Magnetite–poly-1H pyrrole dendritic nanocomposite seeded on poly-1H pyrrole: A promising photocathode for green hydrogen generation from sanitation water without using external sacrificing agent

Maha Abdallah Alnuwaiser; Mohamed Rabia; Asmaa M. Elsayed

doi:10.1515/chem-2024-0106

Article Open Access

Magnetite–poly-1H pyrrole dendritic nanocomposite seeded on poly-1H pyrrole: A promising photocathode for green hydrogen generation from sanitation water without using external sacrificing agent

Maha Abdallah Alnuwaiser , Mohamed Rabia and Asmaa M. Elsayed

Published/Copyright: December 2, 2024

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From the journal Open Chemistry Volume 22 Issue 1

Abstract

The Fe₃O₄ magnetite–poly-1H pyrrole dendritic nanocomposite seeded on additional poly-1H pyrrole film, denoted as Fe₃O₄-P1HP/P1HP, is synthesized by oxidative polymerization utilizing (Fe(NO₃)₃·5H₂O for the pyrrole monomer. The resulting nanocomposite exhibits a notable bandgap of 1.97 eV and demonstrates broad optical absorption up to 625 nm. The structure of each particle consists of numerous smaller internal particles, which are composed of nanofibers of approximately 2.0 nm in length and porous structures of around 5.0 nm. These porous structures cluster together to form a larger configuration, with an overall diameter of ∼230 nm and a length of approximately 300 nm, giving the composite a nano-cactus-like appearance. The fabricated Fe₃O₄–P1HP/P1HP photocathode is inserted into a three-electrode cell to facilitate green hydrogen production from sanitation water without the need for any external sacrificial agent. The performance of H₂ gas generation is assessed by measuring the photocurrent density (J _ph) under light, which serves as an indicator of the efficiency of hydrogen production. The J _ph value reaches −0.23 mA/cm² under light conditions. The highest J _ph values of −0.164 and −0.158 mA/cm² are observed at wavelengths of 340 and 440 nm, respectively. However, as the wavelength reaches 540 nm, the J _ph value decreases to −0.134 mA/cm² and drops to its lowest point of −0.128 mA/cm² at 730 nm, which is comparable to the dark current (J _o). The fabricated photocathode demonstrates a promising hydrogen generation rate of 90 µmol/h cm², reflecting its potential for commercial applications. The combination of this impressive hydrogen production rate, along with the photocathode’s cost-effectiveness and straightforward fabrication process, suggests that this technology could be commercially viable for converting sanitation water into hydrogen gas.

Keywords: poly(1H pyrrole); Fe3O4 ; photocathode; hydrogen generation; sanitation water

1 Introduction

The pursuit of renewable energy sources that are both cost-effective and efficient represents a significant challenge for researchers today. This challenge is driven by the need to create solutions that not only provide sustainable energy but also contribute to an eco-friendly and green chemistry environment [1,2,3]. By advancing renewable energy technologies, researchers aim to lessen our reliance on fossil fuels, which have become increasingly problematic in recent years due to their detrimental effects on the environment. Fossil fuels, once the cornerstone of global energy production, have now become a focal point of concern due to their association with pollution, climate change, and other environmental issues. The extraction, processing, and burning of these fuels release harmful greenhouse gases and other pollutants into the atmosphere, contributing to global warming and environmental degradation. As a result, the urgent need to shift towards renewable energy sources has become a priority for the scientific community. Renewable energy sources such as solar, wind, hydro, and bioenergy offer the promise of a cleaner, more sustainable future. However, the transition to these energy sources is not without its challenges. One of the primary obstacles is the cost associated with developing and implementing these technologies on a large scale. Researchers are tasked with finding ways to make renewable energy more affordable and accessible without compromising on efficiency and effectiveness [2,4].

