X-ray photoelectron spectroscopy investigation of nanoporous NiO electrodes sensitized with Erythrosine B

Nanoporous NiO thin films were prepared onto FTO glass substrates by means of screen-printing and were sensitized with Erythrosine B (EryB) dye. The obtained material was electrochemically treated and characterized with ex-situ X-ray photoelectron spectroscopy in order to gain information beneficial to the application of sensitized NiO as photocathodes of p-type dye-sensitized solar cells (p-DSCs). In particular, EryB-sensitized NiO films underwent a series of electrochemical treatments in LiClO4/Acetonitrile (ACN) electrolyte devised so as to simulate possible conditions the electrode might encounter during operation in the photoelectrochemical cell. Upon potential-cycling in a range where the two NiO faradic events Ni(II)→Ni(III) and Ni(III)→Ni(IV) occur, X-ray photoelectron spectroscopy revealed that Erythrosine B dye experiences a partial detachment from the NiO surface. This detachment seems to be paralleled by the formation of stable (Ni)+(ClO4)- couples. Overall, the EryB dye displayed an acceptable electrochemical stability onto the surface of NiO electrode up to 50 cyclic voltammetries in the range -0.27÷+1.13V vs. Ag/AgCl. These results are useful for the evaluation of electrochemical stability of the dye when this is immobilized onto an electrode surface and are beneficial for a better comprehension of the degradation phenomena operating in real photoconversion device. © 2017 Elsevier B.V

Progress, highlights and perspectives on NiO in perovskite photovoltaics

The power conversion efficiency of NiO based perovskite solar cells has recently hit a record 22.1%. Here, the main advances are reviewed and the role of NiO in the next breakthroughs is discussed

Photoemission study of ferrocenes: insights into the electronic structure of Si-based hybrid materials

We present here the results of synchrotron radiation-excited UV-photoemission investigation and DFT calculations on vinylferrocene (VFC), a redox molecule suitable for applications in molecular electronics. A detailed assignment is discussed of the valence photoelectron spectra (UPS), which provides new data on the electronic structure and offers a partial re-interpretation of previous assignments on VFC based on theoretical and experimental evidences. Furthermore, the present results can allow for a meaningful comparison of photoemission results from the corresponding hybrid obtained by covalently attaching VFC to Si oriented surfaces. © 2008 IOP Publishing Ltd

Enhancement of the performance in Li-O2cells of a NiCo2O4based porous positive electrode by Cr(III) doping

Here we discuss the incorporation of Cr(III) as dopant in the spinel lattice of the NiCo2O4cubic phase and its beneficial effect on the electro-catalytic activity of this material in aprotic Li-O2cells. To this aim, we synthesized highly porous carbon-free self-standing electrodes constituted by nanostructured undoped and Cr-doped NiCo2O4grown on open nickel mesh. These materials were characterized by X-ray diffraction, field emission scanning electron microscopy coupled with energy dispersive spectroscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The performance in aprotic Li-O2cells of the undoped and Cr-doped NiCo2O4electrodes were tested in galvanostatic cycling using a LiTFSI 1 m in tetraethylene glycol dimethyl ether electrolyte without the incorporation of any carbon conductive agent. Cr(III) doping discloses a remarkable enhancement of more than 300% of the discharge capacity at J = 0.1 mA cm−2. Moreover, the Cr-doped NiCo2O4material is capable to give reversible limited capacity ORR/OER for 52 and 45 cycles at 0.2 mA cm−2/0.1 mAh cm−2and 0.1 mA cm−2/0.2 mAh cm−2, respectively, without oxygen flow in static Ar/O2overpressures (pO2= 1bar). Pseudo-Tafel data derived by galvanostatic titrations highlight the beneficial effect of Cr(III) doping on the electrode kinetics both for ORR and OER

Adsorption behavior of I3(-) and I(-) ions at a nanoporous NiO/acetonitrile interface studied by X-ray photoelectron spectroscopy

The adsorption of I- and I3 - anions, i.e., the two species constituting the most common redox couple of dye-sensitized solar cells (DSCs), onto the surface of screen-printed nanoporous NiO was studied by means of X-ray photoelectron spectroscopy (XPS). Nanoporous NiO films were deposited on transparent metallic fluorine-doped tin oxide (FTO) and polarized as working electrodes in a three-electrode cell with differently concentrated I-/I3 - electrolytes to simulate the different conditions experienced by the NiO cathodes during the lifecycle of a p-type DSC (p-DSC) at those atomic sites not passivated by the dye. Bare NiO films were tested also as photocathodes of nonsensitized p-DSCs. The ex situ XPS analysis of I 4d ionization region of both reference and electrochemically treated NiO films showed that the presence of native and electrochemically generated Ni3+ and Ni4+ centers induces fast adsorption/desorption of I- ions and catalyzes their oxidation to I3 - ions. The adsorption phenomena generated by I- and I3 - species on nanoporous NiO electrodes can also induce an effect of electrochemical passivation toward a fraction of charged Ni sites. Such an effect would render these sites inactive for the further realization of those photoelectrochemical processes at the basis of the operation of a p-DSC. © 2016 American Chemical Society

