Direct hydrogen production device and hydrogen production method based on heterojunction photovoltaic cell

Abstract

The invention relates to the technical field of hydrogen production, and particularly discloses a direct hydrogen production device based on heterojunction photovoltaic cells and a hydrogen production method.The hydrogen production device comprises an electrolytic cell and a plurality of HJT photovoltaic cells arranged in the electrolytic cell in series, the electrolytic cell is a non-power-source type electrolytic cell, electrolyte is contained in the electrolytic cell, each HJT photovoltaic cell is of a multi-layer structure, and the HJT photovoltaic cells are connected in series. The multi-layer structure comprises a substrate, the substrate is n-type c-Si, one side of the substrate is provided with two layers from inside to outside, the two layers are n-doped a-Si: H or i / n-a-Si: H and TCO / ITO respectively, the other side of the substrate is provided with two layers from inside to outside, the two layers are p-doped a-Si: H or i / p-n-a-Si: H and TCO / ITO respectively, and every two adjacent HJT photovoltaic cells are arranged upside down. The plurality of HJT photovoltaic cells which are arranged upside down are connected end to end through silver and metal interconnection bands. According to the device disclosed by the invention, the decomposition reaction of the electrolyte is promoted by adopting photoelectric conversion of the HJT photovoltaic cell with a multi-layer structure and combining a double-sided catalytic layer, so that the effect of sustainable PEC hydrogen production is realized.

Description

Technical Field

[0001] This invention belongs to the field of hydrogen production technology, specifically a direct hydrogen production device and method based on heterojunction photovoltaic cells. Background Technology

[0002] Currently, photoelectrochemical hydrogen production technology is considered an important pathway to achieving green hydrogen energy production. Traditional PEC hydrogen production technology mainly relies on III-V group materials (such as GaInP / GaAs), but the high cost and scarcity of these materials limit their feasibility for large-scale applications. Furthermore, other silicon-based photovoltaic technologies (such as PERC and TopCon) cannot be directly used as photoelectrochemical electrodes due to the presence of insulating coatings on their surfaces. Therefore, there is an urgent need to invent and design a direct hydrogen production device and method based on heterojunction photovoltaic cells to achieve efficient, low-cost, and large-scale PEC hydrogen production. Summary of the Invention

[0003] The purpose of this invention is to provide a direct hydrogen production device based on heterojunction photovoltaic cells, which solves the problems of high material costs, scarce resources, and inability to produce hydrogen on a large scale in existing photoelectrochemical hydrogen production devices.

[0004] To address the aforementioned technical problems, this invention provides a direct hydrogen production device based on heterojunction photovoltaic cells. The device includes an electrolyzer and a plurality of HJT photovoltaic cells connected in series within the electrolyzer. The electrolyzer is a power-disconnected type and contains an electrolyte.

[0005] Each HJT photovoltaic cell has a multilayer structure, including a substrate of n-type c-Si. Two layers are formed on one side of the substrate from the inside out: n-doped a-Si:H or i / n na-Si:H and TCO / ITO, respectively. Two layers are formed on the other side from the inside out: p-doped a-Si:H or i / p na-Si:H and TCO / ITO, respectively. Adjacent HJT photovoltaic cells are arranged in an upside-down configuration. Several upside-down HJT photovoltaic cells are connected end-to-end by silver and metal interconnects.

[0006] The first and last HJT photovoltaic cells have HER catalyst and OER catalyst coated on their TCO / ITO surfaces, respectively, forming HER catalyst layers and OER catalyst layers. A separator is provided between the HER catalyst layer and the OER catalyst layer of the first and last HJT photovoltaic cells. The HER catalyst layer is disposed on the same side as the n-doped a-Si:H or i / n na-Si:H and is used as the cathode. The OER catalyst layer is disposed on the same side as the p-doped a-Si:H or i / p na-Si:H and is used as the anode.

[0007] Furthermore, there are 10 HJT photovoltaic cells. The outer side of the separator of the first and last HJT photovoltaic cells is covered with a polydimethylsiloxane protective layer. The first and last HJT photovoltaic cells are used for electrolysis. The other 8 HJT photovoltaic cells (excluding the first and last HJT photovoltaic cells (2)) are used to increase the electrolysis voltage.

[0008] Furthermore, the HER catalyst contains Pt / Ni, and the OER catalyst contains Ni.

