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In this paper, we have systematically studied the structural, morphological, and optical properties of Ni-doped TiO2, synthesized via a simple, cost-effective electrospinning method followed by calcination at 500 C. The nanofibers with a core-shell structure were relatively homogeneous, smooth and randomly oriented, and there were no significant differences in fiber diameters due to Ni2+ content. Core loss mapping using electron energy loss spectroscopy confirmed an even distribution of titanium and relatively uniform nickel in the fibers. It was found that doping with 0.5 mol.% Ni2+ decreased the rutile content, while doping with 1 mol.% Ni2+ resulted in a pure anatase phase with a significantly increased specific surface area (36.6 m2/g). Further increase in Ni2+ content (3-10 mol.%) not only prolonged the response of TiO2 nanofibers to visible light, but also increased the specific surface area (49.5 m2/g), decreased crystallite size (7 nm), and increased rutile content in TiO2 (33 wt.%). Photoluminescence analysis revealed that doping TiO2 with different amounts of Ni2+ leads to a gradual decrease of emission spectra intensity and red shift in the maxima positions. The XPS results confirmed that as the Ni2+ content enlarged, the Ti2+ and Ti3+ content increased significantly, effectively promoting the formation of oxygen vacancies. Raman analysis showed that an increase in nickel content (3-5 mol.%) led to a decrease and shift in peak intensity due to Ti3+ formation and also the possible presence of NiTiO3 phases. HRTEM analysis showed that Ni was doped into the substitution sites of both the anatase and rutile TiO2 lattice but had a stronger influence on the distortion of the anatase phase. The photocatalytic activity of Ni-doped TiO2 nanofibers was explored by analyzing the degradation of an antibiotic, oxytetracycline, monitored in laboratory conditions under visible light irradiation. After 60 minutes of irradiation, the degradation of OTC with 1Ni-TiO2 reac

In this work, titanium dioxide (TiO2) nanofibers doped with 0.5–5 mol% zirconium ions (Zr4+) were synthesized by combining the sol-gel process and electrospinning method, and calcined at 500 °C. The morphological, structural and optical properties of pure and Zr-doped TiO2 nanofibers were investigated. According to the XRD and FTIR analyses, the addition of Zr as a dopant suppressed the transformation of anatase to rutile phase. Scanning electron microscopy showed that all fibers were smooth, fragile and randomly oriented after the calcination process. HRTEM analysis revealed that Zr4+ ions were incorporated at the substitutional sites in the anatase TiO2 crystalline lattice. The photocatalytic efficiency for degradation of methylene blue (MB) was examined for both pure and Zr-doped TiO2 samples. Nanofibers doped with 1% of Zr4+ ions have shown the highest photocatalytic activity of 98%, wich can be explained by considering lower PL intensity in the PL spectrum of this sample, indicating suppressed electron-hole recombination.

Lithium-ion batteries (LIBs) are the most promising energy storage devices on the market today. Their importance is reflected in the fact that LIBs power numerous portable devices and that they are being developed for electric and hybrid electric vehicles [1]. Most commercial LIBs are composed of a graphite anode, which cannot meet high performace requirements [2]. Several transition metal-oxide based hosts have been considered as potential alternatives to the graphite anode, including TiO2. Low cost, high Li-ion insertion potential, low volume expansion and good cycling life make TiO2 a promising anode material. Different polymorphs of TiO2 have been investigated, and preference is given to the anatase phase. Herein, anatase TiO2 nanotube arrays (NTAs) electrode was preapred by anodic oxidation of Ti-foil and subesquent annealing at 400 oC. SEM micrographs show that the nanotubes (NTs) are cylindrical in shape, with an average inner diameter of about 95 nm and wall thickness ~15 nm. In the Raman spectrum, five active modes which correspond to the anatase phase are present. XRD pattern of as-prepared Ti/TiO2 NTAs electrode was recorded, and the strongest diffraction maximum of anatase phase was used for the claculation of the mean crystallite size. The obtained value is 19 ± 1 nm. Electrochemical experiments, which included cyclic voltammery (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic (GS) cycling, were carried out using a termostat in the temperature range from 25 – 55 oC. The 1 M solution of LiClO4 in propylene carbonate was used as an electrolyte in all cases. CV experiments demonstrated an increase in the redox peak intensity and a decrease in peak-to-peak separation at higher temperatures, indicating improvement in Li-ion storage capability and better reversibilty of Li-ion intercalation/deintercalation process. GS cycling showed a large Li-ion insertion capacity of Ti/TiO2 NTAs electrode, high Coulombic efficiency (CE) and good capcity

