The Na0.54MnO2 powder is synthesized by the glycine nitrate method followed by annealing at 950 degrees C. Its crystal structure resembles a 3d tunnel with rod-like shapes, with an average crystallite width of 130 nm and a length in the micron range. The electrochemical performance of the Na0.54MnO2 - based electrode is tested in a NaNO3 solution. During potential cycling, the Na+ ions intercalation/deintercalation processes remain reversible, indicating good stability. For the current densities of 1000, 2000, and 5000 mA g- 1, the calculated specific capacities are 72.6, 66.8, and 57.5 mAh g- 1, respectively. Due to its suitable morphology for easy Na+ ions intercalation/deintercalation and good electrochemical performance, Na0.54MnO2 is a promising cathode material for aqueous Na-ion batteries.

The cobalt crystalline islands (Cocryst) were electrochemically deposited onto a glassy carbon (GC) support and then modified by a facile spontaneous deposition of platinum. The electrocatalytic activity of the resulting Cocryst-Pt core-shell catalyst was evaluated for the oxygen reduction reaction (ORR) in an alkaline medium. The XRD characterization of the Cocryst-Pt islands revealed that the cobalt core had a hexagonal close-packed (hcp) crystalline structure, and that the platinum shell exhibited a crystalline structure with a preferential (111) orientation. SEM images showed that the average lateral size of the Cocryst islands was 1.17 μm, which increased to 1.32 μm after adding platinum. The XPS analysis indicated that the outer layer of the bulk metallic Cocryst islands was fully oxidized. During the spontaneous deposition of platinum, the outer Co(OH)2 layer was dissolved, leaving the cobalt core in a metallic state, while the platinum shell remained only partially oxidized. The high electrochemically active surface area of the Cocryst-Pt/GC electrode, along with a suitable crystalline structure of the Cocryst-Pt islands, contributes to enhancing its ORR activity by providing a greater number of surface active sites for oxygen adsorption and subsequent reduction. The ORR on the Cocryst-Pt catalyst occurs via a four-electron reaction pathway, with onset and half-wave potentials of 1.07 V and 0.87 V, respectively, which exceed those of polycrystalline platinum and a commercial benchmark Pt/C.

Hydrogen evolution reaction (HER) was studied on rhodium nanoparticles electrochemically deposited under the same conditions on glassy carbon (Rh/GC) and on graphene nanoplatelets (Rh/GNPs) supports in 0.5 M H2SO4 solution. SEM revealed that the size of Rh nanoparticles ranged from 50 to 350 nm for Rh/GC and 20 to 70 nm for Rh/GNPs. XPS confirmed the presence of Rh in a low amount of 0.9 at% (6.8 wt%) in Rh/GC and 1.2 at% (8.6 wt%) in Rh/GNPs. The potentials for HER at 10 mA/cm2 are -0.076 V, -0.088, and -0.094 V, and the Tafel slopes are 42, 40, and 42 mV dec- 1 for Rh/GNPs, Rh/GC, and Rh(poly), respectively. Moreover, the Rh/GNPs electrode exhibits a higher Rh turnover frequency (TOF) of 3.7 H2 sites-1 s-1 than Rh/GC whose TOF value is 2.9 H2 sites- 1 s- 1. An exceptionally high HER activity and stability of the Rh/GNPs indicates the strong influence of the GNPs support.

We present a comparative study of the electrocatalytic performance of catalysts obtained by electrochemical and spontaneous deposition of Pt on glassy carbon (GC) and graphene nanoplatelets (GNPs) supports. Pt/GC, with high Pt loading, obtained by electrochemical deposition of Pt, and Pt/GNPs, with low Pt loading, obtained by spontaneous deposition, show the highest activity for the hydrogen evolution reaction (HER) in acid solution. AFM images of Pt/GC reveal that the GC coverage by Pt nanoparticles is 87%, while SEM images of Pt/GNPs do not show the presence of Pt species due to their small amount. XPS analysis confirms that the amount of Pt is 48.1 wt% in Pt/GC and 4.6 wt% in Pt/GNPs. The HER activity of both catalysts is equally high, showing onset potentials close to 0.0V (vs. RHE). The Tafel slopes of 30 mV/dec for Pt/GC and 37 mV/dec for Pt/GNPs indicate different HER mechanisms. (c) 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

