Mott Schottky Research Articles

Anchorage of ZnO quantum dots and CuO on graphene for sonophotocatalytic treatment of pharmaceutical effluent: From experimental data and prediction by advanced machine learning algorithms

Quantum dots (QDs) have recently received much attention as photocatalysts due to their unique properties. Despite the advantages reported for QDs as photocatalysts in literature, their sonophotocatalytic/photocatalytic activity is still hindered by a series of barriers, which limit them to operate after several successive cycles efficiently. The main aim of this work is to fabricate an efficient and recyclable sonophotocatalyst/photocatalyst using ZnO quantum dots (ZQDs), tenorite (CuO), and graphene (G). In this regard, different amounts of ZQDs (ZQDs(x)/G, x= 10, 20, 30, 40, and 50mg) were immobilized on graphene by hydrothermal method and various weight percent of CuO was impregnated on ZQDs(40)/G. The PXRD patterns and Raman spectra confirmed the wurtzite and monoclinic crystal structure for ZQDs and CuO, respectively. Also, FESEM, AFM, and PXRD showed that the mean crystal size of ZQDs increased after immobilization on graphene and impregnation by CuO. PL and Mott–Schottky analyses showed that the presence of GO and CuO in CuO(0.5)/ZQDs(40)/G reduced the recombination of excitons and formed p-n heterogeneous junctions between CuO and ZnO. The VB and CB potential and bandgap energy were obtained using DRS and Mott–Schottky analyses, and the mechanism of tetracycline (TC) degradation was proposed according to active species trapping and H2O2 paper testes. The apparent rate constant (kapp) was 0.030 and 0.060min-1 for photocatalytic and sonophotocatalytic degradation of TC in the presence of CuO(0.5)/ZQDs(40)/G, respectively. The treated effluent of TC showed acceptable performance in growing wheat seeds. The electricity cost estimation showed that (CuO(0.5)/ZQDs(40)/G) consumed less electricity in sonophotocatalytic/photocatalytic TC degradation and could also be used in several successive cycles. Finally, two RF and AdaBoost models based on ML algorithms were developed to predict photocatalytic/sonophotocatalytic degradation. The results showed that the values of statistical metrics, including SAE, MAE, MSE, and RMSE, for the AdaBoost model were relatively lower than those for the RF model, indicating better prediction performance in train and test datasets.

Engineering n-Type and p-Type BiOI Nanosheets: Influence of Mannitol on Semiconductor Behavior and Photocatalytic Activity.

Photocatalytic technology holds significant promise for sustainable development and environmental protection due to its ability to utilize renewable energy sources and degrade pollutants efficiently. In this study, BiOI nanosheets (NSs) were synthesized using a simple water bath method with varying amounts of mannitol and reaction temperatures to investigate their structural, morphological, photoelectronic, and photocatalytic properties. Notably, the introduction of mannitol played a critical role in inducing a transition in BiOI from an n-type to a p-type semiconductor, as evidenced by Mott-Schottky (M-S) and band structure analyses. This transformation enhanced the density of holes (h+) as primary charge carriers and resulted in the most negative conduction band (CB) position (-0.822 V vs. NHE), which facilitated the generation of superoxide radicals (·O2-) and enhanced photocatalytic activity. Among the samples, the BiOI-0.25-60 NSs (synthesized with 0.25 g of mannitol at 60 °C) exhibited the highest performance, characterized by the largest specific surface area (24.46 m2/g), optimal band gap energy (2.28 eV), and efficient photogenerated charge separation. Photocatalytic experiments demonstrated that BiOI-0.25-60 NSs achieved superior methylene blue (MB) degradation efficiency of 96.5% under simulated sunlight, 1.14 times higher than BiOI-0-70 NSs. Additionally, BiOI-0.25-60 NSs effectively degraded tetracycline (TC), 2,4-dichlorophenol (2,4-D), and rhodamine B (Rh B). Key factors such as photocatalyst concentration, MB concentration, and solution pH were analyzed, and the BiOI-0.25-60 NSs demonstrated excellent recyclability, retaining over 94.3% of their activity after three cycles. Scavenger tests further identified ·O2- and h+ as the dominant active species driving the photocatalytic process. In this study, the pivotal role of mannitol in modulating the semiconductor characteristics of BiOI nanomaterials is underscored, particularly in promoting the n-type to p-type transition and enhancing photocatalytic efficiency. These findings provide a valuable strategy for designing high-performance p-type photocatalysts for environmental remediation applications.

