CdS semiconductor photoelectrode with adjustable crystal face as well as preparation method and application of CdS semiconductor photoelectrode

Abstract

The invention discloses a CdS semiconductor photoelectrode with an adjustable crystal face and a preparation method and application thereof, and belongs to the field of electrodes. The preparation method of the CdS semiconductor photoelectrode comprises the following steps: (1) dissolving a water-soluble cadmium salt and a sulfur source in a solvent, mixing to obtain a reaction solution, putting FTO glass into the reaction solution in a manner that a conductive surface faces downwards, and carrying out a hydrothermal reaction; and (2) after the hydrothermal reaction is finished, washing the FTO glass on which the yellow film grows, and then calcining to obtain the FTO glass. The crystal face of the CdS semiconductor photoelectrode is regulated and controlled based on the hydrothermal reaction, and controllable growth of the crystal faces (002) and (100) of CdS crystals is achieved. Wherein the CdS semiconductor photoelectrode with the highest (002) crystal face proportion has the optimal anisotropic charge separation capability, so that auxiliary-light-free charging under high current density is realized, and the auxiliary-light-free charging current density reaches 5.24 mA cm <-2 >.

Description

Technical Field

[0001] The present invention belongs to the field of electrodes, and particularly relates to a CdS semiconductor photo - electrode with adjustable crystal planes, a preparation method thereof, and an application thereof. Background Art

[0002] In the related research of photo - assisted zinc - air batteries, the photo - rechargeable zinc - air / sulfur hybrid battery can not only effectively absorb and utilize solar energy, but also use sulfur oxidation reaction (SOR) to replace the water oxidation reaction (OER), reducing the reaction barrier while completing the purification process of sulfur - rich sewage. This battery provides a new solution to solve the current energy crisis and environmental pollution problems while achieving energy conservation by using solar energy.

[0003] However, the slow charge transfer kinetics of the photo - electrode hinders the efficient progress of SOR, thus affecting the realization of unbiased photo - recharge at high current density. The anisotropic charge separation of photo - generated carriers is of great significance for improving the charge transfer kinetics of the photo - electrode and then realizing the unassisted photo - recharge process of the battery. Generally, the anisotropic transport of photo - generated carriers is crystal - plane - dependent, which is due to the asymmetry of the lattice structure of semiconductor materials causing differences in the migration rates of carriers in different directions.

[0004] As a typical photo - electrode material, CdS has particularly obvious crystal - plane dependence. The difference in charge transport behavior under different exposed crystal planes may significantly affect the performance of the photo - electrode. Although CdS has been widely studied and applied, there is still a lack of in - depth understanding of how to effectively regulate its exposed crystal planes, and the growth law of crystals is still difficult to grasp. This makes it a great challenge to specifically improve the charge transfer kinetics of the photo - electrode, thus hindering the realization of unbiased photo - recharge at high current density.

[0005] Therefore, how to provide a method for controllably regulating the growth of CdS crystals, effectively improving the interfacial charge transfer kinetics of the photo - electrode, and then realizing an unassisted photo - rechargeable zinc - air / sulfur hybrid battery at high current density is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0006] Object of the Invention: The first object of the present invention is to provide a CdS semiconductor photo - electrode with adjustable crystal planes. The second object of the present invention is to provide a preparation method of the above - mentioned CdS semiconductor photo - electrode with adjustable crystal planes. The third object of the present invention is to provide an application of the above - mentioned CdS semiconductor photo - electrode with adjustable crystal planes.

[0007] Technical Solution: The preparation method of the CdS semiconductor photo - electrode with adjustable crystal planes provided by the present invention includes the following steps:

[0008] (1) Dissolve the water-soluble cadmium salt and sulfur source in a solvent and mix to obtain a reaction solution. Then place the FTO glass with the conductive surface facing down into the above reaction solution for hydrothermal reaction;

[0009] (2) After the hydrothermal reaction is completed, rinse the FTO glass with the grown yellow film and then calcine it to obtain a CdS semiconductor photoanode with adjustable crystal planes.

[0010] Further, in step (1), the water-soluble cadmium salt is cadmium nitrate tetrahydrate, the sulfur source is thiourea, and the molar ratio of the water-soluble cadmium salt to the sulfur source is 1:5 to 1:20, preferably 1:16 to 1:20; the solvent is water, and the molar concentration of the water-soluble cadmium salt in the reaction solution is 0.014 to 0.02 mmol / ml.