This study examines the kinetics and mechanism of the oxygen reduction reaction (ORR) on a polycrystalline rhodium electrode (Rh(poly)) in acidic and alkaline media, using rotating disc electrode measurements. This study found that the ORR activity of the Rh(poly) electrode decreases in the order of 0.1 M NaOH > 0.1 M HClO4 > 0.05 M H2SO4 concerning the half-wave potentials. The Tafel slopes for ORR on Rh(poly) in the cathodic direction are 60 and 120 mV dec−1 at low and high overpotentials, respectively, in perchloric acid and alkaline solutions. However, strongly adsorbed sulfate anions hinder the ORR on Rh(poly) in sulfuric acid, leading to higher Tafel slopes. The highest ORR activity of Rh(poly) in an alkaline media suggests the promoting role of the specifically adsorbed OH− anions and RhOH. In all cases, ORR on Rh(poly) proceeds through the 4e-series reaction pathway.

PtAu nanoparticles spontaneously deposited on graphene support, PtAu/rGO, have shown remarkably high catalytic activity for hydrogen evolution reaction (HER) in sulfuric acid solution. SEM images of the PtAu/rGO electrode surface showed that Pt nanoparticles that are non-uniform in size occupy both the edges of previously deposited uniform Au nanoparticles and the edges of graphene support. XPS analysis showed that the atomic percentages of Au and Pt in PtAu/rGO were 0.6% and 0.3%, respectively. The atomic percentage of Au alone on previously prepared Au/rGO was 0.7%. Outstanding HER activity was achieved for the PtAu/rGO electrode, showing the initial potential close to the equilibrium potential for HER and a low Tafel slope of −38 mV/dec. This was confirmed by electrochemical impedance spectroscopy. The chronoamperometric measurement performed for 40 min for hydrogen evolution at a constant potential indicated good stability and durability of the PtAu/rGO electrode.

Pd/GC electrodes were prepared by the electrochemical deposition of palladium on glassy carbon (GC) using PdSO 4 or PdCl 2 salts. As-prepared GC-supported Pd nanoparticles were characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). XPS spectra revealed that the depositing palladium salt anion influences the oxidation state of the deposited Pd, while AFM images showed its effect on Pd nanoparticle size and coverage. The deposition from the PdCl 2 salt solution resulted in smaller palladium nanoparticles, but much higher GC surface coverage than from PdSO 4 . The activity of Pd/GC electrodes towards oxygen reduction was examined in acid and alkaline media using the rotation-disc electrode. Among the different Pd/GC electrodes, the one prepared using PdCl 2 salt with the full Pd coverage has shown the best ORR activity. The ORR occurs through a 4e-series reaction mechanism like on polycrystalline palladium but exceeds its activity concerning the initial potential.

PdPt bimetallic nanoparticles on carbon-based supports functioning as advanced electrode materials have attracted attention due to their low content of noble metals and high catalytic activity for fuel cell reactions. Glassy carbon (GC)-supported Pt and PdPt nanoparticles, as promising catalysts for the oxygen reduction reaction (ORR), were prepared by the electrochemical deposition of Pt and the subsequent spontaneous deposition of Pd. The obtained electrodes were examined using X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM), and electroanalytical techniques. An XPS analysis of the PdPt/GC with the highest ORR performance revealed that the stoichiometric ratio of Pd: Pt was 1:2, and that both Pt and Pd were partially oxidized. AFM images of PdPt2/GC showed the full coverage of GC with PdPt nanoparticles with sizes from 100–300 nm. The ORR activity of PdPt2/GC in an acid solution approached that of polycrystalline Pt (E1/2 = 0.825 V vs. RHE), while exceeding it in an alkaline solution (E1/2 = 0.841 V vs. RHE). The origin of the improved ORR on PdPt2/GC in an alkaline solution is ascribed to the presence of a higher amount of adsorbed OH species originating from both PtOH and PdOH that facilitated the 4e-reaction pathway.

