The climate change imposes to mankind a severe management of CO2 emissions in atmosphere. CO2 valorization through electrocatalysis revealed to be a valuable solution to this global issue. SnO2 is an ...electrocatalyst widely investigated for its capability to reduce CO2 to formic acid. In particular, mesoporous SnO2 offers a high adsorption capability, resulting in a high catalytic activity. In order to improve its performance, Fe-doping is here investigated for the first time. We observed that Fe-doped SnO2 exhibits a remarkable 100% enhancement of the partial current density for HCOOH production at relatively low overpotentials, although keeping the selectivity unchanged.
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•Fe-doped SnO2 is a promising electrocatalyst for CO2 reduction.•The fabrication technique employed makes Fe-doped SnO2 is cheap and easily scalable.•The porous structure offers high adsorption capability, and so a high catalytic activity.•Fe-doped SnO2 electrocatalyst offers remarkable enhancement of the partial current density at relatively low overpotentials.
This paper reports a complex analysis of structural, optical and electrical properties of Cu2ZnSnS4 (CZTS) films, prepared by spin-coating of a sol-gel based on the low-cost and environmentally ...friendly solvent dimethyl sulfoxide (DMSO) and synthesized in low vacuum (0.1Pa). The effect of a short-term low-temperature treatment in air and final annealing under low vacuum (0.1Pa) on the synthesis of CZTS films was tested and analyzed. XRD and Raman spectra have shown the polycrystalline nature of obtained CZTS films with almost a pure kesterite phase content. The average size of crystallites D~60nm in the films was estimated. The value of the band gap Eg≈1.53eV was determined from the analysis of optical characteristics. The analysis of electrical characteristics was carried out in the scope of the model of current transport in polycrystalline materials with electrically active grain boundaries. The determined values of the specific resistance ρ≈2.38Ωcm, the hole density p0≈4.2×1018cm−3 and the effective mobility μp≈0.63cm2/(Vs) demonstrate that the CZTS films under investigation are prospective for the fabrication of highly efficient solar cells.
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•Non-toxic DMSO solvent and high temperature synthesis of CZTS films in low vacuum.•The average size of crystallites in the single phase CZTS films was about 60nm.•Current transport in the CZTS films is governed by the thermionic emission over potential barriers at grain boundaries.
It is shown that the frequency dependence of the phenomenological parameters entering Langmuir kinetic equation describing the surface adsorption could be related to a random distribution of ...relaxation times. A theoretical model based on a generalization of Langmuir isotherm, taking into account a homogeneous distribution of relaxation times is proposed for supercapacitor modeling. Its theoretical predictions agree well with experimental data derived by the analysis of Lissajous figures describing the response of an electrochemical cell excited with a well defined frequency. According to our data, the effective desorption time is a rapidly decreasing function of the frequency of the applied signal, whereas the effective adsorption coefficient is an increasing function of it. The effective relaxation time is independent of the ionic concentration, whereas the effective adsorption coefficient strongly depends on this quantity. A large increase in the adsorption coefficient is reported, for the electrochemical cells with high surface area of the electrodes.
•Evidence of frequency dependence of the parameters entering Langmuir kinetic equation describing surface adsorption.•The desorption time is a decreasing function of the frequency, the adsorption coefficient is an increasing function of it.•Generalization of the theory for linear systems, with a response function given by a distribution of relaxation times.•Modeling the supercapacitor response to an harmonic excitation of small amplitude, where the electrodes are blocking.
The structural, optical, and electrical properties of
p
-type Cu
2
SnS
3
thin films produced by the deposition of a dimethylsulfoxide-based sol gel solution using the centrifugation on substrates ...with subsequent heat treatment of the layers formed have been studied. The conditions of formation of the films using low-temperature short-time treatments in open atmosphere and a final annealing in a low vacuum (0.1 Pa) have been analyzed. The crystallite sizes
D
~ 42 nm in the polycrystalline films have been found using X-ray phase analysis. Their compositions have been confirmed using the Raman spectra and the energy-dispersive X-ray analysis. The optical forbidden band width of direct allowed (
E
g
d
~ 1.25 eV) and direct forbidden (
E
g
df
≈ 0.95 eV) optical transitions have been determined as a result of the light transmission and absorption. Based on the study of the electrical properties using a model of polycrystalline materials, the validity of the produced films with resistivity ρ ≈ 0.21 Ω cm, the hole concentration
p
0
≈ 1.75 × 10
19
cm
–3
, and the effective mobility μ
p
≈ 1.67 cm
2
/(V s) for manufacturing solar cells.
