Izračunavanje prave vrednosti kapaciteta dvojnog sloja iz konstantnog faznog elementa u impedansnim merenjima

Considering literature of electrochemical impedance spectroscopy (EIS) it was discovered that for calculation of the value of double layer capacitance (Cdl) from the constant phase element (CPE) two equations, with or without solution resistance (Rs) could be used. After calculation of Cdl for defined values of CPE constant Ydl, CPE exponent , Rs and charge transfer resistance (Rct), it was confirmed in this work that different results for Cdl were obtained by including Rs in the calculation of Cdl. It was also stated that “it is quite difficult to understand how both parameters (Rct and Rs) could be expressed by the same time constant, i.e. the same parameter .” By investigating the hydrogen evolution reaction (HER) at Ni mesh 40 electrode in the solution of 1 M KOH at 25 oC using EIS measurements, it was shown that different Cdl vs. E plots were obtained using these two equations for Cdl calculation. A simple solution to avoid this problem with detailed explanation, the use of equation without Rs, has been suggested in this work.Razmatrajući literature o elektrohemijskoj impedansnoj spektroskopiji (EIS) ustanovljeno je da za izračunavanje vrednosti kapaciteta dvojnog sloja (Cdl) iz konstantnog faznog elementa (CPE) postoje dve jednačine, jedna u kojoj figuriše otpor elektrolita (Rs) i druga u kojoj ovaj parametar ne figuriše. Izračunavanjem vrednosti Cdl za definisane parametre (Ydl, , Rs, Rct), u ovom radu je pokazano da se dobijaju drugačiji rezultati za Cdl primenom ovih jednačina. Takođe je konstatovano da je neprihvatljivo da oba parametra (Rct i Rs) na isti način zavise od vremenske konstante, odn. od parametra . Ispitivanjem reakcije izdvajanja vodonika na Ni mrežici u rastvoru 1 M KOH na 25 oC korišćenjem impedansnih merenja, pokazano je da su zavisnosti Cdl vs. E, dobijene korišćenjem pomenutih jednačina, različite. Da bi se izbegao ovaj problem predloženo je da se koristi jednačina u kojoj ne figuriše otpor elektrolita (Rs), jer uvodjenje Rs nema korektan fizički smisao

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

Corrected accelerated service life test of electrodeposited NiSn alloys and Ni as cathodes for industrial alkaline water electrolysis

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

Electrochemical behaviour of electrodeposited Pd and PdNi coatings for the ethanol oxidation reaction in alkaline solution

Electrodeposited Pd and PdNi coating samples were tested for ethanol oxidation reaction (EOR) in alkaline solution using cyclic voltammetry (CV), chronoamperometric (CA) and quasi steady-state measurements. All alloy samples showed higher current densities for the EOR than pure Pd coating. The current density increased with increasing the amount of Pd in the PdNi coating and the most active one was found to be Pd0.74Ni0.26. Based on CA measurements a pseudo-steady state is achieved after 1500 s showing that Pd0.74Ni0.26 is more efficient and poisoning more tolerant than other investigated coatings. Upon the end of the current-time transient, the investigated catalysts were subjected to the potential cycling showing the ability to recover activity loss implying the surface composition stability of binary coatings

Mehanizam i kinetika elektrosorpcije sulfatnih anjona na (111) pljosni srebra

The processes of adsorption of sulphate anions onto the (111) face of silver have been investigated by analysis of the cyclic voltammetry and potcntiostatic pulse results. It was shown, by fitting the experimentally recorded θ - E dependences, that the adsorption of anions follows Frumkin adsorption isotherm. The adsorbed structure was found to be less dense than expected for the dense packed anion monolayer and the process was characterized by high value of the interaction parameter and the Gibbs energy of adsorption (f = 16.5 and ΔGoads.θ→0 = - 64 kJ mol 1). From the slope of the Ep.a - log (c0) dependence it was concluded that complete charge transfer between the adsorbed anions and the silver substrate occurs. This is supported by the Ep.a - log v linear dependence in the region of high sweep rates (v > 10 V s 1) with rational value of line slope (≈ 60 mV dec 1) which is possible only if the complete charge transfer reaction occurs. The elcctrosorption process of sulphate anions was found to be complex electrochemical reaction, taking place through three steps. It was proposed that the rate-determining step is the second step, i.e., the electrochemical formation of (SO4)ads species.Proučavan je proces adsorpcije sulfatnih anjona na (111) pljosni monokristalasrebra metodama ciklične voltametrije i potenciostatskih pulseva. Na osnovu eksperimentalno određenih q–E zavisnosti pokazano je da se na adsorpciju može primeniti Frumkinova adsorpciona izoterma. Nađeno je da je gustina adsorbovanog slojamanja nego kada bi sloj bio maksimalno moguće gusto pakovan kao i da adsorpcijukarakterišu visoke vrednosti Frumkinovog parametra interakcije (f = 16,5) i Gibsoveenergije adosrpcije (DGºads,q®0 = –64 kJ mol). Na osnovu nagiba zavisnosti Ep,a –log (c0)zaključeno je da se pri elektrosorpciji odigrava i potpuna izmena naboja anjona sasupstratom. Ovaj zaključak podržava dobijena linearna zavisnost Ep,a – log v u oblastivelikih brzina promene potencijala (v>10 V s–1) sa racionalnom vrednošću nagiba (»60mV dek–1), a koja se može dobiti samo pri odigravanju potpune razmene naboja. Utvrđenoje da je elektrosorpcija sulfatnih anjona složena elektrohemijska reakcija koja seodigrava u tri stupnja. Stupanj koji određuje brzinu ukupne reakcije je drugi stupanj,elektrohemijsko stvaranje intermedijera (SO4)ads