[0011] Further, in step (1), the conditions of the hydrothermal reaction are: reacting at 160 ± 10 °C for 6 to 72 h.

[0012] Preferably, in step (1), an indium salt is further added to the reaction solution. At this time, the conditions of the hydrothermal reaction are: reacting at 160 ± 10 °C for 6 to 24 h; the molar ratio of the water-soluble cadmium salt to the indium salt is 1:0.01 to 1:0.5; the indium salt is indium nitrate hydrate.

[0013] Further, in step (2), the conditions of the calcination are: reacting at 400 ± 5 °C for 60 ± 5 min.

[0014] The present invention provides a CdS semiconductor photoanode with adjustable crystal planes prepared by the above preparation method.

[0015] Further, the main crystal planes of the CdS semiconductor photoanode include (100) crystal plane, (002) crystal plane, and (101) crystal plane. Among them, the proportion of the (002) crystal plane is 23 to 53.5%, and the ratio of the proportion of the (002) crystal plane to the (100) crystal plane is 0.64 to 4.31.

[0016] The present invention also provides an application of the above CdS semiconductor photoanode with adjustable crystal planes in the field of photo-assisted charging zinc-air batteries.

[0017] Principle of the invention: In the present invention, the growth process of CdS crystals is divided into nucleation, early growth, and late shaping. The extension of the hydrothermal reaction time is beneficial to the growth of the (002) crystal plane. In 3+ does not participate in the nucleation and early growth processes of CdS crystals, but only aggregates on the shallow surface of the crystals to induce the growth of the (100) crystal plane. In 3+It is easily bound by the (101) and (002) crystal planes with high surface energy, thereby achieving the effect of inhibiting crystal plane growth; it cannot be stably distributed on the (100) crystal plane with low surface energy, thereby achieving the effect of inducing crystal plane growth.

[0018] The preparation method for crystal plane regulation of CdS crystals provided by the present invention realizes the controllable growth of the (002) and (100) crystal planes of CdS crystals and realizes the morphological change from a hexagonal prism to a hexagonal pyramid. Among them, the CdS semiconductor photoanode with the highest proportion of (002) crystal planes has the best anisotropic charge separation ability, thereby realizing a non-aided photo-charging zinc-air / sulfur hybrid battery under a high current density.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following remarkable effects: (1) The controllable growth of CdS crystals is realized by using a one-step hydrothermal method, providing profound insights into the crystal plane regulation method of semiconductor materials; (2) The dependence of anisotropic charge separation of carriers on the exposed crystal planes is deeply explored through a series of CdS semiconductor photoanodes with different crystal plane ratios, proving the important role of the crystal plane regulation engineering of photoanodes in the non-aided photo-charging process of batteries; (3) The CdS semiconductor photoanode with the highest proportion of (002) crystal planes has the best anisotropic charge separation ability, realizing a photo-assisted charging current density of 5.24 mA cm -2 ; (4) The crystal plane regulation method provided by the present invention can flexibly regulate the crystal plane ratio of CdS crystals according to the hydrothermal duration and In 3+ addition concentration, providing inspiration for consciously optimizing semiconductor materials with ideal exposed crystal planes for photocatalysis, photo-charging batteries, and various potential energy storage systems. Description of the Drawings

[0020] Figure 1 is the X-ray diffraction (XRD) pattern of the materials prepared in Examples 1-11. Among them, (a) is for Examples 1-5, and (b) is for Examples 6-11;

[0021] Figure 2 is the scanning electron microscope (SEM) image of the materials prepared in Examples 1-5. Among them, (a) is for Example 1, (b) is for Example 2, (c) is for Example 3, (d) is for Example 4, and (e) is for Example 5;

[0022] Figure 3 is the scanning electron microscope (SEM) image of the materials prepared in Examples 6-11. Among them, (a) is for Example 6, (b) is for Example 7, (c) is for Example 8, (d) is for Example 9, (e) is for Example 10, and (f) is for Example 11;

[0023] Figure 4Schematic diagrams of the growth process and morphological evolution of CdS crystals of the materials prepared according to Examples 1 - 3 and Examples 6 - 11, where (a) - (c) are Examples 1 - 3, and (d) - (i) are Examples 6 - 11;

[0024] Figure 5 XRD patterns of the materials prepared according to Comparative Examples 1 - 3;

