Improved electrochemical synthesis of Cu–Fe/brass foil alloy followed by combustion for high-efficiency photoelectrodes and hydrogen production in alkaline solutions

2.1 Chemicals

Copper(ii) chloride (CuCl₂, Sigma Aldrich 99%), iron(iii) chloride (FeCl₃, Sigma Aldrich 99%), and (77Cu–33Zn) Foil (Sigma Aldrich 99.99%) as a metal substrate were used. NaOH and Na₂SO₄ were purchased from Sigma Aldrich.

2.2 Electrodeposition of Cu–Fe alloys on brass foil

The cyclic voltammetry deposition was accomplished using Autolab potentiostate. A three-electrode cell was made specifically for the electro-deposition experiments in which, Ag wire reference electrode, a Pt counter electrode. 0.3 mL Al paste is applied to one side of the working electrode through the contacting point with the wire. Before usage, the working electrode is then washed and dried. All voltammograms are measured at a temperature of 35°C and a scanning rate of 50 mV·s⁻¹. The hull cell panels had previously been cleaned with deionized water, dried, and then degreased for 2 min in dichloromethane, after which they had been removed and dried. The cell is filled with distilled water containing Fe ion (0.02–0.25 M) and Cu ion (0.05–0.25 M). Deposit of Ally(i) and Alloy(ii) was obtained by applying potential in the range of −0.35 to −0.38 V with 35 mA·cm⁻² for 30 min (Figure 1(a)).

Figure 1

(a) The electrodeposition process of the Cu–Fe alloy and (b) its applications in optoelectronic measurements.

2.3 Preparation of photoelectrode

The synthesized Cu–Fe/brass is applied as photoelectrode for water splitting reaction. Moreover, the oxides of this alloy under the combustion process (550°C for 20 min) are applied as photoelectrode for hydrogen generation. The hydrogen generation is tested from 0.5 M Na₂SO₄, in which a solar simulator with 400 mW·cm⁻² is applied as a light source with a potential from −1.5 to 1 V (Figure 1(b)).

2.4 Samples characterization

The surfaces of deposited alloys and composites were imaged using a scanning electron microscope (SEM) (Quanta 250 FEG; FEI Company, Eindhoven, Holland), and chemical compositions were quantitatively carefully examined using the accompanied energy-dispersive X-ray (EDX). X-ray diffraction (XRD) charts for the deposited alloys are assessed utilizing an X-ray diffractometer with an X-ray generator (Phillips model PW 1730), diffractometer (PW 1716), and detector (PW 1050/25). Cu (lKa ¼ 0.154 cm⁻¹) was used as an anode at 40 kV ascending voltage, 35 mA current, and 0.02 scanning rate within 2 theta angles ranging from 10 to 80°. X-ray photoelectron spectroscopy (XPS, Thermo ESCALAB 250 Xi) was used to study the specimens’ binding energy and ion valence state. Survey spectra were recorded over a range of 0–1,100 eV for each composition. The high-resolution spectra were taken for 2p_1/2,3/2 level of Fe, Cu, and Zn and for 1s level of oxygen.

