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Promising GeSe nanosheet based thin film photocathode for efficient and stable overall solar water splitting Kang Wang, Dingwang Huang, Le Yu, Kuang Feng, Lintao Li, Takashi Harada, Shigeru Ikeda, and Feng Jiang ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.9b00035 • Publication Date (Web): 04 Mar 2019 Downloaded from http://pubs.acs.org on March 5, 2019
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ACS Catalysis
Promising GeSe nanosheet based thin film photocathode for efficient and stable overall solar water splitting Kang Wang, Dingwang Huang, Le Yu, Kuang Feng, Lintao Li, Takashi Harada, Shigeru Ikeda and Feng Jiang* K. Wang, D. Huang, L. Yu, K. Feng, L. Li, Prof. F. Jiang Institute of Optoelectronic Materials and Technology, South China Normal University, 55 Zhongshan Avenue West, Tianhe District, Guangzhou 510631, P. R. China *Corresponding Author Email:
[email protected] Dr. T. Harada, Research Center for Solar Energy Chemistry, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan Prof. S. Ikeda, Department of Chemistry, Konan University, 9-1Okamoto, Higashinada, Kobe, Hyogo 658-8501, Japan Keywords: GeSe, solar water splitting, photoelectrochemical, photocathode, nanosheet Compound semiconductor GeSe nanosheet based thin films were systematically researched
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for application in solar water splitting. P-type GeSe films obtained from the rapid thermal
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sublimation method have a sheet-like grain structure and a homogeneous elemental
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distribution, which is suitable for application in photocathodes for solar hydrogen production.
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Deposition of a CdS layer on top of GeSe was found to be effective in enhancing the
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photoelectrochemical properties due to the p-n junction formed at the interface of CdS/GeSe
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that enhances the separation rate of photoexcited carriers. Furthermore, the atomic layer
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deposition of the TiO2 overlayer under the CdS/GeSe photocathode not only protects the CdS
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from photocorrosion but also reduces surface recombination, which could generally enhance
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photocathode performance. The obtained Pt-TiO2/CdS/GeSe photocathode generated ~10.5
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mA/cm2 under 0 VRHE and presented an onset potential of ~ 0.45 VRHE. The calculated half
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cell solar to hydrogen efficiency (HC-STH) of the obtained Pt-TiO2/CdS/GeSe photocathode
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was over 1%, and the stacked photocathode exhibited an appreciable photoelectrochemical
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stability of more than 8 hours. It was found that the relationship between H2 evolution amount
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and illumination time is almost linear, with more than 105 μmol of H2 accompanied by
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approximately 54 μmol of O2 evolving throughout the detection period of 3 hours under
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sustained solar light illumination.
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Introduction Solar water splitting for hydrogen evolution offers a sustainable and green source of energy
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from solar power.1-3 One of the most attractive features of this technology is that the light-
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absorbing materials can be directly integrated with catalysts to produce a monolithic device,
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thereby making their use simpler and more cost-effective than the use of separate photovoltaic
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(PV) cells and electrolyzers.4-6 To make this approach competitive with conventional
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hydrogen production from fossil fuels, i.e., steam-methane reforming, the materials for
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photoelectrochemical (PEC) water splitting need to be made from cheap earth-abundant
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elements using a low-cost and scalable processing technique.
