Hydrothermal Synthesis Research Articles

Enhanced Hydrogen Evolution Reaction Activity through Bimetallic Phosphide Integration in ReS2/Re2O7 Heterostructure

AbstractDeveloping a nonprecious and sustainable electrocatalyst in clean energy generation is quite noteworthy. Transition metal chalcogenides, oxides, and phosphides have emerged as promising candidates to substitute Pt‐based catalysts. In this study, we explore the catalytic potential of ReS2, a promising member of the transition metal dichalcogenides (TMD) family, for hydrogen evolution reactions (HER). The formation of rhenium oxide during the synthesis of ReS2 and further incorporation of a bimetallic phosphide NiCuP in a sequential hydrothermal synthesis reveals an excellent HER activity, as demonstrated by photoelectrochemical and electrochemical studies. Notably, the catalyst exhibits a significantly lower overpotential of −0.10 V (corresponding to −10 mA/cm2) and achieves a high current density of approx. −271 mA/cm2 at −0.79 V versus reversible hydrogen electrode (RHE) under light irradiation. The catalyst demonstrates high stability. These findings underscore the potential of NiCuP‐integrated ReS2/Re2O7 as a highly efficient and sustainable catalyst for HER.

Synthesis and Characterization of LaMnO3 Prepared by Hydrothermal Synthesis Method

Abstract LaMnO3 powders were prepared by hydrothermal synthesis method by varying citric acid to metal ions. The ratio of citric acid to metal ions is one of the parameters that have an affect on purity of LaMnO3 prepared by hydrothermal method. It is necessary to control the parameter to obtain the good quality of the final product of LaMnO3. LaMnO3 with variation molar ratio of citric acid to metal ion (CA/M) of 0, 1 and 4 were prepared. To determine the morphology, crystall structure, and phase composition, the powders were characterized by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and X-Ray Diffraction (XRD) techniques. The obtained results revealed that the morphology of sample CA/M = 0 has rod-like shape, CA/M = 1 was in the formed of irregular fine particles that stuck together and formed agglomerates, while the spherical morphology with various diameters were formed in the sample CA/M = 4. The XRD analysis demonstrated that sample CA/M = 1 had a single phase while in sample CA/M = 0 and CA/M = 4 others phase were detected such as La (OH)3 and La2O3. There was a change in crystall structure of the LaMnO3 phase in each sample due to the presence of citric acid. The peaks position in sample CA/M = 0, 1, dan 4 exhibit orthorhombic, rhombohendral and cubic structure with space group of Pnma, R -3c and Pm-3m respectively.

Plant-synthesis of co-doped tin dioxide nanocomposite with magnetic activity and its photocatalytic performance assessment on dyes and pesticides

The hydrothermal method was used to introduce different amounts of Praseodymium ion (Pr3+) (1, 3, 5, 7, 9, and 11 at.%) and Yttrium ion (Y3+) (1, 3, 5, 7, 9, and 11 at.%) into existing SnO2 nanoparticles. A novel nanocomposite was created by combining Fe3O4 and SnO2:Pr3+,Y3+ nanoparticles, resulting in a material with magnetic properties, i.e., Fe3O4/SnO2:Pr3+,Y3+, named FPYS. Subsequently, the hydrothermal synthesis approach was utilized to produce nanocomposites of FPYS in the presence of plant extract. The photodecomposition efficiency of as-synthesized nanocomposite was studied with some selected dyes and pesticides under 50W LED light. The present study focused on experimentally optimising the key parameters like the initial concentration, photocatalyst quantity, photocatalyst reuse, and pH level. By employing the Langmuir-Hinshelwood model, we successfully calculated the rate at which RhB, MB, 2,4-DCP, and MB undergo photocatalytic degradation under optimal conditions (pH = 7, pollutant concentration = 8 ppm, volume of pollutants = 20 mL, and photocatalyst amount = 3 mg). The model showed that MB, RhB, 2,4-DCP, and TCAA have k values of 0.061, 0.062, 0.051, and 0.036 min−1, respectively. The breakdown rate for MB dye was 81% and for RhB dye was 78% with nanocomposite made in the presence of 2 mL of Parkia speciosa extract, which was subjected to LED radiation for 150 min at pH 7. The degradation rates of 2,4-DCP and TCAA differed, i.e., the former was degraded by 68% and the latter by 52%. Pr3+ and Y3+ ions co-doped with SnO2 enhanced the photocatalytic degradation of dyes and pesticides.