[0009] Furthermore, the diaphragm is one of a polytetrafluoroethylene microporous membrane, a polyvinylidene fluoride / polyvinylidene fluoride hybrid membrane, or a polypropylene / polytetrafluoroethylene composite membrane.

[0010] Furthermore, the chemical reaction equation for water electrolysis at the cathode is 4H₂O + 4e⁻. - →2 H2↑+4OH - The chemical reaction equation for water electrolysis at the anode is 2H₂O(l)→O₂(g) + 4H⁺(aq) + 4e⁻, and the chemical equation for the overall reaction in the electrolytic cell is 2H₂O→2H₂↑+O₂↑.

[0011] The direct hydrogen production method based on heterojunction photovoltaic cells uses a direct hydrogen production device based on heterojunction photovoltaic cells to produce hydrogen. The specific steps of the hydrogen production method are as follows:

[0012] S1. Under illumination, photons enter and pass through the HER catalyst layer of the first HJT photovoltaic cell, then sequentially through the TCO / ITO → n-doped a-Si:H or i / n na-Si:H → n-type c-Si structure of each HJT photovoltaic cell (i.e., after the n-side), generating electron-hole pairs inside the n-type c-Si.

[0013] Because each HJT photovoltaic cell has a heterojunction interface between its three front layers—n-doped a-Si:H or i / n na-Si:H, n-type c-Si, and p-doped a-Si:H or i / p na-Si:H—the following electric field distribution is formed:

[0014] Photon → Electron and Hole Pair Generation: After light passes through the electrolytic environment of the electrolytic cell, it sequentially passes through the n-side of each HJT photovoltaic cell. During the light incident process, the TCO / ITO near the n-side becomes conductive on both sides after receiving the photoelectric rays. The electron and hole pairs generated by the conduction are integrated into the n-type c-Si. The generated electrons form an "electron potential well" between the n-type c-Si and the n-doped a-Si:H or i / n na-Si:H, realizing photoelectric conversion and hydrogen generation. The generated hole pairs form a "hole potential well" between the n-type c-Si and the p-doped a-Si:H or i / p na-Si:H.

[0015] Carrier separation: Driven by the built-in electric field of the n-type c-Si in each HJT photovoltaic cell, and under the influence of the "electron potential well" and "hole potential well," electrons and holes are separated. Electrons are pushed from the n-type c-Si to the n-side (i.e., towards the location of the HER catalyst layer), while holes in the n-type c-Si are pushed towards the p-doped a-Si:H or i / p na-Si:H, TCO / ITO sites in each HJT photovoltaic cell (i.e., towards the p-side), thus promoting charge separation.

[0016] Electron transport: Electrons are output from the n-type c-Si of each HJT photovoltaic cell, and sequentially pass through the n-doped a-Si:H or i / n na-Si:H → TCO / ITO → silver → metal interconnection band of each HJT photovoltaic cell. Finally, they are output from the HER catalyst layer of the first HJT photovoltaic cell (i.e., at the cathode) and then participate in the hydrogen evolution reaction in the electrolyte.

[0017] Hole pair transport: Hole pairs are output from the n-type c-Si of each HJT photovoltaic cell, and sequentially pass through the p-doped a-Si:H or i / p na-Si:H→TCO / ITO→silver→metal interconnection band of each HJT photovoltaic cell. Finally, they are output from the OER catalyst layer of the last HJT photovoltaic cell (i.e., at the anode) and then participate in the oxygen evolution reaction in the electrolyte.

[0018] During the hydrogen evolution reaction and oxygen evolution reaction, the photoelectric conversion efficiency is greater than 24%, and the converted current is... Furthermore, the current density generated by photoelectric conversion in each HJT photovoltaic cell during the hydrogen evolution reaction is... ;

[0019] Circuit closure: After electrons enter the electrolyte, ions (OH⁻) in the electrolyte migrate in the electrolyte, and then electrons are released by the OER catalyst layer on the last HJT photovoltaic cell and return to the first HJT photovoltaic cell in series, thus realizing a closed loop.

[0020] The electron circulation path of several HJT photovoltaic cells: After obtaining electrons according to the above photon→electron generation path, the electrons are driven by the ion migration path of the electrolyte and the closed-loop circuit path formed by several HJT photovoltaic cells, and are sequentially transported to the middle series of HJT photovoltaic cells. Finally, they return from the last HJT photovoltaic cell to the HER catalyst layer of the first HJT photovoltaic cell and repeat this path in a cycle.