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Crystalline silicon-, amorphous/poly crystalline silicon- and CIGS-based thin films have
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already proven their great potential for efficient solar water splitting.7-9 However, the high
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cost of the electrolyzer processing of crystalline silicon and amorphous/poly crystalline and
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the noble/toxic elements in CIGS have limited the utilization of these materials. Various
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efforts have been devoted in recent years; however, there is still no solar water splitting
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device that concurrently fulfills the requirements of high efficiency, long-term stability and
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low cost.4, 10-13 In the last few years, several new low-cost and environmentally friendly
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emerging photoabsorbers, such as Cu2ZnSnS4, Cu2BaSn(S,Se)4 and CuSbS2, have exhibited
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great potential for photoelectrochemical solar water splitting.14-19 However, the complex
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composition and easily formed secondary phases of Cu2S, ZnS, Sb2S3 and Cu2SnS3
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themselves also make their processing difficult, which restricts their PEC efficiency and
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stability. Recently, binary compounds such as Sb2Se3 and GeSe were successfully used on
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thin film photovoltaics due to their simple and thermodynamically stable phases. Sb2Se3 and
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GeSe were considered promising new photoabsorbers for solar cells as well as for solar water 2 ACS Paragon Plus Environment
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splitting because of their suitable optical band gaps of approximately 1.3 eV and theoretical
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maximum efficiency of around 30%.20-22 Although these materials have been investigated for
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solar cells, there have thus far been only very few reports on Sb2Se3 as a PEC photoelectrode
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for solar water splitting 20,23,24 : Zhang et al reported that their best photocurrent density, onset
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potential and half cell solar to hydrogen conversion efficiency (HC-STH) reached are -8.6
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mA/cm2 under 0 VRHE, 0.43 VRHE and 0.68%, respectively. 20 And Tilley’ group reported that
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their Sb2Se3 based photocathode using MoSx modification layer generated ~16mA/cm2
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photocurrent density (at 0VRHE) with an onset potential of 0.14VRHE, but the HC-STH
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efficiency was not mentioned. However, there are no reports regarding on the GeSe for solar
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water splitting application but only one report of GeSe being used on a thin film solar cell.
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According to this report, GeSe has great potential for solar cell applications, with a Voc, a Jsc
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and an efficiency of 240 mV, 14.48 mA/cm2 and 1.48 %, respectively. 25 Thus, at the same
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time, GeSe should also be promising for utilization in photoelectrochemical solar water
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splitting; however, there are no reports regarding its application in solar water splitting to date.
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In this work, a GeSe thin film prepared by a simple rapid thermal processed method was
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first found to have significant photocatalytic activity. Schematic diagram 1 presented the
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detail deposition process of this novel rapid deposition approach for GeSe film: we putted the
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substrate inside of a graphic box that contain GeSe powder, and then we moved the graphic
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box into a furnace for rapid thermal treatment for several seconds, after that we obtained the
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GeSe films under the substrate. This deposition approach is utilized in a covered graphic box,
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therefore we called it as rapid box thermal deposition (RBTD), and this method is much
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different from the previous reported deposition approaches such as vapor transfer deposition
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(VTD) and rapid thermal sublimation26,27, detail parameters could find in experimental detail
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in Supporting Information. The growth mechanism of the GeSe nanosheets in our case could
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reference to the reports from Yoon28 and Mukherjee26, the concentration of the GeSe vapor
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determined the density and size of the following grew GeSe nanosheet single crystals. We 3 ACS Paragon Plus Environment
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used the top covered small graphic box contain the GeSe powder source and substrate that
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could largely isolate the GeSe vapor from the outside environment and maintained the high
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concentration of GeSe vapor inside of the box during the deposition process. The dynamic
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behavior of synthetic process could be as follows. At first the sublimation of the source
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powder into gaseous GeSe molecules and then condensation of the gas molecules onto the
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substrates. Continued source molecules adsorbed to growth sites and recrystallization process
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help to grow the nanosheets. The high concentrated GeSe vapor let the GeSe nanosheet
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sufficiently grew and finally results in the dense and big GeSe nanosheet.
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The properties of the GeSe films prepared in this work were also different from that of the
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GeSe films reported in previous reports25,26,28, the GeSe film was consisted with dense and big
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GeSe nanosheets and the GeSe film with such nanostructure showed appreciable and
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advanced photoelectrohemical properties.
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Schematic 1: diagram of the RBTD process of GeSe film
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Furthermore, in this study a novel GeSe thin film photocathode with a maximum HC-STH
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efficiency of over 1% was obtained, and the best onset potential and PEC photocurrent
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density of the GeSe photocathode were 0.45 VRHE and 10.5 mA/cm2 at 0 VRHE, respectively.
