Nedavni razvoj kompozitnih elektrokatalizatora reakcije izdvajanja vodonika na bazi TiO2 nanotubularnih nizova kao nosača

Elektroliza vode u kombinaciji sa obnovljivim izvorima energije, kao što su Sunce ili vetar, predstavlja najefektivniji put za dobijanje ultračistog zelenog vodonika kao goriva sa nultom emisijom ugljenik-dioksida. Šira komercijalizacija elektrolizera vode umnogome zavisi od cene, aktivnosti i radnog veka katalizatora za katodnu reakciju izdvajanja vodonika. Često korišćena strategija za smanjenje sadržaja i povećanje masene aktivnosti skupocenih katodnih nanokatalizatora jeste njihova imobilizacija na provodne nosače sa visokorazvijenom površinom i dobrom mehaničkom i hemijskom stabilnošću. Uređene TiO2 nanotubularne strukture pripremljene anodnom oksidacijom titana su zbog svojih jedinstvenih optičkih, poluprovodničkih i elektronskih karakteristika intenzivno ispitivane za različite primene u fotokatalizi i fotoelektrohemiji [1]. Međutim, tek odnedavno je prepoznat njihov potencijal kao nosača u elektrokatalizi reakcije izdvajanja vodonika [2], pre svega zbog dobre provodnosti u katodnom smeru, trodimenzionalne strukture velike površine, korozione stabilnosti u kiseloj i alkalnoj sredini, ekološke neškodljivosti i niske cene. Ovo predavanje daće kratki osvrt na metode sinteze, strukturna i elektrohemijska svojstva i elektrokatalitičku aktivnost za izdvajanje vodonika nedavno prijavljenih kompozitnih materijala na bazi TiO2 nanotubularnih nizova. Literatura [1] K. Lee, A. Mazare, P. Schmuki, One-dimensional titanium dioxide nanomaterials: Nanotubes, Chem. Rev. 114 (2014) 9385. [2] U.Č. Lačnjevac, V.V. Radmilović, V.R. Radmilović, N.V. Krstajić, RuOx nanoparticles deposited on TiO2 nanotube arrays by ion-exchange method as electrocatalysts for the hydrogen evolution reaction in acid solution, Electrochim. Acta 168 (2015) 178-190

Ni-MoO2 composite cathodes for hydrogen evolution in alkaline solution: Effect of aging of the electrolyte for their electrodeposition

In this work the effect of aging of the electrolyte for electrodeposition of Ni-MoO2 composite coatings on their morphology (scanning electron microscopy), chemical composition (energy-dispersive X-ray spectroscopy), polarization characteristics and the “service life” test performance for the hydrogen evolution reaction (HER) in 32 mass % NaOH at 90°C was investigated. Polarization characteristics and results of the “service life” test of Ni-MoO2 composite coatings obtained after different aging periods of the electrolyte for deposition (suspension of MoO2 powder particles in the solution containing 2 M NH4Cl + 0.2 M NiCl2) were compared with that recorded for De Nora’s commercial Ni+RuO2 cathode coating (DN). It was shown that aging of the electrolyte did not influence the morphology and chemical composition of Ni-MoO2 composite coatings electrodeposited under simulated conditions for their industrial production, while polarization characteristics for the HER were influenced. The best coating, obtained after 180 days of the electrolyte aging, showed completely different (layered) structure of the deposit and significantly better performance than the commercial DN electrode during the “service life” test. [Projekat Ministarstva nauke Republike Srbije, br. 172054

On the kinetics of the hydrogen evolution reaction on Ni-MoOx composite catalysts in alkaline solutions

MoO3 particles were co-deposited with Ni onto smooth or rough Ni supports from modified Watt’s baths of different compositions. Morphology and composition of the electrodeposits were characterized by means of cyclic voltammetry, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy. The electrocatalytic activity of the composite catalysts for H2 evolution in alkaline solutions was determined by quasi-stationary polarization curves. Activity increases with MoOx content in the Ni deposit up to a limiting value. Composite Ni-MoOx catalyst performed high catalytic activity, similar to that of commercial Ni-RuO2 catalyst. Stability tests showed that Ni-MoOx codeposits are stable under condition of constant current and exhibit excellent tolerance to repeated short-circuiting