Hematite Defect Development for Gallic Acid Sensing

AbstractNanostructured iron (III) oxide was prepared by a facile hydrothermal method using poly(triazine imide) (PTI) as a sacrificial template. The physicochemical properties of pristine iron oxide and its analogue obtained in the presence of PTI confirmed strong effect of the latter as the morphology improving agent. Moreover, application of nitrogen rich semiconducting polymer during hydrothermal synthesis increased number of defects. The obtained sample was used as an electroactive additive for carbon‐paste electrode. PTI‐modified sample demonstrated 1.52 times higher oxidation current, and 1.39 lower charge transfer resistance compared to hematite obtained without PTI, as was confirmed by CV and EIS data. Therefore, it was proposed to use the as a sensor for the detection of gallic acid. The developed method showed excellent linearity within a concentration range of 67 nM to 17.7 µM with a detection limit equal to 44 nM and limit of quantification of 132 nM. Stablitity and reproducibility tests, as well as real sample analysis confirmed applicability of the proposed sensor for practical application. Excellent electrochemical properties of the submicron hematite particles are attributed to the developed lattice defects, which served as reaction centers and charge transducing points.

Time-Dependent Hydrothermal Synthesis of La2O3 NPs for Effective Catalytic Activity of Ionic Dye.

Lanthanum oxide was successfully synthesized by hydrothermal method by varying the reaction time such as 6, 12, and 24 h. In XRD, study confirms the presence of a hexagonal structure, and the phase remains the same at different times; the main goal is to assess the average crystallite size of prepared La2O3 nanoparticles, which was found in the range of 6 to 8 nm. An interesting observation from the XRD data was the apparent increase in crystalline nature as the synthesis time was extended. The UV-Vis spectroscopic studies show a change in the band gap when the reaction time is changed. The morphology analysis shows that the image revealed that the particles formed were agglomerated and formed a spherical shape, with diameters ranging between 35 and 86 nm. When tested for photocatalytic activity, the La2O3 nanoparticles show a degradation of methylene blue dye when the time varies. Remarkably, the nanoparticles synthesized exhibited a profound ability to degrade the dye, with an efficiency rate hitting as high as 89% under halogen light illumination.

Microwave-assisted hydrothermal synthesis of αβ-Ni(OH)2 nanoflowers on nickel foam for ultra-stable electrodes of supercapacitors

Transition metal hydroxides (TMHs) are considered promising materials for supercapacitors because of their high theoretical capacitance and tunable morphology. Among TMHs, nickel hydroxide stands out for its multiple oxidation states, facilitating charge storage. This paper reports on a novel microwave-assisted hydrothermal technique employed to synthesize mixed-phase nickel hydroxide nanoflowers directly at the surface of nickel foam substrates with improved electrochemical stability compared to pure phases of nickel hydroxide. The analysis of nickel hydroxide in different phases alpha, beta and mixed-phase materials using physiochemical techniques like XRD, SEM, EDX, RAMAN, FT-IR and TGA is explained. The areal capacitance calculated from GCD tests for α-Ni(OH)2, β-Ni(OH)2 and αβ-Ni(OH)2 is estimated 7.35 F/cm2, 2.66 F/cm2 and 5.12 F/cm2 at a current density of 10 mAcm−2. The mass-specific capacitance calculated from GCD tests for α-Ni(OH)2, β-Ni(OH)2 and αβ-Ni(OH)2 is estimated 2311 Fg−1, 688 Fg−1 and 1511 Fg−1 at a current density of 10 mAcm−2. The cyclic stability test revealed the superior cycling performance of nickel hydroxide in mixed-phase as the cathode of an ultralong supercapacitor with nearly 100% capacitance retention after 5000 cycles at 50 mAcm−2. The proposed synthesis technique advances the efficiency and control of nanostructure geometry, providing insights into the design for electrodes of extreme-performance supercapacitors. However, conventional synthesis methods are time-consuming and energy-intensive. These findings underscore the potential of mixed-phase nickel hydroxide as an outstanding electrode material with extended cyclic performance for supercapacitors, contributing to the improvement of energy storage technologies in the renewable energy landscape.

