The present analysis aims to use existing resources to lower the cost of electrodes and reduce environmental pollution by utilizing waste materials like green algae. In the present research, the hydrothermal carbonization technique was utilized to synthesize a nano sized CuO mixed with activated biochar (CuO@BC) extracted from red sea algae (Chlorophyta). The CuO@BC sample was extensively examined using several advanced physical techniques, such as UV/Visible spectroscopy, FTIR, XED, HRTEM, SEM, EDX, BET, and TGA. The HRTEM indicated that the size of the particles is 32 nm with a larger surface area and without aggregations. The BET analysis of CuO@BC indicates that the material contains pores of a relatively large size and with a pore diameter of about 42.56 A°. The electrochemical analysis of CuO@BC modified glassy carbon electrode CuO@BC/GCE has been investigated using CV, GCD, and EIS techniques. This CuO@BC/GCE shows excellent electrochemical features that are significant for enegy storage applications. The CuO@BC/GCE showed a specific capacitance of approximately 353 Fg−1 which is higher compared to individual materials. Overall, the research outcomes suggest that the CuO@BC/GCE shows potential for use in high-performance supercapacitors as energy storage systems that are eco-friendly and sustainable.
Introduction
Supercapacitors are high-performance energy storage devices due to their long lifetime, short charging times, exceptional safety features, and high power densities1. As a result, there is a greater public interest in energy conversion and storage materials2. Supercapacitors can be categorized into two groups depending on their energy storage mechanism: pseudo capacitors and electrical double-layer capacitors (EDLCs)3. The electrode materials that are sources of carbon are preferred in most supercapacitors which include carbon fiber cloth, activated carbon (AC), carbon nanotube (CNTs), carbon aerogel, and graphene4.
Activated carbon is a carbon matrial that has received attention because of its low cost, abundant source, easy accessibility, and excellent electrochemical properties5. Its stable structure, high carbon content, sizable specific surface area, and high degree of microporosity have made it famous6,7,8. Many natural waste materials such as rice husks, bamboo, corncobs, algae, pinecones, lotus stems, fruit peels, banana peels, and potato peels are transformed into biochar, which provides a large surface area and an abundance of electroactive sites for redox reactions and charge accumulation. Doping heteroatoms add significant properties to the carbon, enabling additional pseudo-capacitance from redox reactions depending on the heteroatoms’ functional group9. Biochar plays an important role in energy storage, electrocatalytic properties, and supercapacitor applications. Due to its porous nature, biochar has gained significant attention in the field of energy applications. The incorporation of metal oxides further enhance its energy storage capabilities10. The distinguishing characteristics of CuO-doped activated biochar include its increased surface area, porosity, and modified surface chemistry due to the incorporation of CuO. Furthermore, CuO acts as a catalyst, promoting chemical reactions that can degrade or transform hazardous compounds, such as organic pollutants or dyes. Finally, the presence of CuO could enhance the biochar’s ability to facilitate these reactions, resulting in more efficient pollutant removal or remediation.
The green algae serve as a source of ecosystem services and biomass for various purposes such as food, nutraceuticals, soil additives, animal feed, and phycocolloids11. To utilize biomass waste and meet energy storage demands, converting such waste into biochar is an effective solution. Research has shown that biochar can act as an effective adsorption material due to its high surface-to-volume ratios, wide availability, sustainability12, and flaw sites. Biochars with hig porosity can be obtained through physical/thermal and chemical activation (such as potassium hydroxide (KOH) and phosphoric acid (H3PO4)). Algae are a developing and sustainable source of biomass, with appreciable photosynthetic efficiency and less competition with food crops due to their requirement for a small land area. They are also known to detoxify the environment in food, agricultural feed, and other co-products13. The chemical structure of the amides produced from red sea algae is introduced in Fig. 1.
Figure 1
figure 1
The chemical structure of the amide produced from Chlorophyta.
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The Metal oxides and activated BC combination holds great potential for improving the performance and efficiency of supercapacitors, which are widely used for energy storage applications. Adding CuO to the electrode material enhances its capacitance, enabling higher energy and power densities. The biochar further contributes to this novel approach by providing a porous structure tht facilitates ion movement and better electrochemical reactions. The synergistic effect of CuO and activated biochar creates an electrode with enhanced charge storage capacity and improved stability. By utilizing these materials, researchers strive to tackle the challenges associated with traditional supercapacitors, such as limited energy density and rapid self-discharge. This inventive collaboration between CuO@BC covers the way for enhanced supercapacitor technology, bringing us one step closer to efficient energy storage solutions for a sustainable future. Rai et al. investigated the electrochemical performance of pure CuO as an electrode material for energy storage14. They used cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) techniques to evaluate its performance. The results showed that CuO exhibited a capacity retention of 392.1 mAhg−1 which indicates its potential for energy storage applications. Dang et al. fabricated CuO nanoparticles with a unique hierarchicl structure and evaluated their electrochemical properties15. The modified CuO nanosheets and nanorods demonstrated a significant improvement in specific capacity, achieving 600 mAhg−1. Furthermore, the modified CuO electrode exhibited excellent stability with minimal capacity fading during cycling.