3.1 Electrodeposition of Cu–Fe alloy

Figure 2(a)–(c) displays cyclic voltammograms for a solution holding both Cu and Fe ions measured at 50 mV·s⁻¹ scan rate and potential range of −2.0 to +2.0 V to determine the appropriate current and potential for the electrodeposition process. A double jacket cell provided with Pt electrodes as working and countering electrodes and a saturated calomel electrode as a reference electrode was used. The FeCl₃ concentrations are varied from 0.02 to 0.25 M, while the CuCl₂ concentrations are varied from 0.05 to 0.25 M. Table 1 shows the basic reaction formula that occurs in the electrolytic reactions. Figure 2(a) shows the first observed anodic peak at E _pa1 = 0.42 V with I _pc1 = 5.2 mA can be attributed to Cu⁺ → Cu²⁺ + e⁻ appear in reaction (4). Also, the second anodic peak of the alloy at E _pa1 = 0.74 mV with I _pc1 = 10.6 mA·cm⁻² can be attributed to Fe⁺² → Fe³⁺ + e⁻ appear in reaction (1) [16]. A third cathodic peak for chlorine ions in solution appear in Table 1 as shown in reaction number 2 (Table 1). The cathodic peak at E _pc1 = + 0.36 V with I _pc1 = −16 mA can be attributed to Cu²⁺ + 2e⁻ → Cu appear at reaction number 8 (Table 1). The second cathodic peak at E _pc1 = −0.04 V with I _pc1 = −28 mA may be also an alloy for Cu/Cu–Fe. A third cathodic peak at E _pc1 = −0.44 V with I _pc1 = −48 mA can be attributed to Fe²⁺ + 2e⁻ → Fe appear at reaction number 9 (Table 1) [12] reduction potential of iron ions is higher than the reduction potential of copper ions. Figure 2(b) shows that the height of the cathodic current peaks and the anodic current peaks are increased with increasing of both FeCl₃ and CuCl₂ concentrations with the same concentration. Figure 2(c) displays cyclic voltammograms for a solution holding both Cu and Fe ions measured at 50 mV·s⁻¹ scan rate and potential range of −2.0 to +0.5 V to determine the appropriate current and potential for the electrodeposition of Cu/Fe alloys. The concentration of FeCl₂ is performed in the range from 0.2 to 0.9 M and CuCl₂ concentration is performed from 0.2 to 0.9 M, in which the cathodic current peak increases with CuCl₂ concentration and then decreases with FeCl₂ concentration.

Figure 2

The electrochemical cyclic voltammetry of CuCl₂ and FeCl₃ electrolyte in (a) 0.25 M for each material, (b) different concentrations (0.05–0.25 M), and (c) different concentrations (0.2–0.9 M) at 50 mV·s⁻¹ and room temperature.

3.2 Structural and morphological properties of the prepared nanomaterials

Then structural properties of the prepared nanomaterials before (alloys) and after the combustion process were investigated using XRD. Figure 3 shows XRD charts for two alloys deposited from different solutions of CuCl₂ and FeCl₃. Figure 3(a) is the XRD pattern for the alloy prepared from the electrolyte, 0.25 M of CuCl₂ with (0.02 M) FeCl₃, while Figure 3(b) is the pattern for the sample prepared using (0.25 M) FeCl₂ and (0.05 M) CuCl₂, Figure 3(c) is sample (b) after deposited and combustion at 550°C, and Figure 3 clearly demonstrates the polycrystalline nature of all deposited Cu/Fe-based films. Intensive peaks observed at 2 theta = 22.46°, 24.59°, 28.2°, 34.5°, 38°, and 46.1° planes for Fe(OH)₃ crystals (JCPDS card number: 38-0032) [17,18] Figure 3(a)–(c) XRD peaks of Cu–Fe were observed at 2 theta = 43.4°, 50.6°, 74.18° and indexed plane of Cu–Fe NPs with (Card pdf.03-065-7002) [19] and 2 theta = 31.2°, 34.6°, 43.4°, planes for CuFeO₂ NPs with (card pdf.75-2146) [19], different phase of CuFeO₂ proving the successful production of this alloy. Also, the intensity its peaks in Figure 3(a) are higher than intensity in Figure 3(b) So these proving that Alloy(I) has high iron percent than Alloy(II) and this confirm the peaks at 2 theta = 31.2, 44.93 and 72.73° are for Fe₂O₃, Cu, Cu–Zn [20–22] and peak at 50.52° is estimated for CuO, CuFe [19,21]. Figure 3(c) shows that XRD data of alloy oxide prove that the material contained component of CuFe₂O₄, CuO (PDF card No.72-1174) [23], and ZnO was observed at 2θ = 56.8° (JCPDS 36-1451) [24].

Figure 3

The XRD charts for the alloy prepared from (a) Alloy(i), (b) Alloy(ii), and (c) alloy oxide.

