Electrodeposition of Mesoporous Ni-Rich Ni-Pt Films for Highly Efficient Methanol Oxidation

Sputtered Cu-doped NiO thin films as an efficient electrocatalyst for methanol oxidation

The efficient electrocatalysts for direct methanol oxidation play an essential role in the electrochemical energy conversion systems for their application in a wide range of portable applications. Consequently, Cu-doped NiO thin films on fluorine-doped tin oxide (FTO) were successfully prepared by the co-sputtering deposition technique, using various deposition times (300, 600, 900, and 1200 seconds), and producing films of different thicknesses (30, 55, 90, and 120 nm, respectively). X-ray diffraction (XRD) revealed the ideal crystallinity of the structure of the prepared films and was used to observe the effect of the thickness of the films on the crystal size. Energy-dispersive X-ray spectroscopy (EDS) confirmed the purity of the deposited film without any contamination. Field emission scanning electron microscopy (FESEM) images confirmed the film thickness increase with increasing deposition time. The surface roughness value of the Cu-NiO 1200 film was found to be 3.2 nm based on the atomic force microscopy (AFM) measurements. The deposited thin films of different thicknesses have been used as electrocatalysts for methanol oxidation at various concentrations of methanol (0, 0.5, 1, and 2 M), and displayed the highest electrocatalytic performance in 1 M methanol. Cu-doped NiO thin films have the advantage as electrocatalysts where they can be used directly without adding any binder or conducting agents, this is because Cu-doped NiO is deposited with high adhesion and strong electrical contact to the FTO substrate. A clear impact on the catalytic activity with increasing film thickness and a correlation between the film thickness and its catalytic activity was observed. The current density increased by about 60% for the Cu-NiO 1200 sample compared to Cu-NiO 300 sample, with the lowest onset potential of 0.4 V vs. Ag/AgCl. All deposited thin films of different thicknesses exhibited high stability at 0.6 V in 1 M methanol. This will open the window toward using physical deposition techniques for optimizing the electrocatalytic activity of different catalysts for electrocatalytic applications.

Roles of TOPO Coordinating Solvent on Prepared Nano-Flower/Star and Nano-Rods Nickel Sulphides for Solar Cells Applications

The present study describes a cheap, safe, and stable chemical process for the formation of nickel sulphide (NiS) with the use of mixed and single molecular precursors. The production pathway is uncomplicated, energy-efficient, quick, and toxic-free, with large-scale commercialization potential. The obtained results show the effect of tri-N-octylphosphine oxide (TOPO) as a coordinating solvent on the reaction chemistry, size distributions, morphology, and optical properties of both precursors. Ni[N,N-benz-N-p-anisldtc] as NiSa, Ni[N,N-benzldtc] as NiSb, and Ni[N-p-anisldtc] as NiSc thermally decompose in a single step at 333-334 °C. The X-ray diffraction peaks for NiSa, NiSb, and NiSc matched well with the cubic NiS nanoparticles and corresponded to planes of (111), (220), and (311). The extrapolated linear part from the Tauc plots reveals band gap values of 3.12 eV, 2.95 eV, and 2.5 eV, which confirms the three samples as potential materials for solar cell applications. The transmission electron microscopy (TEM) technique affirmed the quantum dot size distribution at 19.69-28.19 nm for NISa, 9.08-16.63 nm for NISb, and 9.37-10.49 nm for NISc, respectively. NiSa and NiSc show a clearly distinguishable flower/star like morphology, while NiSb displays a compact nano-rod shape. To the best of the authors' knowledge, very few studies have been reported on the flower/star like and nano-rod shapes, but none with the dithiocarbamate molecular precursor for NiS nanoparticles.

Fabrication of Metal (Cu and Cr) Incorporated Nickel Oxide Films for Electrochemical Oxidation of Methanol

Methanol electrochemical oxidation in a direct methanol fuel cell (DMFC) is considered to be an efficient pathway for generating renewable energy with low pollutant emissions. NiO−CuO and Ni0.95Cr0.05O2+δ thin films were synthesized using a simple dip-coating method and tested for the electro-oxidation of methanol. These synthesized electrocatalysts were characterized by X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS), and Raman spectroscopy. Different electrochemical techniques were used to investigate the catalytic activity of these prepared electrocatalysts for methanol oxidation, including linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and chronoamperometry (CA). In the presence of 0.3 M methanol, the current densities of NiO−CuO and Ni0.95Cr0.05O2+δ thin films were found to be 12.2 mA·cm−2 and 6.5 mA·cm−2, respectively. The enhanced catalytic activity of NiO−CuO and Ni0.95Cr0.05O2+δ thin films may be a result of the synergistic effect between different metal oxides. The Chronoamperometry (CA) results of the mixed metal oxide thin films confirmed their stability in basic media. Furthermore, the findings of electrochemical impedance spectroscopy (EIS) of mixed metal oxide thin films demonstrated a lower charge transfer resistance as compared to the pure NiO, CuO, and Cr2O3 thin films.

