My mnemotechnic trick is to remember, thatĪt anode is occuring anabasis (*) of electrons, upwards from the electrode, i.e. The convention for the primary and secondary (rechargable) cells is to take the latter case as the power source. the cell is in the mode of providing current.the cell is in the mode of electrolysis.The tricky part for the memorising is, anodes and cathodes flip the position, when the current is reversed, depending on if The cathode is the electrode, where substances are gaining electrons and are reduced. The anode is the electrode, where substances are losing electrons and are oxidated. If you then attach an external consumer of electrical work, you can predict the direction of electron flow through the external circuit. Once light hits the cell, the anode becomes negative because electrons are moving toward it from the junction, and the cathode becomes positive because electrons are jumping from it into holes coming from the junction. using and charging a battery), the designation of (+) and (-) switches, so it is uncoupled from the direction the electrons flow through the external wire.įor the photovoltaic cell, maybe this picture helps: Before light hits the cell, anode and cathode are neither negative nor positive. While the designation of anode and cathode is consistent for voltaic and electrolytic cells (i.e. The (+) and (-) designation is confusing even just for electrochemical cells. Unfortunately, anode and cathode are named using different conventions depending on the type of device, see this overview (and beware that the current I sometimes goes in the same direction as the electrons and sometimes not, again depending on conventions). In the photovoltaic cell, electrons flow from junction to anode and holes flow from junction to cathode (or you could say electrons flow from cathode to junction). In the voltaic cell, there is no electron flow inside the cell (there is ion flow instead to balance charges). It makes sense to use the direction of electron flow in the external circuit to define anode and cathode (electrons flow from anode to cathode in the external circuit). So labeling the anode and the cathode relies on an analogy between a voltaic cell and a photovoltaic cell as a source of electrical work. In the solar cell, electrons flow in a closed circuit - round and round in the external circuit and through the device. A solar cell is different from an electrochemical cell in that their is no net chemical reaction. The circuit of charge transport gets completed by ions traveling inside the cell. In an electrochemical cell, the anode is the source of electrons to the external circuit and the cathode is the sink. There is no completed electronic circuit in an electrochemical cell Many more diagrams agreeing with this latter one are found from a simple google search. "*Negative is cathode", it says, and we are back to my question in the top: why do the electrons (black spheres) move towards the negative cathode in that schematic? the following "PANIC"-remembering-rule to remember, which is cathode and which is anode ( from this source, slide 8): If the figure is correct and I am the one being confused, then there are several other cases that seem to teach false. The electrons and holes will then move to the respective anode and cathode, through the donor and acceptor material phase (3). The excitons diffuse in the bulk heterojunction until they either recombine or reach a donor-acceptor interface, where they separate into electrons (black) and holes (white) (2). Light enters the cell through the transparent anode, and is absorbed in the bulk heterojunction layer through generation of excitons (1). Is it a mistake on the drawing or should I re-think my understanding of the terms "anode" and "cathode"?įigure 1. Why would electrons (black spheres) move towards the negatively charged cathode, while positive holes (white spheres) move towards the positively charged electron-absorbing anode? Wouldn't the opposite make sense? the anode is the oxidizing electrode, which accepts electrons?.the cathode is the reducing electrode, which supplies electrons, while. ![]() ![]() My question is only about the naming of electrodes. (The figure text is quoted as well for the sake of context). The below image is a schematic of a polymer solar cell ( Source (WBM)). A maybe (hopefully) simple question about the denotations of "anode" and "cathode".
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