ABSTRACT An innovative route to obtain Ni/NiO core-shell foam-based anodes for lithium-ion batter... more ABSTRACT An innovative route to obtain Ni/NiO core-shell foam-based anodes for lithium-ion batteries is presented. Commercial Ni foams are conformally coated with NiO by ionic liquid-based electrodeposition. The electrochemical behavior of the resulting Ni/NiO electrodes in half coin cells with lithium counter electrode is investigated. The results are qualitatively correlated to the microstructural properties, including effects of the thermal annealing at 500 °C, of the NiO shell. The formation a NiO sub-layer by the thermal oxidation of the Ni foam seems to play a crucial role in the enhanced performance of the annealed Ni/NiO anodes, which exhibit a reversible discharge capacity around 0.8 mAh/cm2. Furthermore, the Ni/NiO core-shell foam-based anodes are evaluated in full coin Li-ion cells with high voltage LiMn0.8Fe0.2PO4 cathode. Promising cyclability is reached in NiO-LMFP coin cells under cycling at 0.4C.
Extremely thin absorber (eta)-solar cells based on ZnO nanowires sensitized with a thin layer of ... more Extremely thin absorber (eta)-solar cells based on ZnO nanowires sensitized with a thin layer of CdSe have been prepared, using CuSCN as hole transporting material. Samples with significantly different photovoltaic performance have been analyzed and a general model of their behavior was obtained. We have used impedance spectroscopy to model the device discriminating the series resistance, the role of the hole conducting material CuSCN, and the interface process. Correlating the impedance analysis with the microstructural properties of the solar cell interfaces, a good description of the solar cell performance is obtained. The use of thick CdSe layers leads to high recombination resistances, increasing the open circuit voltage of the devices. However, there is an increase of the internal recombination in thick light absorbing layers that also inhibit a good penetration of CuSCN, reducing the photocurrent. The model will play an important role on the optimization of these devices. Thi...
The influence of the Zn(2+) concentration and temperature on the electrochemical reduction of O(2... more The influence of the Zn(2+) concentration and temperature on the electrochemical reduction of O(2) in a solution of zinc bis(trifluoromethanesulfonyl)imide (Zn(TFSI)(2)) salt in 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR(14)TFSI) ionic liquid is presented. ZnO nanocrystalline films were then electrodeposited, under enhanced O(2) reduction, at temperatures in the 75-150 °C range. Their morphology, chemical composition, structural and optical properties were analyzed. In contrast to the polar-oriented ZnO usually obtained from aqueous and conventional solvent based electrolytes, nanocrystalline films oriented along non-polar directions, (11 ̅10) and (11 ̅20), were obtained from this ionic liquid electrolyte. A significant content of carbon was detected in the films, pointing to the active participation and crucial effect of pyrrolidinium cation (and/or byproducts) during the electrodeposition. The films showed semiconducting behavior with an optical gap between 3.43 and 3.53 eV as measured by optical transmittance. Their room temperature photoluminescence spectra exhibited two different bands centered at ∼3.4 and ∼2.2 eV. The intensity ratio between both bands was found to depend on the deposition temperature. This work demonstrates the great potential of ionic liquids based electrolytes for the electrodeposition of ZnO nanocrystalline thin films with innovative microstructural and optoelectronic properties.
Extremely thin absorber (eta)-solar cells based on ZnO nanowires sensitized with a thin layer of ... more Extremely thin absorber (eta)-solar cells based on ZnO nanowires sensitized with a thin layer of CdSe have been prepared, using CuSCN as hole transporting material. Samples with significantly different photovoltaic performance have been analyzed and a general model of their behavior was obtained. We have used impedance spectroscopy to model the device discriminating the series resistance, the role of the hole conducting material CuSCN, and the interface process. Correlating the impedance analysis with the microstructural properties of the solar cell interfaces, a good description of the solar cell performance is obtained. The use of thick CdSe layers leads to high recombination resistances, increasing the open circuit voltage of the devices. However, there is an increase of the internal recombination in thick light absorbing layers that also inhibit a good penetration of CuSCN, reducing the photocurrent. The model will play an important role on the optimization of these devices. This analysis could have important implications for the modeling and optimization of all-solid devices using a sensitizing configuration.
ABSTRACT NiO thin films have been successfully deposited by cathodic electrochemical deposition i... more ABSTRACT NiO thin films have been successfully deposited by cathodic electrochemical deposition in N-butyl-N-methylpyrrolidinium bis(trifloromethanesulfonyl)imide room temperature ionic liquid (IL), giving an unambiguous proof of concept of the metal oxide electrodeposition in aprotic ILs without metal hydroxide formation as an intermediate phase. The electrochemical phenomena involved in the deposition process have been analyzed by cyclic voltammetry, pointing out that the electrochemical reduction of Ni2+ may be quenched in oxygenated IL electrolytes. The physico-chemical properties of the obtained NiO thin films have been characterized by electron scanning and atomic force microscopies, X-ray diffraction and Fourier transform infrared X-ray photo-electron spectroscopies. By taking advantage of the present electrodeposition route, ZnO/NiO heterostructures have been built. The current density-voltage characteristic of the resulting device exhibits clear rectifying behavior, with a rectification factor of 3 × 103 at V = ±1 V. This result anticipates a significant potential of the present electrochemical route in the metal oxide electronics.
X-ray absorption and photoelectron spectroscopy with synchrotron radiation are used to systematic... more X-ray absorption and photoelectron spectroscopy with synchrotron radiation are used to systematically determine the energy levels of molecules for dye-sensitized solar cells (including porphyrins and phthalocyanines [1-3]). N 1s absorption spectra combined with ...