Electrodeposition and characterization of Fe-Mo alloys as cathodes for hydrogen evolution in the process of chlorate production

Fe-Mo alloys were electrodeposited from a pyrophosphate bath using a single diode rectified AC current. Their composition and morphology were investigated by SEM, optical microscopy and EDS, in order to determine the influence of the deposition conditions on the morphology and composition of these alloys. It was shown that the electrodeposition parameters, such as: chemical bath composition and current density, influenced both the composition of the Fe Mo alloys and the current efficiency for their deposition, while the micro and macro-morphology did not change significantly with changing conditions of alloy electrodeposition. It was found that the electrodeposited Fe Mo alloys possessed a 0.15 V to 0.30 V lower overvoltage than mild steel for hydrogen evolution in ail electrolyte commonly used in commercial chlorate production, depending on the alloy composition, i.e., the conditions of alloy electrodeposition

Morphology of Different Electrodeposited Pure Metal Powders

As mentioned in other chapters, metal powders obtained by electrolytic processes are mainly dendrites which can spontaneously fall off or can be removed from the electrode by tapping or other similar techniques [1]. Also, powder particles can have other morphological forms, such as flakes or needles, fibrous or spongy, and needle or cauliflower-like ones, and the shape of powder particles depends on the electrodeposition conditions and the nature of the metal.This is the author's version of the accepted, peer-reviewed manuscript: Jović V.D., Nikolić N.D., Lačnjevac U.Č., Jović B.M., Popov K.I. (2012) Morphology of Different Electrodeposited Pure Metal Powders. In: Djokić S. (eds) Electrochemical Production of Metal Powders. Modern Aspects of Electrochemistry, vol 54. Springer, Boston, MA. [https://doi.org/10.1007/978-1-4614-2380-5_2]The published version: [https://cer.ihtm.bg.ac.rs/handle/123456789/4092

Morfologija prahova Fe-Ni legura elektrohemijski istaloženih iz citratno-sulfatnih rastvora

The electrochemical deposition of the Fe-Ni alloy powders from citrate-sulfate containing electrolytes of different Ni/Fe ions concentration ratios at pH 4.5 was examined by the polarization measurements. All polarization curves have a similar shape and are characterized by the presence of two inflection points. The first inflection point reflects the beginning of alloy deposition, while the second one (˜) corresponds to the moment when the cathode reaction becomes determined by the rate of hydrogen bubbles formation. The potentials of Fe-Ni alloys deposition at all investigated Ni/Fe ratios are more positive than those for pure metal powders deposition. As the Ni/Fe ratio decreases, the polarization curves are placed at slightly more positive potentials. The morphology of electrodeposited powder particles was investigated using scanning electron microscopy (SEM). A common characteristic of all Fe-Ni alloy powders is the presence of cone shaped cavities. Powder particles electrodeposited at the ratio Ni/Fe = 9/1 are mainly consisted of nodules of either very flat surface or rough surface, with well defined crystals detected only on a few particles. With the decrease of the Ni/Fe ratio, the presence of well defined crystals on the nodule surface becomes more pronounced. In the powder with the highest amount of Fe (Ni/Fe = 1/3), the whole surface of all particles is covered with crystals of different shapes.Elektrohemijsko taloženje prahova Fe-Ni legura ispitivano je snimanjem polarizacionih dijagrama u citratno-sulfatnim rastvorima pri različitom odnosu koncentracija Ni/Fe jona na pH 4,5. Sve polarizacione krive imaju sličan oblik i okarakterisane su prisustvom dve prevojne tačke na dijagramu. Prva prevojna tačka odgovara početku taloženja Fe-Ni legure, dok druga predstavlja momenat kada ukupna elektrohemijska reakcija postaje kontrolisana brzinom formiranja mehurova vodonika. Potencijali taloženja Fe-Ni legura pri svim ispitivanim odnosima Ni/Fe pozitivniji su od potencijala taloženja čistih metala, pri čemu se sa smanjenjem odnosa Ni/Fe polarizacione krive pomeraju ka malo pozitivnijim vrednostima potencijala. Morfologija čestica prahova ispitivana je korišćenjem skenirajuće elektronske mikroskopije (SEM). Zajednička karakteristika svih prahova Fe-Ni legura je prisustvo šupljina konusnog oblika. Čestice praha istaloženog pri odnosu Ni/Fe = 9/1 uglavnom su sastavljene od čvorića, glatke ili neravne površine, kod kojih se na pojedinim mestima mogu uočiti dobro definisani kristali. Sa smanjenjem odnosa Ni/Fe, prisustvo kristala na površini čvorića postaje sve izraženije, dok su kod praha sa najvećim sadržajem Fe (Ni/Fe = 1/3) na celoj površini čestica prisutni kristali različitog oblika