[0025] Figure 6 SEM images of the materials prepared according to Comparative Examples 1 - 3, where (a) is Comparative Example 1, (b) is Comparative Example 2, and (c) is Comparative Example 3;

[0026] Figure 7 Etching XPS spectrum of the material prepared according to Example 10;

[0027] Figure 8 Photoelectrochemical performance diagrams of the materials prepared according to Examples 1 - 11 and Comparative Examples 1 - 3, where (a) are Examples 1 - 5, (b) are Examples 6 - 11, and (c) are Comparative Examples 1 - 3;

[0028] Figure 9 Performance diagram of a photo - assisted charging zinc - air battery using the material prepared according to Example 3. Detailed implementation manners

[0029] The present invention will be further described in detail below with reference to examples and drawings.

[0030] Example 1: The preparation method of the CdS semiconductor photo - electrode provided in this example specifically includes the following steps:

[0031] (1) Dissolve 0.6 mmol of cadmium nitrate tetrahydrate and 9.6 mmol of thiourea in 35 ml of deionized water to obtain a reaction solution;

[0032] (2) Transfer the prepared reaction solution to a 50 - ml polytetrafluoroethylene inner liner, and place a cleaned FTO glass with a size of 2 * 3 cm against the inner wall of the polytetrafluoroethylene inner liner with the conductive side facing down; finally, place the polytetrafluoroethylene inner liner into a high - temperature reaction kettle and transfer it to an oven, set the temperature to 160 °C, and keep it warm for 6 h.

[0033] (3) After the hydrothermal reaction, wash the FTO glass with the grown yellow film several times with ethanol and deionized water, and calcine it in air at 400 °C for 1 h. The sample is named CdS - 6h.

[0034] Example 2: The preparation method of the CdS semiconductor photo - electrode provided in this example specifically includes the following steps:

[0035] (1) Dissolve 0.6 mmol of cadmium nitrate tetrahydrate and 9.6 mmol of thiourea in 35 ml of deionized water to prepare a reaction solution;

[0036] (2) Transfer the prepared reaction solution to a 50 ml polytetrafluoroethylene liner, and lean a cleaned FTO glass with a size of 2*3 cm against the inner wall of the polytetrafluoroethylene liner with the conductive side facing down; finally, place the polytetrafluoroethylene liner into a high-temperature reaction kettle and transfer it to an oven, set the temperature to 160 °C, and keep it warm for 10 h.

[0037] (3) After the hydrothermal reaction is completed, wash the FTO glass with the grown yellow film several times with ethanol and deionized water, and calcine it in air at 400 °C for 1 h. The sample is named CdS-10h.

[0038] Example 3: The preparation method of the CdS semiconductor photoanode provided in this example specifically includes the following steps:

[0039] (1) Dissolve 0.6 mmol of cadmium nitrate tetrahydrate and 9.6 mmol of thiourea in 35 ml of deionized water to prepare a reaction solution;

[0040] (2) Transfer the prepared reaction solution to a 50 ml polytetrafluoroethylene liner, and lean a cleaned FTO glass with a size of 2*3 cm against the inner wall of the polytetrafluoroethylene liner with the conductive side facing down; finally, place the polytetrafluoroethylene liner into a high-temperature reaction kettle and transfer it to an oven, set the temperature to 160 °C, and keep it warm for 24 h.

[0041] (3) After the hydrothermal reaction is completed, wash the FTO glass with the grown yellow film several times with ethanol and deionized water, and calcine it in air at 400 °C for 1 h. The sample is named CdS-24h.

[0042] Example 4: The preparation method of the CdS semiconductor photoanode provided in this example specifically includes the following steps:

[0043] (1) Dissolve 0.6 mmol of cadmium nitrate tetrahydrate and 9.6 mmol of thiourea in 35 ml of deionized water to prepare a reaction solution;

[0044] (2) Transfer the prepared reaction solution to a 50 ml polytetrafluoroethylene liner, and lean a cleaned FTO glass with a size of 2*3 cm against the inner wall of the polytetrafluoroethylene liner with the conductive side facing down; finally, place the polytetrafluoroethylene liner into a high-temperature reaction kettle and transfer it to an oven, set the temperature to 160 °C, and keep it warm for 48 h.

[0045] (3) After the hydrothermal reaction, the FTO glass with a grown yellow film was washed several times with ethanol and deionized water, and then calcined in air at 400 °C for 1 h. The sample was named CdS-48h.