[0021] Hole circulation path of several HJT photovoltaic cells: After holes are generated according to the above photon→hole generation path, the holes are pushed towards the P side and finally transported sequentially to each HJT photovoltaic cell in series in the middle through the silver and metal interconnects. Finally, when they reach the interface of the OER catalyst layer of the last HJT photovoltaic cell, they are captured by the OER catalyst layer and trigger oxygen evolution.

[0022] S2. The diaphragm separates the hydrogen obtained from the hydrogen evolution reaction and the oxygen obtained from the oxygen evolution reaction into anode and cathode, and collects the evolved hydrogen and oxygen. The collected hydrogen enters the gas-liquid separation system for gas-liquid separation to obtain hydrogen. At the same time, the polydimethylsiloxane protective layer is used to prevent the diaphragm from direct contact with the electrolyte.

[0023] The beneficial effects of this invention are as follows: The device of this invention has a unique structure that can function as both a cathode and an anode through its own structure. By using a multi-layered HJT photovoltaic cell as the photoelectrochemical electrode, and through photoelectric conversion and the dual-sided catalysis of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalysts, photogenerated charge carriers can promote the decomposition reaction of the electrolyte at the anode and cathode of the electrode to produce hydrogen and oxygen. This achieves efficient, low-cost, and sustainable PEC hydrogen production without the need for an external power source, relying solely on light. One set of this device can produce approximately 1 gram of hydrogen per hour, solving the problem of excessive power consumption in existing devices and also solving the problem of battery depletion.

[0024] The device converts solar energy into electrical energy with a photoelectric conversion efficiency greater than 24%, and the converted current is... . Attached Figure Description

[0025] To more clearly illustrate the technical solution of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a structural diagram of the direct hydrogen production device based on heterojunction photovoltaic cells according to the present invention;

[0027] Figure 2 This is a schematic diagram of ten HJT photovoltaic cells connected in series in the direct hydrogen production device based on heterojunction photovoltaic cells of the present invention.

[0028] Figure 3 This is a scaled-down schematic diagram of the first, one of the middle, and the last HJT photovoltaic cells in the direct hydrogen production device based on heterojunction photovoltaic cells of the present invention.

[0029] Figure 4 yes Figure 1 AA cross-sectional views of the first and last HJT photovoltaic cells in the electrolytic cell;

[0030] Figure 5 This is a schematic diagram of each layer of the HJT photovoltaic cell in the direct hydrogen production device based on heterojunction photovoltaic cells of the present invention (except for the HER catalyst layer and the OER catalyst layer).

[0031] In the diagram: 1-hydrogen production unit, 11-electrolyzer, 12-HJT photovoltaic cell, 13-separator, 121-substrate, 122-n-doped a-Si:H or i / n na-Si:H, 123-TCO / ITO, 124-p-doped a-Si:H or i / p na-Si:H, 125-silver, 126-metal interconnect strip, 127-HER catalyst layer, 128-OER catalyst layer. Detailed Implementation

[0032] The technical solutions in the embodiments of the invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0033] In one specific embodiment of the present invention, such as Figures 1-5 As shown, a direct hydrogen production device based on heterojunction photovoltaic cells is disclosed. The hydrogen production device 1 includes an electrolyzer 11 and a plurality of HJT photovoltaic cells 12 arranged in series within the electrolyzer 11. The electrolyzer 11 is a power-disconnected electrolyzer, and the electrolyzer 11 contains an electrolyte.

[0034] Each HJT photovoltaic cell 12 has a multilayer structure, including a substrate 121. The substrate 121 is n-type c-Si. Two layers are formed on one side of the substrate 121 from the inside out: n-doped a-Si:H or i / n na-Si:H 122 and TCO / ITO 123, respectively. In this embodiment, these two layers are preferably i / n na-Si:H and ITO. Two layers are formed on the other side from the inside out: p-doped a-Si:H or i / p na-Si:H 124 and TCO / ITO 123, respectively. In this embodiment, these two layers are preferably i / p na-Si:H and ITO. Adjacent HJT photovoltaic cells 12 are arranged upside down. Several upside-down HJT photovoltaic cells 12 are connected end-to-end by silver 125 and metal interconnects 126.