Anatase TiO2 was prepared in the form of nanotube arrays by anodic oxidation of Ti foil followed by annealing at 400 °C. Electrochemical experiments, which included cyclic voltammetry (CV), galvanostatic (GS) cycling and electrochemical impedance spectroscopy (EIS) were conducted in 1 M solution of LiClO4 in propylene carbonate (PC) at temperatures 25 °C–55 °C. CV experiments, at scan rates 5–50 mV·s−1 , demonstrated with increasing temperature a large increase in the intensity of the redox peaks along with a decrease in the peak-to-peak separation. GS cycling showed large increase of capacity of thin-wall TiO2 nanotubes with increasing temperature, which attains 357 mAh·g−1 at 55 °C during lithiation at current rate 5.3 C, with capacity retention of 98.5% and Coulombic efficiency of 97.5%. Surface storage and development of secondary voltage plateau strongly contribute to such a large capacity value. EIS showed a multiple decrease in solid electrolyte interphase (SEI) layer resistance and charge transfer resistance with temperature rising up to 55 °C.

Pure, samarium (Sm3+) and zirconium (Zr4+) doped titanium dioxide (TiO2) nanofibers were synthesized using the electrospinning method followed by calcination at 500 °C for 1 h. The structure, morphology and optical properties of the obtained nanofibers were investigated as a function of different Sm3+ and Zr4+ contents (0.5–5 mol%). XRD and FTIR analysis showed that addition of Sm or Zr suppressed the transformation of anatase to rutile. After calcination all fibers were smooth, fragile and randomly oriented. HRTEM analysis revealed that doping with Sm didn’t affect the TiO2 crystal lattice whilst Zr4+ ions replaced the substitutional sites in the anatase crystalline lattice. The effects of Sm3+ and Zr4+-dopant content and different doses of photocatalyst on the photodegradation of methylene blue (MB) were monitored under UV-light illumination. TiO2:0.5%Sm3+ and TiO2:1.0%Zr4+ nanofibers have shown the highest photocatalytic activity of 97% and 98% due to red shifting of the band gap towards visible light in the case of Sm and suppressed electron-hole recombination shown in recorded PL spectra in the case of Zr.

This paper reports a detailed study of crystal structure and dielectric properties of ruthenium-substituted calcium-copper titanates (CaCu3Ti4−xRuxO12, CCTRO). A series of three samples with different stoichiometry was prepared: CaCu3Ti4−xRuxO12, x = 0, 1 and 4, abbreviated as CCTO, CCT3RO and CCRO, respectively. A detailed structural analysis of CCTRO samples was done by the Rietveld refinement of XRPD data. The results show that, regardless of whether Ti4+ or Ru4+ ions are placed in B crystallographic position in AA’3B4O12 (CaCu3Ti4−xRuxO12) unit cell, the crystal structure remains cubic with Im3¯ symmetry. Slight increases in the unit cell parameters, cell volume and interatomic distances indicate that Ru4+ ions with larger ionic radii (0.62 Å) than Ti4+ (0.605 Å) are incorporated in the CaCu3Ti4−xRuxO12 crystal lattice. The structural investigations were confirmed using TEM, HRTEM and ADF/STEM analyses, including EDXS elemental mapping. The effect of Ru atoms share in CaCu3Ti4−xRuxO12 samples on their electrical properties was determined by impedance and dielectric measurements. Results of dielectric measurements indicate that one atom of ruthenium per CaCu3Ti4−xRuxO12 unit cell transforms dielectric CCTO into conductive CCT3RO while preserving cubic crystal structure. Our findings about CCTO and CCT3RO ceramics promote them as ideal tandem to overcome the problem of stress on dielectric-electrode interfaces in capacitors.

