ZnO@RuO2 composites: Cost-effective trifunctional electrocatalysts for enhanced OER, HER, and ORR activities in water electrolysis

Affordable catalysts for use in water electrolysis and fuel cells as clean energy sources pose a significant challenge. Currently, platinum group metal catalysts are both expensive and difficult to obtain. In this research, an attempt is made to address this issue by investigating methods to reduce costs. Specifically, the use of RuO2 instead of Ru and the incorporation of a substantial amount of easily available ZnO, which has various applications, are explored. A composite of ZnO@RuO2 in a 10:1 molar ratio was synthesized using microwave processing of a precipitate. To enhance its catalytic properties, the composite was subsequently annealed at 300 and 600 °C. A detailed analysis of the crystal structure, morphology, optical and (photo)electrocatalytic properties of the processed 10ZnO@RuO2 catalyst particles was conducted. The catalytic activity of the prepared composites toward the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in 0.1 M NaOH and 0.1 M H2SO4 was investigated using linear sweep voltammetry (LSV). The measurements were taken both in the dark and under illumination after 60 minutes of exposure. To determine the intrinsic HER and OER activity of the studied catalyst, the LSV data were normalized by the electrochemical surface area (ECSA). Finally, the oxygen reduction reaction (ORR) activity of the catalysts was tested in both alkaline and acidic electrolytes

Zinc oxide-based materials with enhanced sunlight-driven photo- and photo-electro-catalytic activity

Current trend in photocatalysis is to develop efficient semiconductors which can be activated by absorbing sunlight. Which wavelength of sunlight will be absorbed depends on the semiconductor band gap; semiconductors with a wide band gap (> 3 eV) can absorb only UV light (5% of sunlight), while those with a narrow band gap (< 3 eV) can be activated by visible light (45% of sunlight). Zinc oxide (ZnO) is promising semiconductor with band gap of 3.37 eV. Various approaches have been applied to modify its optical properties, for example: incorporation of different metal and nonmetal ions or defects into the crystal structure, particles’ surface sensitization or hydrogenation. In this study, we examined the influence of different defects present in ZnO particles on their photo- and photo-electro-catalytic properties. Processing of ZnO particles were carried out in order to introduce: (1) lattice defects, through microwave procedure, (2) surface defects, through mechanical activation, and (3) surface defects, trough composite with polyethylene oxide. Synthesized particles were characterized by XRD, FESEM, laser diffraction particle size analyzer, Raman, UV-Vis diffuse reflectance and photoluminescence spectroscopy. The results of achieved photo- and photo-electro-catalytic tests indicate that both, structural and surface, defects enhanced sunlight-driven activity of ZnO particles

Improvement of electrochemical properties of ZnO nanoparticles via composites with graphene oxide

Due to their tunable multifunctional properties zinc oxide (ZnO) based materials have attracted extensive scientific and technological attention. Since they combines different properties such as electrochemical activities, chemical and photochemical stability, non-toxicity, biocompatibility, etc. ZnO-based materials have been used for variety of applications in electronics, opto-electronics, biosensing, bioimaging, drug and gene delivery, implants, antimicrobial and anticancer agents, as well as sensing in environmental applications. The main aim of this study was to improve efficiency of ZnO particles toward both electrochemical sensing for environmental application and electrocatalysis. To vary electrochemical properties, series of zinc oxide/graphene oxide (ZnO/GO) composites were synthesized by microwave processing of precipitate in the presence of a different amount (0.1 and 0.5 wt.%) of previously prepared GO as well as reduced GO (rGO). The particles crystal structure and phase composition were investigated by X-ray diffraction and Raman spectroscopy. The particles morphology was observed with FE–SEM while the textural properties (BET surface area and pore volume) were determined by low-temperature adsorption-desorption of nitrogen. The optical properties were studied using UV–Vis DRS and PL spectroscopy. The electrochemical sensing activity of ZnO, ZnO/GO and ZnO/rGO electrodes was tested for detection of bisphenol A in water solution while electrocatalytic activity was tested for water splitting when samples were used as anode materials and evaluated by linear sweep voltammetry in several different electrolytes. Differences in electrochemical activity between the composites were correlated with presence of GO, particles morphology and textural properties

ZnO/RuO2 nanostructured composites with enhanced bifunctional photo-electro catalytic activity toward water splitting

