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

Abstract

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

Novel chlorine doped graphene electrodes for positive electrodes of a vanadium redox flow battery

“…When the Cl2p XPS spectra were analyzed, the covalently bonded peak of chlorine can be seen weakly between 196 and 204 eV (Figure A). Besides, the surface of Cl‐GPGE1 was modified by ―ClO 3 and ―ClO 4 groups according to the peaks at 206.9 and 209.6 eV, respectively (Figure A) . The effects of applied potential on the formation of Cl‐GPGEs can be seen in the C1s and Cl2p XPS spectra of Cl‐GPGE2, Cl‐GPGE3, and Cl‐GO.…”

Effect of Sodium Hydroxide Pretreatment of NiOx Cathodes on the Performance of Squaraine‐Sensitized p‐Type Dye‐Sensitized Solar Cells

“…The defective Ni(III) sites are mostly localized on the surface of the oxide and represent the sites of anchoring of the dye‐sensitizer by virtue of the strong electrophilic character which favours anion adsorption . Moreover, Ni(III) sites interact very strongly with the basic moiety ‐CO 2 − of the dye ,. Based on these findings, it is reasonable to assume that the reaction of nickel oxide with NaOH will mostly consist in the binding of the hydroxide anion to Ni(III) centres with consequent decrease of the surface sites actually available for dye‐anchoring.…”

Effect of Sensitization on the Electrochemical Properties of Nanostructured NiO

“…Such surface-localized species are responsible for the anchoring of the dye sensitizer [68] due to the hydrolysis reaction between the electron deficient site of Ni(III) and the carboxylic group of the colorant [92]. Such a process of sensitization diminishes the positive charge exposed to the electrolyte in passing from the sensitized NiO to the bare NiO with a consequent decrease of the potential difference across the double layer [71].…”

“…Because of these finalities, the study of dye-sensitized electrodes is usually aimed at the analysis of the light absorption properties and at the determination of the efficiency of photoelectrochemical conversion in the process of interest. In this context of research, a less considered (but not less important) aspect is represented by the analysis of the electrochemical properties of the electrode in the dye-sensitized state when the system is in dark conditions (i.e., the evaluation of the electrochemical properties of a photoelectrode in the "blank" state) [68]. In the particular case of dye-sensitized NiO for p-DSC purposes, the observation of a series of effects imparted by the dye sensitizer to the oxide substrate has been previously reported, even in absence of illumination [68][69][70].…”

“…In this context of research, a less considered (but not less important) aspect is represented by the analysis of the electrochemical properties of the electrode in the dye-sensitized state when the system is in dark conditions (i.e., the evaluation of the electrochemical properties of a photoelectrode in the "blank" state) [68]. In the particular case of dye-sensitized NiO for p-DSC purposes, the observation of a series of effects imparted by the dye sensitizer to the oxide substrate has been previously reported, even in absence of illumination [68][69][70]. These effects mostly consisted of the passivation of the NiO surface towards the oxidation of the NiO substrate itself [69][70][71], the observation of additional redox processes based on the immobilized dye (representing the actual redox-active species) [72], and redox processes following the synergy between the dye and oxide due to the spontaneous exchange of electronic charge between the dye and the oxide in the unbiased state [72].…”