EDX spectra are shown in Figure 4(a)–(c) for Cu–Fe alloys: (a) Alloy(i) with 35 mA·cm⁻² for 30 min; (b) Alloy(ii) with 35 mA·cm⁻² for 30 min and (c) Alloy oxide after deposited and combustion at 550°C. The chemical compositions of the examined samples are shown in Table 2. All the spectra show only Fe and Cu and Zn and O signals without any impurity traces from the used chemicals, which indicates the high purity of the deposited Cu/Fe alloys.

Figure 4

EDX spectra for Cu–Fe–Zn–O alloy where (a) Alloy(i), (b) Alloy(ii), and (c) alloy oxide.

The surface morphology of the deposited alloys is studied using an SEM. Figure 5(a) and (b) displays four SEM images for two different Cu/Fe alloys formed on the surface of Cu–Zn foil from distilled water where Figure 5(a) and (b) displays Alloy(i), Figure 5(c) and (d) displays Alloy(ii), and Figure 5(e) and (f) is alloy oxide after heat treatment at 550°C for 20 min. From SEM images, it is evident that the morphology of the alloy can be reformed by governing its chemical composition. SEM images of Alloy(i) in Figure 5(a) and (b) show clear morphological features that suggest the material composition and deposition conditions that formed the surface texture that is shown. The surface morphology of Alloy(i) shows bigger and rougher precipitates than Alloy(ii), as seen in Figure 5(a). The reason for these huge clusters is probably a faster nucleation and development rate of metal phases in Alloy(i), which can happen when the electrolyte solution contains more copper or iron ions or when the applied deposition potential promotes rapid growth. The coarse texture suggests that there is significant agglomeration and less homogeneity in the deposited metal stages. This might be related to the electrochemical conditions that were employed, which might promote less regulated deposition and result in the creation of bigger particles. One intriguing characteristic that points to a notable increase in surface area is the porous structure that resembles coral reefs and is seen in Alloy(i). Alloy(i) is a potential contender for electrochemical processes like the HER because of its porous network, which can promote effective electron transmission. The SEM images in Figure 5(c) and (d) depict Alloy(ii) with a more refined, controlled morphology compared to Alloy(i). Unlike Alloy(i), Alloy(ii) presents a microstructure with thinner, finer precipitates, suggesting a more controlled deposition process. This could indicate a lower nucleation rate, which results in more uniform crystal growth. The fine, fiber-like structures observed in Alloy(ii) may provide a more uniform distribution of metal phases, potentially resulting in different electrochemical behavior compared to Alloy(i). The thinner structure also suggests that the Cu–Fe deposition is more homogeneous. The lower surface roughness in Alloy(ii) as compared to Alloy(i) could limit its surface area and, consequently, its catalytic activity. However, it may be advantageous in applications requiring a stable and smooth surface, such as certain types of optoelectronic or electronic devices. SEM pictures of the oxidized alloy following heat treatment are displayed in Figure 5(e) and (f), demonstrating significant morphological changes. The Cu–Fe alloy’s surface is covered in nano-structured oxides, mostly CuO and FeO₃, as a result of the heat treatment at 550°C. Well-defined oxide phases are promoted by the high-temperature oxidation process and show up in the pictures as distinct, spherical particles and plate-like structures. CuO and FeO₃ in particular are well known for their photocatalytic qualities. Also, SEM images of Figure 5(e) and (f) showed NPs for CuFe₂O₄ [25]. Applications requiring light absorption and photocatalysis, such as solar cells or photocatalytic water splitting, benefit from the material’s increased surface area due to its nanoscale structure. The high nanostructure and porosity seen in Figures 4(f) and 5(e) provide a significant increase in surface area. For optoelectronic and photoelectrochemical applications [26,27], this structural characteristic can improve the material’s capacity for light absorption and electron transport. Because the porous surface of such structures may host a variety of reactions and permit reactants to access the active sites, they are perfect for catalysis and energy applications. Applications where more surface area and effective light trapping are crucial, such as hydrogen evolution, oxygen evolution, and photocatalysis, may benefit greatly from the porous oxide structure found in alloy oxide (Figures 4(f) and 5(e)). Furthermore, because of their high surface area and electron transport capabilities, the CuO and FeO phases may make these materials good options for supercapacitors, batteries, or other energy storage devices. Additionally, the cross-section of Alloy(i) and Alloy(ii) was analyzed using the theoretical Gwydion program, as depicted in Figure 5(a) and (b), respectively. The analysis reveals that Alloy(i) exhibits a significantly more pronounced porous structure compared to Alloy(ii). This enhanced porosity indicates a larger surface area for Alloy(i), which plays a critical role in light trapping. Such a feature makes Alloy(i) particularly advantageous for optical applications. The porous nature of these alloys contributes to their potential to improve the efficiency of light interaction with the material, which is essential for various optoelectronic and photonic devices. By providing a greater surface area, Alloy(i) demonstrates a superior capacity for harnessing and manipulating light, paving the way for its use in advanced optical systems. In contrast, Alloy(ii), with a comparatively lower porosity, may be less effective in these applications. This distinction highlights the importance of structural properties in determining the suitability of materials for specific technological applications, particularly those requiring efficient light absorption and trapping. The findings underscore the relevance of theoretical modeling, such as the Gwydion program, in understanding and optimizing the performance of materials for high-tech applications [28].