[0035] The first and last HJT photovoltaic cells 12 have HER catalyst and OER catalyst coated on their TCO / ITO123 surfaces, respectively, forming HER catalyst layer 127 and OER catalyst layer 128. A separator 13 is provided between the HER catalyst layer 127 and OER catalyst layer 128 of the first and last HJT photovoltaic cells 12. The HER catalyst layer 127 is disposed on the same side as n-doped a-Si:H or i / n na-Si:H122 and is used as the cathode. The OER catalyst layer 128 is disposed on the same side as p-doped a-Si:H or i / p na-Si:H124 and is used as the anode.

[0036] There are 10 HJT photovoltaic cells 12. The first and last HJT photovoltaic cells 12 are covered with a polydimethylsiloxane protective layer 129 on the outside of the separator 13. The first and last HJT photovoltaic cells 12 are used for electrolysis. The other 8 HJT photovoltaic cells 12 are used to increase the electrolysis voltage.

[0037] HER catalysts contain Pt / Ni, while OER catalysts contain Ni.

[0038] The diaphragm 13 is one of a polytetrafluoroethylene microporous membrane, a polyvinylidene fluoride / polyvinylidene fluoride mixed material membrane, or a polypropylene / polytetrafluoroethylene composite membrane.

[0039] The chemical reaction equation for water electrolysis at the cathode is 4H₂O + 4e⁻. - →2 H2↑+4OH - The chemical reaction equation for water electrolysis at the anode is 2H₂Ol→O₂g + 4H⁺aq + 4e⁻, and the chemical equation for the overall reaction in electrolytic cell 11 is 2H₂O→2H₂↑+O₂↑.

[0040] The direct hydrogen production method based on heterojunction photovoltaic cells employs a direct hydrogen production device based on heterojunction photovoltaic cells to produce hydrogen. The specific steps of the hydrogen production method are as follows:

[0041] S1. Under illumination, photons enter and pass through the HER catalyst layer 127 of the first HJT photovoltaic cell 12, then sequentially pass through the TCO / ITO 123 → n-doped a-Si:H or i / n na-Si:H 122 → n-type c-Si structure of each HJT photovoltaic cell 12 (i.e., after the n-side), generating electron-hole pairs inside the n-type c-Si.

[0042] Because each HJT photovoltaic cell 12 has a heterojunction interface between its three front layers—n-doped a-Si:H or i / n na-Si:H122, n-type c-Si, and p-doped a-Si:H or i / p na-Si:H124—the following electric field distribution is formed:

[0043] Photon → Electron and Hole Pair Generation: After light passes through the electrolytic environment of the electrolytic cell, it sequentially passes through the n-side of each HJT photovoltaic cell 12. During the light incident process, the TCO / ITO123 near the n-side becomes conductive on both sides after receiving the photoelectric rays. The electron and hole pairs generated by the conduction are integrated into the n-type c-Si. The generated electrons form an "electron potential well" between the n-type c-Si and the n-doped a-Si:H or i / n na-Si:H122, realizing photoelectric conversion and hydrogen generation. The generated hole pairs form a "hole potential well" between the n-type c-Si and the p-doped a-Si:H or i / p na-Si:H124.

[0044] Carrier separation: Driven by the built-in electric field of the n-type c-Si in each HJT photovoltaic cell 12, and under the influence of the "electron potential well" and "hole potential well," electrons and holes are separated. Electrons are pushed from the n-type c-Si to the n-side (i.e., towards the location of the HER catalyst layer), while holes in the n-type c-Si are pushed towards the p-doped a-Si:H or i / p na-Si:H124, TCO / ITO123 in each HJT photovoltaic cell 12 (i.e., towards the p-side), promoting charge separation.