Ni-(Ebonex-supported Ir) composite coatings as electrocatalysts for alkaline water electrolysis. Part I: Hydrogen evolution

The hydrogen evolution reaction (HER) was studied at electrodeposited Ni and Ni-(Ebonex/Ir) composite coatings in 1 mol dm-3 NaOH solution at 25 °C. The Ni-(Ebonex/Ir) coatings were electrodeposited from a nickel Watts type bath containing different amounts of suspended Ebonex/Ir(30 wt.%) powder particles (0-2 g dm-3) onto a Ni 40 mesh substrate. The electrodes were investigated by cyclic voltammetry (CV), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), electrochemical impedance spectroscopy (EIS) and polarization measurements. It was shown that the roughness factor of coatings increased to a maximum value of 27 with increasing the concentration of Ebonex/Ir particles in the deposition bath, while that of a pure Ni coating was found to be 3.2. In the whole potential range of the HER only one Tafel slope of about -120 mV dec-1 was observed at all polarization curves. Considerably improved intrinsic catalytic activity for the HER compared to pure Ni was achieved with the composite coating deposited from the bath with the lowest concentration of Ebonex/Ir particles (0.1 g dm-3). Further enhancement of the apparent catalytic activity for the HER of Ni-(Ebonex/Ir) composite coatings obtained at higher concentrations of suspended Ebonex/Ir particles in the bath was attributed only to the increase of their electrochemically active surface area. © 2015 Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved

Electrodeposition of cobalt powders with novel three-dimensional structure

Novel three-dimensional cobalt powder structures were successfully prepared by electrodeposition. Electrodeposited cobalt powder was characterized by scanning electron microscopy (SEM) and light microscopy. It was possible to control the morphology and structure of cobalt particles by adjusting process parameters of electrodeposition such as current density and type of working electrode. The morphology and structure of cobalt powders were investigated and the formation mechanism of agglomerate was also discussed

Electrodeposition of iron powder particles of different characteristics

Iron deposits obtained at high current densities and overpotentials are very important from a technological point of view. It has been stated that the open and porous structures of copper or iron deposits obtained at high current densities were ideally suited for use as electrodes in electrochemical devices such as fuel cells, batteries and chemical sensors, while the extremely high surface area is relevant for evaluating some electrochemical reactions. Mainly two types of electrolytes were investigated and these were based on sulfate and chloride electrolytes. With increasing duration of electrolysis, dendrites merge, which is unacceptable for the case of further application. These deposits must be grinded in order to obtain powders. However, in the range of lower acidity the deposits become powdery and, in some cases, may be spongy and sticky. Generally, up to now research indicates that electrodeposition of Fe powders have two steps, deposition of fragile film and grinding. It must be emphasized that we tried and succeeded to obtain Fe powders without grinding process. The aim of this work was to investigate electrodeposition processes of Fe powders from sulfate and chloride electrolytes and morphologies of powder as a function of type of electrolyte and current density.Belgrade, Serbia, June 6-10, 201

Electrodeposition of iron powder particles of different characteristics

Iron deposits obtained at high current densities and overpotentials are very important from a technological point of view. It has been stated that the open and porous structures of copper or iron deposits obtained at high current densities were ideally suited for use as electrodes in electrochemical devices such as fuel cells, batteries and chemical sensors, while the extremely high surface area is relevant for evaluating some electrochemical reactions. Mainly two types of electrolytes were investigated and these were based on sulfate and chloride electrolytes. With increasing duration of electrolysis, dendrites merge, which is unacceptable for the case of further application. These deposits must be grinded in order to obtain powders. However, in the range of lower acidity the deposits become powdery and, in some cases, may be spongy and sticky. Generally, up to now research indicates that electrodeposition of Fe powders have two steps, deposition of fragile film and grinding. It must be emphasized that we tried and succeeded to obtain Fe powders without grinding process. The aim of this work was to investigate electrodeposition processes of Fe powders from sulfate and chloride electrolytes and morphologies of powder as a function of type of electrolyte and current density.Belgrade, Serbia, June 6-10, 201