Figure 5

SEM images of Cu–Fe–Zn–O alloys where (a) and (b) for Alloy(i), (c) and (d) for Alloy(ii), and (e) and (f) alloy oxide. While (g) and (h) are the cross-section morphology of Alloy(i) and (ii), respectively.

3.2.1 XPS

The survey XPS spectrum (Figure 6(a)) clearly showed the presence of the Cu, Fe, Zn, and O elements in alloy at room temperature, which was consistent with the above elemental mapping results. Figure 6(f) clearly shows that the peaks centered at 1022.32 and 1045.40 eV can be attributed to Zn 2p_3/2 and Zn 2p_1/2 species. Figure 6(e) clearly shows that the peak observed at about 932.74 and 952.48 eV relates to metallic Cu 2p_3/2, Cu 2p_1/2 in the alloy [29]. The peaks sited at 712.5 eV in the Fe 2p spectra can be assigned to Fe³⁺ and peaks clearly shown in Figure 6(d) [29]. Also, Figure 6(c) displays peaks for CuLM2. From Figure 6(b), the high-resolution XPS spectra of O_1s were observed at 531.7, 532.45, and 533.3 eV. After fitting with Gaussian–Lorentzian functions, three peaks are discovered in the spectrum; one of them is O_1s peaks at 531.7, corresponding to O_1s in Fe₂O₃ and absorbed oxygen species [29]. The peaks located at 532.45 and 533.3 eV were related to the oxidized state of Fe(iii) [29], respectively. In addition, it is determined that the peak at 532.45 eV reflects H₂O absorbed in the Fe₂O₃ nano-boxes and this matched with M. C. Biesinger’s paper [29]. All the features prove that the sample contains Fe, Cu, and Zn.

Figure 6

XPS spectrum of the as-prepared Alloy(i): (a) survey spectrum of Fe–Cu–Zn–O, (b) binding energy spectrum of O (1S, IS_A,B), (c) binding energy spectrum of CuLM2, (d) binding energy spectrum of Fe 2P, (e) binding energy spectrum of Cu 2P_3/2,1/2, and (f) binding energy spectrum of Zn 2P_3/2,1/2.