NiO nanolayer electrodeposited with Cobalt and Phosphide as a novel supercapacitor with high areal capacitance

In the present work, a novel supercapacitor electrode is fabricated via a two-step synthesis procedure. A NiO nanolayer was initially fabricated on a nickel foam electrode using hydrothermal synthesis to obtain a substrate with a high electrocatalytic area and good adhesive properties. Subsequently, the NiO-decorated nickel foam (NF) was employed as a substrate for the electrodeposition of cobalt and phosphorous. Morphological, structural, and surface characterization, along with various electrochemical tests, were conducted to gain insight into structure-property relationships. The as-prepared electrode (CoP@NF) exhibited excellent electrochemical behavior with an ultra-high areal capacitance of 3340 mF cm−2 at 5 mA cm−2 and high capacitance values even at high current densities. The exceptional electrochemical behavior can be attributed to the morphological and electronic modifications induced by aliovalent doping and the synergetic effect between the different electrode counterparts.

Crystal growth of hydrated calcium silicate synthesized from fly ash and lime milk at 100 °C

To maximize the high-value application of fly ash, this study investigates the incorporation of amorphous silica derived from fly ash as a silicon source and lime milk as a calcium source into microporous calcium silicate powders through dynamic hydrothermal synthesis at 100 °C for a duration of 2 h or less. The products were collected at various synthesis intervals and analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), and thermogravimetric differential scanning calorimetry (TG-DSC). Results indicate that microporous calcium silicate forms through a dynamic reaction that disrupts Si-O bonds, enhancing the mobility of silica-oxygen tetrahedra and generating H2SiO42−groups. Ca2+ ions also interact with these bonds, resulting in Q1 and Q2 forms of silica-oxygen tetrahedra. Phase transformation of calcium silicate at various intervals was noted, beginning with 3CaO·2SiO2·3H2O, shifting to 2CaO·3SiO2·2.5H2O, and finally to CaO·2SiO2·2H2O at 90 min. Thus, microporous calcium silicate evolves from an amorphous C-S-H gel into a crystalline form, featuring diverse calcium silicate minerals with calcium-silicon ratios and particle sizes between 10 and 20 μm, with sizes increasing until the 80-min.

Hydrothermal synthesis of Gd-doped CaO nanoparticles from lemon peel extract for efficient photocatalytic degradation of methylene blue under UV and sunlight

Water pollution, exacerbated by the improper disposal of non-biodegradable dyes from textile and paper industries, poses a significant global threat. Addressing this challenge, the present study focuses on the photocatalytic degradation of methylene blue (MB), a harmful azo dye, using novel Gd-doped CaO NPs synthesized with waste lemon peel extract (LPE) as a green stabilizing agent. The CaO NPs, calcined at 700 °C and subsequently doped with gadolinium (Gd) at concentrations of 2, 4, and 6 mmol via hydrothermal method, were characterized using various techniques. Fourier Transform Infrared Spectroscopy (FTIR) confirmed presence of Ca-O and Gd-O with the bond lengths of 1.7 Å and 1.2 Å, respectively. UV–Visible spectra revealed a bandgap in the range of 3.28 to 2.50 eV. X-ray Diffraction (XRD) patterns confirmed crystallinity with the crystallite size estimated using the Scherrer and William sons-Hall (W-H) methods ranging from 18 to 38 nm and XRD deduced specific surface area between 47 and 98 m2/g. Dynamic Light Scattering (DLS) showed particle size distribution from 38 to 130 nm, and zeta potential values ranging from −13.5 to −19.9 mV. The photocatalytic activity against MB was tested under UV light and natural sunlight at dye concentrations of 10, 15, and 20 ppm. The 4 mmol Gd-doped CaO NPs achieved a remarkable 98 % degradation efficiency within 2 h of sunlight exposure at a 10 ppm dye concentration. The degradation followed a pseudo-first-order reaction, and a possible degradation pathway was proposed for methylene blue. This study concludes that Gd-doped CaO NPs are highly effective, sustainable, and cost-efficient photocatalysts for wastewater treatment.

Microwave-assisted hydrothermal synthesis of highly dispersed cerium–zirconium solid solution on Ti3C2Tx nanosheets as an efficient decontamination towards sulfur mustard simulants

