Operational principles of electrochemical nanoemitter solar cells for photovoltaic and photoelectrocatalytic applications

Application of Electrospun Nanofibers for Fabrication of Versatile and Highly Efficient Electrochemical Devices: A Review

Electrochemical devices convert chemical reactions into electrical energy or, vice versa, electricity into a chemical reaction. While batteries, fuel cells, supercapacitors, solar cells, and sensors belong to the galvanic cells based on the first reaction, electrolytic cells are based on the reversed process and used to decompose chemical compounds by electrolysis. Especially fuel cells, using an electrochemical reaction of hydrogen with an oxidizing agent to produce electricity, and electrolytic cells, e.g., used to split water into hydrogen and oxygen, are of high interest in the ongoing search for production and storage of renewable energies. This review sheds light on recent developments in the area of electrospun electrochemical devices, new materials, techniques, and applications. Starting with a brief introduction into electrospinning, recent research dealing with electrolytic cells, batteries, fuel cells, supercapacitors, electrochemical solar cells, and electrochemical sensors is presented. The paper concentrates on the advantages of electrospun nanofiber mats for these applications which are mostly based on their high specific surface area and the possibility to tailor morphology and material properties during the spinning and post-treatment processes. It is shown that several research areas dealing with electrospun parts of electrochemical devices have already reached a broad state-of-the-art, while other research areas have large space for future investigations.

An electrodeposited inhomogeneous metal-insulator-semiconductor junction for efficient photoelectrochemical water oxidation

The photoelectrochemical splitting of water into hydrogen and oxygen requires a semiconductor to absorb light and generate electron-hole pairs, and a catalyst to enhance the kinetics of electron transfer between the semiconductor and solution. A crucial question is how this catalyst affects the band bending in the semiconductor, and, therefore, the photovoltage of the cell. We introduce a simple and inexpensive electrodeposition method to produce an efficient n-Si/SiOx/Co/CoOOH photoanode for the photoelectrochemical oxidation of water to oxygen. The photoanode functions as a solid-state, metal-insulator-semiconductor photovoltaic cell with spatially non-uniform barrier heights in series with a low overpotential water-splitting electrochemical cell. The barrier height is a function of the Co coverage; it increases from 0.74 eV for a thick, continuous film to 0.91 eV for a thin, inhomogeneous film that has not reached coalescence. The larger barrier height leads to a 360 mV photovoltage enhancement relative to a solid-state Schottky barrier.