[0046] Example 5: The preparation method of the CdS semiconductor photoanode provided in this example specifically includes the following steps:

[0047] (1) Dissolve 0.6 mmol of cadmium nitrate tetrahydrate and 9.6 mmol of thiourea in 35 ml of deionized water to obtain a reaction solution;

[0048] (2) Transfer the prepared reaction solution to a 50 ml polytetrafluoroethylene inner liner, and lean a cleaned FTO glass with a size of 2*3 cm against the inner wall of the polytetrafluoroethylene inner liner with the conductive side facing down; finally, put the polytetrafluoroethylene inner liner into a high-temperature reaction kettle and transfer it to an oven, set the temperature to 160 °C, and keep it warm for 72 h.

[0049] (3) After the hydrothermal reaction, the FTO glass with a grown yellow film was washed several times with ethanol and deionized water, and then calcined in air at 400 °C for 1 h. The sample was named CdS-72h.

[0050] Example 6: The preparation method of the CdS semiconductor photoanode provided in this example specifically includes the following steps:

[0051] (1) Dissolve 0.6 mmol of cadmium nitrate tetrahydrate, 0.006 mmol of indium nitrate hydrate and 9.6 mmol of thiourea in 35 ml of deionized water to obtain a reaction solution;

[0052] (2) Transfer the prepared reaction solution to a 50 ml polytetrafluoroethylene inner liner, and lean a cleaned FTO glass with a size of 2*3 cm against the inner wall of the polytetrafluoroethylene inner liner with the conductive side facing down; finally, put the polytetrafluoroethylene inner liner into a high-temperature reaction kettle and transfer it to an oven, set the temperature to 160 °C, and keep it warm for 24 h.

[0053] (3) After the hydrothermal reaction, the FTO glass with a grown yellow film was washed several times with ethanol and deionized water, and then calcined in air at 400 °C for 1 h. The sample was named 0.01In-CdS.

[0054] Example 7: The preparation method of the CdS semiconductor photoanode provided in this example specifically includes the following steps:

[0055] (1) Dissolve 0.6 mmol of cadmium nitrate tetrahydrate, 0.012 mmol of indium nitrate hydrate and 9.6 mmol of thiourea in 35 ml of deionized water to obtain a reaction solution;

[0056] (2) Transfer the prepared reaction solution into a 50 ml polytetrafluoroethylene liner, and lean a cleaned FTO glass with a size of 2 * 3 cm against the inner wall of the polytetrafluoroethylene liner with the conductive side facing downwards; finally, put the polytetrafluoroethylene liner into a high-temperature reaction kettle and transfer it to an oven, set the temperature at 160 °C, and keep it warm for 24 h.

[0057] (3) After the hydrothermal reaction is completed, wash the FTO glass with grown yellow film several times with ethanol and deionized water, and calcine it in air at 400 °C for 1 h. The sample is named 0.02In-CdS.

[0058] Example 8: The preparation method of the CdS semiconductor photoanode provided in this example specifically includes the following steps:

[0059] (1) Dissolve 0.6 mmol of cadmium nitrate tetrahydrate, 0.03 mmol of indium nitrate hydrate and 9.6 mmol of thiourea in 35 ml of deionized water to prepare a reaction solution;

[0060] (2) Transfer the prepared reaction solution into a 50 ml polytetrafluoroethylene liner, and lean a cleaned FTO glass with a size of 2 * 3 cm against the inner wall of the polytetrafluoroethylene liner with the conductive side facing downwards; finally, put the polytetrafluoroethylene liner into a high-temperature reaction kettle and transfer it to an oven, set the temperature at 160 °C, and keep it warm for 24 h.

[0061] (3) After the hydrothermal reaction is completed, wash the FTO glass with grown yellow film several times with ethanol and deionized water, and calcine it in air at 400 °C for 1 h. The sample is named 0.05In-CdS.

[0062] Example 9: The preparation method of the CdS semiconductor photoanode provided in this example specifically includes the following steps:

[0063] (1) Dissolve 0.6 mmol of cadmium nitrate tetrahydrate, 0.06 mmol of indium nitrate hydrate and 9.6 mmol of thiourea in 35 ml of deionized water to prepare a reaction solution;

[0064] (2) Transfer the prepared reaction solution into a 50 ml polytetrafluoroethylene liner, and lean a cleaned FTO glass with a size of 2 * 3 cm against the inner wall of the polytetrafluoroethylene liner with the conductive side facing downwards; finally, put the polytetrafluoroethylene liner into a high-temperature reaction kettle and transfer it to an oven, set the temperature at 160 °C, and keep it warm for 10 h.