The microwave-assisted hydrothermal method has facilitated the straightforward and efficient production of nanoscale CexZr1-xO2/Ti3C2Tx composites. This technique has greatly shortened the synthesis time several hours required by conventional hydrothermal method to merely 10minutes. Due to the unique mechanism of microwave-hydrothermal synthesis, composites with excellent crystallinity, uniform particle size, and superior degradation capabilities can be obtained without calcination. Our investigation systematically explores the influence of various factors including mineralizer concentration, dispersant types, synthesis duration, cerium-to-zirconium ratio, as well as MXene content on the material properties. Optimal degradation of 2-chloroethyl ethyl sulfide, sulfur mustard simulants, is achieved using PEG1000 as the dispersant, a cerium-to-zirconium ratio of 1:2, along with 15mL of MXene, resulting in a remarkably short half-life of only 6.5min. Furthermore, it is confirmed that the incorporation of cerium atoms into ZrO2 lattice, forming a solid solution that is deposited onto the interlayer and surface of Ti3C2Tx nanosheets, with the composite particles measuring approximately 5.01nm. The reduced size and increased specific surface area, coupled with the synergistic effects of oxygen vacancies and acid-base sites, ultimately contribute to the hydrolysis and elimination reactions occurring on 2-CEES. This research offers fresh perspectives on the development of novel materials for the degradation of chemical warfare agents.

Exploring Synthesis Strategies and Interactions between MOFs and Drugs for Controlled Drug Loading and Release, Characterizing Interactions through Advanced Techniques.

This study explores various aspects of Metal-Organic Frameworks (MOFs), focusing on synthesis techniques to adjust pore size and key ligands and metals for crafting carrier MOFs. It investigates MOF-drug interactions, including hydrogen bonding, van der Waals, and electrostatic interactions, along with kinetic studies. The multifaceted applications of MOFs in drug delivery systems are elucidated. The morphology and structure of MOFs are intricately linked to synthesis methodology, impacting attributes like crystallinity, porosity, and surface area. Hydrothermal synthesis yields MOFs with high crystallinity, suitable for catalytic applications, while solvothermal synthesis generates MOFs with increased porosity, ideal for gas and liquid adsorption. Understanding MOF-drug interactions is crucial for optimizing drug delivery, affecting charge capacity, stability, and therapeutic efficacy. Kinetic studies determine drug release rates and uniformity, vital for controlled drug delivery. Overall, comprehending drug-MOF interactions and kinetics is essential for developing effective and controllable drug delivery systems.

High-efficient synthesis of straw-derived carbon quantum dots for facilitating methanogenic performance in high-load co-digestion of food waste and excess sludge

Anaerobic digestion (AD), as a crucial technology for organic waste resource recovery, faces the challenge of low efficiency in converting high-load organic substance into biogas. In this study, high-load AD system with food waste and excess sludge as co-substrates was constructed. The effect and mechanism of carbon quantum dots (CQD) derived from straw in promoting the performance of AD systems have been studied. The oxidation pretreatment of straw with H2O2 and acetic acid increased the yield of hydrothermal synthesis CQD to approximately 40%. The effect of different CQD on CH4 yield performance was further explored. The cumulative CH4 yield performance of the fermenter was improved after adding CQD. The CQD synthesized from pretreated straw and the nitrogen-doped CQD synthesized using Chlorella as the nitrogen source showed competitive promotion performance, increasing cumulative CH4 yield by 17.71% and 8.87%, respectively. These CQD can effectively accelerate the degradation of dissolved organic matter and thus improve the CH4 yield performance, with the most significant effect of CQD synthesized from pretreated straw. Electrochemical analysis and the correlation analysis between microorganisms and performance parameters showed that these CQD established an electron conductive network to enhance the electron transfer of the system. This well conductive conditions enriched hydrogenotrophic methanogenic (Methanosarcina), electroactive bacteria (Clostridium_sensu_stricto_1), and hydrolytic-acidifying bacteria (norank_f__Bacteroidetes_vadinHA17). This study significantly enhanced the yield of straw-derived CQD through green methods, and deeply revealed the potential promoting mechanisms of biomass-derived CQD by investigating the correlation between system performance and microorganisms in high-load AD systems

Synergistic enhancement of lithium iron phosphate electrochemical performance by organic zinc source doping and crystalline carbon layer capping

In this study, lithium iron phosphate (LFP) is prepared as cathode material by hydrothermal synthesis method and the combined effect of doping and capping is applied to co-modify it. We thoroughly investigate how Zn2+ doping and PA capping layer affect the crystal structure, microscopic morphology, and electrochemical properties of LFP cathode materials. The experimental results show that when co-modified with 5 % Zn2+ doping combined with 7 % PA capping layer, the resulting cathode material exhibits a discharge specific capacity of 165.5 mAh g−1, and the capacity retention rate can still be maintained at a high level of 98.6 % after 200 charge–discharge cycles.

