From Wikipedia, the free encyclopedia
Jump to: navigation, search
WikiProject Chemistry (Rated Start-class, Low-importance)
WikiProject icon This article is within the scope of WikiProject Chemistry, a collaborative effort to improve the coverage of chemistry on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
Start-Class article Start  This article has been rated as Start-Class on the project's quality scale.
 Low  This article has been rated as Low-importance on the project's importance scale.
WikiProject Technology (Rated Start-class)
WikiProject icon This article is within the scope of WikiProject Technology, a collaborative effort to improve the coverage of technology on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.
Start-Class article Start  This article has been rated as Start-Class on the project's quality scale.

Valuable Outbound Links[edit]

I would like to add an outbound link to two great guides and resources that deal with the proper preparation and selection of material on tungsten electrodes. The link is at: Do you feel that this would be appropriate?

do physicists and chemists agree on anode and cathode definitions?[edit]

Hi Michael: The fact that physicists and chemists use opposite conventions for cathode and anode is the cause of much confusion between the two groups. I believe electrical engineers follow the physics convention. This is worth noting up-front, and worth tracing its origin. One must always specify whether positive current is flowing internal or external to the galvanic cell. Chemists never think twice about this, taking internal current (following Faraday). Neither do physicists, taking external current (following, I suppose, people like Thomson). No wonder there is much confusion. The chemists have it right. Physicists are ignorant of the origins of the terminology in Faraday's studies of decomposing electrolytes. The article should address this upfront with a statement like "The terminology for cathode and anode (as well as electrode, electrolyte, cation, and anion) was given by Faraday in his studies of decomposition of electrolytes, where he was concerned with current flow through the galvanic cell. Physicists studying processes within cathode ray tubes (vacuum tubes) are interested in current flow that is external to their voltage source, and this seems to have led to a reversal in the definition of cathode and anode..." (If I have it wrong, please spell it out for me.) 15:56, 14 June 2007 (UTC)

Hi (insert your name here), which opposite conventions are you referring to!? Physicists and chemists agree that anode is where current flows in, and cathode is where current flows out, have a closer look at the chemistry and physics examples given at the top of the article you'll see they all illustrate the same definition. Regarding your internal current vs external current point, it is not a source of confusion in the present definitions in fact, for example when Wikipedia says the anode is the terminal where current flows in, it means unambiguously that it flows from the external part of the circuit into the device. It flows in whether you consider external current or internal current. Do let me know if something still bothers you. MichelJullian 22:28, 14 June 2007 (UTC)

OK. Here's what is bothering me. For a (Daniell) galvanic cell with Zn/Cu, using Faraday's definition the Zn electrode is called the anode (according to Faraday it should attract anions, but instead it "ejects" Zn++ cations, like a good sacrificial anode should) and the Cu electrode is called the cathode (it attracts Cu++ cations). The internal current flows left to right (anode to cathode) and the external current flows right to left (cathode to anode), with the electrons in the external path flowing from left to right. By Ohm's Law applied to the external wire, the electrode on the right -- that is, the cathode (in Faraday's nomenclature) -- is at the higher electrical potential. Now put 50 Daniell cells in series, to drive a (cold) cathode ray tube (imagine a small gap in the external wire). Electrons will jump the gap and flow from left to right (as for a single Daniell cell). Here is my point. In the language of physicists, the electrode the electrons flow from is called the cathode. To me that is NOT the name of the electrode according to Faraday.

Just to make the point more explicitly, let me discuss the 3rd edition (1958) of Page and Adams' "Principles of Electricity". On p. 259 is a picture of what they call a discharge tube, and on its right is the NEGATIVELY charged "cathode". Curiously, and uncharacteristically for a physics text, on pp.170-184 they also discuss electrolysis. They do not define cathode and anode, but they seem to employ chemical usage for these terms, with metal plating onto the cathode. So it seems to me they are, unknowingly, schizophrenic, using one set of definitions in the chemical case and another set of definitions in the cathode ray tube case. If physicists and chemists have different definitions, then it is worthwhile to point this out and, if possible, suggest how that could have come about. 04:13, 15 June 2007 (UTC)

