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To obtain highly efficient yet easily produced water-splitting cathodes, Ni-MoO2 composite coatings were electrodeposited at a Ni foam substrate with an open-pore structure, pore size of 450 µm, in a Watts-type bath. The concentration of MoO2 particles (about 100 nm) was varied, while the intensive mixing of the solution was provided by air bubbling with 0.5 L min−1. Electrodeposition was performed at different constant current densities at room temperature. The morphology and composition of the coatings were investigated by SEM and EDS. The hydrogen evolution reaction (HER) was tested in KOH of different concentrations, at several temperatures, in a three-electrode H-cell by recording polarization curves and EIS measurements. The lowest achieved HER overpotential was −158 mV at −0.5 A cm−2. Up-scaled samples, 3 × 3.3 cm2, were tested in a single zero-gap cell showing decreasing cell voltage (from 2.18 V to 2.11 V) at 0.5 A cm−2 over 5 h in 30% KOH at 70 °C with electrolyte flow rate of 58 mL min−1. Compared to pure Ni foams used as both cathode and anode under the same conditions, the cell voltage is decreased by 200 mV, showing improved electrode performance.

This study investigates the structure, electrochemical behavior and hydrogen evolution reaction (HER) performance of electrodeposited Ru–Co alloy coatings. The alloys were prepared from a 0.75 M Co2+ + 0.025 M Ru3+ solution at various potentials ranging from −0.5 to −1.2 V vs. SCE. Results reveal that the Ru and Co deposition processes are interdependent. The deposition of nobler Ru from the mixed metal solution reaches pure diffusion control already at −0.7 V compared to −1.0 V from a single Ru bath. On the other hand, Co deposition is significantly facilitated in the presence of Ru in the solution. Consequently, as the deposition potential changes from −0.6 to −1.0 V, Ru–Co solid solution coatings characterized by a distinct globular morphology are formed, with their Co content increasing from 22.1/7.4 to 70.2/86.1 wt% for the Cu/Ti2AlC MAX phase substrate applied. The alloy catalysts are found to show much better HER activity and stability in alkaline than in acidic solutions. The best Ru–Co@Ti2AlC sample, electrodeposited at −0.6 V, requires an overpotential of only −95 mV to deliver a current density of −100 mA cm−2 in 1 M KOH, thus outperforming most Ru–Co-based HER electrocatalysts reported to date.

Green Hydrogen Renewable Energy Based Society for Sustainable Economic Development-Challenges and Perspectives Nevenka R. Elezovic University of Belgrade – Institute for Multidisciplinary Research, Center of Excellence for Green Technologies, Kneza Viseslava 1, 11000 Belgrade, Serbia Email: nelezovic@tmf.bg.ac.rs, corresponding author The contemporary industry is mainly based on fossil fuels to be exhausted in near future. It causes environment pollution and greenhouse effect. During the last century the CO2 concentration increased 20%, raising average temperature on Earth. It means undesirable climate changes, biodiversity disorder and natural disasters. The development of alternative power sources is needed. United Nations had recognized problem and global actions have already taken. European Union established main targets until 2030- Climate and Energy Package. The Paris Agreement (2015) adopted by 196 Parties from all over the world facilitated low-carbon solutions. Zero-carbon solutions are increasing in economy, especially the power and transport sectors. ˝The global climate fight will be won or lost in this crucial decade – on our watch. So let’s fight together– and let's win˝ (A. Guterres, UN General Secretary-November 2022). Thus, development of hydrogen production and fuel cells as zero-emission technologies is needed, to achieve sustainability and circular economy. Hydrogen is high efficiency and environmental friendly fuel. It is produced by water electrolysis, industrial procedure processed in alkaline solution, at 80oC. The main disadvantage is still high energy consumption (~ 5kWh m-3 H2). The hydrogen fuel is used in fuel cells, while oxidative agent is oxygen from air. Many researchers' efforts were done to make progress in this area during past decades. State-of-the-art catalysts are noble metals (carbon supported Platinum) – still expensive for large-scale commercial use. In this research novel solutions for fuel cells catalysts based on low loadi

Green Hydrogen Energy Based Economy to Decrease Climate Changes for Environmental Friendly-Sustainable Development Nevenka R. Elrzovic University of Belgrade, Institute for Multidisciplinary Research, Center of Excellence for Green Technologies, Kneza Viseslava 1, 11000 Belgrade, Serbia, nelezovic@tmf.bg.ac.rs Abstract: Intensive fossil fuel application leads to the growing environment pollution, causing the "greenhouse effect". During the 20th century the CO2 concentration increased about 20%, being the main reason for average temperature increase on Earth. This fact has already caused undesirable climate changes. United Nations has recognized environment pollution effects and global actions have already been taken. From Stockholm conference held in 1972 to COP 2022, United Nations announced several declarations to stabilize gas emission and decrease greenhouse effect. European Union has established main targets until 2030, in the frame of Climate and Energy Package, to increase alternative power sources usage and save environment. Thus, the further development of green hydrogen production and fuel cells catalysts as environmental friendly-green technologies are extremely desirable, to achieve sustainable economic development. Hydrogen – high efficiency and environmental friendly fuel, produced by water electrolysis is used in low temperature fuel cells, while oxidative agent is oxygen from air. In this work novel nanostructured materials with noble metal nanoparticles deposited onto ceramics based supports have been investigated as the catalysts for fuel cells, promising alternative power sources. Several ceramic supports were developed - Ti, Sn and W based oxides, doped by Ru or Nb to improve conductivity. Physical-chemical and electrochemical characterization of these novel materials confirmed higher efficiency and long term stability to decrease the costs and increase life time of fuel cells acceptable for commercial application. Biography: Dr Nevenka R. Elezov