Tuning the composition of aromatic binary Self-Assembled Monolayers on copper: An XPS study

In this study, the XPS characterization of different binary aromatic SAMs on copper is presented. The mixed layers, constituted by benzenethiol (BT) and alternatively 4-fluorobenzenethiol (FBT) or 4-acetamidothiophenol (AA), were prepared by two different methods, namely coadsorption from solution and partial substitution of a preformed BT layer. The overall quality and the surface composition of the different SAMs have been assessed as a function of the solution concentration for the former preparation and of the substitution time for the latter. In addition, the parameters contributing to determine the surface composition of the aromatic mixed layers on copper have been identified. (C) 2014 Elsevier B.V. All rights reserved

Degradazione in celle Li-O2

Le celle Li-O2 sono uno straordinario dispositivo di accumulo energetico in grado di sfruttare le eccezionali proprietà della coppia redox Li/O2, rappresentando una concreta soluzione per il trasporto elettrico (in particolar modo per le automobili elettriche), lo stoccaggio massivo di energia “pulita” e per il funzionamento dell’elettronica di nuova generazione. Inoltre lo sviluppo di un’efficacie batteria Li-O2 avrebbe un impatto rivoluzionario nella nostra società portando ad una profonda de-carbonizzazione dei processi industriali e, quindi, una drastica riduzione delle emissioni di CO2 legate alle attività umane [1, 2]. Tuttavia, nonostante gli ingenti fondi investiti in R&D in tutto il mondo negli ultimi dieci anni, l’effettiva realizzabilità delle celle secondarie non acquose Li-O2 e stato dimostrato solo su scala di laboratorio poiché i meccanismi che ne regolano il funzionamento non sono stati ancora del tutto compresi. In particolare, la stabilità dei materiali utilizzati in questi dispositivi non è stata chiaramente dimostrata così come non sono note le possibili vie di degradazione delle componenti. Per esempio, solo recentemente l’ossidazione degradativa indotta dall’anione superossido O2- nei confronti dei materiali carboniosi catodici (SuperP Carbon) ed elettrolitici (solventi eterei) è stata analizzata [3]. Quindi, in questo lavoro sono state assemblate numerose celle Li-O2 utilizzando alcuni dei materiali più promettenti con lo scopo di testarne la reale possibilità di impiego e suggerire possibili alternative. Seguendo lo schema Li/LiTfO in TEGDME/C,O2 sono state effettuate ciclazioni galvanostatiche del dispositivo e sono stati analizzati post mortem i catodi attraverso misure XPS, FTIR e TEM. I risultati hanno mostrato che le ciclazioni elettrochimiche inducono sulla superficie catodica l’accumulo di precipitati organici e inorganici durante la scarica della cella che sono solo parzialmente rimossi durante la carica. La formazione di queste specie suggerisce quindi la presenza di reazioni parassitarie a causa della reattività della matrice del catodo carbonioso. Inoltre, sostituendo il SuperP con Au elettrodepositato su Ni foam, è stata valutata l’ossidazione dell’elettrolita, essendo il TEGDME l’unica fonte di carbonio (Li/LiTfO in TEGDME/Au@Ni, O2). Anche in questo caso gli spettri XPS e Raman confermano la presenza di precipitati organici/inorganici anche dopo pochi cicli ossido-riduttivi. Infine, la comprensione dei meccanismi di degradazione è stata ulteriormente chiarificata attraverso la computazione quanto-meccanica delle superfici di energia potenziale della reattività del DME rispetto all’anione superossido O2- nell’ambiente di reazione delle batterie Li-O2 [4]. [1] Imanishi N, Luntz A, Bruce P. “The Lithium Air Battery: Fundamentals”, New York (USA): Springer, 2014. [2] Chen F, Cheng J. Chemical Society Reviews. 2012, 41, 2172-2192. [3] Carboni M, Brutti S, Marrani AG. ACS Appl. Mater. Interfaces. 2015, 7, 21751-21762. [4] Carboni M, Brutti S, Marrani AG, Spezia R. “Ether Degradation Thermodynamics in Li-O2 Redox Environments”, submitted to J. Phys. Chem. C