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Zinc–air batteries are recognized for their environmental friendliness and high energy density; however, the slow kinetics of the oxygen reduction reaction (ORR) at the air electrode hinder their commercial viability. The research focuses on synthesizing cubic hollow carbon structures derived from Metal–Organic Frameworks (MOFs), which enhance catalytic performance through improved conductivity and mass transfer. The resulting Fe/Fe3C/HCNB catalyst demonstrates a half-wave potential of 0.826 V for ORR and achieves a peak power density of 274 mW cm−2 in zinc–air batteries, surpassing commercial Pt/C catalysts. Electrochemical impedance spectroscopy reveals that the hollow structure enhances hydrophilicity and reduces solution resistance, facilitating greater active site engagement in electrochemical reactions. The study concludes that the unique structural features of Fe/Fe3C/HCNB significantly improve discharge performance and stability, positioning it as a promising alternative for zinc–air battery applications. [ABSTRACT FROM AUTHOR]

The theoretical and computational studies of dye sensitized solar cells (DSSCs) can contribute to a deeper understanding of these types of solar cells. The DSSCs are the novel design of solar cells which could be used as power producing windows or skylights. They represent a particular promising approach to a direct conversion of sunlight into electrical energy at low cost and with high efficiency. The light adsorption occurs in dye molecules adsorbed on a highly porous structure of TiO2 film. Despite the progress in the efficiency and stability of these solar cells, there is still a room of research on some of their operational aspects that are still not understood. One process, for which there is limited information, is the time taken to upload the dye on the TiO2 nanoporous film. The processes followed experimentally for dye uptake is by dipping the TiO2 semiconductor electrode into the dye solution for periods of several hours to several days. However, such long dipping times are not economical for industrial production of DSSCs. The factors controlling this process are not yet fully investigated. We propose a simple model based on the Langmuir isotherms to study and understand the diffusion and adsorption of the dye molecules in TiO2 films. Our computational modelling results show that the adsorption of dye into the TiO2 nanotubes film is controlled by the diffusion coefficient, the adsorption-desorption ratio and the initial dye concentration. Our results show that the initial dye concentration plays an important role on the surface coverage. It is also noted that for a higher concentration shorter immersion time is needed for the sufficient surface coverage. Furthermore, it is observed that for the large values of the adsorption-desorption ratio there is a delay in the diffusion of dye molecules on the surface. [ABSTRACT FROM AUTHOR]

The measurement of solar radiation is difficult to carry out due to the cost and techniques involved especially in developing countries like South Africa. A variety of solar models with different weather parameters as inputs have been used to estimate the global solar radiation around the world. Since air temperature records are readily available around the world, models based on air temperature for estimating solar radiation have been widely accepted. Estimation of global solar radiation (H) from the daily range of air temperature (ΔT) offers an important alternative in the absence of the measured H or sunshine duration. In our present work, the estimation of the monthly average daily global solar radiation for Pretoria has been determined, based on two models: Hargreaves - Samani and Clemence. The performance of the two models is validated by comparing the measured and the estimated global solar radiation for the three different stations under study. The statistical comparison between the estimated and measured value leads to the conclusion that the two temperature models have potential to estimate the global solar radiation in the area under study. [ABSTRACT FROM AUTHOR]

An attempt has been made to employ three different theoretical models for the determination of global solar radiation for the climate conditions of the Vhembe district of Limpopo Province in South Africa. The models are: 1) the Angstrom linear-based model, 2) the Hargreaves and Samani (temperature-based) model, and 3) the Garcia model. These models require the following meteorological data inputs: temperature, sunshine hours, and global solar irradiance on the horizontal surface. The regression coefficients from our previous study were also employed in the calculations. A 4-year (2007--2010) global solar irradiance and temperature data set from the Agricultural Research Council and the actual sunshine data set from the South African Weather Services were used. The monthly average global solar irradiance for the four selected areas of study were computed and compared with the in situ data. The results obtained show that the Angstrom linear and temperature-based models are suitable methods for predicting the global solar irradiance in this study area. The difference between the observed and the predicted data is less than 6.5 MJ/(m² day). Their root mean square error varies between 0.0112 and 0.0368. Graphical representations of the irradiances versus the days of the year showed high values during summer for all the models used. [ABSTRACT FROM AUTHOR]

A range of solution-processed organic and hybrid organic−inorganic solar cells, such as dye-sensitized and bulk heterojunction organic solar cells have been intensely developed recently. TiO2 is widely employed as electron transporting material in nanostructured TiO2 perovskite-sensitized solar cells and semiconductor in dye-sensitized solar cells. Understanding the optical and electronic mechanisms that govern charge separation, transport and recombination in these devices will enhance their current conversion efficiencies under illumination to sunlight. In this work, density functional theory with Perdew-Burke Ernzerhof (PBE) functional approach was used to explore the optical and electronic properties of three modeled TiO2 brookite clusters, (TiO2)n=5,8,68. The simulated optical absorption spectra for (TiO2)5 and (TiO2)8 clusters show excitation around 200–400 nm, with (TiO2)8 cluster showing higher absorbance than the corresponding (TiO2)5 cluster. The density of states and the projected density of states of the clusters were computed using Grid-base Projector Augmented Wave (GPAW) and PBE exchange correlation functional in a bid to further understand their electronic structure. The density of states spectra reveal surface valence and conduction bands separated by a band gap of 1.10, 2.31, and 1.37 eV for (TiO2)5, (TiO2)8, and (TiO2)68 clusters, respectively. Adsorption of croconate dyes onto the cluster shifted the absorption peaks to higher wavelengths. [ABSTRACT FROM AUTHOR]

Dye-sensitized solar cells have attracted rapid interest over the recent years with prospect of emerging as a viable alternative to conventional silicon-based solar cells. Currently organic and inorganic complexes have been widely employed as sensitizers for DSSCs. One of the salient features of dye sensitizer is a strong absorption in the ultraviolet, visible and near-infrared part of the solar radiation spectrum. Light absorption and charge separation is performed by the sensitized dye molecules adsorbed on TiO2 surface. In this work, the time dependent-density functional theory was used to investigate UV-Vis absorption spectra of a series of polyene-diphenylaniline organic chromophores. The HOMO-LUMO energy levels, maximum excitation wavelength, excitation energies and light-harvesting efficiencies of selected dye molecules were simulated. The results showed that, the dyes with methoxy groups in their donor moiety show bathochromic shift and reduced HOMO-LUMO energy gap than the corresponding dyes without methoxy group. The results compare favorably well with other findings. [ABSTRACT FROM AUTHOR]

Zinc-air batteries are recognized for their environmental friendliness and high energy density; however, the slow kinetics of the oxygen reduction reaction (ORR) at the air electrode hinder their commercial viability. The research focuses on synthesizing cubic hollow carbon structures derived from Metal-Organic Frameworks (MOFs), which enhance catalytic performance through improved conductivity and mass transfer. The resulting Fe/Fe 3 C/HCNB catalyst demonstrates a half-wave potential of 0.826 V for ORR and achieves a peak power density of 274 mW cm -2 in zinc-air batteries, surpassing commercial Pt/C catalysts. Electrochemical impedance spectroscopy reveals that the hollow structure enhances hydrophilicity and reduces solution resistance, facilitating greater active site engagement in electrochemical reactions. The study concludes that the unique structural features of Fe/Fe 3 C/HCNB significantly improve discharge performance and stability, positioning it as a promising alternative for zinc-air battery applications.