Photoelectrochemical Hydrogen Production System Using Li-Conductive Ceramic Membrane

Based on the LiLaTiO3 compound, a ceramic membrane for a photoelectrochemical cell was created. The microstructure, phase composition, and conductivity of a semiconductor photoelectrode and a ceramic membrane were studied by using various experimental methods of analysis. A ceramic Li conducting membrane that consisted of Li0.56La0.33TiO3 was investigated in solutions with different pH values. The fundamental possibility of creating a photoelectrochemical cell while using this membrane was shown. It was found that the lithium-conductive membrane effectively works in the photoelectrochemical system for hydrogen evolution and showed a good separating ability. When using a ceramic membrane, the pH in the cathode and anode chambers of the cell was stable during 3 months of testing. The complex impedance method was used to study the conductive ceramic membrane in a cell with separated cathode and anode chambers at different pH values of the electrolyte. The ceramic membrane shows promise for use in photoelectrochemical systems, provided that its resistivity is reduced (due to an increase in area and a decrease in thickness).


Introduction
One of the most promising and environmentally friendly methods for hydrogen evolution is the method of photoelectrocatalytic decomposition of water under the influence of sunlight while using semiconductor materials. For this, a photoelectrochemical (PEC) cell can be used, which consists of a semiconductor photoanode [1], based on A II B VI semiconductors, and a cathode immersed in an electrolyte solution. A II B VI semiconductors, in particular CdSе, are characterized by a relatively small band gap (E g = 1.7 eV) and intense direct transitions, which allow for the efficient absorption of visible light in a relatively thin (several hundred nm) photoactive layer [2]. This semiconductor is stable in a sulfide solution [3][4][5][6], and the spectral dependence of the normalized value of the short-circuit current (I sc ) has a limit for CdSe at λ ≥ 750 nm.
When narrow-gap semiconductors are used in photoelectrochemical cells, the magnitude of the photopotential is insufficient to decompose water, or the process is running at a low efficiency. To solve this problem, one can replace the anodic oxygenevolution reaction with another, such as, for example, the reaction of oxidation sulfide ions 2S 2-+ 2p + → S 2 2- [7][8][9][10][11]. The polysulfide system is also a protector, since the photooxidation of the semiconductor has not been practically observed in it due to the high rate of oxidation of sulfide ions [8,9]. This process takes place with less overvoltage in the electrochemical system, which allows one to more efficiently convert solar energy. In addition, for a more efficient production of hydrogen, it is necessary for the cathode chamber to be filled with electrolyte with pH = 1-2 and the anode chamber with electrolyte with pH = 13-14. The difference between the pH of the solutions in the anode chamber and the cathode To ensure the conductivity of the system with lithium ions' ratio and to minimize the influence of the concentration gradient, lithium ions were added to the electrolyte. The composition of the system under study, as a photoanode, included CdSe-an electrode with an electronic type of conductivity. To increase the photocorrosion resistance, the semiconductor electrode was placed in a polysulfide solution. Pt was used as a cathode, which has a low hydrogen-evolution overvoltage, and was immersed in a solution of 30% H2SO4 + 1M Li2SO4.
The aim of our work was to determine the possibility of using a ceramic membrane based on LiLaTiO3 in a photoelectrochemical cell for hydrogen evolution.

