Powering the Future by Iron Sulfide Type Material (FexSy) Based Electrochemical Materials for Water Splitting and Energy Storage Applications: A Review.

Water electrolysis is among the recent alternatives for generating clean fuels (hydrogen). It is an efficient way to produce pure hydrogen at a rapid pace with no unwanted by-products. Effective and cheap water-splitting electrocatalysts with enhanced activity, specificity, and stability are currently widely studied. In this regard, noble metal-free transition metal-based catalysts are of high interest. Iron sulfide (FeS) is one of the essential electrocatalysts for water splitting because of its unique structural and electrochemical features. This article discusses the significance of FeS and its nanocomposites as efficient electrocatalysts for oxygen evolution reaction (OER), hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), and overall water splitting. FeS and its nanocomposites have been studied also for energy storage in the form of electrode materials in supercapacitors and lithium- (LIBs) and sodium-ion batteries (SIBs). The structural and electrochemical characteristics of FeS and its nanocomposites, as well as the synthesis processes, are discussed in this work. This discussion correlates these features with the requirements for electrocatalysts in overall water splitting and its associated reactions. As a result, this study provides a road map for researchers seeking economically viable, environmentally friendly, and efficient electrochemical materials in the fields of green energy production and storage.

Recent Advances in Polymer Nanocomposites: Unveiling the Frontier of Shape Memory and Self-Healing Properties-A Comprehensive Review.

Shape memory and self-healing polymer nanocomposites have attracted considerable attention due to their modifiable properties and promising applications. The incorporation of nanomaterials (polypyrrole, carboxyl methyl cellulose, carbon nanotubes, titania nanotubes, graphene, graphene oxide, mesoporous silica) into these polymers has significantly enhanced their performance, opening up new avenues for diverse applications. The self-healing capability in polymer nanocomposites depends on several factors, including heat, quadruple hydrogen bonding, π-π stacking, Diels-Alder reactions, and metal-ligand coordination, which collectively govern the interactions within the composite materials. Among possible interactions, only quadruple hydrogen bonding between composite constituents has been shown to be effective in facilitating self-healing at approximately room temperature. Conversely, thermo-responsive self-healing and shape memory polymer nanocomposites require elevated temperatures to initiate the healing and recovery processes. Thermo-responsive (TRSMPs), light-actuated, magnetically actuated, and Electrically actuated Shape Memory Polymer Nanocomposite are discussed. This paper provides a comprehensive overview of the different types of interactions involved in SMP and SHP nanocomposites and examines their behavior at both room temperature and elevated temperature conditions, along with their biomedical applications. Among many applications of SMPs, special attention has been given to biomedical (drug delivery, orthodontics, tissue engineering, orthopedics, endovascular surgery), aerospace (hinges, space deployable structures, morphing aircrafts), textile (breathable fabrics, reinforced fabrics, self-healing electromagnetic interference shielding fabrics), sensor, electrical (triboelectric nanogenerators, information energy storage devices), electronic, paint and self-healing coating, and construction material (polymer cement composites) applications.

Thermochemical Activation of Wood with NaOH, KOH and H3PO4 for the Synthesis of Nitrogen-Doped Nanoporous Carbon for Oxygen Reduction Reaction.

Carbonization of biomass residues followed by activation has great potential to become a safe process for the production of various carbon materials for various applications. Demand for commercial use of biomass-based carbon materials is growing rapidly in advanced technologies, including in the energy sector, as catalysts, batteries and capacitor electrodes. In this study, carbon materials were synthesized from hardwood using two carbonization methods, followed by activation with H3PO4, KOH and NaOH and doping with nitrogen. Their chemical composition, porous structure, thermal stability and structural order of samples were studied. It was shown that, despite the differences, the synthesized carbon materials are active catalysts for oxygen reduction reactions. Among the investigated carbon materials, NaOH-activated samples exhibited the lowest Tafel slope values, of -90.6 and -88.0 mV dec-1, which are very close to the values of commercial Pt/C at -86.6 mV dec-1.

Pt-Coated Ni Layer Supported on Ni Foam for Enhanced Electro-Oxidation of Formic Acid.

A Pt-coated Ni layer supported on a Ni foam catalyst (denoted PtNi/Nifoam) was investigated for the electro-oxidation of the formic acid (FAO) in acidic media. The prepared PtNi/Nifoam catalyst was studied as a function of the formic acid (FA) concentration at bare Pt and PtNi/Nifoam catalysts. The catalytic activity of the PtNi/Nifoam catalysts, studied on the basis of the ratio of the direct and indirect current peaks (jd)/(jnd) for the FAO reaction, showed values approximately 10 times higher compared to those on bare Pt, particularly at low FA concentrations, reflecting the superiority of the former catalysts for the electro-oxidation of FA to CO2. Ni foams provide a large surface area for the FAO, while synergistic effects between Pt nanoparticles and Ni-oxy species layer on Ni foams contribute significantly to the enhanced electro-oxidation of FA via the direct pathway, making it almost equal to the indirect pathway, particularly at low FA concentrations.