[0045] Electron transport: Electrons are output from the n-type c-Si of each HJT photovoltaic cell 12, and sequentially pass through the n-doped a-Si:H or i / n na-Si:H 122 → TCO / ITO 123 → silver 125 → metal interconnect 126 of each HJT photovoltaic cell 12, and finally exit from the HER catalyst layer 127 of the first HJT photovoltaic cell 12, i.e., the cathode, and then participate in the hydrogen evolution reaction in the electrolyte;

[0046] Hole pair transport: Hole pairs are output from the n-type c-Si of each HJT photovoltaic cell 12, and sequentially pass through the p-doped a-Si:H or i / p na-Si:H → TCO / ITO → silver 125 → metal interconnect 126 of each HJT photovoltaic cell 12, and finally output from the OER catalyst layer 128 of the last HJT photovoltaic cell 12, i.e., at the anode, and then participate in the oxygen evolution reaction in the electrolyte;

[0047] During the hydrogen evolution reaction and oxygen evolution reaction, the photoelectric conversion efficiency is greater than 24%, and the converted current is... And the current density converted from photoelectric effect by each HJT photovoltaic cell 12 during the hydrogen evolution reaction is ;

[0048] Circuit closure: After electrons enter the electrolyte, the OH⁻ ions in the electrolyte migrate in the electrolyte, and then the electrons are released by the OER catalyst layer 128 on the last HJT photovoltaic cell 12 and return to the first HJT photovoltaic cell 12 connected in series, thus realizing a closed loop.

[0049] The electron circulation path of several HJT photovoltaic cells 12: After obtaining electrons according to the above photon→electron generation path, the electrons are driven by the ion migration path of the electrolyte and the closed-loop circuit path formed by several HJT photovoltaic cells 12, and are sequentially transported to the eight HJT photovoltaic cells 12 connected in series in the middle. Finally, they return from the last HJT photovoltaic cell 12 to the HER catalyst layer 127 of the first HJT photovoltaic cell 12, and repeat this path in a cycle.

[0050] The hole circulation path of several HJT photovoltaic cells 12: After the holes are generated according to the above photon→hole generation path, the holes are pushed towards the P side and finally transported sequentially through silver 125 and metal interconnect strip 126 to each HJT photovoltaic cell 12 connected in series in the middle. Finally, when they reach the interface of the OER catalyst layer 128 of the last HJT photovoltaic cell 12, they are captured by the OER catalyst layer 128 and oxygen evolution is triggered.

[0051] S2, the diaphragm 13 separates the hydrogen obtained from the hydrogen evolution reaction and the oxygen obtained from the oxygen evolution reaction into anode and cathode, and collects the evolved hydrogen and oxygen. The collected hydrogen enters the gas-liquid separation system for gas-liquid separation to obtain hydrogen. At the same time, the polydimethylsiloxane protective layer 129 is used to prevent the diaphragm 13 from direct contact with the electrolyte.

[0052] The device of this invention has a unique structure that can function as both a cathode and an anode. By using a multi-layered HJT photovoltaic cell 12 as the photoelectrochemical electrode, photoelectric conversion and dual-sided catalysis by combining hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalysts enable photogenerated charge carriers to promote the decomposition reaction of the electrolyte at the anode and cathode of the electrodes, respectively, to produce hydrogen and oxygen. This achieves efficient, low-cost, and sustainable PEC hydrogen production without the need for an external power source, relying solely on light. One set of this device can produce approximately 1 gram of hydrogen per hour, solving the problem of excessive power consumption in existing devices and also addressing the issue of battery depletion.

[0053] The device converts solar energy into electrical energy with a photoelectric conversion efficiency greater than 24%, and the converted current is... In this embodiment, the preferred embodiment is... .

[0054] Calculation process of hydrogen production from 10 units:

[0055] The HJT photovoltaic cell 12 is a heterojunction photovoltaic cell, and 10 HJT photovoltaic cells 12 connected in series form a unit to obtain a sufficient voltage of 7V through illumination, and its current is [missing information]. This drives the reaction between the HER catalyst layer (127) (hydrogen evolution) and the OER catalyst layer (128) (oxygen evolution) in the alkaline electrolyzer.

[0056] Series voltage prediction

[0057] After each HJT photovoltaic cell 12 is loaded with the HER catalyst layer (127) (i.e., the Pt / Ni catalyst layer) (transparency loss, slightly reducing light incidence), its maximum power voltage drops slightly from 0.71V to 0.60V; the remaining 9 HJT photovoltaic cells 12 without the photosensitive catalyst layer (fully encapsulated) can still maintain 0.70V.

[0058] Therefore, the operating voltage that 10 HJT photovoltaic cells in series can provide is approximately:

[0059] The area of ​​a single HJT photovoltaic cell 12 is The output current of a single HJT photovoltaic cell is approximately:

[0060]

[0061] The load in series consists of IR losses and catalytic overpotential in the electrolyte, and the load current is... (Single), the corresponding current is At this point, the normal operating current will drop to near the design target—equivalent to being lower than the theoretical target. A margin of ~18% has been reserved.