Razvoj novih katalizatora za niskotemperaturne gorivne ćelije-izazovi i perspektive Nevenka R. Elezovic1 1 Univerzitet u Beogradu, Institut za multidisciplinarna istraživanja, Kneza Višeslava 1, 11030 Beograd, Srbija *adresa za korespondenciju: nelezovici@tmf.bg.ac.rs Niskotemperaturne gorivne ćelije pripadaju grupi obnovljivih, ekološki prihvatljivih izvora energije. Primena zelenog vodonika kao čistog goriva, dobijenog elektrolizom vode, doprinosi zaštiti životne sredine, dostizanju održivog ekonomskog razvoja i cirkularne ekonomije, kao imperativa u procesu energetske tranzicije sa fosilnih goriva ka obnovljivim izvorima energije. U ovom radu će biti dat pregled razvoja novih materijala za katalizatore u reakcijama redukcije kiseonika i oksidacije vodonika, koje se odbvijaju u niskotemeraturnim vodoničnim gorivnim ćelijama. Naime, današnji komercijalni katalizatori su na bazi platine dispergovane na ugljeničnim nosačima razvijene površine-komercijalno nazvanim Vulkan XC-72 i Ketjen Black. Nedostatak ovih katalizatora je nedovoljna stabilnost, posebno na anodnim potencijalima 1.4 V prema reverzibilnoj vodoničnoj elektrodi, velika cena platine i još uvek velika masa Pt potrebne za isplativu masovnu komercijalizaciju, posebno za redukciju kiseonika, usled velike prenapetiosti i spore kinetike [1,2]. Razvoj novih katalizatora i nosača na bazi metalnih oksida [3] - titanijuma, kalaja, wolframa, kao i drugih neorganskih keramičkih materijala – karbida, nitrida [4] obeležio je poslednjih par decenija u radovima svetskih i naših naučnika iz ove oblasti. Diskutovane su prednosti i nedostaci ovih novih katalizatora u odnosu na komercijalno zastupljene. Takođe je prikazana uporedna analiza aktivnosti i stabilnosti novih platinskih katalizatora na neugljeničnim nosačima u odnosu na komercijalne. Zahvalnica Ovaj rad je finansijski podržalo Ministarstvo nauke, tehnološkog razvoja i inovacija Republike Srbije, u okviru ugovora br. 451-03-47/2023-01/ 200053 Literatura [1] 1 A. M

The oxygen reduction reaction was investigated at 10 monolayers (MLs) of Pt electrodeposited on (Nb–Ti)2AlC substrate. Following the discussion of detailed kinetics and electrodeposition optimisation in the authors’ previous paper, the focus of this research was on stability testing. Previously performed optimisation results showed the best activity shown by 10 monolayers of Pt. Catalyst characterisation was performed by scanning electron microscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. SEM, EDS and XPS analysis showed that the surface was covered with a homogeneous layer of Pt. TEM analysis of a cross-section confirmed the presence of Pt layer of thickness ∼3.5 nm, corresponding to the 10 MLs of Pt. Although the mass activity for the ORR at 0.8 V vs. RHE of 37.4 A g−1 was comparable with the best one for the Pt/C benchmark, US Department of Energy Protocols revealed excellent catalyst stability – the loss of electrochemically active surface area (EASA) was found to be only 9.3%.

MAX phases as the catalysts support materials for green energy related applications Nevenka R. Elezovic University of Belgrade-Institute for Multidisciplinary Research, Center of Excellence for Green Technologies, Kneza Viseslava 1, 11000 Belgrade, Serbia *Corresponding Author E-mail: nelezovic@tmf.bg.ac.rs ABSTRACT MAX phases – specific materials of general formula Mn+1AXn, (MAX) where n = 1 to 4, where M is early transition metal, A is element from the group of Al, Si or P and X is carbon or nitrogen, have attracted great attention in materials science, especially as high performance supports for noble metals group catalysts intended to be used for hydrogen production by water electrolysis, as well as for fuel cells reactions. These materials demonstrated good mechanical properties, high conductivity, high chemical and corrosion stability, especially in the potential range from hydrogen to oxygen evolution that is of great interest for low temperature fuel cells reactions. In this research ultra- low loading platinum layers were deposited onto Ti2AlC and (Nb-Ti)2AlC MAX phases supports and characterized as the catalysts for anode (hydrogen oxidation) and cathode (oxygen reduction) reactions for low temperature fuel cells. Physical-chemical characterization was performed by: Scanning Electron Microscopy (SEM), X-Ray Photoelectron Spectroscopy (XPS), Focus-Ion Beam High Resolution Transmission Electron Microscopy (FIB-HRTEM). The electrochemical characterization for both anode and cathode reactions was done by cyclic voltammetry and linear sweep voltammetry and very good activities were confirmed in comparison to carbon supported commercial catalysts. It should be emphasized that progress beyond state of the art was made in terms of lower Pt loading - being only 18.3 µg cm-2 (for HOR the state of the art is ≈ 50 µg cm-2, while for ORR 200 -400 µg cm-2). These novel catalysts exhibited high durability according to US DOE standardized tests, as well. It is worthy to m