To have an efficient energy storage electrode with a sustainable material, CuO NPs incorporated red sea algae (Chlorophyta) was successfully transformed into activated carbon using a hydrothermal method. The crystalline and morphological properties of CuO@BC composite have been done using various techniques such as UV/Visible, FT-IR, XRD, SEM, EDX, TGA, HRTEM, and BET. Then, the composite has been investigated as a potential electrode material for supercapacitor application. Figure 2 shows the experimental protocol of our thesis. Overall, incorporating biochar from algae with CuO in supercapacitors is a promising approach to creating environmentally friendly, cost-effective, and efficient nergy storage devices with high performance.
Figure 2
figure 2
The experimental procedure of electrochemical measurements of CuO/BC.
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Materials and methods
Preparation of activated carbon from Red Sea Algae biochar (BC)
The red sea algae were collected from the NEOM coast of Saudi Arabia. Chemicals such as copper sulfate (CuSo4 98%), Ammonium hydroxide NH4OH (40%), sulfuric acid (H2SO4 98%), potassium hydroxide (KOH 85%), N-methyl pyrrolidine (NMP), and dimethylformamide (DMF) were purchased from Sigma-Aldrich. The algae were washed with distilled water and dried at room temperature. Once dry, the algae were ground into a fine powder. The powder was pyrolyzed in a tube furnace for 4 h to prepare biochar. The flow rate of nitrogen gas was set to 50 mL per minute and the temperature of the furnace was maintained at 400 °C16. The first step involved adding 10 g of green algae powder to 100 mL of 5 M KOH in a reflux setup. The mixture was refluxed for 5 h at a temperature f 80 °C and with a stirring speed of 150 rpm. The second step required drying the residue from the first step and pyrolyzing it in the tube furnace under a nitrogen gas flow (700 °C, 4 h). Finally, the carbon material (BC) was washed with a solution mixture of Nitric acid (HNO3) and Sulfuric acid (H2SO4) (3:1). The material was then left to dry overnight at 60 °C to reduce impurities from the red algae powder.
Preparation of Cu-modified biochar composite
The hydrothermal method was used to synthesize a Cu-modified biochar composite17. Prior to synthesis, 1 g of BC materials was added to 20 mL of Milli-Q water and the pH value was adjusted at 11 through CuSO4 and NH4OH. 4.75 g of biochar is mixed with 0.25 g of CuO so that the biochar: metal has a ratio of 100:5. The solution was then heated to 120 °C in a 33 mL Teflon-lined autoclave for 12 h. Centrifugation was carried out at 7000 rpm for 20 min, and the substance was purified using a 1:1 ethanol-Milli-Q water mixture at least three imes. The final substance was then filtered and vacuum-dried at low temperatures.
Preparation of CuO@BC NPs modified GCE
To investigate the electrochemical properties of CuO@BC composite, a glassy carbon electrode (GCE) was used. The GCE was cleaned by polishing it with alumina slurry, rinsing it with deionized water, and drying it with nitrogen gas. The GC electrode was de-coated with CuO@BC in the colloidal NPs solution at room temperature for the 2 h absorption time. A typical electrochemical system (CS-300 &150) was utilized to examine electrochemical measurements. The three-electrode system consisted of a counter electrode made of platinum (Pt), a working electrode modified with glassy carbon (GC), and a saturated calomel electrode (SCE) serving as a reference. The CV analysis of the GC electrode was studied in the presence of a potassium hydroxide (KOH 6 M) solution as the electrolyte, with a potential range of − 0.4 to 1.4 V and a scan rate of 50 mVs−1 at room temperature. The dvantage of using alkali KOH electrolytes, compared to other organic electrolytes, is due to their higher concentration of ions and lower resistance for facilitating faster electrode kinetics. The CuO@BC/GCE was placed at room temperature to dry or placed in an oven for a specific amount of time to evaporate the solvent and ensure the adhesion of the nanocomposite to the surface of the electrode. To perform the electrochemical impedance spectroscopy (EIS) test, an amplitude of 5 mV and a frequency range of 0–2000 Hz were used.
