چكيده به لاتين
The growing trend of energy use from fossil fuel sources and the gradual depletion of these sources have raised concerns about the future energy supply. Therefore, the need to use clean and renewable sources such as hydrogen has increased. The synthesis and development of effective electrocatalysts for the production of hydrogen as a clean fuel is very important. In the present study, two types of electrocatalysts were investigated: one based on noble metals, palladium magnetic lignosulfonate (Pd@Fe3O4-lignosulfonate) synthesized through a green method, and the other based on non-noble metals (NiMnLDH-MXene) synthesized through a simple chemical method (co-precipitation). These catalysts were used to improve the water splitting process by increasing the current density, reducing the Tafel slope, and lowering the overpotential.
In the first study, palladium nanoparticles supported on magnetic lignosulfonate were synthesized using Hibiscus rosasinensis L. leaf extract as a reducing/stabilizing agent and used as an efficient electrocatalyst for hydrogen production. The electrochemical production of hydrogen gas was performed using several techniques, including linear sweep voltammetry (LSV), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), electrochemical surface area (ECSA), and chronopotentiometry (CP). The catalyst was introduced in different weight percentages (1.5%, 2.5%, 5%, 10%, and 15%) in the carbon paste electrode (CPE) structure. Its hydrogen production efficiency was evaluated under different pH conditions (0.5 M H2SO4, 1 M NaOH, and PBS). Pd nanoparticles embedded in the magnetic lignosulfonate nanocomposite showed significantly higher hydrogen production efficiency compared to unmodified carbon paste electrodes. Electrochemical experiments showed that the Pd@Fe3O4-lignosulfonate/CPE electrocatalyst, with 10% by weight, exhibited excellent performance in the optimal acidic medium (0.5 M H2SO4) for efficient hydrogen evolution reaction (HER). Specifically, the 10% electrode had an overpotential of -239 mV versus RHE at a current density of 10 mA.cm⁻² and a Tafel slope of 62 mV.dec⁻¹. Additionally, contact angle measurements were used to analyze the electrode surfaces. Given the minimal amount of Pd nanoparticles deposited on the magnetic lignosulfonate and their remarkable hydrogen production efficiency, this catalyst can serve as a suitable cathode for electrochemical hydrogen production without relying on platinum.
In the second study, for the first time, MXene terminated with OH functional groups (Ti₃C₂ (OH) ₂) was combined with a group of two-dimensional semiconductors (NiMnLDH) to improve electrocatalysis performance and investigate the hydrogen production process. In this study, MXene was directly prepared using the HF etching method. For further exfoliation of MXene and the placement of OH functional groups on its surface, dimethyl sulfoxide (DMSO) solvent and KOH10% were used, respectively. To prepare the NiMnLDH-MXene core-shell structure, a simple co-precipitation method was employed without the need for high temperature and long synthesis times. LDH-MXene composites with different ratios (1:1, 2:1, 3:1, 4:1, and 5:1) were synthesized, and their electrocatalytic performance was investigated in 1 M NaOH electrolyte. The electrochemical production of hydrogen gas was carried out using several techniques, including LSV, CV, EIS, ECSA, and CP. The results showed that the LDH-MXene composite had better electrocatalytic performance compared to LDH and MXene. Electrochemical tests demonstrated that the NiMnLDH-MXene electrocatalyst, with a ratio of 5:1, exhibited the lowest overpotential at a current density of 100 mA·cm⁻² (0.710 Vvs. RHE) and 10 mA·cm⁻² (0.460 Vvs. RHE) and a Tafel slope of 220 mV.dec⁻¹. This good performance in alkaline medium (1 M NaOH) for HER is due to the balance between the number of active sites and electron conductivity through the introduction of appropriate amounts of LDH and MXene, which can fully utilize the synergistic effects.