Investigation of Hydrogen and Oxygen Evolution on Cobalt-Nanoparticles-Supported Graphitic Carbon Nitride.

This study focuses on fabricating cobalt particles deposited on graphitic carbon nitride (Co/gCN) using annealing, microwave-assisted and hydrothermal syntheses, and their employment in hydrogen and oxygen evolution (HER and OER) reactions. Composition, surface morphology, and structure were examined using inductively coupled plasma optical emission spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The performance of Co-modified gCN composites for the HER and OER were investigated in an alkaline media (1 M KOH). Compared to the metal-free gCN, the modification of gCN with Co enhances the electrocatalytic activity towards the HER and OER. Additionally, thermal annealing of both Co(NO3)2 and melamine at 520 °C for 4 h results in the preparation of an effective bifunctional Co3O4/gCN catalyst for the HER with the lower Eonset of -0.24 V, a small overpotential of -294.1 mV at 10 mA cm-2, and a low Tafel slope of -29.6 mV dec-1 in a 1.0 M KOH solution and for the OER with the onset overpotential of 286.2 mV and overpotential of 422.3 mV to achieve a current density of 10 mA cm-2 with the Tafel slope of 72.8 mV dec-1.

Effect of Pretreatment on the Nitrogen Doped Activated Carbon Materials Activity towards Oxygen Reduction Reaction.

Nitrogen-doped activated carbons with controlled micro- and mesoporosity were obtained from wood and wastes via chemical processing using pre-treatment (pyrolysis at 500 °C and hydrothermally carbonization at 250 °C) and evaluated as oxygen reduction catalysts for further application in fuel cells. The elemental and chemical composition, structure and porosity, and types of nitrogen bonds of obtained catalyst materials were studied. The catalytic activity was evaluated in an alkaline medium using the rotating disk electrode method. It was shown that an increase in the volume of mesopores in the porous structure of a carbon catalyst promotes the diffusion of reagents and the reactions proceed more efficiently. The competitiveness of the obtained carbon materials compared to Pt/C for the reaction of catalytic oxygen reduction is shown.

Three-Dimensional Au(NiMo)/Ti Catalysts for Efficient Hydrogen Evolution Reaction.

In this study, NiMo catalysts that have different metal loadings in the range of ca. 28-106 µg cm-2 were electrodeposited on the Ti substrate followed by their decoration with a very low amount of Au-crystallites in the range of ca. 1-5 µg cm-2 using the galvanic displacement method. The catalytic performance for hydrogen evolution reaction (HER) was evaluated on the NiMo/Ti and Au(NiMo)/Ti catalysts in an alkaline medium. It was found that among the investigated NiMo/Ti and Au(NiMo)/Ti catalysts, the Au(NiMo)/Ti-3 catalyst with the Au loading of 5.2 µg cm-2 gives the lowest overpotential of 252 mV for the HER to reach a current density of 10 mA·cm-2. The current densities for HER increase ca. 1.1-2.7 and ca. 1.1-2.2 times on the NiMo/Ti and Au(NiMo)/Ti catalysts, respectively, at -0.424 V, with an increase in temperature from 25 °C to 75 °C.

Low Au-content CoAu electrodes for environmental applications.

Six cobalt gold (CoAu) electrodes were prepared by electroless deposition using different gold-containing solutions (acidic and weakly acidic) and different Au deposition times. Characterization of CoAu electrodes was done by scanning electron microscopy with energy-dispersive X-ray spectroscopy, N2-sorption, and X-ray powder diffraction techniques. The possibility of using the prepared electrodes in environmental applications, i.e., for the electrochemical sensing of a trace amount of arsenic(iii) in weakly alkaline media was assessed. Employing the CoAu electrode (prepared by immersing Co/Cu into 1 mM HAuCl4 (pH 1.8) at 30 °C for 30 s) under optimized conditions (deposition potential -0.7 V and deposition time of 60 s), a low limit of detection of 2.16 ppb was obtained. Finally, this CoAu electrode showed activity for arsenic oxidation in the presence of Cu(ii) as a model interferent as well as in real samples. Furthermore, the use of CoAu electrode as an anode in fuel cells, namely, direct borohydride - hydrogen peroxide fuel cells was also assessed. A peak power density of 191 mW cm-2 was attained at 25 °C for DBHPFC with CoAu anode at a current density of 201 mA cm-2 and cell voltage of 0.95 V, respectively. The peak power density further increased with the increase of the operating temperature to 55 °C.