Figure 7(a) shown that the XPS spectra complexes (CuFe₂O₄, CuO, Cu, Fe and Zn): XPS spectra of Cu 2p_3/2, Fe 2p_3/2 and Zn 2p_3/2 could be fitted well with two synthetic curves, indicating that each of Cu ion, Fe ion and Zn ion has 2 possible valences someone might distinguish between materials having the same parent components on the behalf of various oxidation states of existed constituent elements. For example, the presence of Cu²⁺ in CuFe₂O₄ and the presence of Cu⁺ in Cu₂O–CuFe₂O₄ materials could be proven on behalf of different binding energies of Cu²⁺ and Cu⁺, respectively [23,30,31,32]. From Figure 7(b), four peaks are discovered in the spectrum; O_1s, O_1S A, O_1S B, and O_1S C peaks are identical in both XPS spectra and are located at approximately 529.80, 529.89, 531.13, and 531.85 eV, respectively. Also, Figure 7(c) displays peaks for CuLM2, while Figure 7(d) shows the peaks at the binding energies of 712.01 and 715.44 eV in care assigned, respectively, to Fe²⁺ and Fe³⁺ [33]. As seen in Figure 7(e), the detailed XPS spectra of Cu 2p reveal that strong Cu²⁺ satellites might be noticed at a binding energy of 942.5 and 962.5 eV along with a peak at 934.3 eV, which demonstrated that Cu²⁺ is present in CuFe₂O₄ [31,32]. In addition, on the basis of the comparative peak at 932.1 eV, there were Cu⁺ species on the surface of CuFe₂O₄, which could come from the reduction of Cu²⁺ throughout the calcination process. The peak for Cu₂O–CuFe₂O₄ in Figure 7(d) was strong and could be assigned to Cu₂O. Similar results were observed for Cu/Cu₂O/CuO@C catalyst particles [34]. In addition, peak at 934.3 eV and satellite peaks at 942.5 and 962.5 eV prove the formation of Cu²⁺ along with CuFe₂O₄ particles for as-prepared Cu₂O–CuFe₂O₄ NPs [30,33,34]. Figure 7(f) shows that the XPS spectrum of Zn 2p_1/2 reveals the binding energies of Zn 2p_3/2 at about 1,022.31 eV and Zn 2p_1/2 centered at 1,045.34 ev [35], without any noticeable shift after the high-Cu doping.

Figure 7

XPS spectrum of the as-prepared alloy oxide: (a) survey spectrum of Fe–Cu–Zn–O, (b) binding energy spectrum of O (1S,IS_A,B,c), (c) binding energy spectrum of CuLM2, (d) binding energy spectrum of Fe 2P, (e) binding energy spectrum of Cu 2P_3/2,1/2, and (f) binding energy spectrum of Zn 2P_3/2,1/2.

3.3 Open circuit potential (OCP) measurements

Figure 8 shows that the information provided, the study measured the OCPs of deposited Alloy(i), Alloy(ii), and brass foil in a 1 mol·L⁻¹ NaOH solution over 400 s. It was observed that Alloy(ii), Alloy(i), and brass foil initially showed an increase in OCPs in the first few seconds before reaching a steady state. The OCPs became more positive over time, indicating a natural affinity for passivation. However, an increase in the percent of iron in the alloys resulted in a reduction in the steady-state OCP. In summary, the study indicates that the different alloys have varying OCP behaviors in a NaOH solution. The measurements of OCP suggest that the HER on Alloy(i) will occur at lower potentials than other alloys.

Figure 8

Variation of the open-circuit potential with time for the substrate of Alloy(i), Alloy(ii), and brass foil immersed in stagnant aerated (0.5 mol·L⁻¹) NaOH solution at 25°C.

