Innovative study in renewable energy source through mixed surfactant system for eco-friendly environment

Actual plan of research work was proposed for systematic investigating in the field of photogalvanic (PG) cells for solar energy transformation. It was necessary and proposed to carry out experimental work under the solar parameters for PG cells. The object of the research work is to enhance the solar energy conversion into electricity and store it through PG cells. Various parameters were studied in a PG cell having D-Xylose + MB + Brij-35 + NaLS system (mixed surfactants). In this study, the observed optimum results in terms of the open circuit voltage, photopotential, maximum photocurrent, and short circuit current are 921.00 mV, 698.00 mV, 311 uA, and 245.0 uA, respectively. The observed equilibrium photocurrent, current at power point, fill factor, and conversion efficiency were 243.0 uA and 142.0 uA, 0.4521, and 0.6769%, respectively. For individual surfactants, the observed results in terms of the open circuit voltage, photopotential, maximum photocurrent, and short circuit current are 870.00 mV, 635.00 mV, 175 uA, and 90.0 uA, respectively. For individual surfactant system, the observed equilibrium photocurrent, current at power point, fill factor, and conversion efficiency were 84.0 uA and 55.0 uA, 0.3630, and 0.3100%, respectively. The impact of solar energy was studied by varying the various parameters in PG cells. On the basis of above obtained values, the mixed surfactants (NaLS + Brij-35) have experimentally proved the efficient system as the desired object of research with special reference to enhance electrical out and storage of solar energy.


Introduction
Scientific community is compelled to search out the renewable source of energy to feed with non-polluting nature.The fossil fuels are swiftly reaching towards their almost complete depletion.The non-renewable energy sources have their own limitations along with hazardous processes involved and pollution creating environment.Thus, solar energy is the best option to fulfil the energy demand of the whole world.The photosynthesis and photolysis of water are the basis for solar energy contents.The photogalvanic (PG) cells are a photoelectrochemical system based on the "photogalvanic effect" (Rabinowitch 1940).The PG cells are systematically favored in photochemical reaction for renewable energy sources (Rideal and Williams 1925).It was also supported by the research work on optimum efficiency of photogalvanic cells for solar energy conversion (Albery and Archer 1977).These cells are quite different from other solar cells (Memming 1980;Suda et al. 1978;Murthy et al. 1980; Responsible Editor: Philippe Garrigues Highlights • The photogalvanic is emerging field of research.
• Developed photogalvanic cell with special attention to better performance.
• Reduces the cost of the photogalvanic cell for its commercial viability.
• Manuscript contains substantial electrical output, conversion efficiency and storage.
• Global scientific community is compelled to search out the renewable source of energy to feed the whole world.Bayer et al. 2001;Hall et al. 1977).Different kinds of dye as photosensitizer, organic/inorganic chemicals as reductant, and cationic/anionic/neutral surfactant as micelles have been used for the solar energy conversion and storage of PG cells (Lal 2007;Gangotri and Mohan 2013;Gangotri and Gangotri 2010;Lal and Gangotri 2013a;Bhimwal et al. 2013;Rathore et al. 2022).The photogalvanic effect in PG cells using mixed surfactants has been compared for the research output of various systems (Lal and Gangotri 2013a, b).The mixed micellization in PG cells for the electrical output as well as storage capacity were studied (Mao et al. 2013;Thareja et al. 2013;Lee and Lee 2012).The key results were reported on performance investigation of transparent photovoltaic-thermal collectors with horizontal oscillating and rectangular spiral flow patterns (Das et al. 2022)).The PG cells were reported for sensitization of an iron-thiazine photogalvanic cell to the improved match to the insulation's spectrum (Wildes et al. 1977).The favor to PG cell reported for flow field simulation and pressure drop modeling by a porous medium in PEM fuel cells (Chen et al. 2022).Modified and simplified photogalvanic cells with solar energy harvesting using bromo cresol green dye with different electrodes and cell dimensions was studied (Koli et al. 2022).The photogalvanic effect in photogalvanic cell using single surfactant as DSS, tetrazine as a photosensitizer, and EDTA as reductant was reported for solar energy conversion and storage (Jayshree and Mohan 2018), but mixed surfactants using MB xylose were obtained better results (Lal and Gangotri 2013a, b).Photogalvanic effect was studied in photogalvanic cell containing tetrazine EDTA-DSS system (Jayshree and Mohan 2018), and the observed results in terms of the photopotential, photocurrent, conversion efficiency, and fill factor were 493.0 mV, 130.0 mA, 0.6163%, and 0.2800, respectively.PG effect was studied in a PG cell using methylene blue-xylose-NaLS + CTAB system (Lal and Gangotri 2013a, b).The photopotential, photocurrent conversion efficiency, and fill factor were observed 655.0 mV and 190.0 µA.0.4326%, and 0.2870, respectively.Literature survey reveals various methods for renewable energy sources through a mixed surfactant system for an eco-friendly environment.The different groups of scientists are paying their attention to enhance the results by selecting the energy compounds in innovation for noble work for their commercial viability.They have used different dyes, surfactant, and reductant in the solar system but no attention paid to use of mixed surfactant dye reductant combination to enhance the electrical output; therefore, the present work was undertaken.The aim of research on this cell is to increase the electrical output with nonpolluting nature.