HER was examined on various glassy carbon-supported Au and PdAu electrodes in acid solution. The Au/GC electrodes were obtained after Au was electrodeposited on a GC substrate by holding the potential for various times in 0.5 M H2SO4 solution containing AuCl4- ions. PdAu/GC electrodes were obtained after Pd has been added by a spontaneous deposition on previously prepared Au/GC electrodes. Surface morphology and chemical analysis of Au/GC and PdAu/GC electrodes were performed by atomic force microscopy and X-ray photoemission spectroscopy. Electrochemical characterization was performed by cyclic voltammetry in 0.5 M H2SO4 solution, while the linear sweep voltammetry was used to gain insight into the electrocatalytic activity of these electrodes for HER. 30minPd/10minAu/GC electrode consisting of 48% Pd and 65% Au, with the total coverage of the GC substrate with PdAu islands of 70%, showed the best catalytic activity for HER. A remarkable high activity and stability of this electrode makes it a promising catalyst for HER in acid solution. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

PdAu/GC nanoparticles obtained by the electrochemical deposition of gold followed by the spontaneous palladium deposition show a remarkable catalytic activity for the oxygen reduction reaction (ORR) in perchloric acid solution. AFM images reveal the size, shape, and coverage of the GC electrode with Au and PdAu nanoislands. Au/GC electrode with the full GC coverage by the deposited gold islands and activated by potential cycling shows the highest ORR activity. The initial potential for ORR shifts positively for 200 mV compared to polycrystalline gold. With the addition of palladium, the activity for ORR enhances significantly. For the most active PdAu/GC electrode, the initial potential shifts positively for another 250 mV, which coincides with polycrystalline palladium.

Cathodic material for sodium-ion rechargeable batteries based on NaxMnO2 were synthesized by glycine nitrate method and subsequent annealing at high temperatures. Different crystal structures with different morphologies were obtained depending on the annealing temperature: hexagonal layered alpha-Na0.7MnO2.05 nanoplates were obtained at 850 degrees C, while 3-D tunnel structured Na0.4MnO2 and Na0.44MnO2, both with rod-like morphology, were obtained at 800 degrees C and 900 degrees C, respectively. The investigations of the electrochemical behavior of obtained cathodic materials in aqueous NaNO3 solution have shown that Na0.44MnO2 obtained at 900 degrees C has shown the best battery performance. Its initial discharge capacities are 123.5 mA h/g, 113.2 mA h/g, and 102.0 mA h/g at the high current densities of 1000, 2000 and 5000 mA/g, respectively.

Hydrogen evolution reaction (HER) was investigated on reduced graphene oxide (rGO)-supported Au and PdAu nanoparticles in acid solution. The graphene spread over glassy carbon (rGO/GC) was used as a support for the spontaneous deposition of Au and Pd. The resulting Au/rGO and PdAu/rGO electrodes were characterized using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) techniques. Phase AFM images have shown that the edges of the rGO sheets were active sites for the deposition of both Au and Pd. XPS analysis revealed that the atomic percentages of both Au and PdAu nanoparticles were slightly higher than 1%. The activity of the PdAu/rGO electrode for the HER was remarkably high, with the overpotential close to zero. HER activity was stable over a 3 h testing time, with a low Tafel slope of approx. −46 mV/dec achieved after prolonged hydrogen evolution at a constant potential.

Hydrogen evolution reaction (HER) was studied in alkaline solution on Pt(poly) electrode modified by spontaneously deposited Ir nanoislands. Comprehensive insight into the characteristics of the bimetallic Ir/Pt(poly) catalysts was obtained by a combination of Atomic Force Microscopy (AFM), Field Emission Scanning Electron Microscopy (FESEM), X-ray Photoelectron Spectroscopy (XPS) and classical electrochemical techniques. HER investigations have shown that the presence of spontaneously deposited Ir enhances the activity of bare Pt(poly) in alkaline solution. This was attributed to the heterogeneity of the active surface sites and to the electronic interaction between two metals in close contact which together facilitated the adsorption of the H intermediate species.

Hydrogen evolution reaction (HER) was studied on polycrystalline Pd, Pd(poly), decorated by spontaneously deposited Ru nanoislands below full coverage. Surface features of as-prepared bimetallic Ru/Pd(poly) electrodes were explored by Field Emission Scanning Electron Microscopy with Energy Dispersive X-ray Spectrometer. Electrochemical properties and hydrogen evolution activities of obtained electrodes were investigated in an alkaline electrolyte by Cyclic and Linear Sweep Voltammetry, respectively. It was found that the activities of bimetallic Ru/Pd(poly) electrodes for HER significantly exceeded the activity of bare Pd(poly) and approached the activity of Pt, which is the most active material for this reaction. This enhancement was explained by the favorable influence of the electronic interaction between Pd substrate and Ru nanoislands on the adsorption of the reactive H species.