Hydrogen is recognized as a clean fuel of the future, primarily because it produces zero carbon emissions, which positions sustainable H₂ generation as a crucial priority in the energy sector. Among the numerous technologies available for H₂ production, photoelectrochemical (PEC) technology stands out due to its innovative approach to water splitting. This method involves the use of various materials with photoresponsive properties, which harness light energy to drive the chemical reactions needed for hydrogen production. The process is enhanced by the presence of additional electrolytes in the reaction medium, which play a critical role in facilitating the movement of ions. These electrolytes ensure that the necessary charge transfer occurs efficiently, supporting the overall reaction process. The use of PEC technology in hydrogen production offers a promising pathway toward sustainable energy, as it leverages abundant solar energy and water, both of which are renewable resources. However, achieving high efficiency in this process requires the careful selection and optimization of materials with suitable photoresponsive properties. These materials must not only effectively absorb sunlight but also exhibit the necessary chemical stability and catalytic activity to drive the water-splitting reaction over extended periods. Through the advancement of PEC technology and the improvement of materials utilized in this process, researchers are working toward establishing a dependable and sustainable method for large-scale hydrogen generation. This strategy supports the larger objective of decreasing reliance on fossil fuels and minimizing the environmental effects of energy production, ultimately aiding the transition to a cleaner and more sustainable energy future [3,5,6].

Among various photocatalytic metal oxides studied, Wang et al. [7] demonstrated that CuO nanowires are beneficial for light detection in the IR domain. However, they observed a small photocurrent (20 µA) under high application conditions. In addition, ferric oxide has gained particular interest due to its relative abundance, non-toxicity, and affordability. Recent studies have highlighted the potential of nanoscale ferric oxides [8]. Fe₃O₄ is particularly notable for its advantageous properties, such as a 2.1 eV band gap [9], non-toxicity, low cost, and strong chemical stability in aqueous solutions. Furthermore, Fe₃O₄ has various uses in industries, including cement production, water splitting, gas detection, solar energy conversion, lithium-ion battery manufacturing, water purification, and pigmentation. These versatile uses have led to increased interest in the production of iron oxide nanoparticles for these fields [10].

The efficiency of Fe₃O₄ (magnetite) in hydrogen (H₂) production can be significantly enhanced by forming composites with other materials. The synergistic interactions between these combined materials are particularly promising, as they can generate hot electrons that actively engage in the reaction with nearby solutions, thereby boosting hydrogen production [11,12]. Additionally, the direct interaction between the morphology and optical properties of the composite materials plays a crucial role in this process. Porous nanomaterials are especially well suited for such photocatalytic applications due to their unique structure, which offers a high surface area and excellent light absorption capabilities. These characteristics allow for better light harvesting and more efficient charge separation, which are essential for maximizing the photocatalytic activity of Fe₃O₄ composites.

Conducting polymers has some achievements in this area, in which the tunable photophysical properties of P1HP, such as its photothermal conversion ability and Fenton catalysis ability, also enable emerging applications in cancer therapy, including tumor ablation and immune activation [13]. Despite previous studies significantly enhancing materials for H₂ gas generation, several challenges remain. These include issues such as limited production yield, the need for advanced preparation techniques, and the use of highly acidic or basic electrolytes, which can cause rapid and severe corrosion of the electrodes used for H₂ gas generation [14,15]. Therefore, it is essential to explore other technologies and conduct further studies to address these technical challenges.

Herein, the Fe₃O₄-P1HP/P1HP photocathode has been meticulously fabricated and thoroughly analyzed to assess its morphology, chemical composition, electrical properties, and optical behavior. This photocathode has demonstrated exceptional performance in hydrogen gas generation, as evidenced by the J _ph measurements conducted under both general light conditions and various monochromatic light exposures. The study also includes an evaluation of chopped light, which highlights the sensitivity and reproducibility of the fabricated photocathode.