[0062] exist Under these conditions, the corresponding hourly Faraday calculation is as follows:

[0063] ;

[0064] The formula for calculating the groups in hydrogen gas is:

[0065] ⇒

[0066] If we conservatively assume a Faraday efficiency of 90%, the hydrogen production is approximately 1.17 g / H; if we only consider one hydrogen production unit with 10 HJT photovoltaic cells (actual production area is...), then... ,in If it is HER (for the face), then it is about 1g per set per hour, and 10 sets can reach 10g / h.

[0067] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, any equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A direct hydrogen production device based on heterojunction photovoltaic cells, characterized in that, The hydrogen production device (1) includes an electrolyzer (11) and a plurality of HJT photovoltaic cells (12) arranged in series within the electrolyzer (11). The electrolyzer (11) is a power-disconnected electrolyzer, and the electrolyzer (11) contains an electrolyte. Each HJT photovoltaic cell (12) has a multilayer structure, including a substrate (121) of n-type c-Si. Two layers are disposed on one side of the substrate (121) from the inside out: n-doped a-Si:H or i / nn-a-Si:H (122) and TCO / ITO (123). Two layers are disposed on the other side from the inside out: p-doped a-Si:H or i / p na-Si:H (124) and TCO / ITO (123). Adjacent HJT photovoltaic cells (12) are arranged upside down. Several upside-down HJT photovoltaic cells (12) are connected end-to-end by silver (125) and metal interconnects (126). The first and last HJT photovoltaic cells (12) are coated with HER catalyst and OER catalyst on the TCO / ITO (123) surface, respectively, forming HER catalyst layer (127) and OER catalyst layer (128). A separator (13) is provided between the HER catalyst layer (127) and OER catalyst layer (128) of the first and last HJT photovoltaic cells (12). The HER catalyst layer (127) is disposed on the same side as the n-doped a-Si:H or i / n na-Si:H (122) and is used as the cathode. The OER catalyst layer (128) is disposed on the same side as the p-doped a-Si:H or i / p na-Si:H (124) and is used as the anode.

2. The direct hydrogen production device based on heterojunction photovoltaic cells according to claim 1, characterized in that, There are 10 HJT photovoltaic cells (12). The first and last HJT photovoltaic cells (12) are covered with a polydimethylsiloxane protective layer (129) on the outside of the separator (13). The first and last HJT photovoltaic cells (12) are used for electrolysis. The other 8 HJT photovoltaic cells (12) are used to increase the electrolysis voltage.

3. The direct hydrogen production device based on a heterojunction photovoltaic cell according to claim 1, characterized in that, The HER catalyst contains Pt / Ni, and the OER catalyst contains Ni.

4. The direct hydrogen production device based on heterojunction photovoltaic cells according to claim 1, characterized in that, The diaphragm (13) is one of a polytetrafluoroethylene microporous membrane, a polyvinylidene fluoride / polyvinylidene fluoride mixed material membrane, or a polypropylene / polytetrafluoroethylene composite membrane.

5. A direct hydrogen production device based on a heterojunction photovoltaic cell according to claim 1, characterized in that, The chemical reaction equation for water electrolysis at the cathode is 4H₂O + 4e⁻. - →2 H2↑+4OH - The chemical reaction equation for water electrolysis at the anode is 2H2O(l)→O2(g) + 4H⁺(aq) + 4e⁻, and the chemical equation for the overall reaction in the electrolytic cell (11) is 2H2O→2H2↑+O2↑.