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The presented appreciable solar water splitting efficiency of the GeSe-based photocathode is
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even higher than that of the recently emerged promising novel photocathode of CuSbS2 19 and
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Sb2Se3 20,23, indicating great potential in the solar hydrogen evolution of new photocathodes
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based on GeSe materials.
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ACS Catalysis
Results and discussion The GeSe film in this work was prepared by a rapid thermal sublimation, and the
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temperature was found to clearly influence the microstructure, continuity and density of the
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films. Finally, the best temperature was chosen at 500℃, since the GeSe film prepared at
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500℃ has a structure with the appropriate thickness and density suitable for the fabrication of
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photoelectrochemical devices. The optimization of temperature is discussed in Figs. S1-S4 in
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the Supporting Information. The results and discussion shown below in this article relate to
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the GeSe films were prepared at the optimized temperature of 500℃ described above.
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Figure1. Top view photography of GeSe, CdS/GeSe and TiO2/CdS/GeSe (a), SEM image of
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the surface of GeSe film (b), XRD patterns of the GeSe film and GeSe powder (c) and Raman
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spectrum of GeSe film (d), respectively.
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Figure 1a shows a typical top view of photographs of the as-prepared GeSe thin film and
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CdS-covered GeSe and TiO2-covered CdS/GeSe samples. The bare GeSe film shows a white-
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gray color, while after deposition of the CdS layer onto GeSe, the surface color changed to
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black, indicating that the surface of GeSe was most likely fully passivated by the CdS
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overlayer. However, the color became just slightly dark when we further deposited a thin
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TiO2 layer onto the surface of CdS/GeSe. The micromorphology of the GeSe film is shown in
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Figure 1b. The film was filled with numerous sheet-like GeSe crystals, which is similar to the
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previously reported morphology of GeSe.28 The detailed crystal structure of the GeSe film
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was characterized by X-ray diffraction (XRD), and the results are shown in Figure 1c. The 5 ACS Paragon Plus Environment
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prepared GeSe film was grown well with pure phases: all the peaks were well attributed to the
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orthorhombically structured GeSe (JCPDS 48-1226), and the Raman peaks shown in Figure
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1d at 150 cm-1 and 188 cm-1 were assigned as the typical Raman peaks from GeSe. Similar
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results could be found in previous works on GeSe thin films. 25 It was found that the XRD
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peak intensities were different from that of GeSe powder: the intensities of (011), (111) and
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(020) peaks as marked with yellow background in Figure 1c of the GeSe film were much
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higher than that of GeSe powder, while (200), (400), (800) peaks were lower than that of
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GeSe powder, however, the portion of the intensities of the XRD peaks of GeSe film were all
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well matched with the standard PDF card JCPDS 48-1226 as shown in Figure 1c. It is
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suggested that the crystalline growth of the GeSe sheet crystals from the GeSe powder to form
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the GeSe film under Mo/glass substrate results in thus change in XRD peak intensities
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between film and powder. From Figure 2 a,c, we found that the microstructure of the
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obtained GeSe film was found to be fulfilled with sheet liked GeSe nanocrystals, the
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microstructure of the GeSe film prepared by RBTD in this work is much different from the
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compact structure of GeSe film prepared by Xue25 but is comparable with the results reported
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by Yoon28. The concentrate of the GeSe vapor may highly influence the microstructure of the
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following condensed GeSe film under the substrate, the structure of GeSe film from the
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compact structure to sparse small sized nanosheets and dense big sized nanosheets could be
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controlled by adjust the GeSe vapor concentrate. That may be the reason why our GeSe films
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show different microstructure from the others. 25,26,28 The microstructure of GeSe film should
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strongly impact on its photoelectrochemical properties, various relationships between them
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are very useful and should be the effective research directions for the optimizations in solar
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water splitting properties, detail works are on the way.
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ACS Catalysis
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Figure 2 Surface and cross-sectional morphology of GeSe film (a, c ) and CdS covered GeSe
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film (b, d), HRTEM image of GeSe (e), inset is the SAED pattern. STEM image of GeSe (f)
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and the corresponding elemental mappings of Ge (g) and Se (h).