The hydrogen gas production rate was calculated using sanitation water as the electrolyte, notably without the addition of any external sacrificial agents. The Fe₃O₄-P1HP/P1HP photocathode stands out for its efficient hydrogen generation capabilities coupled with cost-effectiveness, positioning it as a promising material. Its unique structural characteristics and robust performance under light conditions indicate that this technology could significantly contribute to sustainable energy solutions, particularly in converting sanitation water into hydrogen gas. The potential for scaling and industrial implementation further enhances the photocathode’s appeal, suggesting that the Fe₃O₄-P1HP/P1HP photocathode could have great behavior in the future of green hydrogen production. As a valuable advancement in this field, it combines innovative design with practical advantages, offering a pathway toward more sustainable and economically viable hydrogen generation processes.

2 Materials and methods

2.1 Materials and characterization techniques

The following chemicals were used in this study: ferric nitrate pentahydrate (Fe(NO₃)₃·5H₂O, 99.9%, Pio-Chem Co, Egypt), ammonium persulfate (NH₄)₂S₂O₈·5H₂O, 99.9%, Pio-Chem Co, Egypt), pyrrole (Across Co., 99.9%, USA), and HCl (36%, Merck, Germany). The sanitation water is supported by the company water (Beni-Suef city, Egypt, thrice treated).

Characterization techniques involved the use of various instruments for chemical analysis. These include the AXIS-NOVA for XPS, the Bruker for FTIR, and the Pro for XRD. To observe 3D and 2D morphologies, Zeiss and Jole devices were utilized for SEM and TEM, respectively. Optical properties were assessed using an Elmer Perkin device.

2.2 Fabrication of Fe₃O₄-P1HP/P1HP photocathode

The fabrication of the Fe₃O₄-P1HP/P1HP photocathode involves two key steps. Initially, a P1HP seeding layer is created on a glass substrate. This P1HP layer is formed by oxidizing pyrrole using (NH₄)₂S₂O₈ in an acidic medium, with the monomer, oxidant, and acid mixed in a ratio of 1:2.5:10. In the subsequent step, the Fe₃O₄-P1HP layer is deposited using a similar oxidation process, but this time with the inclusion of both (NH₄)₂S₂O₈ and iron nitrate nonahydrate (Fe(NO₃)₃·5H₂O maintaining the same ratio. These reagents not only facilitate the oxidation of pyrrole but also contribute to the formation of the Fe₃O₄-P1HP composite. The reaction is carried out in an acidic medium (0.5 M HCl), which significantly improves the morphology of the resulting polymer composite. Figure 1 shows an illustration of the deposition conditions.

Figure 1

The fabrication and the applications of the Fe₃O₄-P1HP/P1HP photocathode inside a three-electrode cell for H₂ gas generation from sanitation water.

2.3 Photocathode for the hydrogen generation photoelectrochemically

Hydrogen generation is accomplished through the electrochemical splitting of sanitation water using a Fe₃O₄-P1HP/P1HP thin film deposited on a glass substrate. The process involves measuring the current density electrochemically with a CHI608E device, where the fabricated photocathode acts as the working electrode. Hydrogen production is evaluated via linear sweep voltammetry, comparing the generated J _ph to the initial J _o. The sanitation water used has a pH of 7.4, and its composition is detailed in Table 1. This method of converting environmentally harmful waste into hydrogen gas marks a significant advancement in waste-to-energy technology. The splitting reaction is conducted photoelectrochemically under a halide lamp (vacuum tube) that provides high-quality white light. The light can be filtered to generate specific monochromatic wavelengths, including 730, 540, 440, and 340 nm, by using various optical filters. These filters, circular and manufactured by Andover Corporation (model AM 106004, USA), allow only the desired wavelengths to pass through. The energy of the incident light is assessed in relation to the bandgap of the Fe₃O₄-P1HP/P1HP thin film photocathode. The hydrogen gas production is estimated by Faraday’s law of electrolysis, as outlined in equation (1) [16]:

(1) H 2 mole = ∫ 0 t J ph . d t F .

