Electrocatalysis of hydrogen evolution reaction on bimetallic nanostructures of PdAu, PtAu, and PdPt on carbon supports

Главни циљ ове докторске дисертације је развијање ефикасних електрокатализатора са што мањим уделом скупих племенитих метала. Електроде направљене депоновањем Au, Pt и Pd на различите угљеничне подлоге, испитиване су за електрокатализу реакције издвајања водоника у киселој средини. Метали су депоновани електрохемијском и/или спонтаном депозицијом на подлоге од стакластог угљеника или редукованог графен оксида. Подлоге су изабране ради њихове добре електричне проводљивости, инертности, ниске цене, као и њиховом доприносу каталитичкој активности услед синергије између подлоге и депонованих честица. Четири испитана система су PdAu и PdPt на стакластом угљенику и PdAu и PtAu на графену. Добијене електроде су карактерисане фотоелектронском спектроскопијом X-зрака помоћу које су одређене хемијске везе, оксидациона стања и атомски удео елемената на површини. Морфолошке карактеристике површине испитане су микроскопијом атомских сила и скенирајућом електронском микроскопијом. Електрохемијска карактеризација електрода одрађена је цикличном волтаметријом и линеарном волтаметријом којим су утврђене каталитичке особине електроде као и могући механизми издвајања водоника. Добијена активност је у већини случајева блиска или чак и боља од активности чисте Pt са далеко мањим уделом племенитих метала, што се може објаснити различитим електронским и геометријским ефектима између два депонована метала, као и између њих и подлоге, а који дају бољу активност него што је активност за сваки од њих појединачно. Стабилност електрода испитана је методом хроноамперометрије и нађено је да су добијене електроде стабилне у испитиваном периоду.The main goal of this doctoral thesis is the development of efficient electrocatalysts with a small amount of costly precious metals. Electrodes made by depositing Au, Pt, and Pd on different carbon supports are tested for electrocatalysis of hydrogen evolution reaction in an acid solution. Metals are deposited by electrochemical and spontaneous deposition on glassy carbon or reduced graphene oxide supports. These supports are chosen for their good electrical conductivity, inertness, low cost, and their contribution to the catalytic activity due to the synergy between support and deposited particles. Four investigated systems are PdAu and PdPt on glassy carbon and PdAu and PtAu on graphene. The obtained electrodes are characterized with photoelectron X-ray spectroscopy to determine chemical bonds, oxidation states, and atomic percentage of elements on the surface. The surface morphological characteristics are determined using atomic force microscopy, in the case of GC support and scanning electron microscopy for graphene support. The electrochemical characterization of electrodes is performed by cyclic voltammetry and linear sweep voltammetry to determine their catalytic performance and a possible mechanism of hydrogen evolution reaction. In most cases, the obtained activity is close to or even better than the activity of pure Pt, but with a far lower share of precious metals. That can be explained by different electronic and geometrical effects between deposited metals and between metals and support, thus contributing to better activity compared to the same bare precious metals or bare bimetallic electrodes. Electrode stability is tested by chronoamperometry, which shows that the investigated electrodes are stable during the testing period

The Effect of Sulphate and Chloride Palladium Salt Anions on the Morphology of Electrodeposited Pd Nanoparticles and their Catalytic Activity for Oxygen Reduction in Acid and Alkaline Media

Pd/GC electrodes were prepared by the electrochemical deposition of palladium on glassy carbon (GC) using PdSO4 or PdCl2 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 PdCl2 salt solution resulted in smaller palladium nanoparticles, but much higher GC surface coverage than from PdSO4. 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 PdCl2 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

Characterization and hydrogen evolution on Pt/nanoplatelets

Finding suitable catalysts for hydrogen evolution reaction (HER) is key for economic production of hydrogen for use in fuel cells. Reducing the amount of expensive noble metals that are used is one of the ways for obtaining such catalysts. Various combinations of different noble metals and various carbon supports have been studied. In this work nanoplatelets (GNP) was used as a support and on it Pt nanoparticles were electrochemically deposited in sub monolayer nanoislands. Obtained Pt/GNP electrode was characterized by X ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) while its electrocatalytic activity was investigated by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and chronoamperometry . XPS analysis showed that the atomic percentages of Pt in Pt/GNP was 1.3% for electhrochemical deposition and 0.3% for spontaneous deposition, respectively. SEM micrographs of Pt/GNP electrode surface showed that Pt nanoparticles occupy mostly the edges GNP support, while elemental maping confirms the distribution of Pt, C and O over the surface of the electrode. Pt/GNP electrode has shown remarkably good performance for HER reaction in 0.5 M H2SO4 acid solution. Outstanding HER activity was achieved, showing the initial potential close to the equilibrium potential for HER and of -0.003 V and a low Tafel slope of about -30 mV/dec. The chronoamperometric measurement performed over 180 min for hydrogen evolution at the constant potential indicates good stability and durability.Twenty-First Young Researchers’ Conference - Materials Science and Engineering: Program and the Book of Abstracts; November 29 – December 1, 2023, Belgrade, Serbi

