A method for improving the performance of a solar charging flow battery by using a foam nickel modified photoelectrode

Abstract

This invention discloses a method for improving the performance of integrated rechargeable flow batteries by modifying photoelectrodes with nickel foam. To verify the effectiveness of this method, a nickel foam layer is modified on the surface of a triple-junction amorphous silicon photoelectrode, increasing the contact area between the photoelectrode and the electrolyte and accelerating interfacial charge transfer, thereby effectively improving the performance of the integrated battery device. Specifically, the nickel foam-modified triple-junction amorphous silicon photoelectrode is integrated with a redox couple of 4,4'-[(9,10-anthraquinone-2,6-diyl)dioxy]dibutyric acid (2,6-DBEAQ) and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxygen radical (4-OH-TEMPO) to construct a rechargeable flow battery device. During photocharging, the photocurrent density of this device is increased by approximately 36%. In 20 charge-discharge cycles, the average solar energy output efficiency of this device reaches 5.7%. This invention has advantages such as strong versatility and significant performance improvement, and can be widely applied to various rechargeable flow battery systems.

Description

Technical Field

[0001] This invention relates to a general method for improving the performance of integrated solar rechargeable flow batteries by modifying photoelectrodes with nickel foam, belonging to the field of solar energy conversion and storage technology. Background Technology

[0002] To address the dwindling supply of fossil fuels and the environmental pollution caused by their use, solar energy conversion and storage have become an inevitable choice for the development of clean energy in the future. Among numerous solar energy utilization technologies, solar redox flow batteries (SRFBs) have received widespread attention in recent years due to their ability to directly store solar energy in the form of chemical energy and further convert it into electrical energy (H. Feng, Adv. Energy Mater. 2022, 12 , 2200469;JQ Lv, Chem. Soc. Rev. 2022, 51 (WJ Li, 1511–1528.). This technology enables the direct conversion and storage of solar energy into chemical energy by combining semiconductor photoelectrodes with light-trapping capabilities with conventional redox flow batteries (RFBs). In such systems, the photoelectrodes trap photons to generate electron-hole pairs, driving oxidation and reduction reactions of the redox couple, thereby achieving efficient conversion of solar energy into chemical energy. The stored chemical energy can then be released as electrical energy through the reverse reaction of the redox couple (WJ Li, 1511–1528.). Nat. Mater. 2020, 19 , 1326–1331; HCFu, Nat. Commun. 2021, 12 (156.). Although several high-performance SRFB systems have been reported, their overall efficiency is still limited by a number of factors, including the properties of the photoelectrode, the activity and potential difference of the redox couple, and the compatibility between the photoelectrode and the redox couple. Notably, current research in this field mainly focuses on developing high-efficiency semiconductor materials and novel redox couples (TD Lopes, 156.). Adv. Energy Mater. 2021, 12 , 2102893;QM Cheng, Adv. Mater. 2017, 29 , 1700312; WJ Li, Adv. Energy Mater. 2019, 9 While research on improving photoelectrode performance through protection and modification strategies is relatively limited, to our knowledge, currently reported methods are quite limited. Examples include depositing Nafion layers to enhance the corrosion resistance of photoelectrodes in acidic media, or coating with carbon layers to improve the electrochemical activity of photoelectrodes (GY Tian, ​​1900918). et al. , Electrochim. Acta 2023, 461 ,142671; SC Liao et al. , Nat. Commun. 2016, 7 , 11474; WC Zhou, et al. , Chem. Eng. J. 2025, 507 (160162.). Although these treatments can improve the performance of SRFB, a universal modification strategy for photoelectrodes is still lacking. Therefore, developing a universal modification method to enhance the performance of photoelectrodes in SRFB is both necessary and of significant scientific importance. Summary of the Invention

[0003] This invention provides a general method for improving the performance of integrated solar rechargeable flow batteries by modifying photoelectrodes with nickel foam, which can be widely applied to various solar rechargeable flow battery systems.

