Achieving Organic Metal Halide Perovskite into Conventional

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Achieving Organic Metal Halide Perovskite into Conventional Photoelectrode: Outstanding Stability in Aqueous Solution and High-Efficient Photoelectrochemical Water Splitting Ran Tao, Zhixia Sun, Fengyan Li, Wencheng Fang, and Lin Xu ACS Appl. Energy Mater., Just Accepted Manuscript • DOI: 10.1021/acsaem.8b02072 • Publication Date (Web): 19 Feb 2019 Downloaded from http://pubs.acs.org on February 19, 2019

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ACS Applied Energy Materials

Achieving

Organic

Metal

Halide

Perovskite

into

Conventional

Photoelectrode: Outstanding Stability in Aqueous Solution and HighEfficient Photoelectrochemical Water Splitting

Ran Tao, Zhixia Sun, Fengyan Li,* Wencheng Fang, Lin Xu* Key Laboratory of Polyoxometalate Science of Ministry of Education, Department of Chemistry, Northeast Normal University, Changchun 130024, China

KEYWORDS: organic metal halide perovskite, photoelectrochemical, photoanodes, solar energy, water splitting

ABSTRACT Organic metal halide perovskite material has attracted intense interest in photovoltaic field due to its excellent optoelectronic properties, but the extreme susceptibility of organolead

halide

perovskite

to

water

seriously

impedes

its

application

for

photoelectrochemical (PEC) conversions in aqueous solution. In this work, we develop an organolead halide perovskite photoanode of conventional electrode structure. The perovskite photoanode was fabricated by using a facile approach and encapsulated with conductive carbon paste and silver conductive paint for waterproof function, and the PEC water splitting was carried out as a model of PEC conversion. For PEC water oxidation, the photoanode achieved a remarkable photocurrent density of 12.4 mA/cm2 at 1.23 V versus reversible hydrogen electrode in alkaline electrolyte. In addition, the as-prepared photoanode of conventional structure exhibited an unprecedented stability, which could be stable in alkaline electrolyte for more than 48 hours. More importantly, the photoanode retained a steady-state response in a continuous operation for at least 12 hours in electrolyte at wide pH range. This 1 ACS Paragon Plus Environment

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work opens a promising avenue toward the practical application of organic metal halide perovskite-based photoelectrodes for efficient PEC conversions in aqueous solution.

INTRODUCTION Considering global energy consumption, solar energy utilization has attracted intensive research effort due to its advantages of secure, clean and sustainable energy with unmatched resource potential.1 One of the direct way to utilize solar energy is the photoelectric conversion including solar cells and photoelectrochemical (PEC) approach. In particular the PEC approach could achieve some significant conversions of solar energy into chemicals and fuels,2 such as PEC water splitting,3-5 PEC reduction of carbon dioxide,6,7 and visible lightdriven organic transformations.8,9 In principle, these PEC conversions of solar energy into chemicals require efficient photoelectrodes to drive anodic and/or cathodic half-reactions. Therefore, the photoelectrode that could directly determine the energy conversion efficiency becomes the key component for PEC systems. The ideal semiconducting materials for photoelectrode need to possess advantageous performances in light absorption, charge separation, and charge transfer. However, because of the existence of electron-hole recombination, crystal defects and inappropriate energy band structures in ordinary semiconductors, the development of superior photoelectrode materials for achieving efficient PEC conversions is still a challenging issue confronting solar energy utilization. In recent years, organic metal halide perovskite emerged as a promising candidate for functional materials and photovoltaic applications.10-14 Especially, solar cells based on organolead halide perovskites have made a new breakthrough in power conversion effciency increasing from initial 3.8% in 2009 to above 23% in 2018.15,16 Many researches in depth have revealed that such remarkable achievements in the type of solar cells mainly rely on the superior semiconducting properties of organolead halide perovskites, including high optical absorption coeffcients, ambipolar charge-carrier mobilities, balanced long electron and hole 2 ACS Paragon Plus Environment