You have it all right, except your conclusion that physicists and chemists have different definitions. In the galvanic cell, as you say, the internal current flows from anode to cathode. In the discharge tube, as you say, electrons flow internally from cathode to anode, i.e. internal current flows from anode to cathode. It's the same. The only difference is polarity, cathode being the positive (highest potential) terminal in the galvanic cell whereas it is the negative terminal in the discharge tube, but anode and cathode definitions are NOT polarity based as is commonly and mistakenly believed, they are current direction based. Besides the "cathode = negative terminal" case is not physics specific, it's the same in electrolytic cells, for which the terms were initially invented. In fact it's the same in all passive devices, as without a source of energy (chemical in the case of the galvanic cell) there is no way you can make internal current run from the lowest to the highest potential. Let me know if the controversy is solved. MichelJullian 06:36, 15 June 2007 (UTC)
BTW, I realized that the "anode and cathode are of fixed polarity" common misconception mentioned above, although discussed at length in this talk page, was not even mentioned in the articles themselves where it would be more useful. I corrected this omission in the illustrating examples paragraph. MichelJullian 13:36, 15 June 2007 (UTC)

The Wikipedia entry on cathode ray indicates that in 1838 Faraday himself studied luminescence in (partially) evacuated glass tubes. It is doubtful that he saw rays, because he had a poor vacuum, and could only see luminescence. I will assume that he called the negative electrode, into which current flows, the cathode (but I really would like to read his notebooks on this). Then, when better vacuums were obtained, cathode rays would have been seen. I'm not happy with the convention, but if Faraday used it for both the interior and exterior of a galvanic cell, I'd better not question it. So I should not be asking when did physicists confuse the interior and exterior of a galvanic cell?, but rather when did physicists start thinking that cathode and anode are voltage-defined? That would likely have been in the 1890's, when physicists lost interest in electrochemical cells and developed an interest in cathode rays and electrons and, eventually, other particles. Thus, assuming that I understand the naming convention, I would be satisfied with definitions of cathode and anode that read something like this:

"The definitions of cathode and anode are current-based, not voltage-based, and depend upon the path along which the current flows. To determine which of two electrodes A and B is the cathode or anode: (1) choose the path between them (which for a Zn/Cu Daniell cell could be either a path through the electrolyte of the interior or through an exterior wire connecting its two electrodes); (2) for this path, define the anode as the electrode from which the current leaves, and the cathode as the electrode into which the current enters. Being path-dependent, the definitions of of cathode and anode for a single loop circuit switch if, rather than choose the interior path, you choose the exterior path. With a Daniell cell, for a path through the cell the Zn electrode is the anode; but for a path through an exterior connecting wire, the Zn electrode is the cathode." At some later point one could note: "For the external connecting wire, electrons leave the cathode to go along the wire to the anode, and this would continue to be true if the wire had a small spark gap through which the electrons passed, thus simulating a cathode ray tube, where the electrons pass from the cathode to the anode." This is still too wordy.

Faraday, in his original article, also talked about "poles", which may have been the other end of his electrodes. It is worth figuring out, but I can't do that at the moment. Sandman42 17:06, 15 June 2007 (UTC)

Hi Sandman, I didn't follow all the intricacies of your example but in the end you're right, the Zn electrode would be both the galvanic cell's anode and the spark gap's cathode. I am tempted to say "and so what?", this does not contradict the present Wikipedia definitions (ACE and CCD in short), which are openly device-based ("enters" or "departs" refers to the device you are considering obviously), no need to specify a path. I still see no disagreement between chemists and physicists. The misconception that electrodes are polarity-defined is not physicist specific either, some chemists exclusively concerned with electrolysis also believe that "the anode is the positive electrode", so they are only right as far as their trade is concerned. Do let me know if anything still bothers you.
Your understanding of Faraday's poles is basically correct, at the time he made a distinction between the electrical terminal itself (the pole) and the surface separating the pole from the electrolyte (the electrode = the current doorway). This nuance has been lost since, as explained in the excellent Ross paper. MichelJullian 22:19, 15 June 2007 (UTC)

What bothers me is that, with this definition, anode and cathode are relative, not absolute, definitions. I think this should be stated up front, as a warning to the reader. Consider a ring centered on the origin, and a point A on the ring at 0 degrees and a point B at 180 degrees. If a bead on the ring moves counterclockwise, then for the bead in the upper quadrants we might say that "start" was at A and "end" will be at B, but for the bead in the lower quadrants we might say that "start" was at B and "end" will be at A. There is method behind the madness, but I find it bothersome that the definition is relative. On the other hand, if a circuit has multiple arms, in some of which there are galvanic cells, then perhaps we can only speak about one arm at a time. Yeah, maybe that's the ticket... However, until physicists (some chemists too, evidently) dig deeply, it will be difficult to unlearn the voltage-based definition. Clearly, I have had that difficulty. I have talked to at least a few other physicists, and they too have been confused on this matter. Mostly, the problem is that it is difficult to unlearn something. Sandman42WMSwiki 23:39, 15 June 2007 (UTC)