Single crystal gold electrodes, Au(hkl), modified by submonolayer deposit of highly active metals from platinum group are convenient bimetallic model systems for fundamental studies of the electrocatalytic activity of various nanostructures for fuel cell reactions. Preparation of such bimetallic electrodes was carried out by spontaneous deposition method, which was monitored by chronopotentiometric measurement of open circuit potential. Surface characterization of the modified bimetallic electrodes, as well as base substrate electrodes, were performed ex situ by atomic force microscopy Simultaneously recorded topographic and phase images provided insight into different characteristics of the bimetallic surfaces, such as the dimensions of the deposited islands, occurrence of the preferential deposition along specific surface sites and the substrate coverage with deposited islands. Phase AFM images display an obvious chemical contrast between two materials, independent of the surface topography enabling thus quite accurate estimation of the surface coverage, particularly important in the cases when the conventional ways are not accurate enough or not applicable. X-ray photoelectron spectroscopy has shown the oxidation state of the surface constituents of the as prepared bimetallic electrodes. Pronounced catalytic activity for hydrogen evolution reaction (HER) of gold single crystals decorated by palladium nanoislands with submonolayer coverage has been reported so far for different Pd/Au(111) nanostructures in acid [1] and alkaline [2] media. Rh/Au(111) bimetallic electrodes, obtained by the same spontaneous deposition method have shown even better catalytic activity for HER in acid solution [3]. The activity was in agreement to the one theoretically predicted for Au(111) surface covered with Rh overlayers, which was comparable to that of Pt(111) [4]. It was shown that among different Rh/Au(111) nanostructures, the one with 50% Rh coverage has shown the highest activity for HER in acid media, starting at approx. 100 mV more positive potential than the most active Pd/Au(111) [1], and very close to the activity of Pt(111), although not exceeding it. Similar order of activity has been reported for HER in alkaline solution [2,5]. Comparison of the catalytic activity of the most active Pd/Au(111) and Rh/Au(111) in acid and alkaline media is shown in Fig. 1. The research is extended to the use of Au(100) electrode as the substrate for the same foreign metals deposition. The comparison of the catalytic activity of bimetallic surfaces consisting of Pd or Rh islands spontaneously deposited with the same coverage on differently oriented gold single crystals have shown that those bimetallic surfaces having Au(111) as substrate is more active than the ones deposited on Au(100) as substrate. The improved catalytic activity of the hereby explored bimetallic electrodes was interpreted by means of geometric and electronic effects of the substrates, which are responsible for different electrocatalytic properties with respect to both constitutive metals. We belive that these results contribute to the current search for the efficient catalyst for HER. [1] M.Smiljanić, I. Srejić, B. Grgur, Z. Rakočević, and S. Štrbac, Electrocatal. 3, 369 (2012). [2] M.Smiljanić, I. Srejić, B. Grgur, Z. Rakočević, and S. Štrbac, Electrochim. Acta 88, 589 (2013). [3] M.Smiljanić, I. Srejić, B. Grgur, Z. Rakočević, and S. Štrbac, Electrochem. Commun. 28, 37 (2013). [4] G. Soldano, E.N. Schulz, D.R. Salinas, E. Santos, and W. Schmickler, Phys. Chem. Chem. Phys. 13, 16437 (2011). [5] S. Štrbac, M. Smiljanić, and Z. Rakočević, J. Electrochem. Soc. 163, D3027 (2016). Figure 1

Polycrystalline Pd electrode, Pd(poly), is modified by Ru nanoislands using spontaneous deposition method. Coverage of Pd(poly) electrode with the deposited Ru are approx. 20, 30 and 50% as estimated from phase atomic force microscopy images. The oxidation state of Pd substrate and the deposited Ru is determined by X-ray spectroscopy (XPS). Electrocatalytic activity of obtained Ru/Pd(poly) bimetallic electrodes is tested towards methanol oxidation in alkaline medium. Cyclic voltammetry and chronoamperometry experiments show the enhanced activity of Ru/Pd(poly) electrodes towards methanol electrooxidation with respect to bare Pd(poly). This is explained by the presence of Ru islands, which provided RuOH and Pd-RuOH sites, necessary for the oxidation of CO as the main intermediate during the oxidation of methanol at lower potentials. 30% Ru/Pd(poly) is the most active of all examined electrodes.