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diffusion lengths and very low exciton binding energy.17-19 Inspired by the superior properties of organolead halide perovskites, one could consider that the introduction of organolead halide perovskites into photoelectrode materials for PEC conversions is certainly a sensible choice. In the PEC system, PEC photoelectrodes directly immersed in electrolytes is more favourable to simplified wiring and saved space.20 However, the extreme susceptibility of organolead halide perovskite to water and moisture has become a critical problem for its practical application in PEC system.21,22 Recently, several of researchers made pioneering works to develope perovskite photoelectrodes for PEC water splitting, as the PEC water splitting into oxygen and hydrogen has been one of the most promising and sustainable strategies for solar energy conversion and storage.3-5 In 2015, Da et al. first reported that a photoanode bearing on the perovskite solar cell was directly immersed in electrolyte for PEC water splitting, and a Ni thin layer was electrodeposited on the solar cell as both the waterproof coating and the hole-transferring catalyst. But the photoanode lost most of its activity after 20 min of continuous PEC measurement.23 Hoang et al. used a carbon nanotube/polymer composite as waterproof layer on the top of photoanode bearing on the perovskite solar cell and maintained the photoanode stability for 30 min.24 Yang et al. prepared a photoanode bearing on the perovskite solar cell using an ultrathin Ni layer as waterproof coating, and the photoanode delivered a photocurrent density of 2.08 mA/cm2 for lasting about 30 min during PEC measurements.25 More recently, Oh et al. developed a versatile lift-off process to fabricate metal-encapsulated perovskite photoanodes, which achieved an operational stability for 6 hours in alkaline electrolyte.26 Unfortunately, these above-mentioned photoelectrodes were all based on the planar perovskite solar cells which included expensive hole transporting materials and Au electrodes. Evidently, the type of perovskite photoelectrodes attached to the planar perovskite solar cells, involving high cost and unsatisfied stability, are not appropriate for practical application of PEC water splitting. 3 ACS Paragon Plus Environment


Hence, the development of the superior perovskite photoelectrode of simple structure, low cost, long-term stability and high efficiency is urgently desired for achieving efficient PEC conversions. In this work, we develop an organolead halide perovskite photoanode of conventional electrode structure. We choice the mixed-cation perovskite (5-AVA)x(MA)1-xPbI3 because 5AVA cations can assist the formation of perovskite crystals in the mesoporous oxide host and induce preferential growth in the normal direction. Compared with the single-cation form MAPbI3, the (5-AVA)x(MA)1-xPbI3 has better surface contact with the TiO2 surface and lower defect concentration.27 The perovskite photoanode was fabricated by using a facile approach and encapsulated with conductive carbon paste and silver conductive paint for both the waterproof function and the photogenerated holes transport, and the PEC water oxidation was carried out as a model of PEC conversion. Moreover, previous reseasrches have confirmed that the conductive carbon can work as a bifunctional material for both effective hole extraction and collection.28,29 Despite the use of simple process and cost-effective materials, the perovskite photoanode achieved a remarkable photocurrent density of 12.4 mA/cm2 at 1.23 V versus reversible hydrogen electrode (RHE) in KOH electrolyte under AM 1.5G illumination. Besides, the as-prepared photoanode of conventional structure exhibited an unprecedented stability, which could be stable in alkaline electrolyte for more than 48 hours. More importantly, the photoanode retained a steady-state response in a continuous operation for at least 12 hours. The stability of the as-prepared photoanode is considerably superior to other perovskite-based PEC photoanodes ever reported.23-26 These results from this work is a breakthrough in developing organolead halide perovskite-based conventional photoelectrode being applicable to PEC conversions in aqueous solution, and its extended application in other PEC conversions should be expectable.