Methodology for set-up and laboratory work for solution preparation
The especially designed PGS (Fig. 1) fabricated H-shaped glass tube having two arms.One arm was completely blackened except for a window and connected with a pt electrode, and another arm was connected with a saturated calomel electrode.The solutions of M/1000 Brij-35, M/1000 NaLS surfactants, M/1000 D-xylose reductant, M/5000 methylene blue dye, 1 M sodium hydroxide, and distilled water were filled in H-shaped to make up 25.00 ml (Koli et al. 2022).During the experiment, both ends of electrodes were connected through the Digital pH meter, carbon pot, micro-ammeter, and resistance key for measurement of the electrical output of the cell circuit.The electric bulb (200 W Filament containing) was used as a light source.The water filter was used to cut off IR radiations for experiment setup.These solutions were prepared in double distilled water for accuracy of electrical results.Sodium hydroxide solutions were standardized by oxalic acid solution by the titration method.These solutions were stored in amber color vessels to protect them from light.The methodology set up is given in Fig. 1 (Lal and Gangotri 2013a, b;Jayshree and Mohan 2018).

Variation of dye-methylene blue (photosensitizer) concentration on the PGS
The 4.00 × 10 −4 M MB concentration is optimum dye concentration for this photogalvanic system (Table 1).During the experiment, it was observed that when increasing the resultant concentration of MB dye (from 3.90 × 10 −4 M to 4.00 × 10 −4 M), the electrical results also increase and attains optimum nature at 4.00 × 10 −4 M of MB dye and then decreases (from 4.00 × 10 −4 M to 4.10 × 10 −4 M) in D-Xylose + MB + Brij-35 + NaLS system.On a lower concentration of MB dye (3.90 × 10 −4 M ), the low number of methylene blue dye limits the absorption of the light source, so the electrical output is low.In contrast, at a higher concentration range of methylene blue (4.10 × 10 −4 M ), there are so many molecules present that the desired light source does not reach the molecule near the electrode (Lal and Gangotri 2013a, b;Jayshree and Mohan 2018).At an intermediate range of MB concentration (4.00 × 10 −4 M ), there are optimum molecules present that the optimum light source does reach the molecule near the electrode and good results were obtained.The observed optimum results in terms of the photopotential, photocurrent, and maximum power were 698.00 mV, 245.00 µA, and 142.00 µW, respectively.The observed results were reported for variation of photosensitizer concentration in the D-Xylose + MB + Brij-35 + NaLS system (Table 1 and Fig. 2).

Variation of D-xylose (reductant) concentration on the PGS
The 2.00 × 10 −4 M D-xylose concentration is the optimum reductant concentration for this photogalvanic system (Table 1).During the experiment, it was observed that when increasing the concentration of D-xylose reductant (from 1.50 × 10 −4 M to 2.00 × 10 −4 M), the electrical output also increases and attains maximum value on particular concentration value (2.00 × 10 −4 M) and then decreases in D-Xylose + MB + Brij-35 + NaLS system (Fig. 3).On a lower concentration range of D-xylose reductant (1.50 × 10 −4 M ), a smaller number of D-xylose reductant molecules are available for electron donation to methylene blue to form the cationic form.In contrast, at a higher concentration of D-xylose reductant (2.50 × 10 −4 M ), there are  1 and Fig. 2).