Pre-inserting Mn2+/Zn2+ into NaV6O15 nanorods as high-stable and long lifespan cathodes for aqueous zinc-ion batteries

Vanadium-based compounds, characterized by diverse crystal structures, exhibit high theoretical capacities, and are regarded as potential cathode materials for aqueous zinc-ion batteries. Despite this, their development has been hindered by the sluggish diffusion of zinc ions and inadequate structural stability. In this study, we fabricated a stable monoclinic NaV6O15 nanorod via a simple hydrothermal synthesis. Mn2+ or Zn2+ ions are introduced into the crystal lattice to augment the interlayer spacing of NaV6O15, thereby enhancing the diffusion kinetics of Zn2+ ions. After pre-intercalating guest ions (Mn2+/Zn2+), the material experiences a morphological evolution from nanorods to nanobelts, which correlates with an expansion of the specific surface area and a proliferation of electrochemically active sites. This morphological alteration is associated with a marked enhancement in reversible capacity, reaching 278.1, 340.4, and 363.9 mAh/g for NVO, MNVO, and ZNVO, respectively, at 0.2 A/g. Furthermore, pre-intercalating guest ions not only expanded the interlayer spacing but also conferred structural robustness, leading to a pronounced enhancement in Zn2+ mobility and cyclability. Remarkably, the ZNVO cathode demonstrated a capacity retention of 118.4 % after 5000 cycles at a high current density of 5 A/g. Additionally, ex-situ XRD and XPS analyses elucidate that the Zn2+ storage in ZNVO is governed by the Zn2+ insertion/de-insertion mechanism. Our research offers a paradigm for the development of cathode materials for aqueous zinc-ion batteries.

Advancements in CuO nanoparticle technology: synthesis, characterization of copper oxide nanoflowers

Abstract Nanostructured materials, including metal and metal oxide nanoparticles, play a crucial role in advancing diverse scientific and technological areas. Transition metal oxides such as CuO are integral to developments in fields like antibacterial treatments, solar energy conversion, sensing technologies, catalysis, magnetic storage, supercapacitors, and semiconductor devices. This research is centered on the hydrothermal synthesis of pure copper oxide nanoflowers, which are noted for their extensive surface areas. Zeta potential analysis, ultraviolet-visible spectrophotometry, field-emission scanning electron microscopy, and Fourier-transform infrared spectroscopy were some of the methods utilized to characterize these nanoparticles. The results showed that band gap energies, crystallite size, and lattice characteristics are all greatly affected by CuO. XRD results indicated a covellite monoclinic polycrystalline structure predominantly orientation with average crystallite sizes around 15.84 nm. FE-SEM imagery depicted the hierarchical, cauliflower-like structure of the CuO nanoparticles. Optical assessments revealed band gap values ranging from 2.58 eV. The findings underscore the broad potential of CuO nanoflowers across various technological applications.

Two-step hydrothermal synthesis of hydrangea-like Bi2O2Se with high performance for supercapacitors

The hydrangea-like structure of Bi2O2Se, composed of ultra-thin nanosheets, was prepared by a 2-step hydrothermal method for supercapacitor applications. The unique hydrangea-like structure of Bi2O2Se, characterized by a substantial specific surface area and abundant pore morphologies, facilitated the infiltration of electrolyte. The presence of bismuth vacancies not only enhanced the conductivity, but also increased the spacing between [Bi2O2]n2n+ and [Se]n2n– layers, creating room for K+ insertion/extraction and augmenting the surface-controlled pseudo-capacitance. Consequently, the hydrangea-like Bi2O2Se exhibited a high specific capacitance of 650 F/g at 1 A/g, excellent rate capability of 62 % from 1–20 A/g, and retained 80 % of its initial capacitance after 2000 cycles.

Direct synthesis of low-silica ZSM-48 zeolite via seed-assisted hydrothermal synthesis with 1,6-hexanediamine as template

ZSM-48 zeolite is characteristic of 10-member ring (10-MR) one-dimensional tubular channel structure and finds extensive applications in catalytic hydroisomerization reactions. Here we developed an efficient synthetic strategy for low-silica ZSM-48 zeolite with a SiO2/Al2O3 ratio at 30∼176 via a seed-assisted hydrothermal synthesis method, overcoming the limit that 1,6-hexanediamine (HDA) template can only be used to synthesize high-silica (i.e., SiO2/Al2O3 ratio >200) zeolites. A two-step crystallization procedure coupled with zeolite seed-assisted synthesis strategy was enrolled to realize well crystallized ZSM-48 zeolites, in which the zeolite nuclei are sufficiently produced at the nucleation temperature at 100 °C for 24 h with the aid of zeolite seeds, and the zeolite growth is proceeded at the crystallization temperature at 160 °C for 48 h. The morphology and particle size of low-silica ZSM-48 have been manipulated by adjusting the synthetic parameters, such as the alkalinity and silicon source of aluminosilicate gel for zeolite, the crystallization manner (static or dynamic crystallization), as well as the presence of additive (i.e., sodium chloride). The as-synthesized ZSM-48 zeolite exhibits a significantly high acid content of 0.194 mmol/g, highlighting its potential as an excellent acidic support for hydroisomerization catalysts. The cost-effective and environmentally friendly synthesis strategy, which is anticipated to expand the application of alkylamine organic templates in the synthesis of low-silica ZSM-48 zeolite.