EXPERIMENTAL SECTION 4 ACS Paragon Plus Environment

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Materials. CH3NH3I (MAI) and HOOC(CH2)4NH3I (5-AVAI) were synthesized according to our previous report.30 The (5-AVA)x(MA)1-xPbI3 precursor solution was prepared according to literature method. The commercial carbon paste (sheet resistance: 20 Ω/□; density: 1.2–1.4 kg L-1; adhesion: 100/100; heat resistance: 90 °C 1000 h-1 with the resistance changing within 10%) was purchased from Shenzhen Dongdalai Chemical Co., Ltd. The silver conductive paint was purchased from Nanjing Chuangyiyou Technology Co., Ltd. All purchased chemicals were used without further purification. Fabrication of Perovskite Photoanodes. Fluorine-doped tin oxide (FTO) glass was cleaned with surfactant and rinsed with acetone and ethanol and deionized water and finally dried by air flow. A mesoscopic structure was fabricated by the reported method with a little modification.27 A compact layer of TiO2 was deposited by spin-coating (2500 rpm) from a precursor solution to act as a hole-blocking layer. The mesoscopic TiO2 layer was deposited by screen-printing of a TiO2 slurry (P25 Degussa) and then sintered at 450 °C for 30min. A 12μm ZrO2 space layer was printed on the top of the TiO2 layer using a ZrO2 slurry, which acted as an insulating layer to prevent electrons from reaching the back contact. A carbon black/graphite layer with the thickness of about 10μm was coated on the top of ZrO2 layer by printing carbon/graphite composite slurry and consequently heating at 400 °C for 30min. Then, the resulting films were infiltrated with a 40wt% perovskite precursor solution by dropping on the top of the carbon black/graphite layer. The above mesoscopic structure containing perovskite was obtained after drying at 50 °C for two hours. All these procedures were carried out on naturally ambient air and room temperature. After that, a carbon black/graphite film and a conductive-carbon (CC) film were coated on the top of the mesoscopic structure by printing carbon/graphite composite slurry and a low-cost commercial CC paste, and then the films were heated at 80 °C for 30min. After that, about 40 µL silver conductive paint was dropped on the CC paste film, and wiped evenly to form a smooth surface. The device was kept on the 50 °C hot plate for about 60 min to dry the silver 5 ACS Paragon Plus Environment


conductive paint. Finally, about 30 µL CC paste dispersed by dibasic ester was drop on the device, and was dried at 80 °C for 20 min. After the above procedures, the perovskite photoanodes were successfully made with the edge of it sealed by epoxy resin. Measurements and Characterization. X-ray diffraction (XRD) analyses were recorded with a Rigaku D/max-3c X-ray diffractometer, using Cu Kα radiation (λ=1.5405Å). Field emission scanning electron microscopy (SEM) (SU-8010, Hitachi) equipped with an energy dispersive spectrum (EDS) was used to investigate the surface and cross-section morphology. Photoelectrochemical (PEC) water splitting measurements were carried out in a quartz cell using the three-electrode system with a Pt wire counter electrode and a saturated calomel electrode as reference electrode in a 1 M KOH electrolyte. A 300 W Xenon lamp with light intensity of 100 mW/cm2 (AM 1.5G) served as the light source to simulate the sunlight. All the photoelectrochemical experiments were recorded on an Ivium workstation (Ivium Stat.h, Ivium Holland, Inc.) at room temperature. The amount of gas evolution and Faradaic effciency of O2 evolution were detected by an online gas chromatograph (Shimadzu GC2014C).

RESULT AND DISCUSSION We fabricated an organic metal halide perovskite photoanode by simple and effective processes. Figure 1a shows the schematic illustration of the as-prepared perovskite photoanode. A TiO2 electron transfer layer is deposited at the bottom and a conductive carbon (CC) paste layer is located on the top, and there is a CC paint layer and a silver conductive (SC) paint layer between the perovskite layer and the top CC paste layer. The CC paste layer can act as a bifunctional film for both effective hole extraction and collection due to its appropriate work function (-5.0 eV) close to that of gold (-5.1 eV).28 Furthermore, the SC paint layer can create a conductive interface with low resistance between the two CC paste layers, and thus the holes can transfer into the top CC paste layer surface, along with the help 6 ACS Paragon Plus Environment