[0065] (3) After the hydrothermal reaction is completed, wash the FTO glass with grown yellow film several times with ethanol and deionized water, and calcine it in air at 400 °C for 1 h. The sample is named 0.1In-CdS.

[0066] Example 10: The preparation method of the CdS semiconductor photoanode provided in this example specifically includes the following steps:

[0067] (1) Dissolve 0.6 mmol of cadmium nitrate tetrahydrate, 0.12 mmol of indium nitrate hydrate, and 9.6 mmol of thiourea in 35 ml of deionized water to obtain a reaction solution.

[0068] (2) Transfer the obtained reaction solution to a 50 ml polytetrafluoroethylene inner liner, and lean a cleaned FTO glass with a size of 2 * 3 cm against the inner wall of the polytetrafluoroethylene inner liner with the conductive side facing down; finally, place the polytetrafluoroethylene inner liner into a high-temperature reaction kettle and transfer it to an oven, set the temperature to 160 °C, and keep it warm for 10 h.

[0069] (3) After the hydrothermal reaction is completed, wash the FTO glass with grown yellow film several times with ethanol and deionized water, and calcine it in air at 400 °C for 1 h. The sample is named 0.2In-CdS.

[0070] Example 11: The preparation method of the CdS semiconductor photoanode provided in this example specifically includes the following steps:

[0071] (1) Dissolve 0.6 mmol of cadmium nitrate tetrahydrate, 0.3 mmol of indium nitrate hydrate, and 9.6 mmol of thiourea in 35 ml of deionized water to obtain a reaction solution.

[0072] (2) Transfer the obtained reaction solution to a 50 ml polytetrafluoroethylene inner liner, and lean a cleaned FTO glass with a size of 2 * 3 cm against the inner wall of the polytetrafluoroethylene inner liner with the conductive side facing down; finally, place the polytetrafluoroethylene inner liner into a high-temperature reaction kettle and transfer it to an oven, set the temperature to 160 °C, and keep it warm for 6 h.

[0073] (3) After the hydrothermal reaction is completed, wash the FTO glass with grown yellow film several times with ethanol and deionized water, and calcine it in air at 400 °C for 1 h. The sample is named 0.5In-CdS.

[0074] Comparative Example 1: The difference from Example 9 is that the hydrothermal time is extended to 24 h, and the specific preparation method is as follows:

[0075] (1) Dissolve 0.6 mmol of cadmium nitrate tetrahydrate, 0.06 mmol of indium nitrate hydrate, and 9.6 mmol of thiourea in 35 ml of deionized water to obtain a reaction solution.

[0076] (2) Transfer the prepared reaction solution into a 50 ml polytetrafluoroethylene liner, and lean a cleaned FTO glass with a size of 2 * 3 cm against the inner wall of the polytetrafluoroethylene liner with the conductive side facing downwards; finally, place the polytetrafluoroethylene liner into a high-temperature reaction kettle and transfer it to an oven, set the temperature to 160 °C, and keep it warm for 24 h.

[0077] (3) After the hydrothermal reaction is completed, wash the FTO glass with grown yellow film several times with ethanol and deionized water, and calcine it in air at 400 °C for 1 h. The sample is named 0.1In-CdS-24h.

[0078] Comparative Example 2: The difference from Example 10 is that the hydrothermal time is extended to 24 h, and the specific preparation method is as follows:

[0079] (1) Dissolve 0.6 mmol cadmium nitrate tetrahydrate, 0.12 mmol indium nitrate hydrate and 9.6 mmol thiourea in 35 ml deionized water to prepare a reaction solution;

[0080] (2) Transfer the prepared reaction solution into a 50 ml polytetrafluoroethylene liner, and lean a cleaned FTO glass with a size of 2 * 3 cm against the inner wall of the polytetrafluoroethylene liner with the conductive side facing downwards; finally, place the polytetrafluoroethylene liner into a high-temperature reaction kettle and transfer it to an oven, set the temperature to 160 °C, and keep it warm for 24 h.

[0081] (3) After the hydrothermal reaction is completed, wash the FTO glass with grown yellow film several times with ethanol and deionized water, and calcine it in air at 400 °C for 1 h. The sample is named 0.2In-CdS-24h.

