enhanced (1523 mA mg–1), suggesting an efficient photo-assisted electrocatalytic methanol oxidation. Different reference electrode such as Ag/AgCl was evaluated under same condition, similar phenomenon was observed. Compare to dark condition, the Pt-CuI/BiOI electrode showed obvious enhanced catalytic performance towards methanol oxidation, as shown in Figure S9.

Figure 3. A: 15th CVs of Pt-CuI/BiOI (a and c) and Pt-BiOI (b and d) electrodes under visible-light irradiation (a and b) and dark (c and d), respectively, in 1.0 M CH3OH/KOH solution. B: The histogram of activities of different electrodes on Pt-BiOI, Pt-CuI and different ratio of CuI in Pt-CuI/BiOI for photoelectrocatalytic oxidation of methanol under visible light and dark conditions. On the other hand, the pure CuI as Pt substrate did not show effective performance of photoelectrocatalytic oxidation of methanol under visible light illumination owing to poor absorption in visible light region. However, when CuI particles were hybridized with BiOI nanosheets as Pt substrate, great enhanced 10


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photoelectrocataltic activities were achieved, in which 5 wt% of CuI showed the best activity, reaching to 6482 mA mg-1 under visible light irradiation (Figure 3B). Compare to pure Pt-BiOI modified electrode under dark and visible light irradiation, 9.2 and 4.3 times were obtained, respectively. Moreover, the effect on the different weight ratios of Pt on the surface of CuI/BiOI was evaluated. As shown in Figure S10, the optimum of Pt loading amout is around 10%. The catalytic actvity decrease with further increase of Pt loading amount might because of the Pt nanopatricles are easily aggregiated in high loading amout. Generally, an efficient interfacial charge transfer/separation is critical step to obtain

high-performance

of

photo-activated

reactions.

To

evaluate

the

photoelectrochemical properties of the Pt-BiOI and Pt-CuI/BiOI modified electrodes, linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and CVs were investigated. As shown in Figure 4A, the current densities of as-prepared Pt-BiOI modified electrode were 352 and 441 mA mg–1 under dark and visible light illumination, respectively, at a given potential of -0.4 V. When Pt-CuI/BiOI was used as working electrode, the corresponding current densities were achieved to 443 and 733 mA mg–1 under dark and visible light illumination, respectively. The improved current densities of in Pt-CuI/BiOI were attributed to introduce the CuI in the composites, which enhances the charge mobility. To further evaluate the interfacial charge mobility, the EIS data were analyzed under dark and visible light irradiation by using Nyquist plots from 0.1 Hz~100 kHz in the same electrolyte. As shown in Figure 4B, the diameter of semicircle arc of as-prepared Pt-CuI/BiOI under visible 11



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light illumination is the smallest, indicating the most effective interfacial charger transport during the photo illuminated process.19,20 The corresponding equivalent circuit were used to fit the EIS data (Figure S11) and the parameters of Rct were summarized in Table S1. It’s easily to see that the Pt-CuI/BiOI displayed smallest resistance under visible light illumination, confirming the effective charger mobility in the Pt-CuI/BiOI.

Figure 4. A and B: LSV (A) and EIS (B) of samples in 1.0 M CH3OH/ KOH solution. C and D: CVs (C) and EIS (D) of samples in K3[Fe(CN)6/K4[Fe(CN)6] mixture solution. The samples used as follows: Pt-CuI/BiOI (a and c) and Pt-BiOI (b and d) modified electrodes under visible-light illumination (a and b) and dark (c and d) conditions. To further show the interfacial charger transfer in the Pt-CuI/BiOI modified electrode, different electrolyte viz. K3[Fe(CN)6/K4[Fe(CN)6] mixtures were acted as 12


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redox probes to investigate the charge transfer efficiency during photoelectrocatalytic reaction. As shown in Figure 4C, CVs curves show the response of the reversible redox couple of Fe(CN)64−/Fe(CN)63−. Similar to above result, the Pt-CuI/BiOI modified electrode under visible light illumination displayed the largest redox peak current density. Moreover, the peaks of above redox potential also shifted to the lower potential. These results suggest an improvement of the interfacial charger transport rate in the as-prepared Pt-CuI/BiOI modified electrode under visible light illumination.20,21 Furthermore, the corresponding EIS spectra of the above electrodes under

dark

and

visible

light

illumination

were

also

measured

in

K3[Fe(CN)6/K4[Fe(CN)6] electrolyte, similar results were observed (Figure 4D). The above phenomena clearly indicate that the introduced CuI promotes the charges trsnsport at the surface of electrode, resulting in the increment of the electrocatalytic reaction rate under visible light irradiation.