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of an electric-field driving force (under bias voltage). The existance of CC paste layer between the perovskite layer and the conductive silver layer could could block the I- anion migration from the perovskite to the conductive silver paint layer; this avoids the possible formation of AgI affecting photoanode stability. The photoanode can directly contact with liquid electrolyte to construct a PEC cell with a reference electrode and a Pt counter electrode. In the construction of the photoanode, it is necessary that the ZrO2 layer acts as an insulating layer to prevent a short-circuit that electrons directly transmit from carbon layer to TiO2 layer instead of via perovskite. Actually, the perovskite is fully infiltrated into the porous ZrO2 by drop-casting process, and thus the ZrO2 is only an insulating support with porous passageway. When the PEC cell works, sunlight shines upon the FTO glass window face of the perovskite photoanode, the photogenerated electrons in perovskite layer are collected by the TiO2 electron

transfer

layer

and

subsequently

flow

toward

the

Pt

wire

counter

Figure 1. (a) Schematic illustration of the perovskite photoanode for PEC water splitting in a standard three-electrode system. The photoanode is back illuminated from the FTO side. (b) X-ray diffraction spectra for TiO2/FTO glass substrate and the perovskite film formed on mesoscopic TiO2/FTO glass substrate.

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electrode through the external circuit, where water can be reduced by accepting electrons to produce H2. At the same time, the photogenerated holes from perovskite layer transfer to the CC layer/electrolyte interface through CC paste layer and SC paint layer where the oxygen evolution reaction occurs. An energy band diagram with band position of each layer is shown in Figure S3. Figure 1b shows X-ray powder diffraction spectrum of perovskite film formed on mesoscopic TiO2/FTO glass substrate. The main diffraction peaks are assigned to the (001), (110), (112), (220), (310), (224), and (314) diffraction planes, which confirms the formation of tetragonal crystal structure of (5-AVA)x(MA)1-xPbI3.27 Figure 2a shows a cross-sectional scanning electron microscope (SEM) image of the perovskite photoanode, and clear interfaces of each layer are evident. The perovskite photoanode consists of a compact TiO2 layer, a 10 μm mesoscopic structure (Figure 2b), a thin CC paste layer and a 50μm SC paint layer. Finally, a 50 μm CC paste layer as the top layer directly contacts with the electrolyte. Among it, the mesoscopic structure is a triple-layer fully printable structure consisting of a double layer of mesoporous


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Figure 2. SEM cross-sectional image of (a) the perovskite photoanode and (b) the triple-layer fully printable mesoscopic structure. Surface morphology of (c) SC paint layer and (d) CC paste layer.

TiO2 and ZrO2 covered by a porous carbon film for filling perovskite, the SC paint layer plays a major role in waterproofing, which we proved it with the tests later. The wavelengthdependent light harvesting efficiency (LHE) was measured and calculated from the measured reflection (R) and transmission (T) as LHE (λ) (%) = 100% - R(λ) (%) - T(λ) (%). In order to eliminate the effect of waterproof layers and carbon, we measured LHE of the mesoporous TiO2 and ZrO2 filled by perovskite, as shown in Figure S4. Due to appropriate band gap of perovskite, the photoanode exhibited high light-harvesting capabilities in the spectral range from the ultraviolet to visible light. Figure S7 show a cross-section of the perovskite photoanode and the corresponding EDS elemental mapping images. Meanwhile, the morphology measurements were also performed for both SC paint layer and CC paste layer and shown in Figure 2c and Figure 2d. The surface particles SC paint layer of are distributed evenly and tightly. In addition, we measured the contact angle of water to characterize hygroscopicity of silver conductive paint. Optical image of contact-angle measurements at ambient condition for water on silver conductive paint layer is shown in Figure S5, and the contact angle of water on the surface of silver conductive paint is 133.6°. Thus the silver conductive paint has good hydrophobicity and plays a vital role in waterproof function. The CC paste layer exhibits a smooth surface with a layered morphology. Combination of the two highly conductive layers with different morphologies can provide perfect protection for the underlying perovskite layer and make thus-prepared perovskite photoanode exhibits high performance and superior stability. The complete preparation processes of the perovskite photoanode are shown in Figure 3, and the preparation details are described in the experimental section. In this work, we used a 9 ACS Paragon Plus Environment


structure where two CC layers are sandwiched with a SC paint layer, the SC paint is highly conductive, solid and waterproof, the CC paste is cheap and chemically stable. The structure can act as guard that protects perovskite from the invasion of electrolyte. Moreover, transportation of the photogenerated holes from perovskite to electrolyte can proceed