Effect of Calcination-Induced Oxidation on the Photocatalytic H2 Production Performance of Cubic Cu2O/CuO Composite Photocatalysts

This study explores the H2 production performance of CuO/Cu2O with different morphology (nanocubes) synthesized by different methods using different sacrificial reagent (lactic acid), compared with the other three reported CuO/Cu2O photocatalysts used for H2 production. A cubic Cu2O photocatalyst was prepared using a hydrothermal method. It was then calcined at a certain temperature to form a cubic Cu2O/CuO composite photocatalyst. XRD, TEM, and XPS spectra confirmed the successful synthesis of cubic Cu2O/CuO composite photocatalysts by calcination-induced oxidation at a certain temperature. As the calcination temperature increases, the crystal phase of the photocatalyst changes from Cu2O to Cu2O/CuO and then to CuO. The effects of calcination-induced oxidation on morphology, light absorption, the separation of photoexcited carriers, and the H2 production activity of photocatalysts were studied. EPR spectra were monitored to analyze the oxygen vacancies in different samples. Mott–Schottky and Tauc plots were utilized to establish the band structure of the composite photocatalyst. Cu2O/CuO is a type II photocatalyst with a heterogeneous structure that helps to improve electron–hole separation efficiency. The H2 production efficiency of Cu2O/CuO composite photocatalyst reaches 11,888 μmol h−1g−1, 1.6 times that of Cu2O. The formation of the Cu2O/CuO heterojunction leads to enhanced light absorption, charge separation, and hydrogen production activity.

Stabilizing Sn/SnO2 Mott–Schottky Heterojunction on Biomass-Derived Carbon Boosting Highly Selective and Robust Formate Production for Electrochemical CO2 Reduction

Stabilizing Sn/SnO₂ Mott–Schottky Heterojunction on Biomass-Derived Carbon Boosting Highly Selective and Robust Formate Production for Electrochemical CO₂ Reduction

Nucleation, Electronic, and Optical Properties of Bi Thin Films Electrodeposited on n‐Si(111) Substrate

This study investigates the electrochemical nucleation and growth mechanisms of bismuth on a monocrystalline n‐Si(111) substrate from an acidic nitrate solution. It also examines the electrical and optical properties of the electroplated films. The qualitative analysis of the experimental current transients reveals a strong agreement with instantaneous nucleation on active sites and three‐dimensional diffusion‐controlled growth. Electrochemical kinetic parameters are derived using the Mirkin–Nilov–Heerman–Tarallo model, which is employed to fit the experimental curves. Electrochemical impedance spectroscopy and Mott–Schottky analysis are used to assess the electronic characteristics of the materials. Scanning electron microscope observations show a uniform, smooth, and continuous deposit. X‐ray diffraction analysis indicates a high texture along the [012] direction of the rhombohedral crystal structure in thin bismuth films with different thicknesses (118, 318, and 611 nm). UV–visible spectroscopy is employed to investigate the optical characteristics of the Bi/Si surface in the 200–1100 nm wavelength range. The study demonstrates that the thickness of the bismuth film affects the absorption response of the Bi/Si heterojunction, showing a notable increase in absorption in the visible and infrared ranges. Furthermore, it is found that the photoluminescence properties of the Bi/Si heterojunction are improved in the visible and infrared ranges.