Познавање површинске структуре вишекомпонентних II–VI полупроводника и утицаја дуготрајног излагања ваздуху на њу значајно је у технолошком и научном смислу. Резултати добијени у овом раду омогућавају боље разумевање процеса на површини испитиваних система (оксидација, сегрегација и миграција елемената), који су уско повезани са њиховим површинским својствима. Метода фотоелектронске спектроскопије рендгенским зрачењем (XPS) је указала на различит састав испитиваних површина, одступање од стехиометријског састава, али и неуниформност састава по дубини узорака на бази CdTe и ZnTe. Због слабо израженог хемијског помераја линија Cd и Zn у XPS спектру, за одређивање хемијских веза које ови елементи граде, у Тези је успешно примењен нови приступ за моделовање Ожеових линија. Одступање од стехиометријског састава може бити последица површинске морфологије, те је овај утицај детаљно размотрен, али је пре свега последица неуниформности састава испитиваних површина по дубини. Површинске концентрације елемената добијене рутинским приступом квантитативној анализи XPS резултата (коришћењем фактора осетљивости) послужиле су за праћење њихове међузависности и једноставну процену површинског састава, а показано је и да постоји компетиција процеса оксидације и адсорпције угљоводоника на површини. Ипак, да би се одредио састав специфичне површинске структуре узорака, која није униформна по дубини те примена фактора осетљивости није могућа, у оквиру ове Тезе је развијен модел који полази од „првих принципа“. Применом модела, уз сазнања која је пружила опсежна анализа XPS и Ожеових спектара, утврђен је тачан састав узорака. Одређене су хемијске фазе присутне у свакој од уочене три површинске области – запреминска област, оксидни слој и слој нечистоћа, и процењена је дебљина површинских слојева узорака., Understanding of the multicomponent II–VI semiconductors surface structure and influence of long term air exposure on it, is a very important question in both, scientific and technological manner. Results presented in this dissertation offers better insight into surface processes of investigated systems (oxydation, segregation and migration of elements), which are closely related to their surface properties. X–ray photoelectron spectroscopy (XPS) reveals different surface structures, variations in stoichiometry and in–depth non–uniform structure of examined samples based on CdTe and ZnTe. Due to poor chemical peak shifts of Cd and Zn lines in XPS spectrum, for chemical bond identification of these elements, the new approach for modeling Auger lines was successfully applied here. Deviation from stoichiometry composition can be a consequence of surface morphology and this influence was considered in detail, but is certainly attributed to non–uniform structure of surfaces in depth. Relative concentrations of elements detected at the surfaces of investigated samples obtained using standard quantitative analysis approach in XPS (using atomic sensitivity factors) served to monitor their correlation and evaluation of surface structure. Furthermore, competiton of two surface processes, oxydation and hydrocarbons adsorption, is established. The model based on first principles is developed in this dissertation, in order to determine the specific surface structure of samples, where using of atomic sensitivity factors is not possible. Application of this model, followed by additional results provided by XPS and Auger spectrum analysis, enables determination of exact in–depth sample structures. Chemical bonds present in each of the three surface areas – bulk, oxide and contamination layer, were determined. Samples surface layers thicknesses were also evaluated.

Samarium and zirconium-doped TiO2 nanofibers (3 and 5 wt.%) were synthesised by a simple modified electrospinning method. The effects of calcination temperature on the size of the as-spun doped titania fibers was investigated. As-spun nanofibers were studied and characterized through thermal gravimetric analysis (TG-DTA), Fourier Transform Infrared Spectroscopy (FTIR) and Scanning electron microscopy (SEM), while the structure and morphology of calcined fibers was studied by X-Ray Diffraction (XRD), Field Emission Electron Microscopy (FESEM) and spectroscopic techniques (FT-IR and DRS UV-vis). The influence of dopant type and amount on the photocatalytic degradation of Methylene blue (MB) was investigated.

Memory effect due to spin-glass state below about 20 K has been illustrated in the hollandite-type α-KxMnO2 monocrystalline nanorods by systematic magnetization measurements including temperature- and time-dependent magnetization curves in low fields. In this work, we succeeded in writing, reading, and deleting 8-bits digital information in the investigated system. These results show that α-KxMnO2 is a good candidate material for a thermal memory cell. The phenomenological droplet model was used in the description of the observed memory effect, whose origin in α-KxMnO2 is associated with bulk properties, doping and frustration. © 2019 Elsevier B.V.