3.4 Electrocatalytic activities

The study investigated the electrocatalytic activity of Cu–Fe–Zn–O cathodes for HERs using electrochemical polarization (ECP) measurements and EC impedance spectroscopies (EISs) in 1 mol·L⁻¹ NaOH solution. The HERs in alkaline liquids take place through three reactions [33,34]. (i) The Volmer reaction is a process in electrochemistry where a water molecule is reduced and hydrogen is adsorbed onto the surface of an electrode. This reaction can be expressed as follows: H₂O + e⁻ > H* + OH⁻ where H* represents an adsorbed hydrogen atom on the electrode surface and OH⁻ represents a hydroxide ion in the electrolyte solution. This reaction is typically the first step in the electrochemical reduction of water to produce hydrogen gas. (ii) The Heyrovsky reaction is a chemical process that involves the desorption of a hydrogen atom from a surface, the formation of hydrogen gas (H₂), and the concurrent reduction of a water molecule. The reaction can be represented by the equation: MH_(ad) + H₂O + e⁻ ↔ M + HO⁻ + H₂. In this equation, MH_(ad) represents a metal hydride adsorbed on the surface. The reaction involves the transfer of an electron (e⁻) from the surface to the water molecule, which results in the reduction of the water molecule to form hydroxide ions (HO⁻) and hydrogen gas (H₂). At the same time, a hydrogen atom is desorbed from the metal hydride, which completes the reaction. Overall, the Heyrovsky reaction is an important process in electrochemistry and catalysis, and it has been widely studied for its potential applications in energy storage and conversion technologies. (iii) The Tafel reaction involves combining two adsorbed hydrogen atoms to form a hydrogen molecule, which is crucial in the mechanisms and kinetics of HERs. The strength of the interaction between the metal (M) and both H₂O and adsorbed hydrogen (H _ads) is important in determining the rates of HERs. While a strong M–H₂O interaction is favorable for water splitting, it can hinder hydrogen desorption. Therefore, a cathode model must balance the formation and dissociation of M–H _ads bonds to achieve high HER rates [12]. The electrocatalytic activity for HERs was evaluated using Cu–Fe–Zn–O cathodes with varying Cu–Fe percentages in a 1 M NaOH solution. The potential measured in the experiment was calibrated with respect to the NHE using the Nernst equation, and the HER was recorded in a pH 13.69 solution. Based on the data presented in Figure 9, the activity of the 80Cu–2Fe–16Zn–2O alloy for HER is higher compared to the 60Cu–0.25Fe–36.75Zn–2O and 77Cu–33Fe alloys. The rate of HER is directly proportional to the cathodic current density, and the best alloy for high hydrogen production is Alloy(i), which can generate a current density of 708 mA Cm⁻² at a potential of 2.04 V. The higher activity of Alloy(i) may be attributed to its nanoporous structure, which has a higher surface area to volume ratio. The synergistic combination of Cu, Fe, Zn, and O in Alloy(i) is also a significant factor in increasing its HER activity. The increase in iron content in the alloy may contribute to the high hydrogen evolution rate due to the structural and morphological properties of the alloy, such as the presence of spherical and granular structures on the surface that produce a rough, high surface area-to-volume ratio.

Figure 9

(a) Cathodic polarization for electrodeposited nano-Alloy(i), Alloy(ii), and brass foil immersed in stagnant aerated (1 mol·L⁻¹) NaOH solution at 25°C, NHE (normal/standard hydrogen electrode), and (b) relation between time (s) and current density (mA·cm⁻²) to study the stability of Alloy(i).

The current density of the Cu–Fe Alloy(i) electrode during the HER is shown in Figure 9b for a maximum duration of 2,000 s. Strong electrochemical stability is indicated by the measurements, which show a constant and stable current density with little variability. This stability implies that the Cu–Fe Alloy(i) electrode maintains its functionality by successfully fending off deterioration in the alkaline environment. Because of this characteristic, it is a great choice for long-term HER applications, where stability throughout prolonged operation is essential for dependable hydrogen production. Table 3 presents the estimated current entities for various electrodes at different potential values. The findings from Figure 9 and Table 3 indicate that as the Fe% increases, there is an increase in current density and, consequently, the rate of hydrogen production. Moreover, the application of a higher potential also leads to an increase in the hydrogen production rate, as stated in Shaban et al. [12].

3.5 EISs

The ECP measurements were verified using EIS measurements. EIS measurements were conducted using a combination of galvanostat/potentiostat frequency analyzer and Autolab 10 potentiostat (Radiometer PGZ100) with software 4. Figure 10 illustrates the EIS spectra (Nyquist plots) for the electroplated Alloy(i), Alloy(ii), and brass foil at hydrogen evolution potentials. The Nyquist plots showed slightly depressed capacitive semicircle shapes with varying radii for the investigated cathodic electrodes. The sample with a smaller radius had a higher hydrogen evolution capacity than the sample with a larger radius, as reported in Rabia et al. [36] and [37]. Therefore, Alloy(i) exhibited a greater HER capacity than the other samples [36], with R _S and R _CT of 0.2 and 25Ω, respectively; this indicates the great behavior of this alloy for the splitting reaction and then the provision of the H₂ gas.