Modulation of Energy Band Positions in Sb2S3 Thin Films for Enhanced Photovoltaic Performance of FTO/TiO2/Sb2S3/P3HT/Au Solar Cell

Antimony sulfide (Sb2S3) has the potential as an absorber material in photovoltaics due to its suitable bandgap and favorable optoelectronic properties. However, its energy band positions are not extensively explored which are essential for effective charge separation and transfer. This study examines the energy band positions of Sb2S3 thin films as a function of annealing temperature. Sb2S3 thin films are grown by a combination of successive ionic layer adsorption and reaction (SILAR) and chemical bath deposition (CBD) method to enhance the crystallinity, tune the bandgap, and overall quality of Sb2S3 films to enhance the photovoltaic performance. Optical bandgap decreases from 2.41 to 1.67 eV from the as‐deposited films to annealed at 300 °C due to changes in interatomic distances. Energy band positions of Sb2S3 films are measured both by cost‐effective electrochemical cyclic voltammetry and Mott–Schottky analysis and validated the findings using ultraviolet photoelectron spectroscopy (UPS). The conductivity of Sb2S3 is found to be n‐type. Thin‐film solar cells are then fabricated by employing Sb2S3 as an absorber layer in an FTO/TiO2/Sb2S3/P3HT/Au structure, achieving an enhanced power conversion efficiency, increasing from 0.4 to 2.8% after annealing. These findings demonstrate the potential of Sb2S3 as a low‐cost absorber material for thin‐film photovoltaics.

Unveiling the Aluminum Doping Effects of In‐Situ Transmogrified Dual‐LDH Heterostructure and Its Fermi‐Level Alignment to Water Splitting Potentials

AbstractThe layered double hydroxide (LDH) captivates the starlight of electrochemical water‐splitting applications due to its stacked layers and larger surface area. A novel approach is reported to integrate CoFe‐LDH/NiAl‐LDH heterostructure through a single‐step in situ transmogrification, harnessing the benefits of LDH. The in situ Raman spectroscopy reveals that aluminum (Al) doping promotes the formation of high‐valent CoIII/IV‐O active species concentration in LDH, whereas without Al dopants, the catalyst predominantly exhibit NiII/III‐O species and underperform the catalytic activity. The projected density of states is very close to the Fermi level positions in Al‐doped samples which significantly enhance the electron transfer processes. The Mott–Schottky studies confirm that both Al40 CoFe30 and Al60 CoFe20 catalysts are p‐type semiconductors, exhibiting a distinct redox behaviors under applied bias. At positive bias, Al60 CoFe20 undergoes downward band bending (accumulation), and align the Fermi‐level near the water oxidation potential, which promotes the oxygen evolution reaction (OER). The negative bias causes upward band bending (deep depletion) in the Al40 CoFe30, and shifts the Fermi‐level near the water reduction potential, and hence facilitates hydrogen evolution reaction (HER). Overall, this study highlights the importance of manipulating Fermi‐level alignment in LDH catalysts through strategic metal doping to achieve targeted water‐splitting reactions.

Electrochemical and microstructural characterization of a precipitation hardened 17-4 steel in different environments

In this study, an in-depth electrochemical characterization of a precipitation hardened 17-4 stainless steel (SS17-4PH) was carried out in combined acidic, alkaline, and chloride environments. The characterizations were carried out through polarization-EIS analysis, Mott-Schottky analysis to characterize the semiconducting properties of the thin oxide films, and a post-mortem scanning electron microscopy (SEM-EDX) analysis to reveal the morphologies after anodic polarization. The electrochemical measurements revealed that the corrosion rate of SS17-4PH samples in acidic-chloride solutions is higher than the sample polarized in only NaCl or NaOH solution. From the Mott Schottky results, the straight lines with a positive slope obtained for the steel samples in different test media show that there is no change in the semi-conducting properties of the passive film. For samples polarized in acidic-chloride medium, the microstructural examination revealed the formation of a foot-like pit and zig-zag degradation structure. This was attributed to the presence of acid in the test media, and the deposition of corrosion products on the sample surface.

Investigations on interfacial complex dynamic processes of Er-BiFeO3 based perovskite solar cell heterostructures