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From the micromorphology observed by SEM, as shown in Figure 2, we know that the as-
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prepared GeSe film consisted of small GeSe sheet crystals (Figure 2a). In contrast to a flat
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surface morphology, such a sheet-like structure in a GeSe film shall obviously decrease
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optical reflections and largely increase the effective contact area between the GeSe and
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electrolyte solutions, enhancing the PEC performance, especially for the PEC photocurrent.
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After deposition of a CdS buffer onto GeSe, the main surface construct generally did not
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change but the small CdS particles homogeneously dispersed at the surface of the GeSe sheets
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and packed well without any exposure of the inner GeSe grains (Figure 2b). The XPS results
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shown in Figure S5 also confirmed the multilayer coverage structure under GeSe films: we 7 ACS Paragon Plus Environment
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only observed obvious XPS peaks from Ge 3d3/2, 3d5/2 and Se 3d5/2, 3d3/2 (Figure S5 a, b) from
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the bare GeSe sample. After deposition of a CdS layer under GeSe, high-intensity Cd 3d
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peaks accompanied by no Ge peaks were detected (Figure S5 c, d), confirming the full
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coverage of GeSe by the CdS layer. In the same case, we only observed Ti 2p peaks, while Cd
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3d peaks disappeared when we deposited TiO2 onto CdS/GeSe, indicating that TiO2 fully
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protected the surface of CdS/GeSe (Figure S5e, f). The cross-sectional morphology shown in
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Figure 2c, d clearly shows that the GeSe sheet grains grew vertically (Figure 2c), and the CdS
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layer was identified as on top of the GeSe film (Figure 2d). The observed thickness of
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approximately 2 μm for the GeSe film is consistent with the results detected from the step
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profile. As shown in Figure 2e, the high-resolution transmission electron microscopy
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(HRTEM) photo of GeSe and the typical selected area electron diffraction (SAED) pattern
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indicated that our GeSe films have an appreciable crystalline quality, and the measured
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interplanar distance of 2.9 Å corresponds to the (011) planes of the orthorhombic GeSe (PDF
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No. 48-1226). The STEM-EDX elemental mappings of Ge and Se shown in Figure 2 f-h
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demonstrated a homogeneous elemental distribution, again confirming the good crystal
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quality of the GeSe film. In addition, relatively macroscale (~ 40×30 μm) elemental mapping
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from SEM-EDX in Figure S6 also showed that Ge and Se are uniformly distributed, which
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agrees well with the microscale (~2×1.5 μm) results from STEM-EDX. The Mott-Schottky
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(MS) plots (Figure S7) in the Supporting Information reveal that the as-prepared GeSe film
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has an appropriate acceptor density (NA, 1.3× 1016 cm-3) and exhibited a positive flat-band
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potential of 0.186 VRHE (Figure S7a). However, the flat-band potential dramatically shifted to
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a significantly negative potential of -0.392 VRHE, and the slope of the MS plot changed from
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positive to negative (Figure S7b) when we deposited a CdS buffer under GeSe (similar to
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other previous reports of CdS 27,28,29,30), which again confirmed that the CdS film entirely
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covered the GeSe film when the high surface sensitivity of the Mott-Schottky test was
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considered. Moreover, the shift in the flat-band potential from -0.392 VRHE to -0.18 VRHE was 8 ACS Paragon Plus Environment
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ACS Catalysis
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also observed when we further deposited a TiO2 layer onto CdS/GeSe, but the slope of the MS
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plot was still negative, indicating n-type conductance of the TiO2 overlayer (Figure S7c).
3 4
Figure3: (a-c) Current−potential curves of Pt- GeSe, Pt-CdS/GeSe, and Pt-TiO2/CdS/GeSe
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electrodes under chopped illumination by AM 1.5G simulated sunlight, (d) HC-STH of the
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best sample of Pt-TiO2/CdS/GeSe, (e) Open circuit voltage (on set potential) of both GeSe
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(black dimond), Pt-CdS/GeSe (red dot) and Pt-TiO2/CdS/GeSe (blue triangle) as a function of
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light intensities using simulated sunlight. The light intensity is attenuated using several neutral
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density filters.