Results and discussion
UV–visible spectroscopy
UV/vis spectrophotometer was used to identify the wavelength of CuO@BC NPs as shown in Fig. 3. The plasmonic peak of the CuO was observed at 426 nm. UV/Vis spectroscopy excites valence electrons from HOMO to LUMO, which then shifts from a lower energy level to an energy level at a higher state (n–σ*, σ–σ*, n–π* and π–π*); this is determined by the ultraviolet spectroscopy & absorption helps to measure the gap in theenergy created during this shift. The color change observed during exposure to plant extract indicates the reduction of Cu+2 into Cu0 nanoparticles. The reason behind this color change was the occurrence of Surface Plasmon resonance (SPR). Free electrons in metal nanoparticles give SPR absorption band at 426 nm. The SPR in the metal nanoparticles was excited, which caused the shading variations. The CuO@BC nanoparticles, which underwent photosynthesis, were periodically monitored using the scanning method during analysis of the sub-sample in the PerkinElmer Lambda 25 spectrometer, equipped with a UV–visible spectrometer. Typically, the conducting electron oscillates at specific wavelength ranges because of the SPR peak shown in Fig. 3A,B. The bioactive compounds and hydroxyl affect the particle size and shape of the CuO@BC synthesis and cause Cu reduction leading to metallic ions reduction18.
Figure 3
figure 3
(A) UV–visible spectra of CuO@BC (B) effect of plant extract at the synthess of CuO@BC.
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FT-IR analysis
The Fourier Transform Infrared Spectroscopy (FTIR) spectrum is helpful in evaluating the vibrations of atoms, the structure of compounds, and the identification of functional groups19. Figure 4 shows the FTIR spectra in the wavenumber region 4000–400 cm−1 for BC and CuO@BC NPs. The peak at 3380 cm−1 confirms the alcoholic or phenolic character of the plant extract, indicating the stretching vibration of O–H bonds. The peak between 2739 and 2379 cm−1 is due to C–H stretching vibration. The peak at 1760 cm−1 is associated with the expanding vibration of keto and carboxylic groups’ C=O. The peak at 1596 cm−1 corresponds to the bending motion of the –C–O–H bond and the extension of the C–C bond. The peaks at 1316 and 1030 cm−1 indicate the bending vibrations of –C–H and –C–O–C. The peaks at 806 and 717 cm−1 confirm the production of H–CO and H–C=C. The reduction in peak intensities, suggests that the activated biochar affects the stability of naomaterials.
Figure 4
figure 4
FT-IR (A) Biochar (B) CuO@BC NPs.
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XRD analysis
The X-ray diffraction (XRD) technique is broadly used to examine the structural properties of particles; hence it helped define the crystalline structure of CuO@BC NPs, as shown in Fig. 5. X-ray diffraction analysis at 30–70° values confirmed that CuO@BC NPs were crystalline. To determine the value of the various Bragg reflection numbers at two thetas whose values are 36°, 39°, 59°, 62°, and 96°, correspond to 002, 111, 202, 113, and 311 set the location in lattice planes, respectively. The spectrum peak intensity for the 002 plane in the lattice structures suggests that CuO@BC has experienced greater expansion compared to the other patterns20. If the remaining peaks are not assigned and if biogenic materials are covering the surface of the CuO@BC, the XRD pattern indicates that the CuO@BC NPs are highly pure. By applying the Debye–Scherrer Eq. (1) and assuming that the average particle size as 32 nm which was corroborated by the method of measuring the particle size from the HRTEM picture and by using the equation21.
(1)
where D stands for the particle size, β is expressed as the full-width half maximum in radian and θ is the Bragg angle.
Figure 5
figure 5
XRD of (A) BC (B) CuO@BC NPs.
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SEM analysis
The surface activity of particles of the materials was usually studied by scanning electron microscopy (SEM) analysis22. This analytical method exposes the surface shape and particle size of the biogenic CuO@BC NPs. The SEM micrograph of BC is shown in Fig. 6A. As seen from the SEM images, BC has sheet-like structures appearing as stacked layers. Biochar structure could be helpful in improving the electrochemical properties that are accompanied by the increase in the surface area and porosity, which in turn provides a higher number of active sites for molecular interactions and charge transport. Furthermore, the stacked layers can create a unique and interconected network for efficient charge transfer and ion mobility. Figure 6B shows the SEM image of CuO@BC NPs, the surface structure of CuO@BC NPs contains a combination of small and round particles related to CuO NP and loaded sheets. The surface morphology shaped a porosity in the material under investigation which can contribute to an increase in the material capacitance23.
Figure 6