Electrodeposited Co-Ru alloys at Ti2AlC suport as the catalysts for hydrogen production by water electrolysis towards sustainable economic development Nevenka Elezovic1*, D. Kutyla2, M. Krstajić Pajić3, U. Lačnjevac1, P. Zabinski2 1*University of Belgrade, Institute for Multidisciplinary Research, Kneza Viseslava 1, 11000 Belgrade, Serbia, *invited-presenting author – nelezovic@tmf.bg.ac.rs 2 Faculty of Non-Ferrous Metals, AGH University of Science and Technology, Mickiewicza Ave. 30, 30-059 Krakow, Poland; 3 University of Belgrade, Faculty of Technology and Metallurgy, 11000 Belgrade, Serbia; Abstract Cobalt-ruthenium alloys were electrochemically deposited at Ti2AlC suport from hloride based acid electrolyte. Thin layers of Co-Ru were obtained by potentiostatic electrodeposition in the potential range of -0.6 V to -1.0 V vs SCE. The chemical composition and physical-chemical characterization have been performed by X-ray Fluorescence spectroscopy (XRF), X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM-EDS). It was found that increasing of Co content in the alloy led to gradual shift of the crystalline structure from HCP to FCC Co-Ru solid solution. The electrochemical characterization of the catalysts was done by linear sweep voltammetry, cyclic voltammetry and electrochemical impedance spectroscopy in alkaline electrolyte. The optimal conditions for deposition of nanocrystalline Co-Ru alloys with superior activity for hydrogen evolution were discussed in terms of activity and stability, as well as commercial acceptable costs for the catalysts production. Acknowledgements: This work was supported by the Ministry of Science and Technological Development Republic of Serbia (Contract No. 451-03-68/2023-14/200053 and Contract No. 451-03-68/2023-14/200135). The authors would like to thank Prof. M. Barsoum, Drexel University–Philadelphia USA for Ti2AlC preparation. Keywords: Electrodeposition; Co– Ru alloys; MAX phases; Hydrogen Renewable Energy; Water split

Platinum layers on MAX phases based supports as advanced materials for low temperature fuel cells application NEVENKA R. ELEZOVIC* *University of Belgrade - Institute for Multidisciplinary Research, Kneza Viseslava 1, 11030 Belgrade, Serbia Proton exchange membrane fuel cells (PEMFCs) are considered as promising future environmental friendly power sources. However, before the commercialization some important issues have to be resolved. MAX phase materials, such as Ti2AlC or (Nb-Ti)2AlC have been considered as perspective materials for variety of applications. These materials demonstrated high chemical and corrosion stability, high conductivity – close to metals′ one, as well as excellent stability in a wide potential range when used for electrochemical systems in water solutions. Moreover, commercialization was achieved at a very reasonable price. Thus, above mentioned materials could be promising alternative for catalyst supports in PEMFCs if compared to state-of-the-art carbon based materials. On the other hand, platinum is considered as the best catalyst for both anode and cathode reactions taking place in PEMFCs: hydrogen oxidation and oxygen reduction, especially in acid solutions. Having in mind the high cost and scarcity of Pt, deposition of ultrathin Pt layers on Max phases could be of great practical importance. In this research a facile and cost effective electrochemical method for successful deposition of thin Pt films (up to 10 monolayers) onto Ti2AlC and (Nb-Ti)2AlC substrate was referred. The obtained catalysts were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscpopy (EDS), and X-ray photoelectron spectroscopy (XPS). The oxygen reduction and hydrogen oxidation reactions were investigated by linear sweep voltammetry at rotating disc electrode (RDE). The results confirmed high activity and excellent stability in comparison to commercial carbon based Pt catalyst. Challenges and perspectives of these novel materials f

Carbon free supported noble metal nanostructures for green energy production-challenges and perspectives Nevenka R. Elezovic University of Belgrade Institute for Multidisciplinary Research- Centre of Excellence for Green Technologies Serbia, e-mail: nelezovic@tmf.bg.ac.rs Abstract: Statement of the problem: The contemporary industrial processes, as well as transportation vehicles power are based on fossil fuels usage. Intensive fossil fuel application leads to the growing environment pollution, causing the "greenhouse effect". During the 20th century the CO2 concentration increased about 20%, being the main reason for average temperature increase on Earth. This fact has already caused undesirable climate changes, connected to animal and plants biodiversity disorder, Sea level rise, melting Arctic Sea ice layers, extreme nature disasters. United Nations has recognized environment pollution effects and global actions to prevent it have already been taken. From Stockholm conference held in 1972 and Kyoto in 1997 um to Paris Climate Agreement 2015 United Nations announced several declarations to stabilize gas emission and decrease greenhouse effect. European Union has established main targets until 2050, in the frame of Climate and Energy Package, to increase alternative power sources usage and save environment for future generations. Thus, the further development of water electrolysis and fuel cells catalysts (the subject of this work), as environmental friendly, green technologies are extremely desirable, to contribute to the environment protection and sustainable development. Hydrogen – high efficiency and environmental friendly fuel, produced by water electrolysis is used in low temperature fuel cells, while oxidative agent is oxygen from air. In this work novel nanostructured materials with noble metal nanoparticles (Pt and Pd) deposited onto carbon free- titanium-oxide based supports have been investigated as the catalysts for fuel cells, promising alternative pow