[0082] Comparative Example 3: The difference from Example 11 is that the hydrothermal time is extended to 10 h, and the specific preparation method is as follows:

[0083] (1) Dissolve 0.6 mmol cadmium nitrate tetrahydrate, 0.3 mmol indium nitrate hydrate and 9.6 mmol thiourea in 35 ml deionized water to prepare a reaction solution;

[0084] (2) Transfer the prepared reaction solution into a 50 ml polytetrafluoroethylene liner, and lean a cleaned FTO glass with a size of 2 * 3 cm against the inner wall of the polytetrafluoroethylene liner with the conductive side facing downwards; finally, place the polytetrafluoroethylene liner into a high-temperature reaction kettle and transfer it to an oven, set the temperature to 160 °C, and keep it warm for 10 h.

[0085] (3) After the hydrothermal reaction is completed, wash the FTO glass with grown yellow film several times with ethanol and deionized water, and calcine it in air at 400 °C for 1 h. The sample is named 0.5In-CdS-10h.

[0086] The samples prepared in Examples 1 - 11 and Comparative Examples 1 - 3 were characterized and performance - tested. The results are shown in Figures 1-9 Tables 1 - 2.

[0087] Figure 1 is the X - ray diffraction (XRD) pattern of the materials prepared according to Examples 1 - 11. It can be seen from the figure that the diffraction peaks of all samples at 25.1°, 26.8° and 28.5° are attributed to the (100), (002) and (101) crystal planes of hexagonal CdS (PDF#97 - 015 - 4187), respectively. Figure 1 In (a) shows that as the reaction time prolongs, the intensity of the XRD diffraction peaks gradually increases, and the relative ratios of the three crystal planes change. Figure 1 In (b) shows that as the addition amount of In 3+ increases, the relative ratios of the three crystal planes also change.

[0088] Figure 2 is the scanning electron microscope (SEM) image of the materials prepared according to Examples 1 - 5. It can be seen that all samples exhibit a hexagonal prism morphology with the bottom surface exposed, but have different grain sizes and distribution states. Figure 2 In (a) is Example 1, where the grain distribution is relatively sparse, and the grain size is about 350 nm. Example 2 ( Figure 2 in (b)) has a denser grain distribution, but the grain size does not change significantly. Figure 2 In (c) is Example 3, where the grain distribution does not change significantly, but the grain size increases to about 500 nm. Figure 2 Examples 4 and 5 shown in (d) and (e) indicate that when the reaction time is further prolonged, the grain distribution becomes crowded, grain stacking occurs, and the grain size further increases.

[0089] Figure 3 is the scanning electron microscope (SEM) image of the materials prepared according to Examples 6 - 11. It can be seen that as the addition amount of In 3+ increases continuously, the morphology of the sample changes from a hexagonal prism to a hexagonal pyramid. Figure 3 In (a) and (b) are Examples 6 and 7, whose morphology, grain distribution and size are relatively close to those of Example 3 ( Figure 2 in (c)). Figure 3 Example 8 shown in (c) indicates that as the content of In 3+ continues to increase, the crystal begins to exhibit a hexagonal prism morphology with the side surface exposed. Figure 3Examples 9 - 11 shown in (d) - (f) indicate that as the In / Cd ratio further increases, the grain size gradually becomes larger, the hexagonal prism morphology exposed on the side becomes more obvious, and finally it turns into a pyramid morphology mainly exposed on the side.

[0090] Table 1 shows the ratios of the three main crystal planes (100), (002), and (101) calculated from the XRD patterns ( Figure 1 ) of the materials prepared according to Examples 1 - 11 and Comparative Examples 1 - 3. The change in the crystal plane ratios of Examples 1 - 5 indicates that as the reaction time is extended from 6 h to 72 h, the proportion of the (002) crystal plane increases from 23.0% to 53.5%, while the proportion of the (100) crystal plane decreases from 35.0% to 12.4%, and the ratio (R) of the (002) crystal plane to the (100) crystal plane increases from 0.66 to 4.31. This change indicates that extending the reaction time is beneficial to the growth of the (002) crystal plane. The change in the crystal plane ratios of Examples 6 - 11 indicates that as the In / Cd ratio gradually increases, the proportion of the (002) crystal plane shows a decreasing trend, while the proportion of the (100) crystal plane shows an increasing trend, and the R value decreases from 1.08 to 0.64. This change indicates that adding In 3+ is beneficial to the growth of the (100) crystal plane.

