Voltaic effect

Chem. chemilumi- nescence explosive reaction exothermic reaction voltaic effect chemical reaction... 

To discuss in more detail the possible peculiarities of photovoltaics in an asymmetrical D-A multilayer structure, we will make a few remarks concerning possible mechanisms of photo-voltaic effect in multilayered structures containing organic dyes (see (34) and also a recent issue of Chemical Reviews devoted to organic electronics and optoelectronics (35)). 

Steam, gas, petrol, and hot-air engines are heat engines a thermopile coupled with an electromotor also constitutes a heat engine. An electromotor is not a heat engine, since its effect is produced at the cost of electrical energy, which may, it is true, ultimately be derived from a heat engine coupled with a dynamo, but may equally well arise from chemical action in voltaic cells absorbing practically no heat from their environment (e.g., the Daniell cell). 

The heat of formation of a substance iji a voltaic cell may therefore be calculated from the measured Peltier effects and the electromotive force. 

Similar considerations apply of course to the opposing electromotive forces of polarisation during electrolysis, when the process is executed reversibly, since an electrolytic cell is, as we early remarked, to be considered as a voltaic cell working in the reverse direction. In this way Helmholtz (ibid.) was able to explain the fluctuations of potential in the electrolysis of water as due to the variations of concentration due to diffusion of the dissolved gases. It must not be forgotten, however, that peculiar phenomena—so-called supertension effects—depending on the nature of the electrodes, make their appearance here, and com-... 

Any self-contained unit having a specific functional purpose, as (a) voltaic cell (battery) to generate electric current, (b) electrolytic cell to effect electrolysis, (c) fuel cell to convert chemical energy into electricity, and (d) solar cell to capture heat from sunlight. All except the last involve use of electrodes and electrolytes. 

The main component of voltaic inefficiency is usually the ohmic loss, compounded by mass-transport-related overvoltage. The extent of coulombic losses depends on the system and may be due to parasitic electrode and/or chemical reactions, self-discharge, and/or shunt currents (in flowing systems wth a common electrolyte). The efficiency, as measured at battery terminals differs from the effective value if a part of the battery s energy is used to operate auxiliaries (e.g., pumps) or if thermal losses are involved (high-temperature batteries). 

However, we can make this process happen by supplying from an external source an electric potential greater than eii- In effect, we have converted the voltaic cell into an electrolytic cell and changed the nature of the electrodes—anode is now cathode, and cathode is now anode (Figure 21.23B) ... 

Volta found that a current was produced when two different metal disks such as silver and zinc were separated by a moist conductor, such as paper soaked in salt water, and brought into contact by a wire. By stacking a collection of silver-moist paper-zinc units, in effect forming a pile, Volta determined that the current intensified. If someone touched the top of such a voltaic pile (as this early battery was called) and put his or her other hand in a dish of salt water that was connected to the bottom metal disk by a strip of metal, that person would feel a continuous, if weak, shock. 

The decrease in electrical resistance of selenium during exposure to light was first observed more than hundred years ago. Later a similar behaviour was also found with a number of other materials, but at that time the potential possibilities of the photo-electrical effect were not utilized practically. Today, however, the situation has changed and, for example, energy conversion with photo-voltaic solar cells has become an important technology. 

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