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Photoelectrochemical properties of the Pt-GeSe, Pt-CdS/GeSe and Pt-TiO2/CdS/GeSe
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photoelectrodes were determined by linear sweep voltammetry (LSV) under AM 1.5G
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simulated solar light (Figure S8) irradiation, as shown in Figure 3a. It was found that bare
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GeSe has a large hydrogen overpotential; therefore, the deposition of Pt catalysts was
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necessary to enhance surface catalysis activity. However, the observed photocurrent of Pt-
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GeSe was still low (Figure 3a). Similar to other photocathodes such as CZTS, CIGS and
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CuSbS2, surface passivation of an n-type CdS layer under the surface of GeSe was found to be 9 ACS Paragon Plus Environment
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effective in enhancing its PEC efficiency due to the p-n junction formed at the interface
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facilitates photoexcited carrier transfer and separation. Figure 3b shows that the
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photocurrents and the onset potential of the Pt-CdS/GeSe photocathode dramatically
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increased (Von-set ~0.4VRHE, J0 VRHE ~3.7 mA/cm2). The effect of CdS on the GeSe
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photocathode can be attributed to the formation of proper heterojunctions, leading to a
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reduced surface recombination velocity of photocarriers. To explore this effect in more detail,
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the energy band alignment of the CdS/GeSe heterojunction was studied. With the XPS
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measurement at the shallow binding energy level region ( 80 mW/cm2). A similar trend in the Voc difference was also observed between
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TiO2/CdS/GeSe and CdS/GeSe: the Voc difference value (∼0.23 V) in low-intensity
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illumination (
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80 mW/cm2). This behavior is reasonable, because it is known that the Voc loss due to trap-
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assisted recombination processes, such as surface recombination, is dependent on the incident
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light intensity. Specifically, the Voc loss is less severe at high illumination intensities, since a
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large portion of the trap states are already filled by the photogenerated carriers, thereby
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reducing the effective nonradiative recombination rate.38
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Figure 4: (a) Net photocurrent (under 0VRHE)-time curves of the Pt/TiO2/CdS/GeSe electrode
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with an active area of about 0.4cm2 under AM 1.5G simulated sunlight. (b) GC analysis of
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Pt/TiO2/CdS/GeSe at 0 VRHE under AM 1.5G simulated sunlight. (c) collected HC-STH 12 ACS Paragon Plus Environment
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efficiency of the typical Pt/TiO2/CdS/GeSe photocathode at different detect days with the
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measured humidity and temperatures of the days during one month.
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Photoelectrochemical stability is another important issue for evaluating the applicable
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potential of a photoelectrode for solar water splitting. The atomic layer deposition (ALD) of
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TiO2 not only improved the surface condition but also efficiently enhanced the PEC stability.
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Figure 4a shows the photocurrent detected at 0 VRHE of Pt-TiO2/CdS/GeSe under sustained
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solar light illumination for 8 hours with 2 rounds of each 4hours. It was found that the
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photocurrent presented a significantly improved stability for more than 8 hours compared
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with that of Pt-CdS/GeSe (Figure S12), but a slight decrease in photocurrent from about 3.7
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mA to 3.1 mA was still observed during the first round of 4 hours (black curves in Figure 4a).