U ovom radu, ispitivana su površinska električna i magnetna svojstva gvožđe-polietilen implantata, sintetisanih jonskom implantacijom pri različitim dozama, u opsegu od 5×1016 jona/cm2 do 5×1017 jona/cm2, i pri energiji od 95 keV. Raderfordovom spektroskopijom rasejanja, Rendgenskom fotoelektronskom spektroskopijom, energijskom disperzivnom spektroskopijom i infracrvenom spektroskopijom, utvrđene su znatne promene sastava površinskog sloja, koje se ogledaju u znatnom udelu gvožđa i nastajanju novih organskih jedinjenja. Mikroskopija atomskih sila je pokazala da je implantacija dovela do promena morfologije površine, i znatno veće površinske hrapavosti. Iz analize transmisionom elektronskom mikroskopijom, utvrđeno je da nakon implantacije dolazi do formiranja nanočestica gvožđa, a da nakon implantacije dozom od 5×1017 jona/cm2 dolazi do formiranja kontinualnog sloja. Merenja slojne otpornosti su pokazala da implantacija gvožđa dovodi do znatnog poboljšanja provodnosti. Magnetna merenja su pokazala da do pojave feromagnetne faze dolazi nakon implantacije dozama od 2×1017 jona/cm2 i 5×1017 jona/cm2. Iz merenja spektroskopskom elipsometrijom se može zaključiti da je nakon implatacije povećan indeks prelamanja i koeficijent apsorpcije u zoni implantacije. Spektroskopija u ultraljubičastoj i vidljivoj oblasti je ukazala na pojavu lokalizovane površinske plazmonske rezonancije čestica gvožđa. Utvrđeno je da površinske energija raste sa implantacionom dozom do doze od 1×1017 jona/cm2, a potom se smanjuje sa povećanjem doze. Pokazano je da su promene hemijskog sastava i morfologije, povezane sa promenama površinskih, električnih i magnetnih svojstava., In this study, the surface electrical and magnetic properties of iron-polyethylene implants, synthesized by ion implantation at different fluences, in the range from 5×1016 ions/cm2 to 5×1017 ions/cm2, and at the energy of 95 keV, were investigated. Rutherford backscattering spectroscopy, X - ray photoelectron spectroscopy, energy dispersive spectroscopy, and infrared spectroscopy have revealed significant changes in the composition of the surface layer, which are reflected in a significant proportion of iron and the formation of new organic compounds. Atomic force microscopy showed that implantation led to changes in surface morphology, and significantly higher surface roughness. From the analysis by transmission electron microscopy, it was determined that after implantation, iron nanoparticles are formed, and that after implantation with a fluence of 5×1017 ions/cm2, a continuous layer is formed. Sheet resistivity measurements have shown that iron implantation leads to a significant improvement in conductivity. Magnetic measurements have shown the occurence of the ferromagnetic phase after implantation at fluences of 2×1017 ions/cm2 and 5×1017 ions/cm2. From the measurements by spectroscopic ellipsometry, it can be concluded that after implantation, the refractive index and the absorption coefficient in the implantation zone increased. Ultraviolet and visible spectroscopy indicated the appearance of localized surface plasmon resonance of iron particles. It was determined that the surface energy increases with the implantation fluence to a fluence of 1×1017 jona/cm2, and then decreases with increasing fluence. It was indicated that the changes in chemical composition and morphology are related to changes in surface, electrical and magnetic properties.

У овој докторској дисертацији описана је хидротермална синтеза наночестичног хематита (α-Fe2O3), као и карактеризација материјала, у сврху његове потенцијалне примене у различитим областима. Синтетисани узорци су карактерисани ренгеноструктурном анализом (XRDP), електронском микроскопијом (SEM и TEM), магнетометријом са вибрирајућим узорком (VSM) и вибрационом спектроскопијом (FTIR и Raman). Извршена је и математичка анализа морфологија честица, применом дескриптора облика на одабране ТЕМ слике узорака..., This doctoral dissertation presented hydrothermal synthesis and characterization of hematite (α-Fe2O3) nanoparticles, towards potential applications in differrent fields. Synthesized sample were characterized with X-ray powder diffraction method (XRDP). electrone microscopy (SEM and TEM), vibrating sample magnetometry (VSM) and vibrational spectroscopy methods (FTIR and Raman). Mathematical analysis of nanoparticle morphology was also conducted, applying shape descriptors on segmented TEM sample images...