In the present investigations, we critically examine the response of thickness variation of the photoactive layer on I-V characteristics of the final optimized Er-doped BiFeO3 (Er-BF) designed devices (Er: 0 %, 4 %, 8 %, and 12 %). The recombination rate, energy band diagrams obtained at a final simulated thickness of the absorber and at the back contact metal work function were investigated for the purpose of barrier formation analysis. To establish the presence of deep defects in the perovskite based heterostructure devices, the measurements of respective designed devices related to capacitance–voltage (C-V), Mott-Schottky (MS) (1/C2-V), and conductance-voltage (G-V) characteristics were thoroughly performed and examined. The change in capacitance (or dielectric constant) induced thermally in the respective designed devices was investigated with the temperature-dependent capacitance-frequency (C-f) characteristics performed under the illumination and dark conditions, respectively. Further, the voltage dependent Nyquist plots were studied. Overall, this work provides critical insights into the impedance response of doped BiFeO3 absorber-based designed perovskite solar cells (PSCs) with cell structure FTO/ZnO/Er-BF/Spiro-OMeTAD/Au. It further facilitates the understanding of various complex electrical processes taking place at the different interfaces during the device operations which are significant for the better optimization and play crucial role in enhancing the overall photovoltaic performance of PSCs.

GPa level pressures on the microstructure evolution of eutectic high-entropy alloys CoCrFeNi(TiNb)0.325 and corrosion resistance

In this study, high-pressure solidification (HPS) was used to systematically investigate the microstructure evolution and corrosion resistance of the designed eutectic high-entropy alloy CoCrFeNi(TiNb)0.325 under ambient pressure, 4 GPa and 7 GPa. With increasing solidification pressure, the eutectic component points continue to move toward the upper left of the phase diagram, and the microstructure of the EHEA changes from eutectic under AP to hypereutectic at 4 GPa. Finally, the eutectic lamellar structure disappears under 7 GPa pressure, and the microstructure shows a divorced eutectic morphology. Mott–Schottky and XPS analyses revealed that the passivation film defect density of the HPS sample was lower than that of the other samples, but because the increase in the FCC/Laves phase spacing promoted pitting nucleation, the sample was difficult to repassivate, thus weakening the pitting corrosion resistance of the HPS sample. This work provides new insights into the relationships among pressure, microstructure, and corrosion performance.

Impact of bath temperature on the optical, structural, and photoelectrochemical properties of thin films of copper (II) oxide synthesized via electrodeposition method

This study investigates how bath temperature influences the properties of CuO thin films grown on FTO substrates using the electrochemical deposition method. CuO films were fabricated at bath temperatures ranging from 40 °C to 80 °C under a constant voltage of 0.5 V, using a bath solution containing copper sulphate, tartaric acid, and sodium hydroxide to maintain pH. CuO films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, UV-Vis spectroscopy, photoluminescence (PL) spectroscopy, photocurrent measurements, Mott-Schottky (MS) measurements, and electrochemical impedance spectroscopy (EIS). XRD analysis definitively verifies the presence of a monoclinic structure in the CuO films, exhibiting a dominant orientation along the (200) plane. Raman analysis identified shifts in characteristic CuO vibrational modes at 270 cm⁻1, 317 cm⁻1, and 605 cm⁻1, reflecting changes in crystallographic structure. SEM revealed that particle size varied significantly with bath deposition temperature increased. UV-Vis spectra showed a systematic decrease in the optical bandgap from 1.67 eV to 1.39 eV with increasing temperature, attributed to improved crystallinity and reduced defect states. PL spectra of CuO thin films indicated two distinct photoluminescence maxima at about 465 nm and 517 nm with difference in the intensity for all samples due to changes in defect density and crystallinity. Photocurrent measurements and Mott-Schottky analyses demonstrated that the CuO films behave as p-type semiconductor, and with increasing the bath temperature the acceptor carrier increased. EIS analyses demonstrated improvements in electrochemical properties, with the flat band potential and charge transfer resistance showing significant temperature dependence. The results indicate that deposition temperature critically affects the structural, optical, and electrochemical performance of CuO thin films, providing insights for optimizing their application in optoelectronic devices and energy systems.

