We report the fabrication and electrochemical characterization of biodegradable and flexible supercapacitors (SCs). The conductive electrodes of these SCs were pieces of compacted coconut fibers coated by graphene nanoplates. An oral electrolyte solution (OES) and rice paper were used as electrolyte and separator, respectively. The SCs' encapsulation was made of gelatin/pectin. According to the electrochemical tests, the maximum capacitance and specific energy of the cell made with the biodegradable components were 670.8 F g −1 and 134.2 Wh kg −1 , respectively. After adding MgTiO 3 nanoparticles (NPs) to the anode, both, the capacitance and specific energy were enhanced by ≈37% and by ≈20%, respectively. For comparison purposes, the OES electrolyte was substituted by a conventional acidic electrolyte (PVA/H 3 PO 4 ) in the SCs, but the capacitance and specific energy obtained were lower (175.9 F g −1 and 35.2 Wh kg −1 ). Interestingly, the biodegradable cells exhibited very long discharge times of 550-600 min and a stable output voltage in the range of 0.54-0.71 V, which has not been observed previously for biodegradable SCs. The SCs made with MgTiO 3 NPs stored charge by redox reactions and the redox centers were oxygen vacancies (defects), Mg 2+ /Mg 0 and Ti 3+ /Ti 4 (the presence of such centers was confirmed by x-ray photoelectron spectroscopy, Raman and absorbance measurements). In general, we demonstrated that the biodegradable SCs are sustainable/eco-friendly energy sources that are promising to substitute the conventional technologies of Li or alkaline batteries made with toxic/corrosive components that contaminate the environment.
The material deposition in aqueous solution, also known as chemical bath deposition (CBD), is a well-established technique for the fabrication of semiconducting thin films. The success of the CBD technique is mainly based on the relatively easy implementation and operation requirements. The CBD has importantly contributed to the development of sensors, optical devices and solar cells applications. In this review, the origins and current state of the art of the CBD technique, the involved physicochemical processes, the growing mechanisms, and the analytical techniques for the estimation of optimal physicochemical conditions for the film deposition are discussed. Emphasis on authors' experience on CBD of CdS, ZnS, Zn (OH) 2 , and ZnO films are here highlighted, following methodologies for a high control of the deposited materials, such as the species distribution diagrams and the solubility curves.
Copper oxide (CuO) films were deposited onto glass substrates by the microwave assisted chemical bath deposition method, and varying the pH of the solution. The pH range was varied from 11.0 to 13.5, and the effects on the film properties were studied. An analytical study of the precursor solution was proposed to describe and understand the chemical reaction mechanisms that take place in the chemical bath at certain pH to produce the CuO film. A series of experiments were performed by varying the parameters of the analytical model from which the CuO films were obtained. The crystalline structure of the CuO films was studied using X-ray diffraction, while the surface morphology, chemical composition, and optical band-gap energy were analyzed by scanning electron microscopy, X-ray photoelectron spectroscopy, and UV–Vis spectrophotometry, respectively. The CuO films obtained exhibited a monoclinic crystalline phase, nanostructured surface morphology, stoichiometric Cu/O ratio of 50/50 at%, and band-gap energy value of 1.2 eV.
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