[0091] Table 2 shows the inductively coupled plasma spectroscopy (ICP) results of the materials prepared according to Examples 9 - 11. The results show that the In contents of Examples 9, 10, and 11 are 0.10, 0.04, and 0.12% respectively. The In contents of the three samples are all at a relatively low level and do not follow the rule of increasing with the increase of the In 3+ addition amount, indicating that In 3+ only plays a role in inducing the growth of crystal planes and regulating the crystal morphology during the crystal growth process.

[0092] Table 1 Ratios of the three main crystal planes (100), (002), and (101) calculated from the XRD patterns of the materials prepared according to Examples 1 - 11 and Comparative Examples 1 - 3 Figure 1 )

[0093]

[0094] Note: In Table 1, the XRD phases of Comparative Example 2 and Comparative Example 3 are mixed phases, and the crystal plane ratios cannot be calculated.

[0095] Table 2 shows the inductively coupled plasma spectroscopy (ICP) results of the materials prepared according to Examples 9 - 11

[0096] Example 9 Example 10 Example 11 Cd (wt%) 70.30 71.02 72.22 S (wt%) 29.60 28.94 27.65 In (wt%) 0.10 0.04 0.12

[0097] Figure 4It is a schematic diagram of the growth process and morphological evolution of CdS crystals of the materials prepared according to Examples 1 - 3 and Examples 6 - 11. It can be seen that Figure 4 In (a) - (c) (Examples 1 - 3), it is the crystal growth process, and the control condition is the reaction time. As the reaction time prolongs, the growth of the (002) crystal plane is promoted, and the larger the R value of the CdS crystal. In (d) - (i) (Examples 6 - 11) in the figure, it is the morphological evolution process, and the control condition is the In 3+ addition amount. As the In 3+ addition amount continuously increases, the growth of the (100) crystal plane is promoted, and the smaller the R value of the CdS crystal.

[0098] Figure 5 It is the X - ray diffraction (XRD) pattern of the materials prepared according to Comparative Examples 1 - 3. It can be seen from the figure that there is no obvious change in the diffraction peaks of Comparative Example 1, but obvious diffraction peaks that do not belong to CdS appear in Comparative Examples 2 and 3. It shows that the higher the addition amount of In 3+ and the longer the reaction time, new phases will be formed.

[0099] Figure 6 It is the scanning electron microscope (SEM) image of the materials prepared according to Comparative Examples 1 - 3. It can be seen that the grain sizes of all comparative examples are larger than those of Examples 9 - 11, and obvious grain stacking phenomena appear. Figure 6 In (a), it is Comparative Example 1, and some regularly - shaped particles appear on the grain surface. In Comparative Example 2 ( Figure 6 in (b)), more regularly - shaped particles can be observed on the grain surface. Figure 6 In (c), it is Comparative Example 3, and pyramidal - shaped grains show a stacking and aggregation phenomenon.

[0100] Figure 7 It is the etched X - ray photoelectron spectroscopy (XPS) pattern of the material prepared according to Example 10. Figure 7 In (a), it can be seen that the peak intensity of Cd 3d increases with the prolonging of the etching time. Figure 7 In (b), it can be seen that the peak intensity of S2p shows the same increasing trend as Cd, and the peak intensity of SO4 2- in the range of 167 - 171 eV weakens with the increase of the etching depth. Figure 7 In (c), it can be seen that the peak intensity of In 3d shows a weakening trend with the prolonging of the etching time. In addition, Figure 7(d) in it shows the change curves of the contents of three elements, Cd, In, and S, with the etching time. It can be seen that as the etching time increases from 8.01 s to 80.09 s, the content of Cd element increases from 28.35% to 40.75%, the content of S element increases from 34.85% to 44.81%, while the content of In element decreases from 36.81% to 14.45%. This result indicates that the In element shows a stepped distribution in the CdS crystal, that is, the content of In element on the sample surface is higher than that in the bulk phase.