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 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 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

Electrochemically exfoliated graphene as support of platinum nanoparticles for methanol oxidation reaction and hydrogen evolution reaction

To enhance the utilization efficiency of platinum (Pt) in electrochemical energy conversion, the precise selection of support materials presents a highly promising strategy. We have developed an efficient and stable bifunctional catalyst for methanol oxidation (MOR) and hydrogen evolution (HER) reaction in an alkaline medium. The Pt-based electrocatalyst, denoted as Pt/e-rGO with low Pt loading was successfully synthesized using graphene sheets as the support via chemical reduction using formic acid as the reducing agent. Graphene sheets are obtained by anodic electrochemical exfoliation of graphite tape. Significant enhancement of intrinsic activity toward MOR and HER was achieved for Pt/e-rGO compared to the commercial Pt/C catalyst. Structural characterization was performed by TEM, SEM and XPS. XPS analysis shows that the graphene is highly reduced. TEM analysis unveiled that the majority of the Pt nanoparticles (NPs) exhibit a diameter in the range of 4-5 nanometers, which is significant because the efficiency of electrooxidation of methanol on supported Pt NPs shows a strong dependence on particle size distribution. Catalyst activity was studied by cyclic voltammetry and linear sweep voltammetry in 0.1M KOH. Electrochemical active surface area (ECSA) was measured by CO-stripping voltammetry and estimated to be 67.93 m2 /g. Current density of 11.28 mA/cm2 ECSA at 0.82 V vs. RHE for MOR is achieved. Onset potential for MOR is 0.55 V vs. RHE. Meanwhile, for HER overporential at the current density -10 mA/cm2 ECSA was 119 mV.Twenty-First Young Researchers’ Conference - Materials Science and Engineering: Program and the Book of Abstracts; November 29 – December 1, 2023, Belgrade, Serbi

Improved Oxygen Reduction on GC-Supported Large-Sized Pt Nanoparticles by the Addition of Pd

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

Low-Loaded Pt Nanoparticles Supported on Electrochemically Exfoliated Graphene as a Sustainable Catalyst for Electrochemical Ethanol Oxidation

Securing ever-increasing energy demands while reducing resilience on fossil fuels is a major task of modern society. Fuel cells are devices in which the chemical energy of various fuels can be converted into clean electricity. Direct ethanol fuel cells (DEFC) are increasingly popular for their eco-friendliness and significantly easier liquid fuel manipulation compared to hydrogen-fed fuel cells. Carbon-supported Pt nanoparticles are considered reference catalysts for fuel oxidation in DEFCs. Several challenges hinder DEFC commercialization: high Pt-loading, Pt poisoning by CO intermediates, and the instability of the Pt and carbon supports. This work demonstrates an efficient electrocatalyst for ethanol oxidation reaction (EOR) composed of Pt nanoparticles supported on electrochemically exfoliated graphene (Pt/el-rGO). Graphene was obtained through anodic electrochemical exfoliation using graphitic tape as the anode, while Pt nanoparticles were synthesized using chemical reduction with formic acid. As-obtained Pt/el-rGO with only 7.5 wt.% Pt was characterized using TEM, SEM, and XPS. Pt/el-rGO exhibited notably higher EOR catalytic activity in an alkaline electrolyte than the Pt/C benchmark. This enhancement can be linked with the functional groups present on the graphene support, which facilitate ethanol dehydrogenation as the first step in the EOR mechanism and thus enhance reaction kinetics on Pt-active sites

Electrochemical Performance of Niobium MXenes with Lanthanum

MXenes are the newest class of two-dimensional nanomaterials characterized by large surface area, high conductivity, and hydrophilicity. To further improve their performance for use in energy storage devices, heteroatoms or functional groups can be inserted into the Mxenes’ structure increasing their stability. This work proposes insertion of lanthanum atoms into niobium-MXene (Nb-MX/La) that was characterized in terms of morphogy, structure, and electrochemical behavior. The addition of La to the Nb-MXene structure was essential to increase the spacing between the layers, improving the interaction with the electrolyte and enabling charge/discharge cycling in a higher potential window and at higher current densities. Nb-MX/La achieved a specific capacitance of up to 157 mF cm-2, a specific capacity of 42 mAh cm-2 at 250 mV s-1, a specific power of 37.5 mW cm-2, and a specific energy of 14.1 mWh cm-2 after 1000 charge/discharge cycles at 50 mA cm-