Table 1

Chemical constitution of the electrolyte (sanitation water) [17]

Material or element	Concentration (µg/l)
Ni³⁺	0.01
F⁻	0.001
Hg²⁺	0.005
Mn²⁺	0.001
Phenols	0.015
Ba³⁺	0.002
NH₃	0.005
Cd³⁺	0.05
Al³⁺	0.003
As³⁺	0.05
Cr³⁺	0.001
Co²⁺	0.002
Pb²⁺	0.005
Zn²⁺	0.005
Cu²⁺	0.00015
Industrial washing	0.05
Fe³⁺	0.0015
Coli groups	4.0 × 0.1 cm³
Ag⁺	0.01
Pesticides	0.02
CN⁻¹	0.01
Other cations	0.01

3 Results and discussion

3.1 Fe₃O₄-P1HP physicochemical characterization

The chemical characterization of Fe₃O₄-P1HP nanomaterials is conducted using various analytical tools, including FTIR spectroscopy, to identify the functional groups associated with the composite. The estimated vibration mode associated with the N–H group in P1HP is observed at 33,408 cm⁻¹, while the P1HP ring groups are identified at 1,551, 1,409, 1,313, 1,188, and 1,036 and 908 cm⁻¹, corresponding to the internal functional groups C–C, C═C, C–N, C–H, and out-of-plane bonds, respectively. The vibration modes of the composite show significant changes in P1HP upon the incorporation of Fe₃O₄. This incorporation substantially affects the bonds within the composite, altering both bond rotation and bond length. These alterations are evident through shifts in the positions of the bonds, as illustrated in Figure 2(a) and Table 2. The redshift observed in the bond positions indicates the impact of the Fe₃O₄ groups, with the bands associated with this oxide appearing at 789 and 625 cm⁻¹. These bands exhibit strong intensity compared to the pristine P1HP, highlighting the significant effect of Fe₃O₄ insertion on the composite structure.

Figure 2

Chemical analyses of the Fe₃O₄-P1HP nanocomposite in comparison to P1HP: (a) FTIR, (b) XRD, (c) and (d) XPS survey, and Fe element, respectively. Optical analysis: (e) absorbance and (f) bandgap estimation.

Table 2

Summary of estimated bonds from Figure 2(a) for the composite formation

Group and its value (cm⁻¹)		Functional group
Fe₃O₄-P1HP	P1HP	Functional group
3,433	3,408	N–H [18]
1,631, 1,548, 1,399, 1,305, 1,187, 1,047, and 921	1,551, 1,409, 1,313, 1,188, 1,036, and 908	P1HP ring [19]
789 and 625	—	Fe–O

The evaluation of the crystalline structure of the fabricated P1HP and Fe₃O₄/P1HP nanocomposite is illustrated in Figure 2(b). This analysis shows promising crystalline characteristics, particularly with regard to the peaks associated with Fe₃O₄, which are not present in the pristine P1HP due to its amorphous nature. The composite displays peaks at 16.7°, 29.6°, 34.9°, 36.1°, 41.4°, 56.4°, 54.8°, and 63.8°, corresponding to the growth directions of (111), (220), (311), (222), (400), (422), (511), and (440) planes, respectively [20]. These crystalline features indicate the successful incorporation of Fe₃O₄ into the composite.

The crystalline size of the nanocomposite is estimated using the Scherrer equation (equation (2)) [21,22], based on the peak observed at 2θ = 29.6°. The resulting crystalline size is calculated to be 53 nm. This fine crystalline size, combined with the favorable crystalline properties, suggests that the Fe₃O₄/P1HP nanocomposite is highly effective for optical applications. Specifically, the composite’s ability to respond to light and utilize photon energy to generate hot electrons is particularly advantageous. These hot electrons can be harnessed for the generation of H₂ gas from wastewater, showcasing the composite’s potential in energy conversion and environmental applications:

(2) D = 0.94 λ β cos θ .