Variation of (NaLS + Brij-35) concentration on the PGS
The 6.40 × 10 −3 M (for NaLS) and 9.00 × 10 −4 M (for Brij-35) are optimum micelles concentration for better results (Table 1).The electric power of the PG cell having D-Xylose + MB + Brij-35 + NaLS system was increased on increasing the concentration of Brij-35 keeping NaLS concentration constant (around its CMC value) and reached at optimum position and decreased on further increase the concentration of Brij-35 (Fig. 4).Then, the concentration of NaLS was increased keeping Brij-35 concentration constant till it reached at optimum position and decreased on further change in concentration of NaLS.On a lower concentration range of both surfactants (NaLS = 6.30× 10 −3 M), and (Brij-35 = 8.90 × 10 −4 M), there is less ability to solubilize the molecules for electron transfer process in hydrophilic-hydrophobic interaction.In contrast, at a higher concentration range of both surfactants (NaLS = 6.50 × 10 −3 M), and (Brij-35 = 9.10 × 10 −4 M), there are a larger number of surfactant molecules being available for electron transfer process in hydrophilic hydrophobic interaction which may reduce electron transfer.At the intermediate range of surfactant concentration (NaLS = 6.40 × 10 −4 M), and (Brij-35 = 9.00 × 10 −4 M), there are significant effects on electrical output for the photogalvanic system.This is because surfactant can help to separate photoproducts through hydrophilic-hydrophobic interaction of the micelles interface.How the mixed surfactants influence performance of the system can be explained on the basis of published study that the NaLS + Brij-35 have the solubilizing effect on MB dye.It was a reported fact that the active reagent-like micelles over its CMC and  resultant dye solubility increases up to some extent (Ageev et al. 2012).Generally, the electrical output increases in the presence of a particular surfactant, due to an increase in solubilization and stabilization properties of dye molecules in the water.The good precipitation may occur in surfactant mixture over individually precipitate of single surfactant in PG cells.The tendency for components to distribute themselves between the unaggregated state and an aggregate may vary from component to component for mixtures.
Therefore, the mixed surfactant composition of a micelle may differ greatly from that of the single surfactant monomer with equilibrium.The processes of interest may depend only on either monomer composition or on aggregate composition.For example, adsorption of surfactant on dye such as MB depends on composition and concentration, and solubilization of dye with micelles depends on micellar composition.The observed results were reported for variation of (NaLS + Brij-35) concentration in the D-Xylose + MB + Brij-35 + NaLS system (Table 4 and Fig. 2).

Variation of (NaLS + Brij-35) concentration on the PGS
The 6.40 × 10 −3 M (for NaLS) and 9.00 × 10 −4 M (for Brij-35) are optimum micelles concentration for better results (Table 1).The electric power of the PG cell having D-Xylose + MB + Brij-35 + NaLS system was increased on increasing the concentration of Brij-35 keeping NaLS concentration constant (around its CMC value) and reached at the optimum position and decreased on further increasing the concentration of Brij-35.Then, the concentration of NaLS was increased keeping Brij-35 concentration constant till it reached at optimum position and decreased on further change in concentration of NaLS.On a lower concentration range of both surfactants (NaLS = 6.30× 10 −3 M), and (Brij-35 = 8.90 × 10 −4 M), there is less ability to solubilize the molecules for electron transfer process in hydrophilic-hydrophobic interaction.In contrast, at a higher concentration range of both surfactants (NaLS = 6.50 × 10 −3 M), and (Brij-35 = 9.10 × 10 −4 M), there are a larger number of surfactant molecules being available for the electron transfer process in hydrophilic-hydrophobic interaction which may reduce electron transfer.At the intermediate range of surfactant concentration (NaLS = 6.40 × 10 −4 M), and (Brij-35 = 9.00 × 10 −4 M), there are significant effects on electrical output for the photogalvanic system.This is because surfactant can help to separate photoproducts through hydrophilic-hydrophobic interaction of the micelles interface.
How the mixed surfactants influence the performance of the system can be explained on the basis of a published study that the NaLS + Brij-35 have the solubilizing effect on MB dye.It was a reported fact that the active reagent-like micelles over its critical micelle concentrations (CMC) and resultant dye solubility increases up to some extent (Ageev et al. 2012).The CMC of nonylphenol ethoxylate (NP-10), dodecyl benzene sulfonate (SDBS), hexadecyl trimethyl ammonium bromide (CTAB), and the binary surfactant mixtures were measured by resonance light scattering (RLS), which were consistent with those obtained from surface tension measurements (Xiang et al. 2022), and organic pollutants are critical for the surfactant-assisted remediation (Zhang et al. (2023).Generally, the electrical output increases in the presence of a particular surfactant, due to an increase in solubilization and stabilization properties of dye molecules in the water.
The good precipitation may occur in surfactant mixture over individually precipitate of a single surfactant in PG cells.The tendency for components to distribute themselves between the unaggregated state and an aggregate may vary from component to component for mixtures.Therefore, the mixed surfactant composition of a micelle may differ greatly from that of the single surfactant monomer with equilibrium.The processes of interest may depend only on either monomer composition or on aggregate composition.For example, adsorption of surfactant on dye such as MB depends on composition and concentration and solubilization of dye with micelles depends on micellar composition.The observed results were reported for variation of (NaLS + Brij-35) concentration in the D-Xylose + MB + Brij-35 + NaLS system (Table 4 and Fig. 2).

