Electromotive force | EPFL Graph Search

In electromagnetism and electronics, electromotive force (also electromotance, abbreviated emf, denoted \mathcal{E} or {\xi}) is an energy transfer to an electric circuit per unit of electric charge, measured in volts. Devices called electrical transducers provide an emf by converting other forms of energy into electrical energy. Other electrical equipment also produce an emf, such as batteries, which convert chemical energy, and generators, which convert mechanical energy. This energy conversion is achieved by physical forces applying physical work on electric charges. However, electromotive force itself is not a physical force, and ISO/IEC standards have deprecated the term in favor of source voltage or source tension instead (denoted U_s). An electronic–hydraulic analogy may view emf as the mechanical work done to water by a pump, which results in a pressure difference (analogous to voltage). In electromagnetic induc

Instantaneous radiation from time-varying electric and magnetic dipoles

Romain Christophe Rémy Fleury, Mohammad Sajjad Mirmoosa

Radiation from magnetic and electric dipole moments is a key subject in the theory of electrodynamics. Although people treat the problem thoroughly in the context of the frequency domain, the problem is still not well understood in the context of the time domain especially if dipole moments arbitrarily vary in time under the action of external forces. Here, we scrutinize the instantaneous power radiated by magnetic and electric dipole moments and report findings that are different from the conventional understanding of their instantaneous radiation found in textbooks. In contrast to the traditional far-field approach based on the Poynting vector, our analysis employs a near-field method based on the induced electromotive force, leading to corrective terms that are found to be consistent with time-domain numerical simulations, unlike previously reported expressions. Beyond its theoretical value, this paper may also have significant impact in the field of time-varying metamaterials especially in the study of radiation from subwavelength meta-atoms, scatterers, and emitters that are temporally modulated.

2020

Nanocrystalline Boron-Doped Diamond as a Corrosion-Resistant Anode for Water Oxidation via Si Photoelectrodes

Petr Ashcheulov, Ladislav Kavan, Florian Le Formal, Kevin Sivula, Jun Ho Yum

Due to its high sensitivity to corrosion, the use of Si in direct photoelectrochemical (PEC) water-splitting systems that convert solar energy into chemical fuels has been greatly limited. Therefore, the development of low-cost materials resistant to corrosion under oxidizing conditions is an important goal toward a suitable protection of otherwise unstable semiconductors used in PEC cells. Here, we report on the development of a protective coating based on thin and electrically conductive nanocrystalline boron-doped diamond (BDD) layers. We found that BDD layers protect the underlying Si photoelectrodes over a wide pH range (1-14) in aqueous electrolyte solutions. A BDD layer maintains an efficient charge carrier transfer from the underlying silicon to the electrolyte solution. SiIBDD photo electrodes show no sign of performance degradation after a continuous PEC treatment in neutral, acidic, and basic electrolytes. The deposition of a cobalt phosphate (CoPi) oxygen evolution catalyst onto the BDD layer significantly reduces the overpotential for water oxidation, demonstrating the ability of BDD layers to substitute the transparent conductive oxide coatings, such as indium tin oxide (ITO) and fluorine-doped tin oxide (FTO), frequently used as protective layers in Si photoelectrodes.

AMER CHEMICAL SOC2018

Modeling the Photostability of Solar Water-Splitting Devices and Stabilization Strategies

Sophia Haussener, Fredy Intelligent Nandjou Dongmeza

The practical implementation of photoelectrochemical devices for hydrogen generation is limited by their short lifetimes. Understanding the factors affecting the stability of the heterogeneous photoelectrodes is required to formulate degradation mitigation strategies. We developed a multiscale and multiphysics model to investigate and quantify the photostability of photoelectrodes. The model considers the photophysical processes in an electrocatalyst-coated semiconductor immersed in electrolyte, and the kinetics of the competing water-splitting and photocorrosion reactions. When applied to 12 promising compound semiconductors for use as photoanodes (GaAs, GaP, InP, GaN, SiC, AlP, AlAs, CdTe, CdS, CdSe, ZnS, and ZnSe), the semiconductor–electrocatalyst interfacial charge transfer rate constant was found to be the most significant parameter for stabilizing the photoelectrodes. Its increase induced a sigmoid-like increase in photostability, and its optimization made it possible to stabilize nine semiconductors. The semiconductor surface back-bond energy also increased the photostability in a sigmoid-like response, and its optimization allowed to stabilize five semiconductors. The increase of irradiance induced a logarithmic drop in photostability, and limiting it to 100 W/m2 could stabilize three semiconductors. We further observed that the photostability in a device of centimeter-scale can vary by more than 50%, showing stable zones and photocorrosion hotspots. The photoelectrode’s length as well as the electrocatalyst and electrolyte conductivities were found to be relevant parameters to impact this heterogeneity in the photostability. Thus, the photostability is not only defined by material properties but also by the specific combination of materials and by the device architecture. The model presented in this study can also be applied to photocathodes and other PEC designs, and can serve as a design tool for understanding, quantifying, and improving the stability.

2022

Modeling the Photostability of Solar Water-Splitting Devices and Stabilization Strategies

Sophia Haussener, Fredy Intelligent Nandjou Dongmeza

2022