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After the 4-hour test, we turned off the light and several hours later we continue to check the
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stability again for the second round of another 4hours (red curves in Figure 4a). It was found
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that the photocurrent detected in the second round is stable too and its variation trend is
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similar with that was detected in the first round: the photocurrent slightly decreased from
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about 3.48mA to 2.96mA during the second round of 4hours. We speculate that the slight
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decrease in the PEC photocurrent was caused by the decrease in Pt, because we did not
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observe any difference in the microstructure of the Pt-TiO2/CdS/GeSe sample before and after
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the stability test (Figure S15). It is difficult to make a conclusion now, and further
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investigations and optimizations for enhancing the PEC stability are under way. Figure 4b
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shows the time course curves of solar hydrogen production performance of Pt-TiO2/CdS/GeSe
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sample from water. It was found that the relationship between H2 evolution amount and
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illumination time is almost linear; more than 105 μmol of H2 accompanied by approximately
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54 μmol of O2 evolved throughout the detection period of 3 hours, indicating the appreciable
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PEC stability of the sample. We conclude that no other reduction/oxidation processes
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occurred due to the faradaic efficiency determined from the ratio of the H2 evolution rate to
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e−/2, which was higher than 95%. Figure S16 shows a typical photo of a working sample, in 13 ACS Paragon Plus Environment
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which distinct small H2 bubbles formed across the whole surface of the Pt-TiO2/CdS/GeSe
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photocathode.
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To further evaluate the application potential of Pt-TiO2/CdS/GeSe photocathode, we
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checked the PEC performance of the Pt-TiO2/CdS/GeSe sample for more than 30 days (the
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sample was placed in air without any protection), as shown in Figure 4c. The temperature and
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humidity were detected before the PEC test in our lab every day. The sample showed superior
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environmental PEC air stability: the HC-STH efficiency of the sample (~0.75%) did not
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change during the 1-month period. The corresponding LSV curves under chopped solar light
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illumination during the 1-month test period were collected in Figure S17, and we did not find
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any clear difference or degradation between them. The photocurrent densities and onset
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potentials detected at different days are around at ~10mA/cm2 (0VRHE) and ~0.4-0.5VRHE,
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respectively. The PEC performance of GeSe photocathode is comparable to the state-of-the-
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art photocathodes based on the emerging compound semiconductor based photocathodes,
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including Sb2Se3, CuSbS2, Cu2O, Cu2BaSn(S,Se)4, CuInS2, and Cu2ZnSnS4[39, 20, 19, 40, 16, 11, 14]
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as collected in Table 1. Although the present PEC performance of the GeSe-based
16
photocathode is still lower than those well-studied binary photocathodes based on the as
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Cu2O40 and CuInS2,11 the GeSe based photocathode showed great potential for solar water
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splitting devices due to the PEC property including efficiency and stability it was presented is
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comparable/higher than the recently emerged novel photocathode from Sb2Se3 and CuSbS2,
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and further optimizations of the GeSe-based photocathode for costeffective PEC devices is
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highly promising. Furthermore, the structure and performances of the photovoltaic devices
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that using the same photoabsorbers always acts as a guidance role/reference to the PEC
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devices. For this instance, we collected the record results of the solar cells based on the same
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photoabsorbers that were listed in Table 1, results were shown in Table S1. It was found that
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GeSe based solar cell has a great potential due to its first reported PV performances shown in
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Table S1 are very promising. Although the PCE efficiency is lower than that of relatively 14 ACS Paragon Plus Environment
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developed solar cells based on CuInS2, Sb2Se3 and Cu2ZnSnS4, the Jsc value of GeSe solar
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cell is appreciate, optimizations in the surface/interface conditions for enhancing the
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photovoltages is the next research direction for PV and PEC devices.
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From the viewpoint of the synthesis process we supposed that the concentrate of the GeSe
5
vapor may highly influence the microstructure of the following condensed GeSe film under
6
the substrate, the structure of GeSe film from the compact structure to sparse small sized
7
nanosheets and dense big sized nanosheets could be controlled by adjust the GeSe vapor
8
concentrate. The microstructure of GeSe film should strongly impact on its
9
photoelectrochemical properties, various relationships between them are very useful and
10
should be the effective research directions for the optimizations in solar water splitting
11
properties, detail works are on the way
12
Over all, GeSe film is a very promising materials for photocathode, which should has a big
13
potential in PEC devices. The presented appreciable optoelectronic properties as well as the
14
high environmental stability of our GeSe-based photocathode indicated its huge application
15
potential not only for solar hydrogen production but also for other electronic devices, such as
16
photovoltaics, light detectors, transistors and so on.