Figure 5. EIS spectra of the Pt-CuI/BiOI electrode in 1.0 M CH3OH/ KOH solution at different potentials under dark (A-C) and visible light irradiation (D-F). 13



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The EIS in different potential range (-0.6~0.0 V) of the Pt-CuI/BiOI modified electrode under dark and visible light irradiation were investigated for observing the methanol oxidation process and photo-assisted effect during photoelectrocatalytic process.22-24

Figure 5A shows the diameter of semicircle arc decreasing from -0.60

V to -0.30 V under dark condition. This is since that during the methanol oxidation process, the CO intermediate species would be generated, however, these CO intermediate species which were easily removed at higher potential when the potential is less than the oxidation potential (-0.25 V).22 When the potential increased from -0.3 to -0.15 V (Figure 5B), the diameter of semicircle arc increased owing to the CO intermediate species poisoning and the oxidation of catalyst at higher potential. The arc reversed to the second quadrant at -0.25 V. This is due to the removal of CO intermediate species from the catalyst surface and the recovery of catalytic active sites at the methanol oxidation potential (-0.25 V).22,23 Furthermore, the further higher potentials from -0.15 V to 0.0 V (Figure 5C), the arcs returned back with a large diameter of semicircle arc. This is since that the CO intermediate species were absent while the cocatalyst of Pt surface were oxidized and decrease the catalytic active sites at such potential.22-24 When the above Pt-CuI/BiOI electrode was upon visible light irradiation, similar variation tendencies were observed while the smaller diameter of semicircle arcs were achieved compared to these under same potential (Figures 5D-5F). These smaller diameters of semicircle arcs suggest smaller charge-transfer resistance due to the effective interfacial charge transfer on Pt-CuI/BiOI electrode under light illumination, resulting in higher photoelectrocatalytic performance. 14


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Figure 6. The photocurrent responses of the Pt-BiOI (a) and Pt-CuI/BiOI (b) under visible light irradiation in 1.0 M CH3OH/ KOH solution at a potential of -0.25 V. To further analyze the photoelectrocatalytic activity of the samples, the responsive photocurrents based on chronoamperometric curves of Pt-BiOI and Pt-BiOI/CuI modified electrode were carried out 1.0 M CH3OH/ KOH solution under visible light irradiation. The illumination was interrupted every 50 s. As seen in Figure 6, the current intensity was rise and fall off clearly when the visible light turned “on” and “off”. Same to above phenomena, the electrode of Pt-CuI/BiOI showed higher photo-responsive current, further indicating effective interfacial charger transport in the CuI/BiOI heterostructure.25,26 To further clarify the function of photo-illumination, the effects of different scan rates on the methanol oxidation on Pt-CuI/BiOI under dark and visible light irradiation were studied (Figure S12). To investigate the transport characteristics of electrode, the diagram of forward peak current ip vs. square root of scan rate (v1/2) was constructed. As shown in Figure S12, the ip shows a linear relation to the v1/2 both 15



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under dark and visible light condition. Accordingly, the photoelectrocatalytic oxidation of methanol on Pt-CuI/BiOI electrode is controlled by the diffusion process.27,28 To demonstrate the different electron-transfer kinetics of Pt-BiOI under dark and visible light irradiation, the diffusion coefficient (D) of the electrode under different condition is compared by using Eq. (1):

Dlight D dark

 ip  ( 1/2 )light = v  ip  ( v1/ 2 ) dark

    

2

(1)