Catalytic activity towards the oxygen reduction reaction (ORR) in 0.5 M H2SO4 was investigated at sub-monolayers and ultra-thin layers (corresponding to 10, 30 and 100 monolayers, (MLs)) of Pt electrochemically deposited on (Nb-Ti)2AlC substrate. Electrochemical deposition of Pt layers on (Nb-Ti)2AlC substrate was achieved from the solution containing 3 mM K2PtCl4 + 0.5 M NaCl (pH 4) under the conditions of convective diffusion (RPM = 400) using linear sweep voltammetry (LSV) at a sweep rate of 2 mV s-1, by determining limiting potential for deposition of each Pt sample from the QPt vs. E curves. The Pt samples were characterized X-ray photoelectron spectroscopy (XPS). XPS analysis showed that practically the whole surface of (Nb-Ti)2AlC substrate is covered with homogeneous layer of Pt, while Pt ion reduction was complete to metallic form – Pt(0) valence state. Then oxygen reduction was studied at rotating disc electrode by cyclic voltammetry and linear sweep voltammetry. Two different Tafel slopes were observed, one close to 60 mV dec-1 in low current densities region and second one ~ 120 mV dec-1 in high current densities region. This novel catalyst exhibited higher activity in comparison to carbon supported one, in terms of mass activity – kinetic current density normalized to Pt loading., Ispitivana je reakcija redukcije kiseonika na tankim slojevima platine u 0.5 mol dm-3 H2SO4. Tanki slojevi platine – čija količina naelektrisanja odgovara 10, 30 i 100 teorijskih monoslojeva Pt su istaloženi na nosaču od (Nb-Ti)2AlC. Za elektrohemijsko taloženje je korišćen rastvor 3 mM K2PtCl4 + 0.5 M NaCl pH = 4, u uslovima konvektivne difuzije (RPM = 400) primenom metode linearne skenirajuće voltametrije (LSV) pri brzini promene potencijala od 2 mV s-1 . Elektrohemijski dobijeni platinski katalizatori na pomenutom nosaču su okarakterisani metodom fotoelektronske spektroskopija X-zraka (XPS), kao i elektrohemijskim tehnikama. Za određivanje realne elektrohemijski aktivne površine elektrode je primenjena ciklična voltametrija, integracijom ispod anodnog dela voltamograma u oblasti adsorpcije vodonika na potpotencijalima. Za ispitivanje kinetike reakcije redukcije kiseonika je korišćena metoda linearne skenirajuće voltametrije na rotirajućoj disk elektrodi. Dobijene su dve vrednosti Tafelovog nagiba, jedna približno 60 mV dek-1 u oblasti malih prenapetosti, a druga ~ 120 mV dek-1 , u oblasti većih gustina struje. Katalitička aktivnost katalizatora je poređena sa vrednostima iz literature dobijenim na platini na ugljeničim nosačima na 0.85 V prema reverzibilnoj vodoničnoj elektrodi, izražena kao kinetička gustina struje po realnoj površini electrode, ili specifična aktivnost – izražena kao kinetička gustina struje po masi platine. Pokazano je da katalizator sa 10 monoslojeva platine poseduje veoma dobru katalitičku aktivnost, posebno izraženu po masi istaložene platine.

Two types of iridium oxide films formed at the Ti-2 AlC substrate were investigated: (1) anodically electrodeposited iridium oxide film from the solution based on IrCl(3)xH(2)O; (2) iridium oxide film prepared by cycling thin layer of electrodeposited Ir in the 0.5 M H2SO4 from - 0.25 to 1.20 V. It was shown that during anodic electrodeposition of iridium oxide film (1) coulombic efficiency decreases with increasing anodic potential, being only 3% atE = 0.7 V vs. SCE and 26% atE = 0.62 V vs. SCE. A pair of peaks corresponding to the transition Ir(III)-oxide/Ir(IV)-oxide was present on the CVs recorded in 0.5 M H2SO4. While cycling pure Ir thin layer in the solution of 0.5 M H2SO4 from - 0.25 to 1.20 V (2) up to 100 cycles, typical CV response was characterized with the prepeak and a pair of peaks corresponding to the Ir(III)/Ir(IV)-oxide transition. With the increase of cycles number to 150, additional peak at potential of 1.0 V appeared. This peak was formed on the account of pair of peaks corresponding to the Ir(III)/Ir(IV)-oxide transition. The oxygen evolution reaction (OER) was investigated at both iridium oxide films. It was shown that the Tafel slope for the OER was similar to 40 mV dec(-1)for the first polarization curve, confirming that the rds was a reaction S-OH - gt S-O-ads + H++ e(-). As the number of recorded polarization curves increased, the activity of both types of iridium oxide films decreased, due to dissolution of iridium oxide films at the potentials of the OER. It is shown that anodically electrodeposited iridium oxide film is more active for the OER than that obtained by cycling electrodeposited iridium layer. However, both iridium oxide films exhibited insufficient stability.

Developing ultraefficient electrocatalytic materials for the hydrogen evolution reaction (HER) with low content of expensive platinum group metals (PGMs) via low-energy-input procedures is the key to the successful commercialization of green water electrolysis technologies for sustainable production of high-purity hydrogen. In this study, we report a facile room-temperature synthesis of ultrafine metallic Ir nanoparticles on conductive, proton-intercalated TiO2 nanotube (H-TNT) arrays via galvanic displacement. A series of experiments demonstrate that a controlled transformation of the H-TNT surface microstructure from neat open-top tubes to disordered nanostripe bundles (“nanograss”) is highly beneficial for providing an abundance of exposed Ir active sites. Consequently, for nanograss-engineered composites, outstanding HER activity metrics are achieved even at very low Ir(III) precursor concentrations. An optimum Ir@TNT cathode loaded with 5.7 μgIr cm−2 exhibits an overpotential of −63 mV at −100 mA cm−2 and a mass activity of 34 A mgIr−1 at −80 mV under acidic conditions, along with excellent catalytic durability and structural integrity. Density functional theory (DFT) simulations reveal that the hydrogen-rich TiO2 surface not only stabilizes the deposited Ir and weakens its H binding strength to a moderate intensity, but also actively takes part in the HER mechanism by refreshing the Ir catalytic sites near the Ir|H–TiO2 interface, thus substantially promoting H2 generation. The comprehensive characterization combined with theory provides an in-depth understanding of the electrocatalytic behavior of H-TNT supported PGM nanoparticles and demonstrates their high potential as competitive electrocatalyst systems for the HER.