Mechanism of formation of the honeycomb-like structures by the regime of the reversing current (RC) in the second range

Electrodeposition of copper in the hydrogen co-deposition range by the regime of reversing current (RC) in the second range has been investigated by determination of the average current efficiency for hydrogen evolution reaction and by scanning electron (SEM) and optical (OM) microscopic analysis of the obtained deposits. Keeping the cathodic current density, the cathodic and the anodic pulses constant in all experiments, the anodic current density (ja) values were varied: 40, 80, 160, 240 and 320 mA cm−2. The Cu deposits produced by the RC regimes with different anodic current density values were compared with that obtained in a constant galvanostatic regime (DC) at the current density equal to the cathodic current density in the RC regimes. The honeycomb-like structures were formed in the DC regime and by the RC regimes with ja of 40 and 80 mA cm−2. The hole size in them was in the 60–70 μm range. Due to the decrease of quantity of evolved hydrogen with increasing anodic current density, the larger dish-like holes with dendrites at their bottom and shoulder were formed with ja values of 160, 240 and 320 mA cm−2. The maximum number of holes, and hence, the largest specific surface area of the honeycomb-like electrodes was obtained with ja = 80 mA cm−2, that can be ascribed to a suppression of coalescence of neighboring hydrogen bubbles. Application of the RC regime also led to the increase of uniformity of structures, what is concluded by cross section analysis of the formed honeycomb-like electrodes. For the first time, mechanism of Cu electrodeposition in the hydrogen co-deposition range by the RC regime in the second range was proposed and discussed.This is peer-reviewed version of the article: Journal of Electroanalytical Chemistry, 2019, 833, 401-410, [https://doi.org/10.1016/j.jelechem.2018.12.021][http://cer.ihtm.bg.ac.rs/handle/123456789/2986

Accelerated service life test of electrodeposited NiSn coatings as bifunctional hydrogen and oxygen evolution catalysts for alkaline water electrolysis

Electrodeposited NiSn alloy coatings were tested for application as cathodes and anodes in the cell for alkaline water electrolysis in 30 wt.% KOH at 80 ºC. The "accelerated service life test" (ASLT) was performed for HER and OER reactions, and compared to those for Ni electrode. The morphology and chemical compositions of the NiSn and Ni coatings were investigated by SEM and EDS, while their surface composition was investigated by XPS before and after the ASLT for both reactions, respectively. It was shown that the cell voltage at j = 0.3 A cm-2 saving with the NiSn electrodes amounts to about 435 mV before 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 and XPS analysis confirmed that some changes occurred during the ASLT, particularly for the oxygen content in the surface layer. This work was financially supported by Ministry of Education, Science and Technological Development Republic of Serbia, under Contract No. 172054. he authors would like to acknowledge networking support by the COST Action MP1407

Ni-MoO2 cathodes for hydrogen evolution in alkaline solutions. Effect of the conditions of their electrodeposition

The electrodeposition of Ni-MoO2 composite coatings is a specific process taking place under defined hydrodynamic conditions. In this work the influence of hydrodynamics, current density, and MoO2 concentration on the electrodeposition of Ni-MoO2 coatings from a suspension of MoO2 particles in a Watt’s type bath were investigated by com-parison of their polarization characteristics for the hydrogen evolution reaction (HER) in 1 M NaOH at room temperature. It was shown that electrolyte and air flow rates influence the process of coating electrodeposition at low concentrations of MoO2. With increases in MoO2 concentration the current density became the main parameter influencing the coatings’ properties. The best coating, with the lowest over-voltage for the HER, was obtained from the suspension containing 3 g dm-3 of MoO2 particles. The over-voltage of this coating was 57 mV lower for the HER at j = –0.3 A cm-2 (the current density used in industrial applications) than that for the commercial De Nora’s Ni + RuO2 electrode