[0004] The general strategy for improving the performance of solar-chargeable flow batteries by modifying photoelectrodes with nickel foam, as described in this invention, is attached. Figure 1 As shown. The photoelectrode used in this invention is a triple-junction amorphous silicon (3jn-a-Si) structure, which contains three layers of amorphous silicon with different band gaps to enhance light absorption and photoelectric conversion efficiency. A piece of nickel foam with a thickness of 0.1~0.4 mm is tightly bonded to the stainless steel substrate of the triple-junction amorphous silicon photoelectrode to modify the photoelectrode. By integrating the nickel foam-modified triple-junction amorphous silicon photoelectrode with a redox pair of 4,4'-[(9,10-anthraquinone-2,6-diyl)dioxy]dibutyric acid (2,6-DBEAQ) and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxygen radical (4-OH-TEMPO), a high-efficiency SRFB device with high cell voltage is constructed. Figure 2 This modification significantly increases the contact area between the photoelectrode and the electrolyte. The SRFB system operates under no bias conditions. Under illumination, the photoelectrode absorbs photons to generate electron-hole pairs. The photogenerated electrons directly reduce 2,6-DBEAQ in the catholyte, while the corresponding holes are transported via an external circuit to the carbon felt auxiliary electrode, where 4-OH-TEMPO is oxidized on the anode side. Continuous electrolyte circulation is achieved via a pump, enabling the device to complete the photocharging process and effectively store solar energy as chemical energy. During discharge, similar to conventional flow batteries, the stored chemical energy is converted back into electrical energy through a reversible redox reaction.

[0005] This invention selects 2,6-DBEAQ and 4-OH-TEMPO as a redox couple for storing solar energy captured by a photocathode. Because 2,6-DBEAQ exhibits excellent electrochemical performance in a strongly alkaline medium, it is dissolved in 0.5 mol L... -1 KCl + 0.5 mol L -1 KOH is used as a redox active material in the mixed supporting electrolyte (pH = 13.4) as the catholyte. Meanwhile, 4-OH-TEMPO is generally soluble in neutral electrolytes, and its electrochemical performance decreases significantly under strongly alkaline conditions; therefore, it is dissolved in 1 mol L... -1 KCl supports the redox active material in the electrolyte, serving as the anolyte. Considering that the thermodynamic potential for water decomposition is 1.23 V under the same pH conditions, this differential pH strategy not only optimizes the electrochemical performance of each active material but also increases the theoretical water decomposition voltage to 1.61 V. Therefore, the 2,6-DBEAQ and 4-OH-TEMPO redox couple can achieve efficient interconversion between chemical and electrical energy. The corresponding battery reaction is represented by the following equation: Cathode: 2,6-DBEAQ + 2e - ⇋ 2,6-DBEAQ 2- E 0 = –0.52 V vs. NHE (1) Anode: 4-OH-TEMPO ⇋ 4-OH-TEMPO + + e - E 0 = 0.80 V vs. NHE (2) Overall reaction: 2,6-DBEAQ + 2(4-OH-TEMPO) ⇋ 2,6-DBEAQ 2- + 2(4-OH-TEMPO + ) E =1.32 V (3) The concentrations of 10 mmol / L were analyzed using a CHI660E electrochemical workstation via cyclic voltammetry (CV). -1 The electrochemical properties of 2,6-DBEAQ and 4-OH-TEMPO were characterized. Measurements were performed using a three-electrode system, with a glassy carbon electrode (3 mm in diameter, 0.0707 cm² area) as the working electrode. 2 The reference electrode is Ag / AgCl (filled with 3.5 mol L). -1 KCl), the counter electrode is a platinum sheet electrode (area 1 cm²). 2Based on the cyclic voltammetry curves of 2,6-DBEAQ and 4-OH-TEMPO, its formal potential relative to the standard hydrogen electrode (NHE) is ( E 0 The potentials are -0.52 V and 0.80 V respectively, therefore the potential difference between them is measured to be 1.32 V. Figure 3 a). To evaluate the long-term cycling stability of the 2,6-DBEAQ and 4-OH-TEMPO redox couple, a redox flow battery (RFB) was assembled using these two materials, and constant current charge-discharge tests were performed. Figure 3 (b, c). This battery employs a two-chamber structure separated by a Nafion 117 ion exchange membrane. The concentrations of 2,6-DBEAQ and 4-OH-TEMPO are both 50 mmol / L. -1 The electrolyte flow rate is 50 mL / min. -1 A carbon felt (2 cm × 2 cm, 3 mm thick) was placed as an electrode in both the catholy and anolyte. RFB was subjected to cyclic charge-discharge testing using a LANHE CT3001 battery testing system. In the constant current cycle test, the charging and discharging current density was set to 10 mA cm⁻¹. -2 The charging cutoff voltage was 1.6 V, and the discharging cutoff voltage was 0.6 V. Throughout the cycle test, the battery's average coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) were 97.7%, 91.8%, and 89.6%, respectively. These results confirm that the redox couple can maintain high energy conversion efficiency during long-term cycling, validating its application potential in SRFB (Synchronous Reduction Fusion Battery). The charge-discharge voltage curves for the 1st, 50th, and 100th cycles show that the charging voltage slightly increases and the discharging voltage slightly decreases with increasing cycle number, which may be due to the reduced activity of the active material and carbon felt electrode.