The hydrogen evolution reaction (HER) was investigated at sub-monolayers of iridium electrodeposited on Ti2AlC substrate. The lowest amount of electrodeposited iridium was 3 close-packed (111) monolayers (3 ML), while the highest one was 22 ML (3, 5, 10, 15 and 22 ML). The lowest and the highest amounts of iridium were electrodeposited by linear sweep voltammetry (LSV), while the other three samples were electrodeposited by controlled potential coulometry, from the solution containing 1 mM, or 3 mM K3IrCl6 + 0.5 M Na2SO4 (pH 6.2) at 70 °C. The HER was investigated by polarization and electrochemical impedance spectroscopy (EIS) measurements. Polarization curves for iridium sub-monolayers equal, or higher than 6 ML showed low Tafel slope of -14 to -16 mV dec-1 up to about -0.1 A cm-2, while at higher current densities the Tafel slopes increased, varying between -40 and -72 mV dec-1. The highest value of exchange current density (jo) was obtained for 6 ML of electrodeposited iridium, being -27.89 A g-1. The overpotential at j = -0.3 A cm-2 could be determined for samples containing 15 ML and 22 ML of iridium, being 82 mV., Izdvajanje vodonika ispitivano je u rastvoru sumporne kiseline na elektrohemijski istaloženim slojevima (od 3 monosloja do 22 monosloja) iridijuma na podlozi od Ti2AlC. Najmanja i najveća količina iridijuma (3 i 22 monosloja) elektrohemijski su istaložene metodom linearne voltametrije, dok su preostala tri uzorka (6, 10 i 15 monoslojeva) elektrohemijski istaložena pri konstantnom potencijalu do potrebne količine naelektrisanja iz rastvora 1 mM, ili 3 mM K3IrCl6 + 0.5 M Na2SO4 (pH 6.2) na temperaturi rastvora od 70 °C. Reakcija izdvajanja vodonika ispitivana je na svim elektrodama snimanjem polarizacionih krivih. Za uzorak sa 22 monosloja Ir primenjena je i metoda impedanse. Polarizacione krive za uzorke sa 6, 10, 15 i 22 monosloja Ir bile su okarakterisane malom vrednošću Tafel-ovog nagiba od -14 to -16 mV dek-1 u oblasti gustina struja do -0.1 A cm-2, dok se Tafel-ov nagib povećavao pri većim gustinama struja varirajući od -40 do -72 mV dek-1. Najveća vrednost specifične gustine struje izmene (jo) dobijena je kod uzorka sa 6 monoslojeva Ir i iznosila je - 27.89 A g-1. Za uzorke sa 15 i 22 monosloja Ir vrednost prenapetosti pri gustini struje j = -0.3 A cm-2 (uslovi industrijske proizvodnje vodonika) iznosila je 82 mV.

The hydrogen evolution reaction (HER) was investigated in 0.5 M H2SO4 at thin iridium layers electrodeposited on Ti2AlC substrate. Five samples, varying in thickness from 4.5 nm to 255 nm, were electrodeposited from the solution containing K3IrCl6 + Na2SO4. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were applied for morphology and chemical composition analysis. Metallic iridium was detected by X-ray photoelectron spectroscopy (XPS). The HER was investigated by polarization and electrochemical impedance spectroscopy (EIS) measurements. Polarization curves were characterized with the low Tafel slopes -18 mV dec(-1), while at higher current densities increased up to -56 mV dec(-1). The overpotential at j = -0.1 A cm(-2) was-45 mV, while at j = -0.01 A cm(-2) varied from 25.1 mV to 36.1 mV. These novel catalysts exhibited excellent activity, especially under industrial conditions of hydrogen production (j = -0.3 A cm(-2)) the determined overpotentials were between 66 and 69 mV only.

Low loading PtAu nanoparticles supported on high area carbon were synthesized by water-in-oil microemulsion method and examined for formic acid and methanol oxidation. Prepared catalyst powder was characterized by Xray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). These techniques revealed that the catalyst contains rather agglomerated quasi-spherical particles, similar to 4 nm diameter, composed of a solid solution of Pt and Au with only similar to 4 at% of Au. In spite of such low Au content, both onset and peak potentials for CO oxidation are shifted some 150 mV to more positive values in comparison to Pt synthesized in the same manner due to stronger binding of CO as a result of notable electronic effect. It is important that this small quantity of Au also significantly influences oxidation of formic acid promoting direct path and suppressing indirect path in formic acid oxidation in a degree as expected by a much larger quantity of Au. Such improvement could be due exclusively by ensemble effect of high number of small Pt domains which formation could be possible only by very fine dispersion of such low Au quantity. High number of small Pt domains is corroborated by lower activity for methanol oxidation in comparison to Pt catalyst synthesized by the same procedure. These results emphasize the importance of the Au dispersion on the surface of Pt over its quantity in PtAu catalyst with regards to both, the ensemble and the electronic effects.

Low loading PtAu nanoparticles supported on high area carbon were synthesized by water-in-oil microemulsion method and examined for formic acid and methanol oxidation. Prepared catalyst powder was characterized by Xray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). These techniques revealed that the catalyst contains rather agglomerated quasi-spherical particles, similar to 4 nm diameter, composed of a solid solution of Pt and Au with only similar to 4 at% of Au. In spite of such low Au content, both onset and peak potentials for CO oxidation are shifted some 150 mV to more positive values in comparison to Pt synthesized in the same manner due to stronger binding of CO as a result of notable electronic effect. It is important that this small quantity of Au also significantly influences oxidation of formic acid promoting direct path and suppressing indirect path in formic acid oxidation in a degree as expected by a much larger quantity of Au. Such improvement could be due exclusively by ensemble effect of high number of small Pt domains which formation could be possible only by very fine dispersion of such low Au quantity. High number of small Pt domains is corroborated by lower activity for methanol oxidation in comparison to Pt catalyst synthesized by the same procedure. These results emphasize the importance of the Au dispersion on the surface of Pt over its quantity in PtAu catalyst with regards to both, the ensemble and the electronic effects.