Assessing the Chemical Stability and Cytotoxicity of Electrodeposited Magnetic Mesoporous Fe-Pt Films for Biomedical Applications

The development of feasible micro/nanoplatforms for various biomedical applications requires holistic research that explores scalable synthesis and design pathways and imposes an interdisciplinary integration of materials science, physical, medical, chemical, and biological knowledge. Thanks to their unique characteristics (i.e., structure, large specific surface areas, tuneability, versatility, and integrity), mesoporous materials have emerged as potential candidates for being part of micro/nanoplatforms for therapeutic, monitoring, and diagnostic applications. In this context, Fe-Pt mesoporous materials are excellent candidates to be part of biomedical micro/nanoplatforms, thanks to their chemical nature, structure, and magnetic properties, which endow them with magnetic locomotion, high cargo capability of therapeutic agents inside the mesoporous cavity, and large surface area for surface functionalization. However, the chemical stability in biological media and cytotoxicity of the Fe-Pt mesoporous material (without considering the effects of architecture and shape) are pivotal elements that determine the suitability of these materials for biomedical applications. This work demonstrates the following: (i) the potential of electrochemical deposition, based on the use of block copolymer micellar solutions as electrochemical media, as an easy, inexpensive, and scalable strategy to synthesize mesoporous Fe-Pt components with tunable chemical composition, porosity, magnetism, and shape (in this case films, but other architectures like nanowires can be easily fabricated using simultaneously hard templates); (ii) the excellent corrosion stability, which is comparable to bulk Au, and minimal chemical dissolution in biological media after 160 h of immersion (∼0.88% of Fe and ∼0.0019% of Pt), which confirms the robustness of Fe-Pt; and (iii) negligible cytotoxicity on HaCaT cells (human immortalized keratinocytes), which reinforces the biocompatibility of Fe-Pt mesoporous structures. Also, the presence of Fe-Pt mesoporous films seems to induce a slight increase in cell viability. These results confirm the biocompatibility of Fe-Pt mesoporous films, making them suitable for biomedical applications.

Impedance Spectroscopic Study of Nickel Sulfide Nanostructures Deposited by Aerosol Assisted Chemical Vapor Deposition Technique

This research aims to synthesize the Bis(di-isobutyldithiophosphinato) nickel (II) complex [Ni(iBu₂PS₂)] to be employed as a substrate for the deposition of nickel sulfide nanostructures, and to investigate its dielectric and impedance characteristics for applications in the electronic industry. Various analytical tools including elemental analysis, mass spectrometry, IR, and TGA were also used to further confirm the successful synthesis of the precursor. NiS nanostructures were grown on the glass substrates by employing an aerosol assisted chemical vapor deposition (AACVD) technique via successful decomposition of the synthesized complex under variable temperature conditions. XRD, SEM, TEM, and EDX methods were well applied to examine resultant nanostructures. Dielectric studies of NiS were carried out at room temperature within the 100 Hz to 5 MHz frequency range. Maxwell-Wagner model gave a complete explanation of the variation of dielectric properties along with frequency. The reason behind high dielectric constant values at low frequency was further endorsed by Koops phenomenological model. The efficient translational hopping and futile reorientation vibration caused the overdue exceptional drift of ac conductivity (σ_ac) along with the rise in frequency. Two relaxation processes caused by grains and grain boundaries were identified from the fitting of a complex impedance plot with an equivalent circuit model (R_g C_g) (R_gb Q_gb C_gb). Asymmetry and depression in the semicircle having center present lower than the impedance real axis gave solid justification of dielectric behavior that is non-Debye in nature.