To further emphasize the chemical characteristics of the fabricated Fe₃O₄/P1HP nanocomposite, XPS analyses are presented in Figure 2(c). These analyses illustrate the significant elemental oxidation behavior of both the organic and inorganic components within the composite. Specifically, the carbon and nitrogen elements are estimated at 285.2 and 401 eV, respectively. Oxygen (O), associated with the elements that form the inorganic structure through its connection with iron, is detected at 532 eV.

The XPS analysis also provides detailed information on the oxidation states of iron within the Fe₃O₄ material, highlighting the presence of both Fe²⁺ and Fe³⁺ states. This is clearly shown in Figure 2(d), where the peaks corresponding to Fe²⁺ are identified at 711.2 and 724.5 eV for the Fe2p_3/2 and Fe2p_1/2 orbitals, respectively. In contrast, the peaks for Fe³⁺ are observed at slightly higher binding energies, with Fe2p_3/2 and Fe2p_1/2 orbitals at 714.5 and 727.8 eV, respectively [20]. The combination of these oxidation states confirms the formation of the Fe₃O₄ structure within the P1HP polymer network, contributing to the overall integrity and functionality of the Fe₃O₄/P1HP nanocomposite. This well-defined Fe₃O₄ structure embedded in the P1HP polymer is crucial for its enhanced optical properties. The nanocomposite exhibits significant photon absorption capabilities, making it highly effective for applications in renewable energy sources. The interaction of Fe₃O₄ with the P1HP matrix not only stabilizes the composite structure but also enhances its ability to harness photon energy efficiently. This property is particularly advantageous for generating hot electrons, for hydrogen production from wastewater.

The optical properties of the synthesized Fe₃O₄-P1HP nanocomposite, in comparison to P1HP, are depicted in Figure 2(e). The analysis shows significant changes in absorbance, marked by various peaks that reflect its responsiveness to incident photons. The Fe₃O₄-P1HP composite exhibits a broad absorbance spectrum extending up to 625 nm, reflecting its improved optical properties. Within this range, two distinct peaks are observed, corresponding to the two components of the composite: P1HP shows a UV peak, while Fe₃O₄ displays a visible peak. Beyond 625 nm, the composite’s absorbance decreases, attributed to lower absorption values in the near-IR region. In contrast, P1HP exhibits an absorbance peak limited to 390 nm. Both materials share a common mechanism for these peaks, involving electron transfer and collection in the conduction band. However, the composite shows superior optical properties due to the larger absorbance regions, resulting in a higher quantity of collected electrons.

To highlight this difference, the bandgap values of both materials were estimated. The Fe₃O₄-P1HP composite has a bandgap of approximately 1.97 eV, whereas P1HP has a bandgap of 3.2 eV. These values were determined using the Tauc equation (equations (3) and (4)) [23,24], based on the absorbance coefficient (α):

(3) α h ν = A ( h ν − E g ) 1 / 2 ,

(4) α = 2 , 303 d A .

This comparison underscores the significant enhancement in the optical behavior of the Fe₃O₄-P1HP composite, making it more effective in photon absorption and related applications.

The synthesized Fe₃O₄-P1HP nanocomposite exhibits impressive morphology characterized by a highly porous nanostructure resembling a nano-cactus, as shown in Figure 3(a). This composite features excellent particle distribution, with porous regions between molecules contributing to its unique structure [25,26]. Each particle comprises numerous smaller internal particles, as depicted in Figure 3(b), which consist of nanofibers approximately 2.0 nm in length and porous structures around 5.0 nm. These porous structures aggregate to form a larger shape with an overall diameter of about 230 nm and a length of about 300 nm, resembling a nano-cactus. This morphology is advantageous for photon absorbance, as photons are trapped within the structure, allowing photon energy to be efficiently transferred to the particles. This process is conducive to the formation of hot electrons, which are then collected in the conducting band of the material [27,28].