Experimental Section
Lithium-lanthanum titanate LiLaTiO3 was obtained by solid-phase reactions. The highly pure starting reagents were: La2O3, Li2CO3, TiO2 rutile. The homogenizing grinding of stoichiometric amounts of the starting reagents, as well as the synthesized mixture, was carried out in a planetary centrifugal mill Retsch PM-100 (Kiwa International Cert GmbH, Hamburg, Germany). The fusion of the mixture was carried out at 1050 °C for 2 hours. The resulting blanks were pressed and sintered in an air atmosphere at 1300 °C for 2 hours. From the obtained blanks, discs with a thickness of 0.7 mm were cut, 1.35 mm and 20.5 mm in diameter. The design of the PEC cell allows for tightly fixed membranes and prevents the electrolytes from mixing. The density of ceramic LiLaTiO3 samples was measured by the pycnometric and geometric methods. The microstructure of the ceramic was examined by using a JEOL JSM-6510 (JEOL Ltd., Tokyo, Japan) microscope. To study the conductivity of the LiLaTiO3 ceramic, the contacts were prepared by firing them on a silver-containing paste. For impedance studies in the 32 MHz-0.1 Hz range, an impedance analyzer 1260A Impedance/Gain-Phase Analyzer (Solartron Analytical) was used. The electrical equivalent circuit and the values of its components were determined by using the ZView computer program. The temperature-dependence conductivity of the ceramic sample from Li0.56La0.33TiO3 was determined according to the procedure described in [21]. X-ray diffraction (XRD) analysis was performed on a DRON-4-07 X-ray diffractometer.
The current-voltage characteristics were measured on a model of a photoelectrochemical cell with two different electrodes with an area of 2 cm 2 (CdSe electrode) and 1 cm 2 (Pt electrode) by using a P-8S potentiostat (Elins, Zelenograd, Russia). The design of the cell made it possible to separate the cathode and anode chambers with a membrane (Figure 1). The following solutions served as electrolytes (anode/cathode chambers, respectively): 1M NaOH + 1M Na2S + 10% LiOH/30% H2SO4 + 1M Li2SO4 and 1M NaOH + 1M Na2S + 10% LiOH/30% KOH + 2M LiOH. To determine the load characteristics, a The aim of our work was to determine the possibility of using a ceramic membrane based on LiLaTiO 3 in a photoelectrochemical cell for hydrogen evolution.

Experimental Section
Lithium-lanthanum titanate LiLaTiO 3 was obtained by solid-phase reactions. The highly pure starting reagents were: La 2 O 3 , Li 2 CO 3 , TiO 2 rutile. The homogenizing grinding of stoichiometric amounts of the starting reagents, as well as the synthesized mixture, was carried out in a planetary centrifugal mill Retsch PM-100 (Kiwa International Cert GmbH, Hamburg, Germany). The fusion of the mixture was carried out at 1050 • C for 2 h. The resulting blanks were pressed and sintered in an air atmosphere at 1300 • C for 2 h. From the obtained blanks, discs with a thickness of 0.7 mm were cut, 1.35 mm and 20.5 mm in diameter. The design of the PEC cell allows for tightly fixed membranes and prevents the electrolytes from mixing. The density of ceramic LiLaTiO 3 samples was measured by the pycnometric and geometric methods. The microstructure of the ceramic was examined by using a JEOL JSM-6510 (JEOL Ltd., Tokyo, Japan) microscope. To study the conductivity of the LiLaTiO 3 ceramic, the contacts were prepared by firing them on a silver-containing paste. For impedance studies in the 32 MHz-0.1 Hz range, an impedance analyzer 1260A Impedance/Gain-Phase Analyzer (Solartron Analytical, Farnborough, UK) was used. The electrical equivalent circuit and the values of its components were determined by using the ZView computer program. The temperature-dependence conductivity of the ceramic sample from Li 0.56 La 0.33 TiO 3 was determined according to the procedure described in [21]. X-ray diffraction (XRD) analysis was performed on a DRON-4-07 X-ray diffractometer.