Electrodeposited Ni-Rich Ni-Pt Mesoporous Nanowires for Selective and Efficient Formic Acid-Assisted Hydrogenation of Levulinic Acid to γ-Valerolactone

In pursuit of friendlier conditions for the preparation of high-value biochemicals, we developed catalytic synthesis of γ-valerolactone by levulinic acid hydrogenation with formic acid as the hydrogen source. Both levulinic and formic acid are intermediate products in the biomass transformation processes. The objective of the work is twofold: the development of a novel approach for milder synthesis conditions to produce γ-valerolactone and the reduction of the economic cost of the catalyst. Ni-rich Ni-Pt mesoporous nanowires were synthesized in an aqueous medium using a combined hard-soft-template-assisted electrodeposition method, in which porous polycarbonate membranes controlled the shape and the Pluronic P-123 copolymer served as the porogen agent. The electrodeposition conditions selected favored nickel deposition and generated nanowires with nickel percentages above 75 atom %. The increase in deposition potential favored nickel deposition. However, it was detrimental for the porous diameter because the mesoporous structure is promoted by the presence of the platinum-rich micelles near the substrate, which is not favored at more negative potentials. The prepared catalysts promoted the complete transformation to γ-valerolactone in a yield of around 99% and proceeded with the absence of byproducts. The coupling temperature and reaction time were optimized considering the energy cost. The threshold operational temperature was established at 140 °C, at which, 120 min was sufficient for attaining the complete transformation. Working temperatures below 140 °C rendered the reaction completion difficult. The Ni₇₈Pt₂₂ nanowires exhibited excellent reusability, with minimal nickel leaching into the reaction mixture, whereas those with higher nickel contents showed corrosion.

Influences of pH and EDTA Additive on the Structure of Ni Films Electrodeposited by Using Bubble Templates as Electrocatalysts for Hydrogen Evolution Reaction

The structure of Ni films is essential to their electrocatalytic performance for hydrogen evolution reaction (HER). The pH value and EDTA (ethylene diamine tetraacetic acid) additive are important factors for the structure control of electrodeposited metal films due to their adjustment of metal electrocrystallization and hydrogen evolution side reactions. The structures of Ni films from 3D (three-dimensional) porous to compact and flat structure are electrodeposited by adjusting solution pH values or adding EDTA. It is found that when pH value increases from 7.7 to 8.1, 3D porous films change to compact films with many protrusions. Further increasing the pH value or adding 0.1 M EDTA causes compact and flat films without protrusions to appear. When pH ≤ 7.7, hydrogen bubbles with large break-off diameter are easily adsorbed on film surface acting as porous structure templates, and the electroactive ion species, Ni²⁺ and Ni(NH₃)_n²⁺ complexes with low coordination number (n ≤ 3), possess high reduction overpotential, which is beneficial to forming protrusions and smaller particles. So, porous Ni films are electrodeposited. In solutions with pH ≥ 8.1 or 0.1 M EDTA, Ni(NH₃)_n²⁺ complexes with high coordination number (6 ≥ n ≥ 3) and hexadentate chelate are formed. Due to the improved wettability, bubbles with a small break-off diameter rapidly detach the film surface resulting in strong stirring. The reduction overpotential is reduced, leading to the formation of larger particles. Therefore, the solution leveling ability increases, and it is difficult to form protrusions, thus it forms a compact and flat film. The 3D porous film exhibits excellent catalytic performance for HER due to the large catalytic activity area.

Synthesis and Characterization of Ni-Pt Alloy Thin Films Prepared by Supercritical Fluid Chemical Deposition Technique

Ni-Pt alloy thin films have been successfully synthesized and characterized; the films were prepared by the supercritical fluid chemical deposition (SFCD) technique from Ni(hfac)₂·3H₂O and Pt(hfac)₂ precursors by hydrogen reduction. The results indicated that the deposition rate of the Ni-Pt alloy thin films decreased with increasing Ni content and gradually increased as the precursor concentration was increased. The film peaks determined by X-ray diffraction shifted to lower diffraction angles with decreasing Ni content. The deposited films were single-phase polycrystalline Ni-Pt solid solution and it exhibited smooth, continuous, and uniform distribution on the substrate for all elemental compositions as determined by scanning electron microscopy and scanning transmission electron microscopy analyses. In the X-ray photoelectron spectroscopy (XPS) analysis, the intensity of the Pt 4f peaks of the films decreased as the Ni content increased, and vice versa for the Ni 2p peak intensities. Furthermore, based on the depth profiles determined by XPS, there was no evidence of atomic diffusion between Pt and Ni, which indicated alloy formation in the film. Therefore, Ni-Pt alloy films deposited by the SFCD technique can be used as a suitable model for catalytic reactions due to their high activity and good stability for various reactions.