The Ag, Pd and AgPd alloys of different morphologies and compositions were electrodeposited onto Au and glassy carbon (GC) disc electrodes from the solution containing 0.001 M PdCl2 þ 0.04 M AgCl þ 0.1 M HCl þ 12 M LiCl under the conditions of non-stationary (RPM ¼ 0, samples AgPd1 and AgPd2) and convective diffusion (RPM ¼ 1000, sample AgPd3). Electrodeposited alloy layers were characterized by the scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). Oxygen reduction reaction (ORR) was investigated on all coatings in 0.1 M NaOH solution saturated with oxygen. The j-E curves for the ORR were recorded by two proced- ures: (1) samples were cycled with 5 mV s 1 from open circuit potential (OCP) to 0.8 V for Ag and AgPd alloys (or 0.6 V for pure Pd) and back; (2) samples were cycled with 5 mV s 1 from open circuit po- tential to 0.45 V (formation of Ag2O, in the case of Pd formation of PdO and PdO2), from 0.45 V to 0.60 V and back to the OCP. Significant catalytic activity for the Ag and AgPd alloys was detected after cycling electrodes in the potential region of Ag2O formation and reduction. Increase of the catalytic activity for AgPd alloys was, for the first time in the literature, ascribed to the presence of a certain amount of Ag2O which could not be completely reduced during the reverse sweep from 0.45 V to 0.6 V. Catalytic activity of AgPd alloys was found to be closely related to the amount of non-reduced Ag2O (most probably in the form of Ag-hydroxide). In the absence of such treatment, the catalytic activity for the ORR on electro- deposited Ag and AgPd alloy coatings was not detected.

Formic acid is one of the most promising small organic molecules that can be used as fuel in polymer electrolyte fuel cells. These systems are recognized as high-efficiency energy conversion devices which could offer energy generated from electrochemical processes. At carbon supported platinum nanoparticles as state of the art anodic catalysts formic acid oxidation reaction (FAOR) proceeds through a dual path mechanism that includes the formation of CO in the indirect reaction pathway. Since CO is a catalytic poison, the best way to address this problem is to synthesize catalysts that would either provide prompt CO oxidation and removal, or favour the direct reaction pathway to completely avoid CO formation and electrode poisoning. PtAu systems are considered as efficient catalysts for FAOR due to the ensemble effect of Au on Pt, however the optimal ratio of these two elements is still quite vague. Given the experience with water in oil microemulsion synthesis for preparation of shape controlled Pt nanoparticles,1 bimetallic PtAu/C nanocatalysts were synthesized by the same procedure, following a simultaneous precursor reduction methodology.2 The amount of the capping agent used, was varied in order to cause formation of nanoparticles with different shape (cubic or tetrahedron like). Addition of a very low, but very finely dispersed amount of Au significantly increases the catalytic activity, and also affects kinetic of the particle growth, influencing the particle shape. Ordered structure of these particles contributes to their stability as well. These results were obtained by Electrochemical and High Resolution Transmission Electron Microscopy characterization (HRTEM) with Energy Dispersive X-ray Spectroscopy (EDXS), along with X-Ray Diffraction and (XRD) and X-Ray Photoelectron Spectroscopy (XPS).

Low loading PtAu nanoparticles supported on high area carbon were synthesized by water-in-oil microemulsion method and examined for formic acid and methanol oxidation. Prepared catalyst powder was characterized by Xray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). These techniques revealed that the catalyst contains rather agglomerated quasi-spherical particles, similar to 4 nm diameter, composed of a solid solution of Pt and Au with only similar to 4 at% of Au. In spite of such low Au content, both onset and peak potentials for CO oxidation are shifted some 150 mV to more positive values in comparison to Pt synthesized in the same manner due to stronger binding of CO as a result of notable electronic effect. It is important that this small quantity of Au also significantly influences oxidation of formic acid promoting direct path and suppressing indirect path in formic acid oxidation in a degree as expected by a much larger quantity of Au. Such improvement could be due exclusively by ensemble effect of high number of small Pt domains which formation could be possible only by very fine dispersion of such low Au quantity. High number of small Pt domains is corroborated by lower activity for methanol oxidation in comparison to Pt catalyst synthesized by the same procedure. These results emphasize the importance of the Au dispersion on the surface of Pt over its quantity in PtAu catalyst with regards to both, the ensemble and the electronic effects.

The "corrected accelerated service life test for hydrogen evolution reaction" (CASLT-HER), designed for application of certain electrode materials as cathodes in the cell for alkaline water electrolysis in 30 % KOH at 80 degrees C, was performed at electrodeposited NiSn alloy and Ni 40 mesh electrodes. The Ni 40 mesh was slightly etched, while the NiSn alloy coating was electro-deposited from the bath containing pyrophosphate, glycine, SnCl2 and NiCl2 onto Ni 40 mesh to the thickness of approximately 40 mu m. It is shown that the NiSn cathode possess from maximum 0.77 V to minimum 0.30 V better over-potential than the Ni 40 mesh electrode during the 5 years of their exploitation at the conditions of industrial alkaline water electrolysis. It is also shown that both electrodes should be held at j = -0.3 A cm(-2) for at least 5 h in order to establish stable overpotential response. The limiting overpotential values for applying cyclic voltammetry (CVs, to mimic "polarity inversion") should be determined in a separate experiment before the CASLT-HER and should be adjusted during the application of CVs.