U ovoj doktorskoj disertaciji ispitivani su elektroliti na bazi binarnih smeša imidazolijumovih jonskih tečnosti i laktona koji su pogodni za primenu u litijum-jonskim baterijama. Fizičkohemijska svojstva binarnih smeša jonskih tečnosti na bazi imidazolijum katjona i bis (trifluorometilsulfonil)imidnog anjona i laktona ispitana su u celom opsegu molskih udela i na različitim temperaturama. Na osnovu izmerenih gustina, viskoznosti i električne provodljivosti izračunati su različiti fizičko-hemijski parametri i diskutovane interakcije između komponenata smeša. Ispitana je termička i elektrohemijska stabilnost odabranih elektrolita. Na osnovu dobijenih rezultata, prvo je odabran odgovarajući lakton koji je kasnije kombinovan sa jonskim tečnostima na bazi imidazola, koje se međusobno razlikuju u dužini bočnog niza katjona. Na osnovu fizičko-hemijskih svojstava na različitim temperaturama i pri različitim sastavima binarnih smeša diskutovan je način organizacije njihovih komponenata. U binarne smeše koje su se pokazale kao najperspektivnije sa stanovišta električne provodljivosti, viskoznosti, elektrohemijske stabilnosti i (ne)zapaljivosti dodata je litijumova so. Tako dobijeni ternarni sistemi su okarakterisani u zavisnosti od koncentracije litijumove soli. Odabrani elektroliti upotrebljeni su za ispitivanje performansi litijum-jonske ćelije sa elektrodama na bazi anatas TiO2 nanocevi. Cikličnom voltametrijom i galvanostatskim cikliranjem ispitane su performanse ćelije u toku 350 ciklusa punjenja i pražnjenja. Na osnovu ciklovoltametrijskih merenja izračunati su koeficijenti difuzije jona Li + i energija aktivacije za difuziju. Kombinacijom jonskih tečnosti i laktona moguće je dobiti elektrolite smanjene viskoznosti, povećane električne provodljivosti, povećane termičke stabilnosti usled međusobnog stabilizacionog efekta laktona na, In this doctoral dissertation, binary mixtures based on imidazolium ionic liquids with lactones were tested for use in lithium-ion batteries. The physicochemical properties of binary mixtures of imidazolium based ionic liquids with bis (trifluoromethylsulfonyl)imide anions and lactones were examined throughout the whole composition range and at different temperatures. Based on the measured densities, viscosity and electrical conductivity, various physical chemical parameters and discrete interactions between the components of the mixture are calculated. Thermal and electrochemical stability of selected binary mixtures were examined. Based on obtained results was selected lactone which is later combined with imidazolium based ionic liquid, differing from each other in the length of the cation. Based on the physico-chemical properties at different temperatures and in the different compositions of binary mixtures, the way of organizing their components is discussed. Lithium salt is added to the binary mixtures that have been shown as the most perspective from the standpoint of electrical conductivity, viscosity, electrochemical stability and (non)flammability. The resulting ternary systems are characterized according to the concentration of lithium salt. The selected electrolytes were used to test the performance of the lithium-ion cell with anatase TiO2 nanotubular electrodes. Cyclic voltammetry and galvanostatic cycling tested the cell's performance during the 350 charge and discharge cycles. Based on cyclic voltammetric measurements, the Li + ion diffusion coefficients and activation energies for diffusion were calculated. Combination ionic liquid and lactone could be obtained electrolytes with lower viscosity, higher electrical conductivity, improved thermal stability due to stabilization effect of lactone on imidazolium base