Figure 3. Schematic illustration of the processes to fabricate perovskite photoanode.

availably because the SC paint layer and CC layers create a tight interface with low resistance between perovskite and electrolyte. It should be noted that we did not use any catalyst for water oxidation in this work, which reduced the cost of materials and the complexity of the processes. Therefore, the processes of fabricating perovskite photoanode are compatible for large-scale production. Moreover, we consider that the combination of high conductivity and waterproofing is widely applicable and can also be adapted to other perovskite-based photoelectrodes. Previous reports on perovskite photoelectrodes for solar water splitting have been tested mainly in near-neutral electrolytes because the n-i-p perovskite solar cells and even the protective layers are easily corroded in strong acid or alkaline electrolytes.23-25 However, in near-neutral environment, severe pH gradient near electrode surfaces and electrode kinetics are slower than in acidic or alkaline environments. In addition, stoichiometric mixtures of H2 10 ACS Paragon Plus Environment

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and O2 may be generated for recombination of products.3,31 Hence perovskite photoelectrodes should be able to withstand and perform in an acidic or alkaline environment. We first assessed the water resistance of the perovskite photoanode by placing it in strong alkaline electrolyte solution (1 M KOH, pH=14). An unprotected photoanode (i.e., without the SC paint layer and CC layers) was also assessed for comparison. In the absence of illumination and electrochemical bias, the perovskite photoanode exhibited unprecedented stability in strong oxidizing environment and began to show faint signs of degradation after 48 h (Figure S2, Supporting Information), while the unprotected photoanode was completely degraded within 90 s (Figure S1, Supporting Information). Subsequently, we conducted PEC measurements of the perovskite photoanodes. As shown in Figure 1a, the PEC water oxidation activities of the perovskite photoanodes were performed in a three-electrode system with the photoanode, a saturated calomel electrode (SCE), and a Pt wire as the working, reference, and counter electrodes, respectively. In the voltammogram for the oxygen evolution reaction (Figure 4a), the perovskite photoanode



Figure 4. (a) Voltammogram of perovskite photoanodes with SC paint layer (red curve) and without SC paint layer (black curve) under simulated illumination, under dark (green curve), and CC paste electrode (blue curve) as a reference. (b) Photocurrent responses of perovskite photoanodes with and without SC paint layer. (c) EIS spectra measured at 1.23 VRHE in a 1 M KOH electrolyte. Inset: equivalent circuit used for the fit and simulation. (d) Photographic image of the perovskite photoanode when it works.

achieves a photocurrent density of approximately 12.4 mA/cm2 at 1.23 V versus reversible hydrogen electrode (RHE), which corresponds to light-driven water oxidation to O2 (red curve in Figure 4a). To explore the effect of SC paint layer on photoanode’s performance, we conducted PEC measurements of the perovskite photoanodes without SC paint layer in same condition, and it showed a photocurrent density that was basically the same as the photoanode with SC paint layer (black curve in Figure 4a). It is proved that the SC paint layer has no effect on photoanode’s PEC performance. As control experiment, we carried out the response of the perovskite photoanode in dark and exhibits almost no current (green curve in Figure 4a), indicating that most of the current at the irradiated photoanode is actually photocurrent. The CC paste layer direct contacts with the electrolyte, thus we carried out the response of a bare FTO covered by CC paste as a reference, as shown the blue line in Figure 4a. An overpotential at 10 mA/cm2 is measured to be 0.66 V and the potential difference between the perovskite photoanode and the CC paste electrode is the photovoltage obtained by the perovskite material (~0.7 V). To further explore the PEC performance of the perovskite photoanodes, photocurrent response measurements upon illumination on/off cycles were carried out at a constant bias voltage of 1.23 V (vs. RHE). As shown in Figure 4b, both the photoanodes with and without SC paint layers show steady and reproducible anodic photocurrent responses when the irradiation is switched on and off, and the performance of the perovskite photoanodes were 12 ACS Paragon Plus Environment