Modulation of the Microstructure and Enhancement of the Photocatalytic Performance of g-C3N4 by Thermal Exfoliation

This work explores the impact of reaction temperature during thermal exfoliation treatment of bulk-g-C3N4 in the air atmosphere on the structure and performance of the resulting CN photocatalyst. The analysis conducted using XRD, FT-IR, XPS, SEM, and elements mapping tests, illustrated an increase in nitrogen-vacancy and oxygen content on the surface of the CN photocatalyst, resulting in a porous and sparse structure, changes in crystal size, and improved visible light absorption performance. The photocatalytic reduction experiments of hexavalent chromium (Cr(VI)) showed that the CN-540 showed the highest reduction rate of 96.9%, with a reaction rate constant 6.21 times that of bulk-g-C3N4. After 100 min of illumination, the photocatalytic degradation rates of CN-540 for TC-HCl and RhB were 66.7% and 60.6%, respectively. The TOC test results indicated mineralization rates of 51.5% for TC-HCl and 46.6% for RhB. Room temperature fluorescence spectroscopy (PL), transient photocurrent response (TPC), and electrochemical impedance spectroscopy (EIS) measurements confirmed the excellent photogenerated charge carrier separation and transport efficiency of CN-540. The photocatalytic mechanism for reducing Cr(VI) by CN-540 was elucidated based on the active species •OH and •O2– and Mott-Schottky (M-S) tests. This study provides experimental data for optimizing the photocatalytic performance of g-C3N4 and paves a new way for developing efficient photocatalysts. Copyright © 2024 by Authors, Published by BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Ligand modulated charge transfers in Z-scheme configured Ni-MOF/g-C3N4 nanocomposites for photocatalytic remediation of dye-polluted water

The development of photocatalysts must be meticulous, especially when they are designed to degrade hazardous dyes that cause mutagenesis and carcinogenesis. In this meticulous approach, Ni-based metal–organic frameworks with different ligands, including terephthalic acid (NTP), 2-aminoterephthalic acid (NATP), and their composite with g-C3N4 (NTP/GCN, and NATP/GCN) have been synthesized using hydrothermal method. Structural analysis by XRD and ATR-IR revealed synergistic properties due to robust chemical interactions between the NATP-MOFs and GCN systems. A flower-like morphology was observed for both NTP and NATP, while their composites showed mixed-particulate structures mimicking the morphology of GCN. Optical analyses indicated visible-light driven properties with modulated recombination resistance in the system. Among the synthesized bare and composite systems, NATP/GCN exhibited the highest photocatalytic degradation efficiency for the cationic rhodamine B dye (~ 93% in 120 min), while it was relatively less efficient for the anionic Congo red dye, (~ 64% in 120 min). The insights gained from the fundamental characterizations including Mott–Schottky, scavenger, and electrochemical impedance analysis revealed that the amino-groups in NATP/GCN composite offered the band edge potentials suitable for the effective generation of energetic radical species with the improved carrier delocalization, recombination resistance, and charge transfer properties in the composite system through Z-scheme formation. Parametric investigations by varying the concentration of catalyst, dye, and pH along with recycle studies, demonstrated the excellent stability of the developed composites for sustainable photocatalytic applications.

Enhanced water splitting on (010) facet-exposed BiVO4 photoanode with improved carrier injection efficiency

Transition metal oxide semiconductors, noted for their stability and suitable bandgap, are promising photoanodes for water splitting. Surface engineering is critical to tackle issues like low carrier mobility and charge recombination, stemming from atomic arrangement and Fermi level differences. While exposing dominant crystal facets boosts photocatalytic capability, it can hinder carrier injection into the electrolyte. In this study, BiVO4 films with various facet exposures were synthesized and characterized using scanning electron microscopy and x-ray diffraction to confirm their morphology and crystalline structure. Mott–Schottky analysis was employed to investigate changes in the band structure near the semiconductor–electrolyte interface, revealing that high (010)-BiVO4 facet exposure enhances carrier separation but reduces injection efficiency. The results from photoconductive atomic force microscopy tests demonstrated that enhanced band bending at the semiconductor interface improves hole transfer. Coating the (010)-BiVO4 photoanode with MoS2 and an amorphous ZrO2 interlayer yielded a photocurrent density of 0.6 mA cm−2 at 1.2 V (vs RHE) under AM 1.5 G illumination, tripling the pristine photoanode's performance and nearly tripling water splitting efficiency. Mechanism revealing the improved photoelectrochemical performance is attributed to a greater band bending on the BiVO4 surface, enhancing hole injection dynamics. This work provides a feasible strategy for a deeper understanding of the intrinsic mechanisms of facet engineering and improving the activity of photoanodes.