The current-voltage characteristics were measured on a model of a photoelectrochemical cell with two different electrodes with an area of 2 cm 2 (CdSe electrode) and 1 cm 2 (Pt electrode) by using a P-8S potentiostat (Elins, Zelenograd, Russia). The design of the cell made it possible to separate the cathode and anode chambers with a membrane (Figure 1). The following solutions served as electrolytes (anode/cathode chambers, respectively): 1 M NaOH + 1 M Na 2 S + 10% LiOH/30% H 2 SO 4 + 1 M Li 2 SO 4 and 1 M NaOH + 1 M Na 2 S + 10% LiOH/30% KOH + 2 M LiOH. To determine the load characteristics, a polysulfide solution of 1 M NaOH + 1 M Na 2 S was used, similarly to [5,9,22,23]. Comparative currentvoltage characteristics were measured in a cell using electrolytes of 1 M Na 2 S + 1 M NaOH и 1 M NaOH + 1 M Na 2 S + 10% LiOH for the CdSe electrode, as well as 30% KOH and 30% KOH + 2 M LiOH for the Pt electrode. A silver chloride electrode connected through a salt bridge was used as a reference electrode. A KGM 9-70 (Yugra Invest, TOO; Kazakhstan, Pavlodar halogen lamp was used as a light source (lamp power was 70 W). The incident light power was measured using a PD300-UV (Ophir-Spiricon, North Logan, UT, USA) head photodiode and a NOVA II display (Ophir-Spiricon, North Logan, UT, USA). The photosensitive CdSe semiconductor film was formed by the electrochemical method on a 0.4-mm-thick VT1-0 titanium substrate. The substrate was preliminarily degreased in acetone, followed by etching for 1-2 min in a mixture of acids: HF, 0.75 mol L −1 ; HNO 3 , 3.17 mol L −1 . Then, electrochemical treatment was carried out in a solution of 0.7 mol L −1 H 2 SO 4 (mode: E = 0.2-0.65 V; sweep 10 mV s −1 ; 5 cycles). The electrochemical deposition of a semiconductor CdSe film was carried out in the potentiostatic mode on a titanium substrate at the potential E = −0.6 V (±0.03 V) relative to a silver-chloride reference electrode. The current density was j = 0.7-2 mA cm −2 , and the time was 30 min. For electrolysis, a sulfuric acid electrolyte was used with the following components: H 2 SO 4 , 0.7-2 mol L −1 ; H 2 SeO 3 , 0.003-0.005 mol L −1 ; CdSO 4 , 0.02-0.03 mol L −1 . The annealing of the CdSe electrode was carried out in an air atmosphere at 470 • C for 3 h. Then, the surface was activated in an aqueous solution: HCl, 5 mol L −1 , HNO 3 , 0.27 mol L −1 for 4-5 s at room temperature. The surface of the CdSe semiconductor film was studied using a scanning electron microscope JSM 6700F (JEOL Ltd., Tokyo, Japan).

Results and Discussion
The results of the XRD analysis ( Figure 2) of a sintered ceramic sample with the composition LiLaTiO 3 show that the main phase is solid solutions with a perovskite structure of the rhombohedral system (space group R3c) with the unit cell parameters: a ≈ 5.48 Å and c ≈ 13.42 Å; similar results were obtained in [21,24,25].
ative current-voltage characteristics were measured in a cell using electrolytes of 1M Na2S + 1M NaOH и 1M NaOH + 1M Na2S + 10% LiOH for the CdSe electrode, as well as 30% KOH and 30% KOH + 2M LiOH for the Pt electrode. A silver chloride electrode connected through a salt bridge was used as a reference electrode. A KGM 9-70 (Yugra Invest, TOO; Kazakhstan, Pavlodar halogen lamp was used as a light source (lamp power was 70 W). The incident light power was measured using a PD300-UV (Ophir-Spiricon, USA) head photodiode and a NOVA II display (Ophir-Spiricon, USA).