Steps towards highly-efficient water splitting and oxygen reduction using nanostructured ß-Ni(OH)2.

ß-Ni(OH)2 nanoplatelets are prepared by a hydrothermal procedure and characterized by scanning and transmission electron microscopy, X-ray diffraction analysis, Raman spectroscopy, and X-ray photoelectron spectroscopy. The material is demonstrated to be an efficient electrocatalyst for oxygen reduction, oxygen evolution, and hydrogen evolution reactions in alkaline media. ß-Ni(OH)2 shows an overpotential of 498 mV to reach 10 mA cm-2 towards oxygen evolution, with a Tafel slope of 149 mV dec-1 (decreasing to 99 mV dec-1 at 75 °C), along with superior stability as evidenced by chronoamperometric measurements. Similarly, a low overpotential of -333 mV to reach 10 mA cm-2 (decreasing to only -65 mV at 75 °C) toward hydrogen evolution with a Tafel slope of -230 mV dec-1 is observed. Finally, ß-Ni(OH)2 exhibits a noteworthy performance for the ORR, as evidenced by a low Tafel slope of -78 mV dec-1 and a number of exchanged electrons of 4.01 (indicating direct 4e--oxygen reduction), whereas there are only a few previous reports on modest ORR activity of pure Ni(OH)2.

Selective catalytic reduction of NO by NH3 using Mn-based catalysts supported by Ukrainian clinoptiolite and lightweight expanded clay aggregate.

In this study, Mn-based multicomponent catalysts supported by two different carriers (lightweight expanded clay aggregate and the Ukrainian clinoptiolite) were prepared by electroless metal deposition method and tested for the selective catalytic reduction of NO with ammonia (NH3-SCR de-NO). Prior to the activity test, all the catalysts prepared were characterized by inductively coupled plasma optical emission spectroscopy, field emission scanning electron microscopy (FESEM), energy dispersive X-ray mapping, X-ray photoelectron spectroscopy, H2-TPR and NH3-TPD techniques. The particular interest of the present study was focused on the investigation of the carrier's role in the NO catalytic reduction and the promoting effect provided by the incorporation of the small amount of Pt (0.1 wt.%) in the Mn-based catalytic layer. The results revealed that the carrier's role in the NO catalytic conversion can be considered as a factor determining the effectiveness of the conversion process. Ukrainian clinoptiolite was proved to be a more attractive carrier for the preparation of the effective SCR de-NO catalysts due to its intrinsic sorption capacity, surface acidity and the redox potential. The high NO conversion efficiency provided by the Mn-based clinoptiolite-supported catalysts can be explained by the synergistic effect between the carrier and the active species deposited. It was shown that both the Mn97.6Cu2.4/clinoptiolite and the Mn97.5Co2.5/clinoptiolite catalysts can be successfully applied as the low-temperature (100-300°C) catalysts for NH3-SCR de-NO. When the NO removal efficiency varies in the range of 86-91%, the additional incorporation of Pt in the active layer in the amount of 0.1 wt.% can enhance the NO reduction by about 5% on average.

Platinum Nanoparticles Modified Copper/Titanium Electrodes as Electrocatalysts for Borohydride Oxidation.

In this study, sodium borohydride oxidation has been investigated on the platinum nanoparticles modified copper/titanium catalysts (PtNPsCu/Ti), which were fabricated by employing the electroless copper plating and galvanic displacement technique. ICP-OES, XRD, FESEM, and EDX have been used to characterize PtNPsCu/Ti catalysts' composition, structure, and surface morphology. The oxidation of sodium borohydride was examined on the PtNPsCu/Ti catalysts using cyclic voltammetry and chrono-techniques.

Bimetallic Co-Based (CoM, M = Mo, Fe, Mn) Coatings for High-Efficiency Water Splitting.

Bimetallic cobalt (Co)-based coatings were prepared by a facile, fast, and low-cost electroless deposition on a copper substrate (CoFe, CoMn, CoMo) and characterized by scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray diffraction analysis. Prepared coatings were thoroughly examined for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline solution (1 M potassium hydroxide, KOH) and their activity compared to that of Co and Ni coatings. All five coatings showed activity for both reactions, where CoMo and Co showed the highest activity for HER and OER, respectively. Namely, the highest HER current density was recorded at CoMo coating with low overpotential (61 mV) to reach a current density of 10 mA·cm-2. The highest OER current density was recorded at Co coating with a low Tafel slope of 60 mV·dec-1. Furthermore, these coatings proved to be stable under HER and OER polarization conditions.