17 18 19
Table 1. Tabulated PEC performance of the state-of-the-art photocathodes based on emerging compound semiconductor based thin-film photoabsorbers
20 21
Conclusions 15 ACS Paragon Plus Environment
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1
In summary, novel binary-compound semiconductor GeSe thin films prepared by RTS were
2
systematically researched for application in solar water splitting. The obtained GeSe films
3
were observed to be pure in phase with homogeneous elemental distribution in stoichiometry
4
and consisted of vertically grown sheet-liked grains and a light-trapping surface structure,
5
suitable for application in solar hydrogen production devices. Deposition of a CdS layer under
6
GeSe was found to be effective in enhancing the PEC properties due to the type II p-n
7
heterojunction band alignment was formed at the interface of CdS/GeSe that facilitates the
8
separation of photoexcited carriers. Furthermore, the ALD TiO2 overlayer under the
9
CdS/GeSe photocathode not only protects the CdS from photocorrosion, thereby enhancing
10
the PEC stability, but also reduces surface recombination, which could generally enhance the
11
photocathode’s performance. The obtained Pt-TiO2/CdS/GeSe photocathode generated ~10.5
12
mA/cm2 under 0 VRHE and an onset potential of ~ 0.45 VRHE. The calculated HC-STH
13
efficiency reached over 1%, and thus, the stacked photocathode exhibited appreciable stability
14
of more than 8 hours. It was found that the relationship between H2 evolution amount and
15
illumination time is almost linear, with more than 105 μmol of H2 and approximately 54 μmol
16
of O2 evolving throughout the detection period of 3 hours, indicating the appreciable PEC
17
stability and solar water splitting efficiency of the Pt-TiO2/CdS/GeSe photocathode.
18
The presented appreciable photoelectrochemical properties of the GeSe photocathode,
19
which are even higher than those of the currently emerging and promising novel
20
photocathodes based on CuSbS2 19 and Sb2Se3,20,23 indicated that GeSe has great potential in
21
solar hydrogen evolution. We believe that the solar-to-hydrogen conversion efficiency as well
22
as the stability of the GeSe-based photocathode will be enhanced again in the future via
23
systematic optimization of material preparation, surface/interface improvements and other
24
techniques. Further investigations are under way.
25 26
Supporting Information 16 ACS Paragon Plus Environment
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ACS Catalysis
1
The Supporting Information is available free of charge on the ACS Publications website at
2
DOI: XXXX
3
Experimental detail, raman spectrum of the GeSe film prepared under 480℃, 500℃ and
4
530℃, XRD patterns of the GeSe films prepared under 480℃, 500℃ and 530℃, XPS
5
detection results of the GeSe film, CdS/GeSe and TiO2/CdS/GeSe, Surface morphology of
6
GeSe film, elemental mapping of Ge and Se, elemental ratios of Ge and Se detected from
7
EDS, mott-schottky curves of GeSe, CdS/GeSe and TiO2/CdS/GeSe, the comparison of the
8
used solar simulator with the standard AM 1.5G solar spectrum data, transmittance of
9
CdS/glass and GeSe/glass, Tauc curves of CdS/glass and GeSe/glass, energy diagram of
10
TiO2/CdS/GeSe photocathode, photocurrent Vs. time of Pt-CdS/GeSe detected under 0VRHE,
11
the incident photon conversion efficiency (IPCE) of Pt-TiO2/CdS/GeSe photocathode were
12
shown in Fig.S1-S17.
13 14
Author Information
15
Corresponding Author
16
*e-mail:
[email protected] 17
Notes
18
The authors declare no competing financial interest.
19 20
Acknowledgements
21
This work was supported by National Natural Science Foundation of China (No. 61704060)
22
and “Outstanding Young Talent Project” of South China Normal University
23 24 25
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TOC
2 3
As a new photocathode, earth abundant binary compound GeSe nanosheet based stack film
4
presented a significant solar hydrogen evolution property with a maximum half-cell solar to
5
hydrogen conversion efficiency above 1% and appreciable long-time photoelectrochemical
6
stability over 8 hours.
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