6. A direct hydrogen production method based on heterojunction photovoltaic cells uses the direct hydrogen production apparatus based on heterojunction photovoltaic cells as described in any one of claims 1-5 to produce hydrogen, characterized in that, The specific steps of the hydrogen production method are as follows: S1. Under illumination, photons enter and pass through the HER catalyst layer (127) of the first HJT photovoltaic cell (12), and then sequentially pass through the TCO / ITO (123) → n-doped a-Si:H or i / n na-Si:H (122) → n-type c-Si structure of each HJT photovoltaic cell (12), that is, after passing through the n side, electron-hole pairs are generated inside the n-type c-Si. Since there is a heterojunction interface between the three layers in front of each HJT photovoltaic cell (12)—n-doped a-Si:H or i / n na-Si:H (122), n-type c-Si, and p-doped a-Si:H or i / p na-Si:H (124)—the following electric field distribution is formed: Photon → Electron and Hole Pair Generation: After passing through the electrolytic environment of the electrolytic cell, light passes through the n side of each HJT photovoltaic cell (12) in sequence. During the incident process, the TCO / ITO (123) near the n side becomes conductive on both sides after receiving the photoelectric rays. The electron and hole pairs generated by the conduction are integrated into the n-type c-Si. The generated electrons form an "electron potential well" between the n-type c-Si and the n-doped a-Si:H or i / n na-Si:H (122), realizing photoelectric conversion and hydrogen generation. The generated hole pairs form a "hole potential well" between the n-type c-Si and the p-doped a-Si:H or i / p na-Si:H (124). Carrier separation: Under the driving force of the built-in electric field of the n-type c-Si in each HJT photovoltaic cell (12) and the action of the "electron potential well" and "hole potential well", electrons and holes are separated. Electrons are pushed from the n-type c-Si to the n side, that is, to the location of the HER catalyst layer. Holes in the n-type c-Si are pushed to the p-doped a-Si:H or i / p na-Si:H (124) and TCO / ITO (123) of each HJT photovoltaic cell (12), that is, pushed to the p side, which promotes charge separation. Electron transport: Electrons are output from the n-type c-Si of each HJT photovoltaic cell (12) and pass sequentially through the n-doped a-Si:H or i / n na-Si:H (122) → TCO / ITO (123) → silver (125) → metal interconnect (126) of each HJT photovoltaic cell (12). Finally, they are output from the HER catalyst layer (127) of the first HJT photovoltaic cell (12), that is, after being transported to the cathode, they participate in the hydrogen evolution reaction in the electrolyte. Hole pair transport: Hole pairs are output from the n-type c-Si of each HJT photovoltaic cell (12) and pass through the p-doped a-Si:H or i / p na-Si:H→TCO / ITO→silver (125)→metal interconnection band (126) of each HJT photovoltaic cell (12) in sequence. Finally, they are output from the OER catalyst layer (128) of the last HJT photovoltaic cell (12), that is, after being transported to the anode, they participate in the oxygen evolution reaction in the electrolyte. During the hydrogen evolution reaction and oxygen evolution reaction, the photoelectric conversion efficiency is greater than 24%, the converted current is 35-38 mA / cm², and the current density converted by each HJT photovoltaic cell (12) during the hydrogen evolution reaction is 13-16 mA / cm². Circuit closure: After electrons enter the electrolyte, ions (OH⁻) in the electrolyte migrate in the electrolyte, and then the OER catalyst layer (128) on the last HJT photovoltaic cell (12) releases electrons back to the first HJT photovoltaic cell (12) in series, thus realizing a closed loop; The electron circulation path of several HJT photovoltaic cells (12): After obtaining electrons according to the above photon → electron generation path, the electrons are driven by the ion migration path of the electrolyte and the closed-loop circuit path formed by several HJT photovoltaic cells (12), and are sequentially transported to the eight HJT photovoltaic cells (12) connected in series in the middle. Finally, they return from the last HJT photovoltaic cell (12) to the HER catalyst layer (127) of the first HJT photovoltaic cell (12) and repeat this path in a cycle. Hole circulation path of several HJT photovoltaic cells (12): After the holes are generated according to the above photon→hole generation path, the holes are pushed to the P side and finally transported to each HJT photovoltaic cell (12) in series in the middle through silver (125) and metal interconnect strip (126). Finally, when they reach the interface of the OER catalyst layer (128) of the last HJT photovoltaic cell (12), they are captured by the OER catalyst layer (128) and trigger oxygen evolution. S2. The diaphragm (13) separates the hydrogen gas obtained from the hydrogen evolution reaction and the oxygen gas obtained from the oxygen evolution reaction into anode and cathode, and collects the evolved hydrogen gas and oxygen gas. The collected hydrogen gas enters the gas-liquid separation system for gas-liquid separation to obtain hydrogen gas. At the same time, the polydimethylsiloxane protective layer (129) is used to isolate the diaphragm (13) from direct contact with the electrolyte.

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