The demand for affordable and accessible catalysts to replace the expensive and scarce resourced platinum group metals (PGMs) has become increasingly vital. Since they combine different properties such as electrochemical activities, chemical and photochemical stability, non-toxicity, etc. ZnO-based materials have been examined for potential applications in electronics, optoelectronics, sensing in environmental applications as well as catalysis. This study focused on cost reduction of PGM materials by introducing RuO2 as a substitute for Ru and decreasing the amount of RuO2 through the incorporation of abundant and versatile ZnO. A composite of ZnO/RuO2 in a 10:1 molar ratio was synthesized using a microwave processing of a prepcipitate. To enhance its catalytic properties, the composite was subsequently annealed at 300 and 600 C. The physicochemical characteristics of the ZnO/RuO2 composites were analyzed using X-ray powder diffraction (XRD), Raman and Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), UV-Vis diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy. Furthermore, the electrochemical activity of the samples was assessed through linear sweep voltammetry in both acidic (0.1 M H2SO4) and alkaline (0.1 M NaOH) electrolytes. Remarkably, the ZnO/RuO2 composites exhibited excellent bifunctional catalytic activity for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in both types of electrolytes

Synthesis temperature influence on the structure, morphology and electrochemical performance of NaxMnO2 as cathode materials for sodium-ion rechearchable batteries

The lithium-ion batteries are the most commonly used for energy storage in portable devices. Since lithium is relatively rare on earth but rapidly consumed, it is necessary to find an adequate replacement. Owing to the similar chemical properties of sodium and lithium, but much higher availability, sodium ion batteries are one of the best candidates to replace lithium-ion batteries. A variety of materials such as manganese oxide, vanadium oxide or phosphate can be used as an electrode material (anode and cathode) in sodium ion batteries due to the high ability of intercalation of sodium. In this work, NaxMnO2 powder was synthesized by glycine nitrate method. The precursor powder was annealed for four hours at different temperatures: 800, 850, 900 and 950 °C. The characterization of the obtained materials was carried out using following methods: X-ray diffraction (XRD), scanning electron spectroscopy with energy dispersive X-ray spectroscopy (SEM/EDS) and transmission electron spectroscopy with energy dispersive Xray spectroscopy (TEM/EDS). Electrochemical properties were studied using cyclic voltammetry and chronopotentiometry in an aqueous solution of NaNO3. The layer structured Na0.7MnO2.05 with sheet-like morphology and Na0.4MnO2 with 3-D tunnel structure and rod-like morphology was obtained at 800 oC and 900 oC respectively. Na0.44MnO2 with rod-like morphology was annealed at 900 and 950 oC. 3D-tunnel structure Na0.44MnO2 obtained at 900 oC showed the best electrochemical behaviour in aqueous NaNO3 solution

Synthesis and characterization of Na0.4MnO2 as cathode material for aqueous sodium-ion batteries

The application of rechargeable batteries is growing significantly and there is a need for developing cheaper batteries with good performances. Sodium-ion batteries could be a viable option due to higher abundance of sodium against lithium mineral resources, its low price and similar principles intercalate Na+ ions as Li+ ions in lithium-ion batteries. Different materials as manganese oxides and vanadium oxide are used as electrode materials in sodium batteries. Na0.44MnO2 was regarded as one of the most promising cathode materials for sodium-ion batteries due to its high specific capacity and good cyclability. In this work, Na0.4MnO2 was synthesized using glycine-nitrate method (GNM). The structure of synthesized powder was characterized by X-Ray Diffraction (XRD), while the particles morphology was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The elemental mapping was performed by energy-dispersive Xray spectroscopy (EDS). XRD results showed that the phase structure of Na0.4MnO2 was orthorhombic with tunnel structure. TEM and SEM micrographs of obtained powder material showed uniformed rod-like shape particles with the average lengths and widths of 300 nm and 80 nm, respectively and EDS analysis confirmed that the sample contains Na, Mn, and O in an appropriate ration. The electrochemical behavior of Na0.4MnO2 was investigated by cyclic voltammetry (CV) in a saturated aqueous solution of NaNO3 at scan rates from 20 to 400 mV•s-1. The initial discharge capacity of Na0.4MnO2 in NaNO3 solution was 50 mA•h•g- 1, while after 15 cycles its value increased for 9%. while the efficiency (the ratio of the capacity charge and discharge) was amounting to ~ 95%. This indicates that material synthesized by GNM can be used as cathode material in aqueous sodium-ion batterie

Synthesis and Characterization of Na0.4MnO2 as a Positive Electrode Material for an Aqueous Electrolyte Sodium-ion Energy Storage Device

Due to the increasing use of batteries in everyday life and in industry, there is a need for developing cheaper batteries than the widely used lithium ion batteries. Lower price and higher abundance of sodium compared to lithium mineral resources intensified the development of Na-ion batteries. Aqueous lithium/ sodium rechargeable batteries have attracted considerable attention for energy storage because they do not contain flammable organic electrolytes as commercial batteries do, the ionic conductivity of the aqueous electrolyte is about two orders of magnitude higher than in non-aqueous electrolyte and the electrolyte salt and solvent are cheaper. Various materials such as manganese oxides, vanadium oxide and phosphates have been used as electrode materials (cathodic and anodic) in sodium batteries due to high sodium intercalation ability in both, organic and aqueous electrolytes. The most frequently used type of manganese oxides are Li–Mn–O or Na–Mn–O systems due to their tunnel or layered crystal structures which facilitate the lithium/sodium intercalation-deintercalation. In this work, a glycine-nitrate method (GNM) was applied for the synthesis of cathode material Na0.4MnO2