A platinum nanocatalyst on Sb doped tin oxide support (Sb-SnO2) was synthesized and characterized as a catalyst for oxygen reduction reaction in 0.1 mol dm(-3) NaOH solution at 25 degrees C. Sb (5%) doped tin oxide support was synthesized by a modified hydrazine reduction procedure. The platinum nanocatalyst (20% Pt) on Sb-SnO2 support was synthesized by a borohydride reduction method. The synthesized support and catalyst were characterized by high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) and X-ray diffraction technique (XRD). X-ray photoelectron spectroscopy was applied to characterize the chemical status of elements before and after Pt-treatment. XPS spectra of Sn 3d, Pt 4f, Sb 3d and O 1s revealed that the Pt-deposition on Sb-SnO2 support induced the reduction of the Sn(4+) oxidation state to Sn(2+) and Sn(0) states, while Pt remained in the metallic state and Sb was in the (3+) oxidation state. Homogenous Pt nanoparticle distribution over the support, without pronounced particle agglomeration, was confirmed by HRTEM technique. The average Pt particle size was 2.9 nm. The electrochemically active Pt surface area of the catalyst was determined by the integration of the cyclic voltammetry curve in the potential region of underpotential deposition of hydrogen, after double layer charge correction, taking into account the reference value of 210 mu C cm(-2) for full monolayer coverage. This calculation gave the value of 51 m(2) g(-1). The kinetics of the oxygen reduction reaction with Pt/[Sb-SnO2 catalyst was studied by cyclic voltammetry and linear sweep voltammetry using a rotating gold disc electrode. Two different Tafel slopes were observed: one close to 60 mV dec(-1) in the low current density region, and another at similar to 120 mV dec(-1) in the higher current densities region, as was already referred in previous reports for the oxygen reduction reaction with polycrystalline Pt, as well as with different Pt

The Pd and three AgPd alloy layers (AgPd1, AgPd2 and AgPd3) were electrodeposited onto Au disc electrodes from the solution containing high concentration of chloride ions (>12 M). All coatings were investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), anodic linear sweep voltammetry (ALSV), while their surface composition was investigated by X-ray photoelectron spectroscopy (XPS). The AgPd1 and AgPd2 samples were electrodeposited at different constant current densities (−0.178 mA cm−2 and -0.415 mA cm−2 respectively) to the charge of −0.2 C cm−2 (thickness ∼ 0.18 μm) at a stationary disc electrode, while the sample AgPd3 was electrodeposited to the charge of −3.0 C cm−2 (thickness ∼ 2.8 μm) at a constant current density of −7.0 mA cm−2 under the conditions of convective diffusion. Samples AgPd1 and AgPd2 had similar morphologies of low roughness, while the morphology of AgPd3 was characterized by large crystals and higher roughness. The most active and the most poisoning tolerant coatings for ethanol oxidation reaction (EOR) are the AgPd3 and AgPd1 alloy samples, containing 72.6 at.% Ag – 27.4 at.% Pd and 84.7 at.% Ag – 15.2 at.% Pd respectively (XPS analysis). In this study, we demonstrated for the first time that the activity for the EOR at AgPd alloys was closely related to the amount of non-reduced Ag2O (most probably as Ag – hydroxide). Accordingly, all AgPd alloy samples had to be cycled in the potential region of Ag2O formation and reduction before the investigation of the EOR, in order to provide their catalytic activity towards the EOR. © 2018 Hydrogen Energy Publications LLC

The AgPd alloys were electrodeposited onto Au and glassy carbon disc electrodes from the solution containing 0 001 mol dm(-3) PdCl2 + 0.04 mol dm(-3) AgCl + 0.1 mol dm(-3) HCl + 12 mol dm(-3) LiCl under the non-stationary diffusion (quiescent electrolyte) and convective diffusion (omega = 1000 rpm) to the different amounts of charge and at different current densities. Electro-deposited alloy layers were characterized by the anodic linear sweep voltam-metry (ALSV), scanning electron microscopy, energy dispersive X-ray spectro-scopy (EDS) and X-ray photoelectron spectroscopy (XPS). The compositions of the AgPd alloys determined by the EDS were almost identical to the theoretically predicted ones, while the compositions obtained by XPS and ALSV analysis were similar to each other, but different from those obtained by EDS. Deviation from the theoretically predicted values (determined by the ratio j(L)(Pd)/j(Ag)) was more pronounced at lower current densities and lower charges of AgPd alloys electrodeposition, due to the lower current efficiencies for alloys electrodeposition. The ALSV analysis indicated the presence of Ag and Pd, expressed by two ALSV peaks, and in some cases the presence of the additional peak, which was found to correspond to the dissolution of large AgPd crystals, formed at thicker electrodeposits (higher electrodeposition charge), indicating, for the first time, that besides the phase structure, the morphology of alloy electrodeposit could also influence the shape of the ALSV response. In addition to Ag and Pd, the XPS analysis confirmed the presence of AgCl at the surface of samples electrodeposited to low thicknesses (amounts of charge).

The Pd and three AgPd alloy layers (AgPd1, AgPd2 and AgPd3) were electrodeposited onto Au disc electrodes from the solution containing high concentration of chloride ions (>12 M). All coatings were investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), anodic linear sweep voltammetry (ALSV), while their surface composition was investigated by X-ray photoelectron spectroscopy (XPS). The AgPd1 and AgPd2 samples were electrodeposited at different constant current densities (-0.178 mA cm(-2) and -0.415 mA cm(-2) respectively) to the charge of -0.2 C cm(-2) (thickness similar to 0.18 mu m) at a stationary disc electrode, while the sample AgPd3 was electrodeposited to the charge of -3.0 C cm(-2) (thickness similar to 2.8 mu m) at a constant current density of -7.0 mA cm(-2) under the conditions of convective diffusion. Samples AgPd1 and AgPd2 had similar morphologies of low roughness, while the morphology of AgPd3 was characterized by large crystals and higher roughness. The most active and the most poisoning tolerant coatings for ethanol oxidation reaction (EOR) are the AgPd3 and AgPd1 alloy samples, containing 72.6 at.% Ag - 27.4 at.% Pd and 84.7 at.% Ag - 15.2 at.% Pd respectively (XPS analysis). In this study, we demonstrated for the first time that the activity for the EOR at AgPd alloys was closely related to the amount of non-reduced Ag2O (most probably as Ag - hydroxide). Accordingly, all AgPd alloy samples had to be cycled in the potential region of Ag2O formation and reduction before the investigation of the EOR, in order to provide their catalytic activity towards the EOR.