Figure 3

The morphological estimation of the Fe₃O₄-P1HP composite: (a) and (b) SEM at various magnifications, and (c) TEM. (d) SEM of the P1HP pristine polymer.

This morphological feature is further confirmed through TEM analysis, as illustrated in Figure 3(c). The porous structure, evident in the TEM image, underscores the superior behavior of the Fe₃O₄-P1HP nanocomposite. The variation in color from faint to dark in the TEM images highlights the distinction between the organic P1HP and the inorganic Fe₃O₄ components, indicating a strong interface in the composite formation. The nanopores and nanoparticles are consistently around 5.0 nm in size.

Conversely, P1HP itself possesses notable features related to the formation of porous structured particles with a semi-circular shape. These particles exhibit unique porosity and size characteristics. This remarkable morphology contributes to the development of the Fe₃O₄-P1HP composite with its distinctive nano-cactus structure.

3.2 Fe₃O₄-P1HP/P1HP photocathode for the green hydrogen study

The study focuses on green hydrogen production through photoelectrochemistry, using a specially fabricated Fe₃O₄-P1HP/P1HP photocathode as the primary electrode within a three-electrode cell. This cell employs sanitation water as the electrolyte, with the aim of converting this water into green hydrogen gas. The use of sanitation water offers significant advantages due to its harmful nature and enrichment with heavy metals, which promote the electrolysis reaction necessary for H₂ gas formation. The process of H₂ gas generation occurs in several steps, beginning with the formation of OH radicals. These radicals attack additional H₂O molecules, facilitating the production of H₂ gas. The reaction is driven by hot electrons generated on the surface of the Fe₃O₄-P1HP/P1HP photocathode when exposed to light. These electrons are produced in high density and are subsequently transferred to H₂O via a reduction reaction.

The impact of light on the Fe₃O₄-P1HP/P1HP photocathode’s performance is assessed through linear sweep voltammetry (Figure 4(a)) and chopped light measurements (Figure 4(b)). Figure 4(a) shows the effect of photon incidence in activating hot electrons from the Fe₃O₄-P1HP/P1HP surface, resulting in an increased production of H₂ gas. This is evidenced by the photocurrent density reaching −0.23 mA/cm², a significant improvement relative to the J _o of −0.128 mA/cm². This indicates that photons greatly enhance the Fe₃O₄-P1HP/P1HP photocathode’s efficiency, as both Fe₃O₄ and P1HP are photocatalytic materials enriched with hot electrons. These electrons are transferred from P1HP to Fe₃O₄, generating a strong electric field that initiates and drives the water-splitting reaction. The observed J _ph value highlights the promising potential of this approach for effectively splitting harmful sanitation water. Additionally, using sanitation water makes this a cost-effective process, especially when combined with the low-cost materials and techniques used, including the glass substrate for the thin-film deposition of the Fe₃O₄-P1HP/P1HP photocathode.

Figure 4

PEC testing of green H₂ gas production using the fabricated Fe₃O₄-P1HP/P1HP photocathode with wastewater as the electrolyte: (a) linear sweep voltammetry analysis showing the relationship between potential and current density, and (b) study under chopped light illumination.

The sensitivity and reproducibility of the photocathode are further validated through the chopped light current measurements shown in Figure 4(b). The consistent J _ph and J _o relative to alternating light and dark conditions indicate the excellent stability of this photocathode. This stability is attributed to the P1HP material, which coats the Fe₃O₄ layer and acts as a protective barrier, enhancing the photocathode’s resistance to corrosion. The overall results demonstrate that the Fe₃O₄-P1HP/P1HP photocathode not only achieves efficient hydrogen generation but also maintains high stability and reproducibility, making it a viable option for green hydrogen production from sanitation water.