[0006] To improve the photoelectrochemical performance of triple-junction amorphous silicon photoelectrodes, a nickel-foam-modified photoelectrode was developed by tightly bonding nickel foam to its stainless steel substrate. Commercial triple-junction amorphous silicon solar cells were cut into 2 cm × 2 cm sheets for use as photoelectrodes. To enhance photoelectrochemical performance and stability, a piece of nickel foam [thickness 0.1–0.4 mm, pore density 50–200 PPI (PPI represents the average number of pores per inch)] was used to modify the photoelectrode. The nickel foam was cut into 1.2 cm × 1.2 cm pieces and placed on a fluororubber gasket with a 1 cm × 1 cm window in the center. The photoelectrode was then placed on top of the nickel foam, and the entire assembly was securely fixed to the gasket using epoxy resin. In this configuration, the nickel foam is in direct contact with the photoelectrode, and no conductive adhesive is used. As a comparison, an unmodified photoelectrode was also prepared by directly bonding the triple-junction amorphous silicon sample to the gasket without using nickel foam. Linear sweep voltammetry was used to test unmodified and modified triple-junction amorphous silicon photoelectrodes (using a two-electrode system) to evaluate the effect of nickel foam modification. At 100 mW / cm², -2 Under illumination, both photoelectrodes exhibited an open-circuit voltage of approximately 2.0 V and a voltage of –5.8 mA cm⁻¹ in electrolyte-free tests. -2 The short-circuit current density indicates that they have stable and consistent photoelectrochemical behavior. Figure 4 a). When the photoelectrode is immersed in 50 mmol L -1 In 2,6-DBEAQ catholyte, using a carbon felt electrode as the counter electrode, the short-circuit current density of the unmodified photoelectrode was –4.9 mA cm⁻¹. -2 The photoelectrode modified with nickel foam achieved -5.7 mA cm⁻¹. -2 ( Figure 4 b). These results indicate that nickel foam modification can effectively improve photoelectrochemical performance.

[0007] The solar rechargeable flow battery (SRFB) device designed in this invention consists of two symmetrical compartments, such as... Figure 2As shown. The front compartment serves as the photocathode chamber, equipped with a 1 cm × 1 cm optical window for illumination. A triple-junction amorphous silicon (3jn-a-Si) photocathode is tightly fitted to the optical window, with one side receiving light and connected to the external circuit via conductive copper foil, and the other side in contact with the catholyte. Additionally, a carbon felt electrode (2 cm × 2 cm, 3 mm thick) is placed in the front compartment as an inert electrode, which contacts the titanium current collector to conduct current during discharge. The rear compartment contains a carbon felt electrode (2 cm × 2 cm, 3 mm thick), which has a dual function: forming a circuit with the triple-junction amorphous silicon photocathode to complete the photocharging process, and forming an independent circuit with the carbon felt electrode in the front compartment to achieve the discharge process. An electrolyte distributor circulates the electrolyte in and out via a peristaltic pump. In the central region of the SRFB device, the catholyte and anolyte are separated by a Nafion 117 ion exchange membrane. Gaskets are used to seal and insulate between the compartments to ensure safe operation.