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not affected by the SC paint layer for a period of time. As can be seen from Figure 4d , the active area of the perovskite photoanode produces oxygen gas when it works, and H2 is evolved from Pt wire electrode. To gain further insight into the effect of SC paint layers on photoanodes, electrochemical impedance spectroscopy (EIS) measurements on perovskite photoanodes with and without SC paint layers were carried out in the frequency range of 1 × 10-1–1 × 105 Hz under illumination, and the results are shown in Figure 4c as Nyquist plots. The inset in Figure 4c shows the equivalent circuit to simulate the Nyquist plot. The similar diameters of the arcs illustrate the almost equivalent valves of charge transfer resistance (Rct) for two photoanodes, which might derive from the CC paste layer covered both photoanodes,25 serving as the top layer in direct contact with the electrolyte. In the details, the photoanode without SC paint layer exhibited a slight smaller diameter probably because of the absence of silver layer which leads to the surface of the top CC layer is smoother. At the same time, the series resistances (Rs) of the photoanode with SC paint layer was smaller than that of the photoanode without SC paint layer, this might be because the SC paint layer with low resistance connected the upper and lower CC paste layers tightly. These parameters can account for the similar PEC performance for both two perovskite photoanodes, considering that the divergences of Rs and Rct are not significant. The H2 and O2 evolution during PEC water splitting reaction were proved and quantified by a gas chromatography. It is determined that the generated gas is H2 and O2 by comparing the standard gas. The amount of O2 evolution was detected by an online gas chromatograph for quantifcation at regular intervals. The quantity and retention time of the gases were calibrated with standard gas sample. The Faradaic effciency of O2 evolution was calculated by comparing the amount of O2 evolved and the charge passed through the system. The Faradaic effciency for O2 evolution on the photoanode was calculated to be more than 80% (Figure S8), demonstrating that the observed photocurrent was mainly ascribed to O2 production. We 13 ACS Paragon Plus Environment


calculated applied bias photon-to-current efficiency (ABPE) of the perovskite photoanodes calculated by using its J-V curves, as shown in Figure S9. The maximum ABPE of 0.85% and 0.88% were achieved by the photoanodes with and without SC paint layers, respectively. To calculate the change in transfer and transport efficiency, Na2SO3 was used to evaluate the efficiency because oxidation of Na2SO3 is easier than water thermodynamically and kinetically and have 100% surface transfer efficiency.32 Figure S10 shows the currentpotential plots for photoanodes with and without Na2SO3. And the surface charge transfer efficiency of the photoanodes with and without SC are 94% and 92%, respectively. It is well-known that stability is an important index for evaluating the PEC performance of perovskite-based photoanodes, and we measured long-term performance of our perovskite photoanodes. Figure 5a shows current versus time curve of perovskite photoanodes in 1M KOH electrolyte at a constant potential of 1.23 V versus RHE under illumination. The perovskite photoanode with SC paint layer showed a significantly enhanced stability

Figure 5. (a) Current versus time graph of perovskite photoanode at an applied potential of 1.23V versus RHE under simulated AM 1.5 G solar illumination (100 mW/cm2) in 1 M KOH solution, (b) in 1 M HCl and 0.5 M Na2SO4 solution.

compared with the photoanode without SC paint layer. Combined with the PEC and EIS measurements, we can prove that SC paint layer can retain the PEC performance of the 14 ACS Paragon Plus Environment