The photosensitive CdSe semiconductor film was formed by the electrochemical method on a 0.4-mm-thick VT1-0 titanium substrate. The substrate was preliminarily degreased in acetone, followed by etching for 1-2 min in a mixture of acids: HF, 0.75 mol L −1 ; HNO3, 3.17 mol L −1 . Then, electrochemical treatment was carried out in a solution of 0.7 mol L −1 H2SO4 (mode: E = 0.2-0.65 V; sweep 10 mV s −1 ; 5 cycles). The electrochemical deposition of a semiconductor CdSe film was carried out in the potentiostatic mode on a titanium substrate at the potential E = −0.6 V (0.03 V) relative to a silver-chloride reference electrode. The current density was j = 0.7-2 mA cm −2 , and the time was 30 minutes. For electrolysis, a sulfuric acid electrolyte was used with the following components: H2SO4, 0.7-2 mol L −1 ; H2SeO3, 0.003-0.005 mol L −1 ; CdSO4, 0.02-0.03 mol L −1 . The annealing of the CdSe electrode was carried out in an air atmosphere at 470 °C for 3 h. Then, the surface was activated in an aqueous solution: HCl, 5 mol L −1 , HNO3, 0.27 mol L −1 for 4 -5 sec at room temperature. The surface of the CdSe semiconductor film was studied using a scanning electron microscope JSM 6700F (JEOL Ltd., Tokyo, Japan).

Results and Discussion
The results of the XRD analysis ( Figure 2) of a sintered ceramic sample with the composition LiLaTiO3 show that the main phase is solid solutions with a perovskite structure of the rhombohedral system (space group R 3 c) with the unit cell parameters: a ≈ 5.48 Å and c ≈ 13.42 Å; similar results were obtained in [21,24,25]. In addition, the presence of low-intensity peaks of the P4/mmm tetragonal phase was observed, corresponding to the same chemical composition of LiLaTiO3 as in the rhombohedral phase. In addition, the presence of low-intensity peaks of the P4/mmm tetragonal phase was observed, corresponding to the same chemical composition of LiLaTiO 3 as in the rhombohedral phase.
According to [26], a tetragonal phase in the form of locally ordered nanoregions was even observed in hardened samples. Table 1 shows the structural parameters of a LiLaTiO 3 ceramic sample.   According to [26], a tetragonal phase in the form of locally ordered nanoregions was even observed in hardened samples. Table 1 shows the structural parameters of a LiLaTiO3 ceramic sample.  Figure 3 shows a micrograph of a cleavage of a LiLaTiO3 ceramic sample. As can be seen from the photograph, the grain size of the ceramic is 2-10 microns. When measuring the density of LiLaTiO3 ceramic samples by the geometric method, the closed porosity contributes to the obtained value. Therefore, a comparison of values obtained by the pycnometric and geometric methods makes it possible to estimate the value of the closed porosity. For the samples under investigation, the value of geometric density was close to the values of pycnometric density and differed by up to 10-15 %.
The XRD analysis of the surface of a CdSe electrode obtained by electrochemical deposition on a titanium substrate and subsequent annealing showed the formation of a hexagonal CdSe phase (Figure 4). When measuring the density of LiLaTiO 3 ceramic samples by the geometric method, the closed porosity contributes to the obtained value. Therefore, a comparison of values obtained by the pycnometric and geometric methods makes it possible to estimate the value of the closed porosity. For the samples under investigation, the value of geometric density was close to the values of pycnometric density and differed by up to 10-15%.