The difference of the diffusion coefficients (Dlight/Ddark) under dark and visible light irradiation is calculated with the value of 7.4. This result indicates that the visible light irradiation improved the D and electron transport kinetics of electrode, resulting in better photoelectrocatalytic methanol oxidation performance.27,28 To further demonstrate the superior catalytic ability of the CuI/BiOI composites, the above electrodes were evaluated for photoelectrocatalytic degradation of methylene blue (MB) pollutants. As shown in Figure 7A, when CuI/BiOI was used as working electrode, about 87% of MB pollutants were degraded under 2 hours visible light irradiation. Compare to pure BiOI (ca. 68%) and CuI (ca. 8%) served as the working electrodes for photoelectrocatalytic degradation of MB molecules, respectively. The reaction rate constant is calculated by follow Eq. (2)29:

-

dC = kC dt

(2)

where k is the rate constant, C is the concentration of MB pollutants, and t is the reaction time. As shown in Figure 7B, there is a nice linear correlation between 16


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ln(C/C0) and the reaction time (t), suggesting that the decomposition reaction of MB pollutants follows the first–order kinetics. The corresponding rate constants of CuI/BiOI, BiOI, and CuI were determined to be 1.03, 0.57, and 0.04 h–1, respectively, in which the CuI/BiOI showed the highest catalytic performance among three electrodes. The stability of CuI/BiOI was also evaluated for the degradation of MB pollutant with three successive runs under visible light irradiation. Figure 7C shows no significant changes in the three runs of catalytic performances, indicating that the as-prepared CuI/BiOI samples can be worked as stable photoelectrocatalysts for the photoelectrocatalytic applications.

Figure 7. (A) Photoelectrocatalytic activities and (B) kinetic linear simulation curves over CuI/BiOI (a), BiOI (b) and CuI (c) for the degradation of MB pollutants under visible light illumination. (C): Photoelectrocatalytic degradation of MB solution over CuI/BiOI electrode for three successive runs under visible light irradiation. 17



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Based on the above result, the introduced CuI can significantly enhanced photoelectrocatalytic performance of the BiOI through the enhanced charge separation. The mechanism of the charge separation is shown in Figure 8. Owing to nice absorption of BiOI in visible light region, when the BiOI species was irradiated by visible light, electrons and holes will be generated in the conduction band (CB) and valence band (VB) of the BiOI, respectively. As other results reported, the VB of CuI and BiOI are around 0.6 V and 2.46 V vs NHE.4,14 The holes from the VB band of BiOI easily transferred to the VB band of the CuI, resulting in high-efficiency of charger separation. Finally, the holes will react with the surface adsorbed OH−/H2O to form hydroxyl radicals (•OHs). These •OHs have strong oxidizing ability, which will oxidize the adsorbed methanol or organic pollutants.30 On the other hand, the electrons will move to the circuit by external electric field, which prevent the charges carries recombination.

Figure 8. Schematic illustration for photoelectrocatalytic oxidation of methanol and MB process on Pt-CuI/BiOI modified electrode under visible light irradiation. CONCLUSIONS 18


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In conclusion, highly efficient visible-light-driven CuI/BiOI heterostructures were designed by using one-pot solvothermal route. After deposited Pt nanoparticles, the Pt-CuI/BiOI modified electrode can be worked as efficient photoelectrocatalyst for the catalytic oxidation of methanol and organic pollutant. Owing to the different energy band diagram of CuI and BiOI, the photogenerated electron-hole pairs of the excited BiOI under visible light irradiation can be separated efficiently, in which CuI acted as holes transport channel for the oxidization of methanol and organic pollutants. Compared to pure BiOI, the heterostructure of CuI/BiOI displayed 4.3 and 1.8 times for oxidation of methanol and MB, respectively. The efficient charger separation between BiOI and CuI contributes the distinctly enhanced photoelectrocatalytic performances. This research will encompass significant work towards an innovative construction of high-performance photoelectrocatalysts for solar energy conversion.

ASSOCIATED CONTENT

Supporting Information. The SEM, TEM, EDX, XRD, XPS, CVs and equivalent circuit of samples, effects on different weight ratio of Pt and different scan rate of samples towards methanol oxidation.

AUTHOR INFORMATION Corresponding Author *E–mail: [email protected] (M. Zhu); [email protected] (J. Pan). Notes: The authors declare no competing financial interest.

ACKNOWLEDGMENT 19



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The authors appreciate the National Natural Science Foundation of China (grant number 21603111, 11475242). This work was also sponsored by K.C. Wang Magna Fund in Ningbo University.

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CuI as Hole-Transport Channel for Enhancing Photoelectrocatalytic

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