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photoanode while greatly improve its stability. As shown the red curve in Figure 5a, the perovskite photoanode with SC paint layer exhibited a stable response for several hours. Quantitatively, the photoanode without SC paint layer lost most of its activity during about 2 h continuous working, while the perovskite photoanode with SC paint layer remained more than 70% of its initial value after continuous working that lasted for 12 h. Previous reports indicate that perovskite photoanodes lose most of the activity with in 6 h at most,24 thus the remarkable improvement in stability of our perovskite photoanodes is really an impressive step forward. To be a versatile photoanode for PEC water splitting, it is desirable that the photoanode can operate steadily in electrolytes with wide pH range. We therefore performed long-term PEC tests on the perovskite photoanode in electrolytes besides the alkaline one (Figure 5b). In 0.5 M Na2SO4 solution (pH = 7), the photoanode can maintain ca. 78% of its initial photocurrent density after 12 h continuous illumination. Similarly, when we used 1 M HCl as electrolyte (pH = 1), the photoanode can retain ca. 70% of its initial photocurrent density after 12 h continuous illumination. To further investigate the photoanode stability, we measured the XRD patterns of the perovskite photoanode after continuous working for 12 hours in all pH values (Figure S6). It is shown that there were formations of PbI2 in photoanode after continuous working in acidic and alkaline condition. It can be seen from Figure S6 that the appearance of PbI2 peaks indicates a partial degradation of perovskite after long-term photoelectrochemical process; this is because the presence of mesoscopic TiO2 could induce the degradation of hybrid lead halide perovskite under ultraviolet light irradiation, which has been reported in previously published literature.33 Also, using SEM images, we investigate on the morphological change of the photoanode surface before and after the PEC stability experiments. Figure S11a shows the morphology of photoanode before PEC stability tests, and Figure S11 (b), (c), (d) show the morphology of photoanode after PEC stability tests in acidic, neutral, alkaline condition, respectively. It is obvious that there is no change in surface 15 ACS Paragon Plus Environment


morphology of photoanode before and after the photoelectrochemical stability tests. Although our perovskite photoanodes have been sealed up as far as possible, the electrolyte slowly seeped through the existent pinholes when working for long hours. We consider that the wide applicability of the present perovskite photoanode for solar oxygen production in different electrolytes, which enables it to be an attractive candidate for effective solar fuel production.

CONCLUSIONS In summary, we have fabricated an organic metal halide perovskite-based photoanode of conventional structure for efficient PEC conversions in aqueous solution. The perovskitebased photoanode was encapsulated with conductive carbon paste and silver conductive paint for both the waterproof function and the photogenerated holes and electrons transport. The rational design endowed the photoanode with high efficiency and outstanding stability. For the PEC water oxidation, the as-prepared photoanode achieved a photocurrent density of 12.4 mA/cm2 at 1.23 V versus RHE in alkaline electrolyte under AM 1.5G illumination and was stable for more than 48 hours under a strongly oxidized environment. More importantly, the photoanode materials are low-cost and commercial, along with simple fabrication process; these are certainly favourable to practical application. These results from this work is a breakthrough in developing organolead halide perovskite-based conventional photoelectrode being applicable to PEC conversions in aqueous solution, and its extended application in other PEC conversions should be expectable.

ASSOCIATED CONTENT Supporting Information The water resistance of the perovskite photoanodes in strong alkaline electrolyte solution. Band diagram of each layer in perovskite photoanode. The wavelength-dependent light 16 ACS Paragon Plus Environment

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harvesting efficiency (LHE) of the mesoporous TiO2 and ZrO2 filled by perovskite. Optical image of contact-angle measurements at ambient condition for water on silver conductive paint layer. SEM images of a cross-section of the mesoscopic structure contained perovskite and the corresponding energy dispersive spectrum. Evolution of H2 and O2 gases measured by gas chromatography with Faradaic efficiency and photocurrent for the perovskite photoanode at 1.23 VRHE. The ABPE of the perovskite photoanodes with and without SC. Currentpotential plots for perovskite photoanodes measured without and with 0.1 M Na2SO3.

AUTHOR INFORMATION

Corresponding Author *E-mail: [email protected], [email protected];

Acknowledgment The authors are thankful for the financial support from the Natural Science Foundation of China (Grant No. 21671035, 21571029). References (1) Lewis, N. S. Research Opportunities to Advance Solar Energy Utilization. Science 2016, 351, No. aad1920. (2) Montoya, J. H.; Seitz, L. C.; Chakthranont, P.; Vojvodic, A.; Jaramillo, T. F.; Nørskov, J. K. Materials for Solar Fuels and Chemicals. Nat. Mater. 2016, 16, 70-81. (3) Grätzel, M. Photoelectrochemical Cells. Nature 2001, 414, 338-344.



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Achieving Organic Metal Halide Perovskite into Conventional

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