The XRD analysis of the surface of a CdSe electrode obtained by electrochemical deposition on a titanium substrate and subsequent annealing showed the formation of a hexagonal CdSe phase (Figure 4). Membranes 2022, 11, x FOR PEER REVIEW 6 of 12 It was found from SEM microscopic studies that the average size of electrochemically deposited CdSe particles is less than 2 μm ( Figure 5).  Figure 6 shows the load characteristics of the CdSe-Pt cell in the polysulfide system after annealing of the CdSe photoelectrode and its activation. Figure 6 shows that the surface activation leads to an increase in the efficiency of the photoelectrode. Characteristically, after activation of the photoelectrode, the open-circuit voltage increases most significantly, while the short-circuit current changes little. It was found from SEM microscopic studies that the average size of electrochemically deposited CdSe particles is less than 2 µm ( Figure 5).  It was found from SEM microscopic studies that the average size of electrochemi cally deposited CdSe particles is less than 2 μm ( Figure 5).  Figure 6 shows the load characteristics of the CdSe-Pt cell in the polysulfide system after annealing of the CdSe photoelectrode and its activation. Figure 6 shows that the surface activation leads to an increase in the efficiency of the photoelectrode. Character istically, after activation of the photoelectrode, the open-circuit voltage increases mos significantly, while the short-circuit current changes little.  Figure 6 shows the load characteristics of the CdSe-Pt cell in the polysulfide system after annealing of the CdSe photoelectrode and its activation. Figure 6 shows that the surface activation leads to an increase in the efficiency of the photoelectrode. Characteristically, after activation of the photoelectrode, the open-circuit voltage increases most significantly, while the short-circuit current changes little. Membranes 2022, 11, x FOR PEER REVIEW 7 of 12 Figure 6. Loading characteristics of a CdSe photoelectrode after annealing (1) and after its activation (2). The solution was: 1M Na2S + 1M NaOH. The counter electrode is platinum. Lighting power is 16 mW cm −2 .
As can be seen from Figure 7, the photoanode ensures a hydrogen evolution on platinum in both cases. This is evidenced by the intersection of curves 1 and 2, as well as Figure 6. Loading characteristics of a CdSe photoelectrode after annealing (1) and after its activation (2). The solution was: 1M Na 2 S + 1M NaOH. The counter electrode is platinum. Lighting power is 16 mW cm −2 .
The current-voltage characteristics of the cell were measured in solutions with different pH values and a Li 0.56 La 0.33 TiO 3 ceramic membrane (thickness 0.7 mm), where platinum plates (with an area of 1 cm 2 ) served as electrodes. It was found that the cathode currents reach limiting values of 300-450 µA, after which they do not increase. Figure 7 shows the comparative current-voltage characteristics of the CdSe photoanode and the platinum cathode in the cell without a membrane (curves 1, 2) and with electrode chambers separated by a Li 0,56 La 0,33 TiO 3 ceramic membrane (thickness 0.7 mm) (curves 3, 4). The current-voltage characteristics of the cell were measured in solutions with different pH values and a Li0.56La0.33TiO3 ceramic membrane (thickness 0.7 mm), where platinum plates (with an area of 1 cm 2 ) served as electrodes. It was found that the cathode currents reach limiting values of 300-450 μA, after which they do not increase. Figure 7 shows the comparative current-voltage characteristics of the CdSe photoanode and the platinum cathode in the cell without a membrane (curves 1, 2) and with electrode chambers separated by a Li0,56La0,33TiO3 ceramic membrane (thickness 0.7 mm) (curves 3, 4).  (2,4) in electrolytes: 1M Na2S + 1M NaOH (1); 30% KOH (2); 1M NaOH + 1M Na2S + 10% LiOH (3); 30% KOH + 2M LiOH (4). Curves (3,4) obtained in the cell with electrode chambers separated by a Li0.56La0.33TiO3 ceramic membrane.
As can be seen from Figure 7, the photoanode ensures a hydrogen evolution on platinum in both cases. This is evidenced by the intersection of curves 1 and 2, as well as As can be seen from Figure 7, the photoanode ensures a hydrogen evolution on platinum in both cases. This is evidenced by the intersection of curves 1 and 2, as well as curves 3 and 4. For the cell with a ceramic membrane, the currents flowing in the system are lower than in a cell without a membrane. This indicates a high internal resistance of the membrane.
The complex impedance method was used to study the conductivity of a cell with separated cathode and anode chambers at different pH values and platinum electrodes with an area of 1 cm 2 , where the membrane was a LiLaTiO 3 ceramic material with different thicknesses (0.7 mm and 1.35 mm). Figure 8 shows the impedance hodographs in alkaline and acidic solutions.
