A new route to control texture of materials: Nanostructured ZnFe2O4 photoelectrodes

Studies were conducted to investigate the influence of deposition solution composition (methanol ≤ the deposition solvent ≤ ethanol) on their physical and chemical properties that matters in the aerosol formation and subsequent decomposition during the aerosol assisted chemical vapour deposition (AACVD) of ZnFe2O4 electrodes. The FEGSEM studies found that the change of composition of deposition solution produced a dramatic change in the ZnFe2O4 electrode texture. The ZnFe2O4 electrodes deposited from methanol as well as predominately methanolic solvents had a relatively compact morphology. In contrast, the electrodes deposited from ethanol as well as predominately ethanolic solvents showed highly textured rod-like structure at nanoscale. The change in electrode texture is explained in terms of changes occurred in precursor decomposition pathways from heterogeneous and homogeneous when the composition of deposition solution is systematically varied. The photoelectrochemical (PEC) properties of all ZnFe2O4 electrodes were studied by recording JeV characteristics under AM1.5 illumination and the photocurrent spectra. The textured electrodes exhibited a significantly higher photocurrent compared to their compact counterparts. This is attributed to the improved photogenerated minority carrier collection at the ZnFe2O4/electrolyte interface as the average feature size gradually decreased. The photocurrent density (at 0.25 V vs. Ag/AgCl/3M KCl) increases rapidly when the electrode is deposited from the solvent containing 60% ethanol and above, which is in close agreement with the textural changes taken place in ZnFe2O4 electrodes.Web of Scienc

Enhanced performance of flexible dye-sensitized solar cells: Electrodeposition of Mg (OH) 2 on a nanocrystalline TiO2 electrode

Nanocrystalline TiO2 photoanodes were prepared on a conductive indium–tin oxide coated polyethylene naphthalate (ITO-PEN) plastic substrate by the doctor-blade method to fabricate flexible dye-sensitized solar cells (DSCs). The surface of the photoanode was coated with Mg(OH)2 by electrodeposition and the deposition time was systematically varied (2, 4, 6, 8, and 10 min). Electrodeposited Mg(OH)2 was confirmed by IR and energy dispersive X-ray (EDX) analysis. The surface morphology was studied by scanning electron microscopy. The internal surface area of TiO2 was studied against the deposition time by taking into account the projected surface area of the photoelectrode and it shows that the internal surface area of the photoelectrode was reduced as the Mg(OH)2 deposition time increased. The performance of flexible DSCs on various deposition times of Mg(OH)2 was evaluated on the basis of their photocurrent density–voltage characteristics. Among the deposition times, 2 min showed the best performance in Voc on a treated flexible DSC, with resulting 847 mV and a photocurrent density of 7.13 mA/cm2, providing an overall light-to-electricity conversion efficiency of 4.01%. This photovoltage is among the highest attained for a flexible DSC to date. This notable increment in Voc at a thin layer of Mg(OH)2 was attributed to the suppression of recombination of photogenerated electrons via the exposed surface of ITO as well as TiO2 without influencing the internal surface area of the photoanode significantly

Renewable hydrogen economy outlook in Africa

Hydrogen presents an opportunity for Africa to not only decarbonise its own energy use and enable clean energy access for all, but also to export renewable energy. This paper developed a framework for assessing renewable resources for hydrogen production and provides a new critical analysis as to how and what role hydrogen can play in the complex African energy landscape. The regional solar, wind, CSP, and bio hydrogen potential ranges from 366 to 1311 Gt/year, 162 to 1782 Gt/year, 463 to 2738 Gt/year, and 0.03 to 0.06 Gt/year respectively. The water availability and sensitivity results showed that the water shortages in some countries can be abated by importing water from regions with high renewable water resources. A techno-economic comparative analysis indicated that a high voltage direct current (HVDC) system presents the most cost-effective transportation system with overall costs per kg hydrogen of 0.038 $/kg, followed by water pipeline with 0.084$/kg, seawater desalination 0.1 $/kg, liquified hydrogen tank truck 0.12$/kg, compressed hydrogen pipeline 0.16 $/kg, liquefied ammonia pipeline 0.38$/kg, liquefied ammonia tank truck 0.60 $/kg, and compressed hydrogen tank truck with 0.77$/kg. The results quantified the significance of economies of scale due to cost effectiveness of systems such as compressed hydrogen pipeline and liquefied hydrogen tank truck systems when hydrogen production is scaled up. Decentralization is favorable under some constraints, e.g., compressed hydrogen and liquefied ammonia tank truck systems will be more cost effective below 800 km and 1400 km due to lower investment and operation costs