ABSTRACT An innovative route to obtain Ni/NiO core-shell foam-based anodes for lithium-ion batter... more ABSTRACT An innovative route to obtain Ni/NiO core-shell foam-based anodes for lithium-ion batteries is presented. Commercial Ni foams are conformally coated with NiO by ionic liquid-based electrodeposition. The electrochemical behavior of the resulting Ni/NiO electrodes in half coin cells with lithium counter electrode is investigated. The results are qualitatively correlated to the microstructural properties, including effects of the thermal annealing at 500 °C, of the NiO shell. The formation a NiO sub-layer by the thermal oxidation of the Ni foam seems to play a crucial role in the enhanced performance of the annealed Ni/NiO anodes, which exhibit a reversible discharge capacity around 0.8 mAh/cm2. Furthermore, the Ni/NiO core-shell foam-based anodes are evaluated in full coin Li-ion cells with high voltage LiMn0.8Fe0.2PO4 cathode. Promising cyclability is reached in NiO-LMFP coin cells under cycling at 0.4C.
Extremely thin absorber (eta)-solar cells based on ZnO nanowires sensitized with a thin layer of ... more Extremely thin absorber (eta)-solar cells based on ZnO nanowires sensitized with a thin layer of CdSe have been prepared, using CuSCN as hole transporting material. Samples with significantly different photovoltaic performance have been analyzed and a general model of their behavior was obtained. We have used impedance spectroscopy to model the device discriminating the series resistance, the role of the hole conducting material CuSCN, and the interface process. Correlating the impedance analysis with the microstructural properties of the solar cell interfaces, a good description of the solar cell performance is obtained. The use of thick CdSe layers leads to high recombination resistances, increasing the open circuit voltage of the devices. However, there is an increase of the internal recombination in thick light absorbing layers that also inhibit a good penetration of CuSCN, reducing the photocurrent. The model will play an important role on the optimization of these devices. Thi...
The influence of the Zn(2+) concentration and temperature on the electrochemical reduction of O(2... more The influence of the Zn(2+) concentration and temperature on the electrochemical reduction of O(2) in a solution of zinc bis(trifluoromethanesulfonyl)imide (Zn(TFSI)(2)) salt in 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR(14)TFSI) ionic liquid is presented. ZnO nanocrystalline films were then electrodeposited, under enhanced O(2) reduction, at temperatures in the 75-150 °C range. Their morphology, chemical composition, structural and optical properties were analyzed. In contrast to the polar-oriented ZnO usually obtained from aqueous and conventional solvent based electrolytes, nanocrystalline films oriented along non-polar directions, (11 ̅10) and (11 ̅20), were obtained from this ionic liquid electrolyte. A significant content of carbon was detected in the films, pointing to the active participation and crucial effect of pyrrolidinium cation (and/or byproducts) during the electrodeposition. The films showed semiconducting behavior with an optical gap between 3.43 and 3.53 eV as measured by optical transmittance. Their room temperature photoluminescence spectra exhibited two different bands centered at ∼3.4 and ∼2.2 eV. The intensity ratio between both bands was found to depend on the deposition temperature. This work demonstrates the great potential of ionic liquids based electrolytes for the electrodeposition of ZnO nanocrystalline thin films with innovative microstructural and optoelectronic properties.
Extremely thin absorber (eta)-solar cells based on ZnO nanowires sensitized with a thin layer of ... more Extremely thin absorber (eta)-solar cells based on ZnO nanowires sensitized with a thin layer of CdSe have been prepared, using CuSCN as hole transporting material. Samples with significantly different photovoltaic performance have been analyzed and a general model of their behavior was obtained. We have used impedance spectroscopy to model the device discriminating the series resistance, the role of the hole conducting material CuSCN, and the interface process. Correlating the impedance analysis with the microstructural properties of the solar cell interfaces, a good description of the solar cell performance is obtained. The use of thick CdSe layers leads to high recombination resistances, increasing the open circuit voltage of the devices. However, there is an increase of the internal recombination in thick light absorbing layers that also inhibit a good penetration of CuSCN, reducing the photocurrent. The model will play an important role on the optimization of these devices. This analysis could have important implications for the modeling and optimization of all-solid devices using a sensitizing configuration.
ABSTRACT NiO thin films have been successfully deposited by cathodic electrochemical deposition i... more ABSTRACT NiO thin films have been successfully deposited by cathodic electrochemical deposition in N-butyl-N-methylpyrrolidinium bis(trifloromethanesulfonyl)imide room temperature ionic liquid (IL), giving an unambiguous proof of concept of the metal oxide electrodeposition in aprotic ILs without metal hydroxide formation as an intermediate phase. The electrochemical phenomena involved in the deposition process have been analyzed by cyclic voltammetry, pointing out that the electrochemical reduction of Ni2+ may be quenched in oxygenated IL electrolytes. The physico-chemical properties of the obtained NiO thin films have been characterized by electron scanning and atomic force microscopies, X-ray diffraction and Fourier transform infrared X-ray photo-electron spectroscopies. By taking advantage of the present electrodeposition route, ZnO/NiO heterostructures have been built. The current density-voltage characteristic of the resulting device exhibits clear rectifying behavior, with a rectification factor of 3 × 103 at V = ±1 V. This result anticipates a significant potential of the present electrochemical route in the metal oxide electronics.
X-ray absorption and photoelectron spectroscopy with synchrotron radiation are used to systematic... more X-ray absorption and photoelectron spectroscopy with synchrotron radiation are used to systematically determine the energy levels of molecules for dye-sensitized solar cells (including porphyrins and phthalocyanines [1-3]). N 1s absorption spectra combined with ...
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Papers by Eneko Azaceta