Membranes 2022, 11, x FOR PEER REVIEW 8 of 12 curves 3 and 4. For the cell with a ceramic membrane, the currents flowing in the system are lower than in a cell without a membrane. This indicates a high internal resistance of the membrane. The complex impedance method was used to study the conductivity of a cell with separated cathode and anode chambers at different pH values and platinum electrodes with an area of 1 cm 2 , where the membrane was a LiLaTiO3 ceramic material with different thicknesses (0.7 mm and 1.35 mm). Figure 8 shows the impedance hodographs in alkaline and acidic solutions. When compiling an equivalent electrical circuit of the studying system, it is necessary to take into account the effect of the charge transfer process at the membrane-electrolyte interface, charge transfer in the membrane volume, intergrain contact resistance, etc. [27][28][29]. The optimal equivalent electrical circuit of the system and the values of its parameters, obtained by using the ZView computer program, are presented in Table 2. According to the above diagram, CPE-2 and R3 correspond to the process of charge transfer at the interface; CPE-1 and R2 reflect the diffusion of lithium ions in the membrane volume, which determines membrane impedance at a low frequency ( Figure  8); R1 is the intergranular contact resistance, including a small electrolyte resistance. In this case, when the thickness of the LiLaTiO3 membrane changed from 1.35 mm to 0.7 mm, the values of R1 and R2 were directly proportional to its thickness. When compiling an equivalent electrical circuit of the studying system, it is necessary to take into account the effect of the charge transfer process at the membrane-electrolyte interface, charge transfer in the membrane volume, intergrain contact resistance, etc. [27][28][29]. The optimal equivalent electrical circuit of the system and the values of its parameters, obtained by using the ZView computer program, are presented in Table 2. According to the above diagram, CPE-2 and R3 correspond to the process of charge transfer at the interface; CPE-1 and R2 reflect the diffusion of lithium ions in the membrane volume, which determines membrane impedance at a low frequency ( Figure 8); R1 is the intergranular contact resistance, including a small electrolyte resistance. In this case, when the thickness of the LiLaTiO 3 membrane changed from 1.35 mm to 0.7 mm, the values of R1 and R2 were directly proportional to its thickness.
Based on complex impedance plots in Nyquist coordinates obtained at different temperatures, a plot of the conductivity versus return temperature 1/Т for a Li 0.56 La 0.33 TiO 3 ceramic sample has been constructed in a frequency area where the frequency dependence of the impedance is close to linear (Figure 9). The conductivity of the Li 0.56 La 0.33 TiO 3 ceramic material corresponds to the values described in the literature [30].
The activation energy was calculated to be 0.27 eV, which indicates the main contribution to the bulk resistance low-frequency impedance, which was determined by the diffusion of lithium ions in the bulk of the material.  Based on complex impedance plots in Nyquist coordinates obtained at different temperatures, a plot of the conductivity versus return temperature 1/Т for a Li0.56La0.33TiO3 ceramic sample has been constructed in a frequency area where the frequency dependence of the impedance is close to linear (Figure 9). The conductivity of the Li0.56La0.33TiO3 ceramic material corresponds to the values described in the literature [30]. The activation energy was calculated to be 0.27 eV, which indicates the main contribution to the bulk resistance low-frequency impedance, which was determined by the diffusion of lithium ions in the bulk of the material. Similar results were obtained by the authors of [31]. It has been established that the thinner the thickness of the ceramic electrolyte, the lower the internal resistance and the a b  Based on complex impedance plots in Nyquist coordinates obtained at different temperatures, a plot of the conductivity versus return temperature 1/Т for a Li0.56La0.33TiO3 ceramic sample has been constructed in a frequency area where the frequency dependence of the impedance is close to linear ( Figure 9). The conductivity of the Li0.56La0.33TiO3 ceramic material corresponds to the values described in the literature [30]. The activation energy was calculated to be 0.27 eV, which indicates the main contribution to the bulk resistance low-frequency impedance, which was determined by the diffusion of lithium ions in the bulk of the material. Similar results were obtained by the authors of [31]. It has been established that the thinner the thickness of the ceramic electrolyte, the lower the internal resistance and the a b Similar results were obtained by the authors of [31]. It has been established that the thinner the thickness of the ceramic electrolyte, the lower the internal resistance and the higher the operating voltage of the lithium-air cell. Thus, with a ceramic electrolyte thickness of 0.7 mm, the operating voltage of the element is 0.46 V, with a thickness of 0.41 mm it is 1.06 V, and with a thickness of 0.25 mm it is 1.63 V (in all cases, the discharge current density was 0.4 mA cm −2 ).