The electric responses of electrochemical capacitors produced with electrodes build up of reduced graphene oxide (rGO) deposited on Fluorine-doped tin oxide (FTO) coated glass have been ...experimentally investigated by cyclic voltammetry measurements. According to our experimental data, the parametric curve of the current in the circuit versus the external voltage is a continuous curve without discontinuity points respect to the inversion points of the external voltage. A few equivalent electric circuits able to reproduce the electric response of the capacitor are discussed. The dependence of the area delimited by the parametric cyclic voltammetry curve on the elements of the circuit is investigated. The possible evaluation of the effective capacitance of the capacitor by the numerical evaluation of the area delimited by the parametric curve is critically discussed and the limit of the procedure is underlined. A model based on the Poisson-Nernst-Planck theory with adsorbing electrodes is developed and used to fit the experimental voltammogram. The agreement between the theoretical model and the experimental data is good, indicating the importance of the adsorption phenomenon in the electric response of electrochemical capacitor to an external electric field.
The interface between the semiconductor and the dye is one of the fundamental parameters that directly impact the dye sensitized solar cell (DSSC) performance. In this paper the coupling between a ...prototype organic sensitizer and inorganic oxides is studied by a combined experimental and theoretical approach. In particular, the interface properties of the hemi-squaraine molecule (CT1) anchored onto the TiO2 and ZnO surfaces are investigated. Experimental results evidence that, beside the comparable surface coverage of the dye on both the oxides and the very fast chemisorption kinetics, TiO2 photoanodes give much larger solar cell efficiency values. Theoretical calculations based on density functional theory and time dependent density functional theory show that this difference is due to the stronger electronic coupling occurring between the CT1 anchoring group (the squaric acid) and the TiO2 surface. In this case, chemisorption induces a larger red-shift in the dye optical absorption which extends the range of harvestable frequencies if compared to the isolated dye. Moreover, the CT1/TiO2 system is characterized by an extended electron delocalization of the lowest unoccupied molecular orbital involving the substrate cations, which gives rise to easier electron injection, as confirmed by the incident photon-to-electron conversion efficiency measurements. This study demonstrates that a given dye anchoring group, although being able to form strong chemical bonds with different oxide surfaces, may be responsible for very different DSSCs performances depending on the electronic rearrangement that it undergoes upon attachment to the substrate.
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•N719 dye loading optimization of sheet-like ZnO photoanodes has been carried out.•Dye adsorption on photoanodes is monitored by two UV–vis spectroscopic approaches.•An active real ...time methodology is compared with the standard passive technique.•Passive techniques give insights of reaction between dye and front surface of oxide.•Active monitoring technique gives information regarding actual sensitization time.
The peculiarly critical sensitization of zinc oxide with Ru-based dyes is the serious problem that prevents this semiconductor oxide from achieving photoconversion efficiencies in dye-sensitized solar cells (DSCs) comparable to those obtained with TiO2. Within this framework, methodologies for the optimization of the sensitization procedure of this material in acidic environments prove to be essential. In this paper, in view of streamlining the critical sensitization procedure of sheet-like zinc oxide-based DSC photoanodes with Ru-based dye, a comparative study on active and passive evaluations of N719 dye loading on sheet-like ZnO nanostructures are reported. For the active in-situ spectroscopic approach, a home-made set-up has been appropriately designed and developed for real time monitoring the dye adsorption on the ZnO-based photoanodes, whereas the standard passive dye loading measurements were performed after the electrodes had been sensitized for different time periods in the dye solutions of different concentrations. The dye adsorption results are carefully analyzed and correlated to the photovoltaic conversion efficiency and the incident photon-to-electron conversion efficiency (IPCE) of the corresponding ZnO-based DSCs, fabricated by employing our customized microfluidic architecture. The obtained results show that the real time monitoring of the dye absorption can be successfully employed for optimizing the sensitization conditions of ZnO-based photoanodes for DSCs. When applied online in a large scale production system for dye-sensitized solar cells, the proposed active method will permit to save both time and materials.
Dye-sensitized solar cells (DSSCs) have received great attention over the past decade for their high energy conversion efficiency, relatively easy fabrication process and low production cost. ...However, at present, some practical difficulties such as solvent evaporation, leakage of liquid electrolyte and sealing stability remain serious obstacles to their convenient application.
An innovative microfluidic DSSC housing system is here proposed. Sealing performances of such architecture were examined by dynamic fluidic tests and good sealing for pressure up to 50kPa and temperature of 80°C was obtained, avoiding leakages and bubble formation.
Current–voltage and impedance spectroscopy measurements were used to determine the photovoltaic performance of the cell. Results were compared to the ones obtained with DSSC prototypes assembled in our laboratory following a standard procedure, and higher efficiency values have been obtained.
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