Na0.44Mn02 as a cathode material for aqueous sodium-ion batteries

The application of rechargeable batteries is growing significantly and it became the nlost important field for largescale electric energy storage. While lithiuln-ion batteries (LIBs) have great commercial success, due to their large energy and power density, their application was limited because of the availability of lithiunl and its high cost. Sodiunl-ion batteries (SIBs) can be a promissing alternative due to the huge availability of sodium, its low price and similar intercalating electrochelnistry to LIBs. Among various Na-ion battery materials, low-cost and tunnel-type, Na0.44Mn02 (NMO) was regarded as one of the most pronlising cathode materials for sodium-ion batteries, because of its high theoretical specific capacity (122 rnA h g1) and good cyclability [2]. In this work, for the synthesis of NMO powder, rapid glycine-nitrate nlethod (GNM) was used, which, on the basis of the literature review, has not been used to synthesize this material so far

ZnO-based nanostructured electrodes for biosensors: Corrosion behavior in Ringer’s physiological solution

Over the last decade, due to its numerous unique features that can achieve single biomolecule detection, zinc oxide have been examined as potential electrochemical biosensor for medical diagnosis. Previous studies proved success of ZnO-based materials in determining various biomolecules such as glucose, cholesterol, uric acid, etc. The materials being used as biosensors require special characteristics including high corrosion resistance. The main goal of this study was to examine biocorrosion characteristics of ZnO materials in Ringer’s physiological solution as a function of immersion time. Six different ZnO nanostructured powders were synthesized by microwave processing with an aid of citric acid and CTAB in different weight amount (5, 10, and 20 wt.%). To comprehend the influence of physicochemical characteristics of ZnO samples on biocorrosion, decisive features such as the crystal structure, morphology, textural properties, and surface chemistry were systematically investigated and correlated with biocorrosion activity. The biocorrosion activity of the samples was measured by potentiodynamic polarization technique. The measurements were performed on a potentiostat using a conventional three-electrode cell and a Ringer’s solution as the electrolyte. Platinum foil and a standard calomel electrode (SCE) were used as the counter and the reference electrode, respectively, while FTO glass was used as the working electrode. The working electrode was coated with a thin film of ZnO ink prepared by mixing of a ZnO powder as an active material and Nafion solution as a binder. Prepared specimens were immersed in 100 ml of Ringer’s solution for different immersion times ranging from 30 min to 7 days. The immersed specimens were then characterized by potentiodynamic polarization techniques in the potential range from -0.2 to +0.3 V vs SCE, at the scan rate of 0.1 mVs-1. We found that all examined ZnO samples has low biocorrosion activity. Slight differences in biocorrosion activity between the samples are determined by particles morphology, textural properties and surface chemistry influenced by used surfactants

Investigation of hydrogen evolution reaction on ZnO/rGO

The hydrogen evolution reaction (HER) is one of the indispensable parts of the water splitting process and is increasingly being researched [1]. The main goal of this study was to enhance the electrochemical properties of nanostructured zinc oxide (ZnO) particles toward HER. In order to enhance their electrochemical properties, ZnO nanoparticles were precipitated onto graphene oxide (GO) to form a ZnO/GO composite which was in situ reduced before electrochemical measurements toward HER. A composite of ZnO/GO (0.1 and 0.5 wt.%) was synthesized using a microwave processing of a precipitate. X-ray diffraction analysis (XRD), Raman spectroscopy, and field emission scanning electron microscopy (FESEM) were used to investigate the structural and morphological characteristics of composite materials. The diffractograms showed narrow reflections with relatively high intensities, which implies high crystallinity of composite materials. Raman spectra of ZnO/GO_0.5 shows a higher intensity D- and G-bands, attributed to GO, than ZnO/GO_0.1 confirming a larger amount of graphene oxide. FESEM images of composite samples show nanostructured particles. Before HER measurements, the electrode prepared by a mixture of ZnO/GO composite, nafion and ethanol/water solvent, was in situ reduced at potential -1.4 V in 0.1 M KCl to get ZnO/rGO. HER activity was investigated in NaOH by linear voltammetry. ZnO/rGO_0.5 showed increased electrochemical activity as a result of the evolution of hydrogen starting earlier and the higher current density