[0101] Performance test of semiconductor photoanode:

[0102] The semiconductor photoanodes obtained in Examples 1 - 11 and Comparative Examples 1 - 3 were respectively subjected to photoelectrochemical performance tests, and Example 3 was subjected to the performance test of a light-assisted rechargeable zinc-air battery. The specific test method for photoelectrochemical performance is as follows: On an electrochemical workstation (gamry), with a Pt foil as the counter electrode and an Ag / AgCl electrode as the reference electrode, under AM1.5G simulated solar irradiation (a Newport 150W xenon lamp equipped with an AM 1.5G filter), the light intensity was calibrated to 100 mW cm -2 , and the irradiation area was controlled at 1 cm 2 . The specific test method for the performance of the light-assisted rechargeable zinc-air battery is as follows: The semiconductor photoanode was immersed in a KOH or Na2S / Na2SO3 electrolyte, the zinc foil was immersed in ZnSO4, and they were separated by a Nafion membrane (117). In addition, the irradiation area was 1 cm 2 , and the light source used was a 365 nm LED lamp (PLS-LED100C BeijingPerfectlight 100 mW cm -2 ).

[0103] Figure 8 is the photoelectrochemical performance diagram of the materials prepared according to Examples 1 - 11 and Comparative Examples 1 - 3. Figure 8 It can be seen that Example 3 has much higher photoelectric performance than other samples. Figure 8 As can be seen from (a) in it, as the reaction time prolongs, the current density of the CdS electrode shows a trend of first increasing and then decreasing, and the best photoelectric performance is achieved when the reaction duration is 24 h. Figure 8 As can be seen from (b) in it, compared with Example 3, the initial potential and current density of Examples 6 - 11 both show a downward trend, and the greater the addition amount of In 3+ , the greater the impact on the photoelectric performance, until the photocurrent density of Example 11 reaches the lowest at 1.23 V vs. RHE. Figure 8It can be seen from (b) and (c) that the current densities of Comparative Example 1 - Comparative Example 3 are lower than those of Example 9 - Example 11, respectively.

[0104] Figure 9 It is the performance diagram of the photo-assisted charging zinc-air battery of the material prepared according to Example 3. Figure 9 It can be seen that in the "KOH∥ZnSO4" electrolyte system, the battery assembled from Example 3 can be charged with a stable photocurrent of about 3.47 mA cm -2 ; while in the "Na2S∥ZnSO4" electrolyte system, the battery assembled from Example 3 can be charged with a stable photocurrent of about 5.24 mA cm -2 to achieve the auxiliary-light-free charging process at a high current density.

Claims

1. A method for preparing a CdS semiconductor photoelectrode with adjustable crystal surface, characterized in that: The following steps are involved: (1) dissolving a water-soluble cadmium salt and a sulfur source in a solvent and mixing them to obtain a reaction solution, and then placing the FTO glass in the reaction solution with the conductive surface facing downward to perform a hydrothermal reaction; (2) After the hydrothermal reaction is completed, the FTO glass on which the yellow film is grown is rinsed and then calcined to obtain a CdS semiconductor photoelectrode with adjustable crystal surface.

2. The preparation method according to claim 1, characterized in that: In step (1), the water-soluble cadmium salt is cadmium nitrate tetrahydrate, the sulfur source is thiourea, and the molar ratio of the water-soluble cadmium salt to the sulfur source is 1:5 to 1:

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3. The preparation method according to claim 1, characterized in that: In step (1), the solvent is water, and the molar concentration of the water-soluble cadmium salt in the reaction solution is 0.014-0.02 mmol / ml.

4. The preparation method according to claim 1, characterized in that: In step (1), the hydrothermal reaction is carried out at 160±10° C. for 6 to 72 hours.

5. The preparation method according to claim 1, characterized in that: In step (1), indium salt is also added to the reaction solution, and the conditions of the hydrothermal reaction are: reacting at 160±10° C. for 6 to 24 hours.

6. The preparation method according to claim 5, characterized in that: The molar ratio of the water-soluble cadmium salt to the indium salt is 1:0.01 to 1:0.5; and the indium salt is indium nitrate hydrate.

7. The preparation method according to claim 1, characterized in that: In step (2), the calcination conditions are: reacting at 400±5°C for 60±5min.

8. A CdS semiconductor photoelectrode with adjustable crystal surface obtained by the preparation method according to any one of claims 1 to 7.

9. The CdS semiconductor photoelectrode with adjustable crystal plane according to claim 8, characterized in that: The main crystal planes of the CdS semiconductor photoelectrode include (100) crystal plane, (002) crystal plane and (101) crystal plane, wherein the (002) crystal plane accounts for 23-53.5%, and the ratio of the (002) crystal plane to the (100) crystal plane is 0.64-4.

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10. Application of the CdS semiconductor photoelectrode with adjustable crystal plane as claimed in claim 8 in the field of light-assisted charging zinc-air batteries.

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