Rh/Au(100) and Rh/Au(111) electrodes with Rh coverage below a monolayer are prepared by a spontaneous deposition method. Electrodes are characterized by AFM and XPS. Hydrogen evolution reaction (HER) is studied by linear sweep voltammetry in 0.1 M HClO4 solution. Results for gold single crystals with 50% Rh coverage, which have shown the best catalytic activity for HER are presented in this work. Enhanced catalytic activity of such bimetallic electrodes compared to the ones with higher Rh coverage is ascribed to the presence of smaller Rh islands, which provide suitable active surface sites. Rather strong electronic interaction between Rh deposit and gold substrates, which is manifested by the upshift of Rh3d5/2 photoelectron line, also contributes to their activity. Structural effect is manifested through a higher activity of 50% Rh/Au(111) than 50% Rh/Au(100), which is consistent with the difference in activity of respective bare gold single crystals.

Iridium nanoislands are spontaneously deposited on Au(111) from (1 mMIrCl(3) center dot xH(2)O + 0.5 MH2SO4) depositing solution. Atomic Force Microscopy images of the obtained Ir/Au(111) bimetallic surfaces show that gold surface is fully covered with nanosized Ir islands after only 3 min of deposition. X-Ray Photoelectron Spectroscopy analysis shows that the deposit consists of a mixture of adsorbed hydrated IrCl3 and to a lesser extent of Ir(OH)(3). Cyclic Voltammetry characterization in 0.5 M H2SO4 solution does not show clear Hupd region prior to hydrogen evolution reaction (HER). Linear Sweep Voltammetry measurements show pronounced catalysis of HER on Ir modified Au(111) surface compared to bare Au(111). With prolonged Ir deposition, the observed limited increasing activity for HER of Ir/Au(111) surfaces is in accordance with the limited Ir/Au(111) surface morphology changes. (c) The Author(s) 2018. Published by ECS.

The objective of this study was to investigate the modification of materials used in wastewater treatment for possible antimicrobial application(s). Granulated activated carbon (GAC) and natural clinoptilolite (CLI) were activated using Cu2+- and Zn2+- ions and the disinfection ability of the resulting materials was tested. Studies of the sorption and desorption kinetics were performed in order to determine and clarify the antimicrobial activity of the metal-activated sorbents. The exact sorption capacities of the selected sorbents, GAC and CLI, activated through use of Cu2+- ions, were 15.90 and 3.60 mg/g, respectively, while for the materials activated by Zn2+- ions, the corresponding capacities were 14.00 and 4.72 mg/g,. The desorption rates were 2 and 3 orders of magnitude lower than their sorption efficacy for the Cu2+-, and Zn2+-activated sorbents, respectively. The intermediate sorption capacity and low desorption rate indicated that the overall antimicrobial activity of the metal-modified sorbents was a result of metal ions immobilized onto surface sites. The effect of antimicrobial activity of free ions desorbed from the metal-activated surface may thus be disregarded. The antimicrobial activities of Cu/GAC, Zn/GAC, Cu/CLI and Zn/CLI were also tested against Escherichia coli, Staphylococcus aureus, and Candida albicans. After 15 min exposure, the highest levels of cell inactivation were obtained through the Cu/CLI and the Cu/GAC against E. coli, 100.0 and 98.24%, respectively. However, for S. aureus and yeast cell inactivation, all Cu2+- and Zn2+-activated sorbents proved to be unsatisfactory. A characterization of the sorbents was performed by X-ray diffraction (XRD), X-ray photo electron spectroscopy (XPS), and field emission scanning electron microscopy (FE-SEM). A concentration of the adsorbed and released ions was determined by inductively coupled plasma-optical emission spectroscopy (ICP-OES) and mass spectrometry (ICP-MS). The results showed that the antimicrobial performance of the activated sorbents depended on the surface characteristics of the material, which itself designates the distribution and the bioavailability of the activating agent.