[0008] use Figure 2 The architecture shown was used to test the performance of the integrated solar rechargeable flow battery device during photovoltaic charge / discharge cycles. The performance of the solar rechargeable flow battery device was evaluated through cyclic charge / discharge tests using a LANHE CT3001 battery testing system. The cathode and anolyte solutions were 50 mmol / L. -1 2,6-DBEAQ solution and 50 mmol L -1 A 4-OH-TEMPO solution containing supporting electrolytes at different pH values ​​was prepared. The flow rates of both the catholyte and anolyte were maintained at 50 mL / min. -1 A Nafion 117 ion-exchange membrane was used as the separator. During photocharging, the SRFB device, without external bias, was powered by simulated sunlight (100 mW cm⁻¹) provided by a xenon lamp. -2 The device was charged. The charging cutoff time was set to 30 minutes. During discharge, the device operated in RFB discharge mode with a discharge current of 6 mA until the battery voltage dropped to 0.6 V. First, an SRFB device without nickel foam-modified photoelectrodes was tested at 100 mW cm⁻¹. -2 Operating under illumination ( Figure 5 During the 10 cycles of photocharging, the photocurrent density showed a slight decreasing trend, from 4.7 mA cm⁻¹ in the first cycle. -2 It dropped to 3.7 mA cm⁻¹ in the tenth cycle. -2 The average value is 3.9 mA cm⁻¹. -2This limited photocurrent density constrains the overall performance of the device. For SRFB devices using unmodified nickel foam photoelectrodes, the average solar output power efficiency (SOEE) over 10 cycles is approximately 3.9%, with average coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) of 84.9%, 90.8%, and 77.0%, respectively. Solar rechargeable flow batteries (SRFB) equipped with nickel foam (0.3 mm) modified photoelectrodes achieve a performance of 100 mW / cm². -2 Overall charge-discharge performance under illumination conditions over 20 cycles ( Figure 6 During unbiased operation, the photocurrent density remained stable at 5.3 mA cm⁻¹ over 20 cycles. -2 The SRFB exhibits enhanced stability. Over 20 cycles, its average coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) were 88.0%, 86.1%, and 76.0%, respectively. Notably, its average solar output energy efficiency (SOEE) reached 5.7%, more than 1.5 times higher than that of an SRFB using an unmodified nickel foam photoelectrode. These results demonstrate that the SRFB device equipped with a nickel foam-modified photoelectrode combines excellent energy conversion capability with good operational stability.

[0009] The main features and advantages of this invention are as follows: 1. The method of using nickel foam to modify the photoelectrode to improve the performance of integrated solar rechargeable flow batteries is applicable to various solar rechargeable flow battery systems. 2. The method of using nickel foam to modify the photoelectrode can significantly improve the performance of integrated solar rechargeable flow batteries. 3. By optimizing the structural parameters of the nickel foam modification layer (such as thickness, porosity, and pore density), the solar energy output efficiency can be further improved. Attached Figure Description

[0010] Figure 1 (a) Schematic diagram of the internal structure of a nickel foam-modified triple-junction amorphous silicon photoelectrode. (b) Schematic diagram of the structure and working principle of an integrated solar rechargeable flow battery (SRFB) device equipped with a nickel foam-modified triple-junction amorphous silicon photoelectrode.

[0011] Figure 2 A schematic diagram of the integrated solar-charged flow battery device designed in this invention.

[0012] Figure 3 (a) On a glassy carbon electrode, at a scan rate of 100 mV s -1 Cyclic voltammetry (CV) curves recorded under the following conditions: 10 mmol L -1 2,6-DBEAQ dissolves in a solution containing 0.5 mol / L -1KCl and 0.5 mol L -1 In the mixed supporting electrolyte of KOH, and 10 mmol L -1 4-OH-TEMPO dissolves in 1 mol L -1 KCl supports electrolytes. (b) Contains 50 mmol L -1 2,6-DBEAQ and 50 mmol L -1 Voltage-capacity curves of a redox flow cell with 4-OH-TEMPO electrolyte at 10 mA cm⁻¹ -2 100 cycles were measured at a constant current density. The figure shows the voltage behavior at cycles 1, 50, and 100. (c) The redox flow cell at 10 mA cm⁻¹ -2 Coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) measured over 100 cycles at constant current density.