Figure 10

Nyquist plots for the prepared alloys at the hydrogen evolution potential in 1 mol·L⁻¹ NaOH stagnant naturally aerated aqueous liquid at 25°C.

Water splitting in this system is classified as a first-order reaction, with its kinetics analyzed based on the generated current density. The current density serves as an indicator of the reaction rate for hydrogen (H₂) production. A higher current density corresponds to an accelerated reaction rate and, consequently, increased hydrogen generation [38,39]. The Alloy(i) demonstrates a significantly higher current density, indicating a faster reaction rate. This enhanced performance can be attributed to Alloy(i)’s superior structural and electronic properties, which promote efficient charge transfer and improved catalytic activity. As a result, the amount of hydrogen produced by Alloy(i) is promising. The observed differences in reaction kinetics highlight the critical role of material properties in determining the efficiency of water-splitting reactions. Alloy(i)’s ability to sustain a higher reaction rate positions it as a more effective candidate for hydrogen production, making it a promising material for renewable energy applications. This analysis underscores the importance of optimizing alloy composition and surface characteristics to maximize the current density and, ultimately, hydrogen yield in photoelectrochemical systems. Increasing of current density under illumination is attributed to photoexcitation, in which when exposed to light, the alloy oxide absorbs photons, providing sufficient energy to excite electrons from the VB to the CB. This transition generates electron–hole pairs (e⁻–h⁺), which are crucial for the alloy oxide’s function as a photoelectrode. The alloy oxide comprises two primary phases, CuFeO₂ and CuFe₂O₄, both recognized for their effective visible light absorption. CuFeO₂, with an optimal bandgap of approximately 1.5 eV, is particularly efficient at capturing visible light. Meanwhile, CuFe₂O₄, with a slightly larger bandgap, enhances the process by enabling additional pathways for charge generation and separation, essential for photocatalytic and photoelectrochemical reactions. Together, these phases facilitate electron transfer to CuFeO₂ and subsequently to the Cu–Fe alloy, driving the reduction of H₂O molecules to produce hydrogen (H₂). The generated OH radicals further aid water splitting, boosting overall efficiency. Moreover, the surface morphology, characterized by rough and agglomerated structures as observed in SEM images, increases the surface area available for photon absorption and provides numerous active sites. This unique structure also promotes the effective separation of electron–hole pairs, significantly enhancing the material’s photocatalytic performance.

3.6 Electrical study of the optoelectronic device

The photodetection capabilities of the Cu–Fe–Zn–O burning NPs alloy material were tested under a solar simulator with a power density of 400 mW·cm⁻². The J _ph values measured under dark and light conditions were 2.54 and 33 mA·cm⁻², respectively. The significant increase in J _ph under light indicates that the Cu–Fe–Zn–O NPs alloy is an efficient photodetector. Additionally, the response of the alloy oxide NP alloy to applied potential increases under light due to the generation of electron–hole pairs in the photocatalytic nanoporous material, as reported in references [40–42].

The relationship between light power intensity and the generated J _ph value is semi-linear within the range of −0.36 to 0.31 V (as shown in Figure 11). This relationship is attributed to the excitation reaction of the electron–hole pair complex, as stated in reference [43]. The good fitting value indicates that the photodetector has high sensitivity to light, according to Wang et al. [43]. The reason for the increase in Jph with increasing light intensity is due to the effect of more photons on the thin film of alloy oxide NPs, leading to the generation of more charged electrons in the CB. The photoresponsivity (R) of the system was determined to be 500 mA·W⁻¹ [44], calculated based on the current density and incident light intensity. This value highlights the photodetector’s impressive performance compared to other oxide-based systems, such as ZnO/Cu₂O and β-Ga₂O₃/GaN, as well as polymer-based materials like P3HT-ZnO, which typically report R values ranging from 1 to 10 mA·W⁻¹ [13–15,45].

Figure 11

Optoelectronic properties of the Cu–Fe alloy annealed at 550°C in (0.2 mol·L⁻¹) Na₂SO₄ as a photodetectors for J _ph−V curves.