When studying the parameters of a photoelectrochemical cell, it was found that the Li 0.56 La 0.33 TiO 3 ceramic membranes effectively operated in the PEC system for the hydrogen evolution. A CdSe photoanode and a Pt cathode were used for measurements of the photocurrent in the photoelectrochemical cell. Figure 10 shows plots of the short-circuit photocurrent versus time for a PEC cell when the photoanode is illuminated in different electrolytes and for a LiLaTiO 3 membrane. charge current density was 0.4 mA cm ).
When studying the parameters of a photoelectrochemical cell, it was found that the Li0.56La0.33TiO3 ceramic membranes effectively operated in the PEC system for the hydrogen evolution. A CdSe photoanode and a Pt cathode were used for measurements of the photocurrent in the photoelectrochemical cell. Figure 10 shows plots of the short-circuit photocurrent versus time for a PEC cell when the photoanode is illuminated in different electrolytes and for a LiLaTiO3 membrane.
In practical applications in a PEC cell, large values of the hydrogen-evolution current are realized when using alkaline and acidic electrolytes in the anode and cathode chambers, respectively (Figure 10a). Smaller values of the hydrogen-evolution current are realized when using alkaline electrolytes in the anode and cathode chambers ( Figure  10b). When testing a photoelectrochemical cell under illumination with a ceramic mem- Figure 10. Dependence of the photocurrent on time for a PEC cell with a Li 0.56 La 0.33 TiO 3 membrane (a,b). The electrolytes in anode/cathode chamber, respectively: (a) 1 M NaOH + 1 M Na 2 S + 10% LiOH/30% H 2 SO 4 + 1 M Li 2 SO 4 ; (b) 1 M NaOH + 1 M Na 2 S + 10% LiOH/30% KOH + 2 M LiOH. The light power was 16 mW cm −2 .
In practical applications in a PEC cell, large values of the hydrogen-evolution current are realized when using alkaline and acidic electrolytes in the anode and cathode chambers, respectively (Figure 10a). Smaller values of the hydrogen-evolution current are realized when using alkaline electrolytes in the anode and cathode chambers (Figure 10b). When testing a photoelectrochemical cell under illumination with a ceramic membrane that separates the cathode and anode chambers, the pH in the cathode chamber remained stable for an operation time of 3 months.
Thus, ceramic membranes show promise for use in photoelectrochemical systems in cases where their resistivity is reduced (due to an increase in area and a decrease in thickness).

Conclusions
We showed the fundamental possibility of creating a photoelectrochemical cell for hydrogen production by using a ceramic membrane based on Li 0.56 La 0.33 TiO 3 . The parameters of a photoelectrochemical cell in alkaline and acidic electrolytes have been studied. The ceramic membrane in the electrochemical cell showed a good separating ability, but due to a high resistance, it had large polarization losses. The complex impedance method was used to study the conductivity of a membrane in a cell with separated cathode and anode chambers at various pH values. The conductivity was studied by using a membrane with a thickness of 0.7 mm to 1.35 mm. The optimal equivalent circuit and the values of its parameters were determined. It was found that when the membrane thickness changed from 1.35 mm to 0.7 mm, its resistance was directly proportional to its thickness.