Looking at the articles for electrode, cathode, and anode, I note from the figures presented that only for the first would it be possible to state that the definition is absolute. For the cathode and anode the figures are for Cu and Zn in a Daniell cell. That would imply that the definition is absolute, which we agree it is not. So there is a problem with these articles. Sandman42 WMSwiki 23:44, 15 June 2007 (UTC)

Misprint above! Missing NOT. Replace the above paragraph by:

Looking at the articles for electrode, cathode, and anode, I note from the figures presented that only for the first would it be possible to state that the definition is NOT absolute. For the cathode and anode the figures are for Cu and Zn in a Daniell cell. That would imply that the definition is absolute, which we agree it is not. So there is a problem with these articles. Sandman42 02:30, 16 June 2007 (UTC)

I agree it's difficult to unlearn the voltage polarity based definition, I found it difficult myself as recently as last year. The root of the confusion in my case, and others I know, was that since positive cations go to the cathode I concluded erroneously that the cathode must necessarily be negative :-) Indeed the anode and cathode figures only show one example so they lack generality. But it's an interesting one, in that it contradicts the "anode is positive and cathode is negative" most common misconception, and it shows positive ions moving away from the negative electrode and towards the positive electrode (under chemical power). What do you suggest to improve generality, more figures showing other examples maybe, e.g. with the other polarity such as a diode drawing? MichelJullian 07:07, 16 June 2007 (UTC)
Oh I see what you meant by absolute I had missed your point, you mean showing the particular electrode in isolation is meaningless wrt voltages and currents. Note the caption right underneath each figure links to the full galvanic cell device with both electrodes , so there can be no confusion I would have thought. MichelJullian 08:09, 16 June 2007 (UTC)

Someone please fix cathode &/or anode: Both state electrode through which (positive) electric current flows. Thanks

No fix needed, positive current flows through both indeed but not in the same direction: through the anode it flows in (anode current enters), and through the cathode it flows out (cathode current departs). MichelJullian 08:34, 4 July 2007 (UTC)

unhappy with the definitions of cathode and anode[edit]

This is a continuation of the above "do physicists..." section.

The present Wikipedia definition of cathode is "A cathode is an electrode through which (positive) electric current flows out of a polarized electrical device. Mnemonic: CCD (Cathode Current Departs)." I don't like this definition for many reasons, but here are two. (1) Why does the device have to be polarized? In a cathode ray tube the medium is a vacuum, which isn't really polarized. What is meant by "polarized"? I can't read minds. Moreover, it stops the reader. (2) I don't necessarily dislike mnemonics, but if one is inventing them, the reader should be warned. I call up the phrase "sacrificial anode" to remind me of which is which.

I do not have a good suggestion for a short, snappy definition of cathode or anode. At the very least the figures should show the full Daniell cell, and the text should make it clear that the definition is not absolute, giving an example with the Daniell cell and a connecting wire. I'll try again at a reasonable definition.

"The definitions of cathode and anode are current-based, not voltage-based. Because these definitions depend on the path of current flow, they are relative rather than absolute. Consider the accompanying figure of a Daniell cell. Chemists and electrochemists tend to be interested in the interior of the cell, where the current enters the electrolyte from the Zn electrode (for this interior path called the anode) and leaves by the Cu electrode (for this interior path called the cathode). Physicists and electrical engineers tend to be interested in the exterior of the cell, where the current enters an external wire from the Cu electrode (for this exterior path called the anode) and leaves through the Zn electrode (for this exterior path called the cathode). From the cell perspective the cathode is positive and the anode is negative. From the wire perspective the cathode is negative and the anode is positive. From both perspectives the Cu is positive and the Zn is negative. When communicating with others about "cathode" and "anode" it is important to state whether one is considering the viewpoint of an active device (the galvanic cell) or a passive device (the wire)."

Related to this, note that physicists use the convention I=(V2-V1)/R for a resistor (so current flows from high V to low V), but I=[E-(V2-V1)]/r for a battery (so current flows from the low V terminal to the high V terminal). In the limit of emf E=0, the sign convention for a zero emf battery (which still has a resistance) is opposite that for a resistor. That's wacko, but physicists live with it because then the terminal voltage is E when there is no current flow.