Characterisation of electrochromic viologen-modified nanocrystalline TiO2 films by frequency-resolved optical transmission spectroscopy

A nanocrystalline TiO2 film electrode on conductive glass was modified with the viologen compound, bis(2-phosphonylethyl)-4,4′-bipyridinium dichloride, to form an electrochromic layer. Electrochemical reduction of the modified electrode in 0.1 M LiClO4 γ-butyrolactone solution is accompanied by a change of colour from transparent to blue. The process was studied by cyclic voltammetry, optical transmittance, electrochemical impedance and modulated transmittance at 370 and 630 nm. The study shows that the dynamic optical responses at the two wavelengths can be used to follow the coupled relaxation of the viologen and electron concentrations in the nanocrystalline layer. Keywords: Bipyridinium, Electrochromic, Impedance, Nanocrystalline, Titanium dioxide, Viologe

Preparation of nanocrystalline TiO2 electrodes for flexible dye-sensitized solar cells: influence of mechanical compression

Nanocrystalline TiO2 electrodes were prepared using binder-free TiO2 paste on conductive ITO-PEN substrates by the doctor-blade method at significantly low temperature (140 °C), and the electrodes were further processed under different compressions (10–60 MPa) in order to improve interparticle connections and adhesion between the nanoparticles and the ITO-PEN substrate. TiO2 electrodes compressed at 30 and 40 MPa had relatively less cracks with low crack width. Electrode compressed at 30 MPa showed the highest internal surface area. Electrode prepared at this compression showed the best dye-sensitized solar cell (DSC) performance with Voc of 805 mV, Jsc of 9.24 mA cm–2, and an overall efficiency of 4.39%. Electrochemical impedance spectroscopy (EIS) studies of the sandwiched cells employing bare nanocrystalline TiO2 electrode and Pt counter electrode in I–/I3– electrolyte showed that electrode compression significantly influences the stability of the cells. EIS data suggested that degradation/corrosion processes may take place on ITO-PEN for sandwiched cells made by TiO2 electrodes compressed at all pressures. Thirty and 40 MPa compressions showed a minor degradation of ITO. The recombination dynamics at the TiO2/electrolyte interface were influenced by the changes in the nanostructured electrode internal surface area, changes in electron transport properties (due to improved sintering), and possible degradation/corrosion of ITO-PEN. Open-circuit voltage decay (OCVD) measurements showed that the DSC made by the 30 MPa compressed TiO2 electrode had the highest decay time, indicating low recombination properties, which is in a good agreement with other data

Preparation of nanocrystalline TiO2 electrodes for flexible dye-sensitized solar cells: influence of mechanical compression

Nanocrystalline TiO2 electrodes were prepared using binder-free TiO2 paste on conductive ITO-PEN substrates by the doctor-blade method at significantly low temperature (140 °C), and the electrodes were further processed under different compressions (10–60 MPa) in order to improve interparticle connections and adhesion between the nanoparticles and the ITO-PEN substrate. TiO2 electrodes compressed at 30 and 40 MPa had relatively less cracks with low crack width. Electrode compressed at 30 MPa showed the highest internal surface area. Electrode prepared at this compression showed the best dye-sensitized solar cell (DSC) performance with Voc of 805 mV, Jsc of 9.24 mA cm–2, and an overall efficiency of 4.39%. Electrochemical impedance spectroscopy (EIS) studies of the sandwiched cells employing bare nanocrystalline TiO2 electrode and Pt counter electrode in I–/I3– electrolyte showed that electrode compression significantly influences the stability of the cells. EIS data suggested that degradation/corrosion processes may take place on ITO-PEN for sandwiched cells made by TiO2 electrodes compressed at all pressures. Thirty and 40 MPa compressions showed a minor degradation of ITO. The recombination dynamics at the TiO2/electrolyte interface were influenced by the changes in the nanostructured electrode internal surface area, changes in electron transport properties (due to improved sintering), and possible degradation/corrosion of ITO-PEN. Open-circuit voltage decay (OCVD) measurements showed that the DSC made by the 30 MPa compressed TiO2 electrode had the highest decay time, indicating low recombination properties, which is in a good agreement with other data