Variation of diffusion length on the PGS
The current parameter of the cell (i max , i eq ) and initial rate of generation of photocurrent of PG cell having D-Xylose + MB + Brij-35 + NaLS system were observed with change in diffusion lengths (distance between two electrodes).It was found that with an increase in diffusion length, maximum photocurrent (i max ) and rate (µA min −1 ) go on increasing, but the equilibrium photocurrent (i eq ) shows negligible small decreasing trends.So, virtually, it may be considered unaffected by the change in diffusion length.On a lowest diffusion length (3.6 cm), the lowest number of dye molecules limits the absorption of the light source, so the photocurrent is obtained as minimum value (255.00 µA) and the initial generation of photocurrent (7.51 A/min) was obtained.In contrast, at a highest diffusion length (4.8 cm), there are the highest numbers of dye molecule absorption of the light source, so the better results were obtained (Lal and Gangotri 2013a, b;Jayshree and Mohan 2018).At the highest diffusion length, maximum photocurrent (274.00 µA), equilibrium photocurrent (235.00 µA), and initial generation of photocurrent (7.73 A/min) were obtained.The observed results were reported for variation of diffusion length in the D-Xylose + MB + Brij-35 + NaLS system (Table 2).

Variation of electrode area of the cell on the PGS
The current parameter-maximum photocurrent (i max ) and equilibrium photocurrent (i eq )-of PG cell having D-Xylose + MB + Brij-35 + NaLS system was observed that these were a regular increase in maximum photocurrent, but equilibrium photocurrent was almost independent on increase in electrode area rather affected in the reverse direction.The observed results were reported for variation of electrode area in the D-Xylose + MB + Brij-35 + NaLS system (Table 3).

(i-V) characteristics (current-voltage) of the PGS
In the PG cell having D-Xylose + MB + Brij-35 + NaLS system, the short circuit current i sc was measured by an electrical circuit.It is observed that the highest value of photopotential V pp and photocurrent were measured.The highest value of potential obeyed in the circuit is known as potential at power point corresponding to the highest value of short circuit current is known as current at power point i pp .These four values ( i sc, V oc , V pp , and i pp ) were used to determine the fill factor of PGS and the formula to determine the power point of the system.The values of the fill factor of cell (η) and the power point of cell (pp) were obtained, 0.4521 and 64.23 µW, respectively.The fill factor was calculated using the following Eq. 1 (Lal 2007;Gangotri and Mohan 2013a;Gangotri and Gangotri 2010;Lal and Gangotri 2013b;Bhimwal et al. 2013).
where V pp is the value of potential, i pp is current at the power point, V oc is the open circuit voltage, and i sc is the short circuit current

Error analysis
An analytical method was developed to the PG cell parameters, through the use of the current-voltage (I-V) characteristics under optimum illumination conditions.Accurate knowledge of the PG cell parameters under different illumination conditions was important to PG design and performance (Fig. 1).Several attempts have been made to examine the dependency of the PG cell.The rate change in PG cell parameters was values-based, and the performance of the PG systems is dependent on dye reductant surfactant concentration.Therefore, it is important to determine the optimal value of concentration to achieve electrical output.The dependency on fill factor (η) of PG cell parameters of methylene blue dye-based solar cells with various structures has been investigated (Fig. 5).The analytically predicted values of V pp and i pp decreased with increases of V oc and i sc .The decrease of η may be due to light conductivity in the PG cells.The theoretically computed values of the open circuit voltage V oc and conversion efficiency (CF) showed good agreement with the experimentally measured values at various Vpp × i pp .The performance was dependent on the product of the I sc , V oc , and CF.Thus, it is important to find the optimal value to get the several studies that have provided information on the PG cell.The parameters and performance under normal illumination and considering the value of concentrating sunlight, it is also important to examine the dependence of those parameters on η under illumination conditions.