Porous fluorine-cerium nanosheets anchored with FeOOH quantum dots for synergistic enhanced visible-light-driven photo-Fenton degradation of phenol

The utilization of two-dimensional (2D) materials to construct heterogeneous catalysts provides opportunities for environmental remediation, while the incorporation of porous structures can further enhance catalytic performance. In this work, a porous 2D FeOOH/fluorine-cerium (F-Ce) nanosheet composite was designed and synthesized by a simple impregnation-precipitation method. The unique 2D porous structure of F-Ce promoted the high dispersion of FeOOH quantum dots (QDs) (∼1.4 nm) and their tight integration to form S-scheme heterojunctions. This structure offered a greater number of active sites, and significantly improved the capacity of light absorption and the separation and migration efficiency of photogenerated carriers, thus improving catalytic activity. This catalyst achieved a phenol removal rate of 98.1 % within 20 min during the photo-Fenton reaction, which significantly surpasses pure FeOOH (32.9 %) and F-Ce (21.7 %) alone. In particular, the optimized 14FeOOH/F-Ce catalyst achieved more than 95.0 % degradation efficiency within a remarkably short period of 5 min. Mott Schottky and in situ irradiated X-ray photoelectron spectroscopy (ISI-XPS) studies demonstrated that the S-scheme charge transfer mechanism of this heterojunction synergistically enhanced the catalytic activity of the Fenton-like reaction. This study provides valuable insights for designing efficient 2D porous heterojunction catalysts for visible-light-driven Fenton applications.

Partial‐Oxidation Enabling Homologous Ru/RuO2 Heterostructures With Proper d‐Dand Center as Efficient and Durable Cathode Catalysts for Ultralong Cycle Life in Li–O2 Batteries

AbstractThe sluggish cycle kinetics is one of the major obstacles to the commercial application of Li–O2 batteries (LOBs), despite their large theoretical energy density. Efficient and long‐term durable cathode catalysts are urgently desired to strengthen their cycle stability and rate performance. Density functional theory calculations reveal that Ru/RuO2 Mott–Schottky heterostructures can manipulate the adsorption capacities of intermediates by modulating the d‐band center and redistribute interfacial charges, enabling efficient redox kinetics, reducing overpotentials, and optimizing the growth pathway of discharge products. Herein, a wet impregnation approach followed by partial oxidization of Ru nanodots to construct homologous Ru/RuO2 heterostructures as advanced cathode catalysts for boosting the electrochemical activities of LOBs is employed. They exhibit superior electrochemical performance, including high discharge specific capacity (17 120 mAh g−1 at 200 mA g−1), small overpotential (0.96 V), and ultralong cycle lifetime of 1209 cycles (>2400 h) at 500 mA g−1. Over 1260‐h stable cycle in air atmosphere at 500 mA g−1 demonstrates the potential application prospects of the Ru/RuO2 heterostructures in Li‐air batteries. Multiple ex/in situ measurements and theoretical calculation are conducted to investigate the optimizing mechanism of electrochemical performances.

N2O Assisted Ethane Transformation into Ethylene Using NiO−CeO2−ZrO2 Catalysts

AbstractNiO−CeO2 and NiO−CeO2−ZrO2 catalysts have been synthesized, electrochemically characterized (Mott‐Schottky (MS) measurements and Electrochemical Impedance Spectroscopy), physicochemically characterized (by N2 adsorption, XRD, Transmission Electron Microscopy and XPS) and tested in the N2O assisted ethane oxydehydrogenation. The use of low Zr‐loadings (Zr/Ce=0.1 at. ratio) has led to the optimal results in the ethylene production, improving those obtained by the Zr‐free NiO−CeO2 catalyst. However, high Zr‐loadings have meant a decrease in the olefin production. The catalytic results obtained have been explained considering the amount of oxygen vacancies, the crystalline phases formed and, especially, the nature of the surface Ni species. Importantly, the use of N2O as an oxidizing agent leads to a remarkable improvement in the selectivity to the olefin compared to that obtained employing molecular O2. Then, for a given ethane conversion the selectivity to ethylene is ca. 15 points higher using N2O than using O2. Another additional positive aspect of this NiO−CeO2−ZrO2 catalyst is its high catalytic stability.