Predmet rada ove doktorske disertacije usmeren je na detaljno ispitivanje strukturnih, morfoloških, i magnetnih svojstava različitih polimorfa mangan-dioksida sintetisanih hidrotermalnom metodom. Proučavani su polimorfi β-MnO2 tetragonalne rutilne strukture i α-KxMnO2 tetragonalne holanditne strukture. Ispitivani materijali dobijeni su različitim postupcima sinteze i oni su ispitivani rendgenostrukturnom analizom, skenirajućom elektronskom mikroskopijom, metodom energetski disperzivne spektrometrije, ramanskom i infracrvenom spektroskopijom, metodom elektronske paramagnetne rezonancije i primenom merenja magnetizacije pomoću SQUID-magnetometra u konstantnom (DC) i promenljivom (AC) spoljašnjem magnetnom polju. Na osnovu merenja skenirajuće elektronske mikroskopije utvrĎeno je da svi ispitivani materijali poseduju morfologiju nanoštapića, što je potvrĎeno i mikrostrukturnom karakterizacijom na osnovu rendgenostrukturnih merenja. Na osnovu merenja vibracione spektroskopije potvrĎene su strukturne karakteristike ispitivanih materijala. Kod β-MnO2 materijala koji poseduje jednostavniju rutilnu strukturu, infracrvenom spektroskopijom detektovana je dodatna traka koja potiče od čestica drugačije veličine i/ili oblika, dok su ramanskom spektroskopijom uspešno detektovane dve dodatne trake koje potiču od strukturno neureĎenog i nestehiometrijskog regiona MnO2-δ na površini nanoštapića. PotvrĎeno je da β-MnO2 materijal ima antiferomagnetni prelaz na 93 K, a za α-KxMnO2 materijale ustanovljeno je kompleksnije niskotemperatursko ponašanje. α-KxMnO2 materijali holanditne strukture ispoljavaju reentrant ponašanje spinskog stakla: stanje spinskog stakla se javlja na temperaturama niţim od temperature na kojoj se javlja slabo feromagnetno ureĎenje. Stanje superspinskog stakla na niskim temperaturama kod oba α-KxMnO2 materijala nedvosmisleno je potvrĎeno kroz ispitivanje magnetnih relaksacija, starenja i memorijskih efekata. Merenja elektronske paramagnetne rezonancije kod β-MnO2 i, The research topic of this doctoral dissertation is a detailed study of structural, morphological and magnetic properties of different polymorphs of manganese dioxides that are hydrothermally synthesized. Polymorphs β-MnO2 with tetragonal rutile-type structure and α-KxMnO2 with tetragonal hollandite-type structure were studied. Investigated materials have been obtained by different synthesis pathways and they were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Raman and infrared spectroscopy, electron paramagnetic resonance (EPR) and DC and AC magnetization measurements. SEM images showed nanorod shape of all specimens, while microstructure characterization done by XRD measurements revealed that crystallites have an elongated rod-like shape and hence, it confirmed the anisotropic morphology. Based on vibrational spectroscopic measurements, structural characteristics of investigated materials have been confirmed. In the infrared spectrum of β-MnO2 with a simpler rutile-type structure, the additional band that originates from particles of different shape and/or size has been obtained, while in the Raman spectrum, additional bands that originate from the presence of nonstoichiometric and disordered MnO2-δ on the surface of nanorods, have been obtained. Magnetic ordering of β-MnO2 is antiferromagnetic below 93 K, while α-KxMnO2 materials possess more complicated low-temperature behaviour of the reentrant spin-glass type: the onset of the spin-glass state occurs at temperatures below the weak ferromagnetic ordering. Low-temperature superspin-glass state has been confirmed through the investigations of magnetic relaxations, aging and memory effects. EPR measurements of β-MnO2 and α-K0.15MnO2 show the appearance of two types of Mn4+ ions having different local cationic environment: (i) Mn4+ ions in Mn4+-rich environment and (ii) Mn4+ ions in mixed-valence Mn4+/Mn3+ environment. For β-MnO2 material mixed

NiA and NiX zeolites were prepared and characterised using XRD, FTIR and SEM, and subsequently tested as electrodes for hydrogen (HER) and oxygen (OER) evolution reactions in alkaline media. Linear sweep voltammetry and chronoamperometry techniques showed that NiA has higher catalytic activity for these two reactions, as evidenced by higher current densities, which can be correlated with a higher weight fraction of Ni in this electrocatalyst than in the NiX and with its higher conductivity. HER and OER kinetic parameters, including Tafel slope, exchange current density and apparent activation energy were evaluated. Electrochemical impedance spectroscopy analysis yielded values of the resistance of the solution, charge transfer and mass transfer, as well as double layer capacitance and pseudo-capacitance of the working electrode, at different potentials and temperatures. Unlike the HER, during which the mass transfer resistance of the adsorbed intermediate is dominant in the case of NiA, the OER impedance response is controlled by the charge transfer process itself at the potentials of interest for these process. The overall resistance related to the HER is lower for NiA than for NiX. © 2018 Hydrogen Energy Publications LLC