Cell performance and conversion efficiency on the PGS
The D-Xylose + MB + Brij-35 + NaLS system has shown good storage capacity.This storage capacity of cell has been studied at certain external load (2019.83Ὠ).The D-Xylose + MB + Brij-35 + NaLS system terminated the light source at the value of photocurrent observed at the power point of the PG cell by applying an electric load from the light source.The time was recorded at which the photogalvanic cell has reached to half the value of the power in off-light mode.
The performance of the cell was determined in terms of t 1/2 .Determination of PG cell performance is reported in terms of t 1/2 , and its observed value was 126.00 min in the dark (Lal andGangotri 2013a, Jayshree andMohan 2018).PG cell conversion efficiency was determined as 0.6769% (by using Eq. 2) (Gangotri and Mohan 2013;Gangotri and Gangotri 2010;Lal and Gangotri 2013b;Bhimwal et al. 2013).Cell performance and conversion efficiency were reported for the PG cell in D-Xylose + MB + NaLS + Brij-35 System (Table 4 and Fig. 2).
where V pp is the photopotential at power point of the cell, i pp is the photocurrent at power point of the cell, and A is the electrode area of the cell.

Mechanism
Experimentally, the following chemical transformation takes place, indicating the flow of electrons in current.The proposed photochemical mechanism for solar radiation energy transformation is given for the current generation (Gangotri and Gangotri 2010;Lal and Gangotri 2013a;Bhimwal et al. 2013).

Illuminate chamber
MB molecules (photosensitizer) were getting excited and excite MB to accept electron and transfer to xylose

Photochemical reaction at platinum electrode
The semi or leuco form of MB (dye) loses an electron to the electrode and converts into the original dye molecule.

At counter electrode
Methylene blue molecules (photosensitizer) gain an electron from the electrode and convert into semi or leuco form of dye molecule, and finally, methylene blue (leuco/semi form) and the reductant (oxidized form) combine to give the original methylene blue (MB) dye and xylose reductant (R) molecules, and the whole photochemical cyclic process continues.
where MB is methylene blue (dye), MB* is the excited form of methylene blue, MB -is the semi or leuco form of methylene blue, R is reductant (xylose), and R + is the oxidized form of the reductant.

Conclusion
The PG cells played a main role in the reduction in their cost to make commercial viability by selecting the proper redox couple, with respect to a sustainable environment.The mixed surfactants have not only enhanced the electrical output of the cell but also enhanced the energy conversion.The photogalvanic cells may be the best fuel cell in the field of solar radiation transformation and potential, with respect to current parameters.The effects will be made to develop the PG cell having higher electrical output than the reported photogalvanic systems.For D-Xylose + MB + Brij-35 + NaLS system, photopotential and photocurrent were observed at 698.00 mV and 311.00 uA, respectively.The impact of solar energy was studied by varying the various electrical parameters.The D-Xylose + MB + Brij-35 + NaLS PGS performance was found at 126.00 min in the absence of light.This value is relatively higher than recently published work containing cell dimensions (70.00 min, Koli et al. 2022), DSS-tetrazine EDTA (100.00 min, Jayshree and Mohan 2018), and Sodium Lauryl Sulphate-Indigo Carmine dye-Formic acid Bromo cresol green dye (115.00 min, Koli et al. 2022).The used concentrations of dye, reductant, and surfactant were very low (Table 1).The optimum concentrations were 4.00 × 10 −4 M, 2.00 × 10 − 4 M, 6.40 × 10 − 3 M, and 9.00 × 10 − 4 M, for dye MB, reductant xylose, and surfactants (NaLS, Brij-35), respectively.Therefore, our study aim was fully in favor of nonpolluting nature and ecofriendly environment.The present work reports advancement over earlier work (Lal and Gangotri 2013a; Jayshree and Mohan 2018) by employing cell performance enhancer surfactants, NaLS, instead of mixed surfactants.The efficient systems, if reached to the desired extent of reduced cost and overall efficiency, may replace the existing solar cells in the market and would be capable of feeding the electrical demand of humanity.

Fig. 1
Fig. 1 Methodology set up for PG cell

Fig. 2 Fig. 3
Fig. 2 Performance of the PG cell

Table 1
a larger number of reductantJayshree and Mohan 2018)le for electron donation to methylene blue to form the cationic form which hinders the methylene blue(Lal and Gangotri  2013a, b;Jayshree and Mohan 2018).At the intermediate range of D-xylose reductant concentration (2.00 × 10 −4 M ), there are optimum numbers of D-xylose reductant molecules present that form favorable conditions for semi or leuco form of dye molecules, and good results were obtained.The observed optimum results in terms of the maximum photopotential, maximum photocurrent, and maximum power were 698.00 mV, 245.00 µA, and 142.00 µW, respectively.The observed results were reported for variation of D-xylose reductant concentration in the D-Xylose + MB + Brij-35 + NaLS system (Table

Table 4
, the efficiency of the PG cell with mixed surfactant has tremendously increased with special reference to current parameters, power, conversion efficiency, and t 1/2 value (the storage capacity) almost the doubled of the charging time of the cell