[0013] Figure 4 (a) Under electrolyte-free conditions, linear sweep voltammetry (LSV) was used at a rate of 10 mV / s. -1 The scan rate is at 100 mW cm -2 (a) Current density-voltage curves of nickel foam-modified and unmodified photoelectrodes measured under illumination and dark conditions. (b) At 50 mmol L -1 In the 2,6-DBEAQ catholyte system, linear sweep voltammetry (LSV) was used at a frequency of 10 mV / s. -1 The scan rate is at 100 mW cm -2 Current density-voltage curves of nickel foam-modified photoelectrode and unmodified photoelectrode measured under illumination and dark conditions.

[0014] Figure 5 (a) A solar-chargeable flow battery device using an unmodified nickel foam photoelectrode, at 100 mW / cm². -2 (a) The curves showing the changes in photocharging voltage and photocurrent density over time during 10 cycles of unbiased operation under illumination. (b) The curves showing the changes in discharge voltage over time when the SRFB device is discharged at a constant current of 6 mA over 10 cycles. (c, d) The coulombic efficiency (CE), voltage efficiency (VE), energy efficiency (EE), and solar power output efficiency of the SRFB device measured over 10 cycles.

[0015] Figure 6 (a) A solar-chargeable flow battery using nickel foam-modified photoelectrodes, at 100 mW / cm². -2(a) The curves showing the changes in photocharging voltage and photocurrent density over time during 20 cycles of unbiased operation under illumination. (b) The curves showing the changes in discharge voltage over time when the SRFB device is discharged at a constant current of 6 mA over 20 cycles. (c) The coulombic efficiency (CE), voltage efficiency (VE), energy efficiency (EE), and solar output energy efficiency (SOEE) of the SRFB device measured over 20 cycles. Detailed Implementation

[0016] An embodiment of the present invention is as follows: A triple-junction amorphous silicon photocathode is modified with a nickel foam with a thickness of 0.3 mm and a pore density of 110 PPI. The nickel foam-modified triple-junction amorphous silicon photocathode is integrated with a 2,6-DBEAQ and 4-OH-TEMPO redox couple to construct a solar rechargeable flow battery device. The solar rechargeable flow battery equipped with the nickel foam-modified photoelectrode achieves a 100 mW / cm² performance. -2 The overall charge-discharge performance under illumination over 20 cycles is as follows: During unbiased operation, the photocurrent density remained stable at 5.3 mA cm⁻¹ over 20 cycles. -2 The SRFB exhibits enhanced stability. Over 20 cycles, its average coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) were 88.0%, 86.1%, and 76.0%, respectively. Its average solar output power efficiency (SOEE) reached 5.7%, more than 1.5 times higher than that of the SRFB using an unmodified nickel foam photoelectrode. These results demonstrate that the SRFB device equipped with a nickel foam-modified photoelectrode possesses both excellent power conversion capability and good operational stability.

Claims

1. A general method for improving the performance of integrated solar rechargeable flow batteries by modifying photoelectrodes with foamed nickel, characterized in that, The photoelectrode serves as the photocathode or photoanode of the solar rechargeable flow battery, and its surface is modified with a nickel foam layer; the modification of the nickel foam layer can significantly improve the performance of the solar rechargeable flow battery.

2. The general method for improving the performance of integrated solar rechargeable flow batteries by modifying photoelectrodes with nickel foam as described in claim 1, characterized in that, The thickness of the nickel foam is 0.1~0.4 mm, and the pore density is 50~200 PPI (PPI represents the average number of pores per unit inch).

3. The general method for improving the performance of integrated solar rechargeable flow batteries by modifying photoelectrodes with nickel foam as described in claim 1, characterized in that, Nickel foam is in direct contact with single-junction or multi-junction semiconductor photoelectrodes to increase the contact area between the photoelectrodes and the electrolyte, accelerate interfacial charge transfer, and thus improve the performance of solar rechargeable flow batteries.

Images