Advanced and sustainable EMI shielding composites: Natural rubber-nitrile rubber blends enhanced with hydrothermally synthesized Polyaniline Nanofibers and spinel strontium ferrites

Conductive fillers, such as metals and carbon compounds, often exhibit lower compatibility with polymer matrices, leading to agglomeration phenomena that negatively impact the processing and performance of composites. Polyaniline (PANI) nanofibers, with their high conductivity, rapidly create conductive pathways upon contact, reducing current leakage and dielectric loss in composites. To address the compatibility challenges between fillers and matrices, this study adopts a simple, cost-effective approach for synthesizing highly efficient EMI shielding composites. Specifically, we employ hydrothermal synthesis to enhance the properties of PANI nanofibers and spinel strontium ferrites, significantly improving their performance as filler particles. By modifying the morphology of the conductive fillers and incorporating magnetic particles wrapped with an insulating polymer layer, we enhance filler-matrix compatibility. Notably, the synthesized system is a composite made of natural rubber, highlighting its relevance and importance in the current era. This approach not only improves compatibility but also leverages the sustainable properties of natural rubber, making it a significant advancement in the field of EMI shielding materials. In this paper, we report a flexible EMI shielding composite with efficient EM wave absorption, prepared using a natural rubber-nitrile rubber blend as the matrix, and hydrothermally synthesized improves polyaniline nanofibers and spinel strontium ferrite as functional fillers. The shielding efficiency (SET) increases up to 36 dB with different PANI-SrFe2O4wt percentages. This demonstrates the potential of composite for high-performance applications.

A 2D open framework zinc phosphate and its high proton conductance properties at medium and low temperature

A 2D open-framework zinc phosphate [C3N2H12][Zn2(HPO4)3] (1) was synthesized by solvothermal method. The inorganic anion layer is constructed from Zn2P2O12 cluster units and the interlayer spaces are filled by the diprotonated DAP molecules. The resultant compound had high purity and thermal stability by PXRD and TG analysis. This compound exhibited strongly temperature and humidity dependent proton conductivity, and its highest proton conductivity achieves 2.36 × 10−2 S.cm−1 at 100 %RH and 333 K. Moreover, the important effect of the dense hydrogen bond network in elevating the proton conductivity was explored through comparing the structure and proton conduction behavior between 1 and [C3N2H12][Zn(HPO4)2] (2), which synthesized via the same hydrothermal reaction process, and only a slight difference in the amount of DAP.

Integrated experimental and DFT-based study on pH-dependent photoelectrochemical performance of Ca2Fe2O5

In this study, photoelectrochemical (PEC) performance of Ca2Fe2O5 nanoflakes were explored to understand corrosion and degradation tendency. Ca2Fe2O5 nanoflakes were synthesized via a modified two step thermochemical method consisting of hydrothermal reaction and chemical conversion. Detailed characterization using SEM, XRD, and TEM confirmed the highly crystalline and (200) faceted Ca2Fe2O5 nanoflake morphologies. PEC measurements, conducted in six distinct electrolyte conditions, revealed significant photocurrent variations with respect to pH change, highlighting pH 11 as the optimal environment. Electrochemical impedance spectroscopy (EIS) was applied to elucidate charge transfer rate depending on the hydrogen evolution reaction (HER) mechanisms. Furthermore, DFT calculations provided insights into the surface interactions of Ca2Fe2O5 with hydrogen and hydroxide absorbates, elucidating the electronic and structural change during PEC reactions. The simulation demonstrated that, while hydrogen adsorption induced Fe-O bond dissociation, hydroxide adsorption showed minimal effect on surface bonds. HER overpotentials were calculated for both Tafel and Volmer step, elucidating the facile and stable HER in OH terminated surface environments. These findings underscore the importance of alkaline electrolyte environment in optimizing the PEC stability and efficiency of Ca2Fe2O5 photocathodes.