The sensitivity of the fabricated Fe₃O₄-P1HP/P1HP photocathode was investigated by analyzing its response under varying light wavelengths and frequencies, achieved using a series of optical filters that selectively pass the desired wavelengths (as shown in Figure 5(a)). The study reveals that the photocurrent density increases with the photon energy, indicating a strong correlation between photon energy and the photocathode’s performance [29–31]. The maximum J _ph values were observed at 340 and 440 nm, with corresponding values of −0.164 and −0.158 mA/cm², respectively. However, at 540 nm, the J _ph value decreased to −0.134 mA/cm² and reached its lowest point of −0.128 mA/cm² at 730 nm, a value that is essentially equivalent to J _o. This indicates that photons at 730 nm have no significant impact on the photocathode’s performance.

Figure 5

The influence of monochromatic light on the PEC testing of green H₂ gas production using the fabricated Fe₃O₄-P1HP/P1HP photocathode with wastewater as the electrolyte: (a) testing with optical filters at different wavelengths ranging from 340 to 730 nm, and (b) the resulting J _ph values under these various optical filters at −0.8 V.

The variation in J _ph values across different wavelengths highlights the photocathode’s differing responsiveness to photons of various energies, underscoring the sensitivity of the fabricated Fe₃O₄-P1HP/P1HP photocathode. Figure 5(b) estimates the data obtained from the analysis, offering a clear comparison of the photocathode’s response to different wavelengths.

To better understand the effect of photon energies on the fabricated photocathode, the photon energies at specific wavelengths (340, 440, and 540 nm) are compared with the bandgap energy of the material, which is 1.97 eV. According to equation (5), the photon energies at 340, 440, and 540 nm are 3.6, 2.8, and 2.3 eV, respectively, all of which exceed the bandgap energy. As a result, these photons are capable of exciting electrons into the conduction band, causing the generation of hot electrons and a corresponding increase in the J _ph values.

However, the photon energy at 730 nm is 1.7 eV, which is lower than the bandgap energy. Because this energy is insufficient to promote electrons to the conduction band, it fails to generate hot electrons, resulting in a J _ph value that closely matches J _o. This lack of response at 730 nm further emphasizes the relationship between the photon energy and photocathode’s ability to generate a photocurrent [31,32]:

(5) E = hv .

The amount of H₂ gas generated was calculated using equation (1), as depicted in Figure 6. The results show a significant production of H₂ gas, measured at 0.09 mmol/cm² h. This impressive value highlights the potential of the fabricated Fe₃O₄-P1HP/P1HP photocathode for industrial applications in commercial hydrogen synthesis. In addition to the high yield, the photocathode offers technical advantages such as cost-effectiveness and the use of sanitation water as an electrolyte. These factors make the fabricated photocathode a promising and superior option relative to previous studies, as shown in Table 3.

Figure 6

The estimated green H₂ produced moles using the fabricated Fe₃O₄-P1HP/P1HP photocathode with sanitation water as the electrolyte.

Table 3

Comparison of the generated H₂ gas through the fabricated Fe₃O₄-P1HP/P1HP photocathode relative to other previous studies

Photoelectrode	J _ph (mA/cm²)	Electrolyte
Polypyrrole/graphene oxide [33]	0.1	Sewage water
Polypyrrole/NiO [34]	0.11	Sewage water
Poly-3-methyl aniline/graphene oxide [35]	0.09	Sewage water
Cr₂S₃-Cr₂O₃/poly-2-aminobenzene-1-thiol [18]	0.017	Sewage water
Poly-O-aminothiophenol/intercalated iodide composite [16]	0.12	Red Sea water
Fe₃O₄-P1HP/P1HP (this work)	0.16	Sewage water

4 Conclusions

The Fe₃O₄-P1HP/P1HP photocathode is constructed by the oxidation of pyrrole in the presence of Fe(NO₃)₃, which is carried out on a thin seeding film of P1HP. The resulting Fe₃O₄-P1HP composite features porous structures that cluster together, forming a larger configuration with an overall diameter of ∼230 nm and a length of ∼300 nm. This structure, with dendritic formations of about 2.0 nm on the surface, gives the composite a unique nano-cactus-like appearance.