Potentiostatic electrodeposition of copper, indium, and cadmium sulfides for CO2 electroreduction: A path toward sustainable hydrogen generation

This study focuses on the potentiostatic electrodeposition of copper indium and cadmium sulfide (CuS, In2S3, and CdS) thin films on copper substrates, aiming to develop efficient electrocatalysts for the electrochemical reduction of CO2 and sustainable hydrogen generation. Utilizing Cu Kα radiation for X-ray diffraction (XRD) analysis, the crystal structures of the electrodeposited films were confirmed, revealing well-defined crystalline phases. The films exhibited average particle sizes of 55.99 nm for CuS, 50.37 nm for In2S3, and 63.51 nm for CdS. Cyclic voltammetry and chronoamperometry were employed to optimize the deposition parameters, ensuring efficient nucleation and growth of the metal sulfide films. The electrochemical performance of the synthesized electrocatalysts was rigorously tested, demonstrating their potential for CO2 reduction under optimized conditions with the highest efficiency for CdS electrodes. Additionally, the electrodeposited CuS and CdS are of the p-type, and In2S3 is of the n-type semiconductor were studied and verified by the Mott–Schottky test. CuS, In2S3, and CdS were found to have donor and acceptor concentrations (ND) of 1.68 × 106, 1.44 × 105, and 8.9 × 105 cm3, respectively. The photoelectrochemical measurements of the electrodeposited metal sulfides were studied at ambient temperature and under illumination, providing higher photocurrent responses for CdS and demonstrating its strong potential as a photoelectrode material for CO2 reduction. This work underscores the significance of facile electrochemical synthesis methods in developing cost-effective and scalable electrocatalysts, paving the way for their integration into photoelectrochemical systems for green energy applications.

Enhanced electrocatalytic OER activity following electrochemical pre-cathodic treatment of Mn-substituted nickel ferrite

In this study, the electronic engineering of a high-valent active site for enhanced oxygen evolution reaction (OER) was achieved through the electrochemical pre-cathodic treatment method (EPCTM). This method involves applying a cathodic potential to the drop-cast working electrode of Mn-substituted nickel ferrite (Ni1−xMnxFe2O4; where x = 0.0, 0.2, and 0.4) electrocatalysts. X-ray photoelectron spectroscopy analysis revealed an increase in the ratios of Ni3+/Ni2+ and Mn3+/Mn2+ in Ni1−xMnxFe2O4 after EPCTM followed by OER, leading to an enhancement in electrochemical OER current density at 600 mV overpotential by 3.65 times for x = 0.0, 5.56 times for x = 0.20, and 4.72 times for x = 0.40. This enhancement was further supported by a decrease in the slope of the anodic Tafel equation after EPCTM, indicating improved efficiency of the interaction between the working electrode and electrolyte, as a lower Tafel slope suggests better charge exchange at the electrode–electrolyte interface. The positive slope in the Mott–Schottky (MS) plot for all Ni1−xMnxFe2O4 samples confirmed the p-type nature of the electrocatalysts. Additionally, the significant decrease in the slope of the linear portion of the MS plot indicated an increase in carrier concentration after electrochemical pre-cathodic treatment in all Ni1−xMnxFe2O4 samples. This increase in p-type carrier concentration supports the observed increase in the Ni3+/Ni2+ ratio for OER after EPCTM.

Mechanistic Analysis of Anodic Oxidation of Gold in KOH (0.1 M) Solution Using the Point Defect Model

The potentiostatic, anodic formation of gold oxide at potentials of 0.55 to 0.80 V versus SHE in aqueous KOH (0.1 M) was studied using an impedance-based Point Defect Model (PDM). The film thickness and refractive indices at each formation potential were estimated using spectroscopic ellipsometry. The thickness of the oxide increases linearly with increasing applied voltage within this range. Mott-Schottky (MS) analysis showed that gold oxide formed in KOH (0.1 M) is an n-type semiconductor, and the dominant defect (Aui3+) density is calculated to be in the order of 1021–1022 (1/cm3). The steady-state current density of the oxide formation was independent of voltage, also in agreement with an n-type oxide. Reasonable agreement between PDM predictions and experimental observations of dominant defect density, steady-state current density, and thickness, demonstrates the value of the PDM in this system.