Electrodeposited NiSn alloy coatings onto Ni 40 mesh substrate were tested for application as cathodes and anodes in the cell for alkaline water electrolysis in 30 wt% KOH at 80 degrees C. The "accelerated service life test" (ASLT) was performed for the hydrogen evolution reaction (HER), as well as for the oxygen evolution reaction (OER), and compared to that recorded for the Ni coating (Ni-dep) and Ni-mesh for both reactions. The morphology and chemical compositions of the NiSn and Ni coatings were investigated by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), while their surface composition was investigated by X-ray photoelectron spectroscopy (XPS) before and after the ASLT for both reactions, respectively. By measuring the potential at j = 0.3 A cm (-2) it was shown that during the ASLT the NiSn alloy coating catalytic activity for the HER decreases (about 24 mV after 25 cycles), while the catalytic activity for the OER increases (about 50 mV after 25 cycles), so that the cell voltage decreases for about 26 mV. The Ni-dep and Ni-mesh electrodes catalytic activity was found to increase for the HER (for about 103 mV), as well as for the OER (for about 52 mV) during the ASLT. Hence, the cell voltage for the Ni-dep and Ni-mesh electrodes decreased from 2.402 V to 2.245 V during the ASLT, while that for the NiSn electrode decreased from 1.967 V to 1.941 V. The cell voltage saving with the NiSn electrodes amounts to about 435 mV before the ASLT and about 304 mV after the ASLT. SEM results showed that no changes in the morphology of as prepared samples could be detected after the ASLTs for both reactions. EDS analysis confirmed that some changes occurred during the ASLT, particularly for the oxygen content in the surface layer. Similar conclusions were made from the XPS analysis.

Platinum nanocatalyst at nano-tungsten carbide was synthesized, characterized and tested for oxygen reduction reaction (ORR) in 0.1 mol dm−3 NaOH, at 25 °C. Tungsten-carbide islands on nano-tungsten particles (WC) was synthesized from gel prepared by using nanoparticles of WO3, previously produced from W-powder oxidized in H2O2. The support was porous material with high specific surface area (177 m2 g−1). The WC supported Pt (10 wt.%) catalyst was prepared by borohydride reduction method. X-ray diffraction of the catalyst demonstrates successful reduction of Pt precursor to metallic form. STEM analysis of Pt/WC catalyst showed the existence of Pt particles lower than 2 nm in size, even the clusters of Pt atoms. Electrochemically active surface area of Pt was determined from adsorption/desorption charge of hydrogen atoms. Catalytic activity of the synthesized catalyst for ORR was studied by cyclic voltammetry and linear sweep voltammetry at rotating disk electrode. The onset potential on Pt/WC for ORR, comparing with Pt/Vulcan, was shifted to the positive potentials for about 150 mV. Pt/WC catalyst shows one Tafel slope of −0.105 V dec−1, remarkable catalytic activity expressed either through the value of the current density per real surface area, or through the mass activity and excellent stability.

In order to point out the effect of the support to the catalyst for oxygen reduction reaction nano-crystalline Nb-doped TiO2 was synthesized through a modified sol-gel route procedure. The specific surface area of the support, SBET, and pore size distribution, were calculated from the adsorption isotherms using the gravimetric McBain method. The support was characterized by X-ray diffraction (XRD) technique. The borohydride reduction method was used to prepare Nb-TiO2 supported Pt (20 wt.%) catalyst. The synthesized catalyst was analyzed by TEM technique. Finally, the catalytic activity of this new catalyst for oxygen reduction reaction was investigated in acid solution, in the absence and the presence of methanol, and its activity was compared towards the results on C/Pt catalysts. Kinetic analysis reveals that the oxygen reduction reaction on Nb-TiO2/Pt catalyst follows four-electron process leading to water, as in the case of C/Pt electrode, but the Tafel plots normalized to the electrochemically active surface area show very remarkable enhancement in activity of Nb-TiO2/Pt expressed through the value of the current density at the constant potential. Moreover, Nb-TiO2/Pt catalyst exhibits higher methanol tolerance during the oxygen reduction reaction than the C/Pt catalyst. The enhancement in the activity of Nb-TiO2/Pt is consequence of both: the interactions of Pt nanoparticles with the support and the energy shift of the surface d-states with respect to the Fermi level what changes the surface reactivity. © 2010 Elsevier B.V.

The influence of poisoning of MoOx-Pt catalyst by CO on the kinetics of H2 oxidation reaction (HOR) at MoOx-Pt electrode in 0.5 mol dm-3 HClO4 saturated with H 2 containing 100 ppm CO, was examined on rotating disc electrode (RDE) at 25 °C. MoOx-Pt nano-catalyst prepared by the polyole method combined with MoOx post-deposition was supported on commercial carbon black, Vulcan XC-72. The MoOx-Pt/C catalyst was characterized by TEM technique. The catalyst composition is very similar to the nominal one and post-deposited MoOx species block only a small fraction of the active Pt particle surface area. MoOx deposition on the carbon support can be ruled out from the EDAX results and from the low mobility of these oxides under used conditions. Based on Tafel-Heyrovsky-Volmer mechanism the corresponding kinetic equations from a dual-pathway model were derived to describe oxidation current-potential behavior on RDE over entire potential range, at various CO coverages. The polarization RDE curves were fitted with derived polarization equations according to the proposed model. The fitting showed that the HOR proceeded most likely via the Tafel-Volmer (TV) pathway. A very high electrocatalytic activity observed at MoOx-Pt catalyst for the hydrogen oxidation reaction in the presence of 100 ppm CO is achieved through chemical surface reaction of adsorbed CO with Mo surface oxides. © 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.