The Fe₃O₄-P1HP/P1HP photocathode demonstrates strong performance in H₂ gas generation, as indicated by the photocurrent density (J _ph) measurements. Under light conditions, the J _ph value reaches −0.23 mA/cm². When exposed to monochromatic wavelengths, the photocathode achieves its highest J _ph values at 340 and 440 nm, recording −0.164 and −0.158 mA/cm², respectively. However, as the wavelength reaches 540 nm, the J _ph value declines to −0.134 mA/cm², eventually reaching its lowest point of −0.128 mA/cm² at 730 nm, which is comparable to J _o. This variation in J _ph values across different wavelengths reflects the photocathode’s sensitivity to photon energies and its efficiency in generating hydrogen.

The fabricated photocathode exhibits a promising hydrogen generation rate of 90 µmol/h cm², showcasing its potential for industrial applications. The high hydrogen production rate, combined with the cost-effectiveness and ease of fabrication, indicates that this photocathode could be commercially viable for converting sanitation water into hydrogen gas. Its impressive performance, along with the economic and practical benefits, positions the Fe₃O₄-P1HP/P1HP photocathode as a strong contender for future large-scale H₂ production.

In summary, the Fe₃O₄-P1HP/P1HP photocathode offers a combination of efficient hydrogen generation and cost-effectiveness, making it a promising material for commercial applications. The unique structure and high performance under light conditions suggest that this technology could play a significant role in sustainable energy solutions, particularly in the conversion of sanitation water into hydrogen gas. With its potential for scalability and industrial use, the Fe₃O₄-P1HP/P1HP photocathode represents a valuable advancement in green hydrogen production.

Acknowledgments

Princess Nourah bint Abdulrahman University Researchers Supporting Project number (PNURSP2024R186), Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia.

Funding information: This research was financially supported by Princess Nourah bint Abdulrahman University Researchers Supporting Project (number PNURSP2024R186), Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia.
Author contributions: Maha Abdallah Alnuwaiser: writing, funding, and ordering the work. Mohamed Rabia and Asmaa M Elsayed: conducting experiments and writing.
Conflict of interest: The authors have no conflict of interest.
Ethical approval: This study does not include any human or animal studies.
Data availability statement: All data generated or analyzed during this study are included in this article.

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Received: 2024-08-16

Revised: 2024-10-02

Accepted: 2024-10-06

Published Online: 2024-12-02

This work is licensed under the Creative Commons Attribution 4.0 International License.

Articles in the same Issue

https://doi.org/10.1515/chem-2024-0106

Keywords for this article

poly(1H pyrrole); Fe3O4; photocathode; hydrogen generation; sanitation water

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Magnetite–poly-1H pyrrole dendritic nanocomposite seeded on poly-1H pyrrole: A promising photocathode for green hydrogen generation from sanitation water without using external sacrificing agent

Article

Abstract

1 Introduction

2 Materials and methods

2.1 Materials and characterization techniques

2.2 Fabrication of Fe3O4-P1HP/P1HP photocathode

2.3 Photocathode for the hydrogen generation photoelectrochemically

3 Results and discussion

3.1 Fe3O4-P1HP physicochemical characterization

3.2 Fe3O4-P1HP/P1HP photocathode for the green hydrogen study

4 Conclusions

Acknowledgments

References

Articles in the same Issue

Articles in the same Issue

Articles in the same Issue

2.2 Fabrication of Fe₃O₄-P1HP/P1HP photocathode

3.1 Fe₃O₄-P1HP physicochemical characterization

3.2 Fe₃O₄-P1HP/P1HP photocathode for the green hydrogen study