Sandman42 18:27, 16 June 2007 (UTC)

1) polarized = polarity matters, e.g. a resistor or a wire is not polarized, a battery or a diode or a CRT is polarized. The device has to be polarized because it wouldn't make sense to talk about a resistor's or a wire's anode.
2) mnemonics aren't generally attributed, have you ever seen it mentioned anywhere who authored the well known LEO "Loss of Electrons = Oxidation" mnemonic? As long as what the mnemonic says translates accurately the definition without harming its universality (which is not the case of your "sacrificial anode" suggestion, as there is nothing sacrificial about e.g. a CRT's anode), making up a mnemonic is no more an original creation than any particular arrangement of words making up a sentence in the article. Cf "mnemonics" section in this page for more on this. Needless to say I will be quite happy if someone comes up with better mnemonics than the present ones, or any better wording for the definition for that matter.
3) the fact that definition is current direction based rather than voltage polarity (+ or -) based is already quite explicit.
4) I submit the non-absoluteness of the defs doesn't deserve more mention _in the definitions themselves_ than saying that the definition is relative to a device, which is perfectly clear already: " electrode through which (positive) electric current flows out of a polarized electrical device". Many properties or definitions are similarly not absolute BTW, e.g. the "+" pole of a battery can be the "-" pole of another when they are connected in series, you will certainly agree that this goes without saying.
5) About your point that current flows "downhill" wrt potential, it's not at all a matter of physicists specific convention as you seem to suggest, it is true, but only for resistive devices, not when some source of power pushes current uphill as discussed in the GC example below each definition. Again, no disagreement between physicists and chemists.
Let me know if the definitions and examples make more sense to you in the light of the above arguments. About the drawings, replacing the partial view of the GC by a full view would be a good thing indeed, provided you find a way to highlight clearly the electrode under focus in each article (e.g. by graying the rest of the image?). MichelJullian 10:09, 17 June 2007 (UTC)

(1) Thanks for explaining this. But I don't see how the cathode and anode in a cathode ray tube are polarized, especially for what is called a cold cathode, so that both electrodes are at the same temperature. The voltage can be reversed and then one can have anode rays (positive ions), something that actually was studied in the 19th century. If polarization is needed, then my earlier discussion of a wire external to a Daniell cell, with which I thought you had agreed, was inapplicable, because (as I understand things now) the definitions of cathode and anode don't apply to things like wires. I'm still puzzled. As far as I can tell, both wires and cathode ray tubes are unpolarized. Anyway, I think you are telling me that for a wire as an external connection I should consider the Zn as the anode, just as for the Daniell cell. Please correct me if I am wrong. (The hardest thing is to unlearn something.)

(2) As mnemonics go, CCD isn't bad (but also CCD=Charge-Coupled Device).

(3) I agree that current vs voltage is already explicit.

(4) Now that I appreciate that the definition is restricted to polarized devices I am less bothered. But the issue of the Daniell cell connected by a wire or spark gap (=cathode ray tube) in the exterior arm puzzles me. For the wire do I continue to think of the Zn as the anode and the Cu the cathode, but for the spark gap (=cathode ray tube)) I reverse them? I'm not trying to give you a hard time; I really don't know. All of the general definitions puzzle me, in the absence of examples.

(5) When I invoked current flowing downhill (relative to voltage), the context was Ohm's Law, which applies only to passive devices like resistors.

(6) About the drawings: one could just leave the full GC, but give more information in the caption and in the text. I am a strong believer in redundancy. Some people try to get their information from the figures alone; some use the figures as entries to the article; some read the article and refer to the figures only when appropriate. Sandman42 17:58, 17 June 2007 (UTC)

(1) and (4) the ART obtained by polarizing your CRT in reverse has a different current-voltage characteristic, especially if the vacuum is such that there is not enough gas inside to make anode rays with, in which case your device is effectively a diode ---the archetype of a polarized device. I see we are interested in the same things (everything basically), but let's not digress too much, our discussion has already doubled the length of this already initially lengthy talk page :) When we say polarization is needed, well I suppose you could talk about your wire's anode if you really wanted to ---in which case in your example I maintain it wouldn't be the Zn but the Cu, because that's where current enters the device (the wire in this case!), ACE "anode current enters", remember? ;-) ---, but there wouldn't be much point. We agree on all the other points (2,3,5,6). If you have specific ideas for the figures or the captions or the text, you could propose them here first so we can refine them together if you wish. Thanks for this interesting discussion in any case. MichelJullian 10:35, 18 June 2007 (UTC)
I realize (after I have already replied, as usual ;-) that your actual question in (4) was whether a non polarized device would have its anode and cathode reverted wrt a polarized device connected in its stead, the answer is no!!!!!! It's not that the definitions of A and C switch for a non polarized device, it's just that it simply doesn't have an anode and a cathode, just two uncommitted leads which you can connect either way without changing the behavior, e.g. a resistor or a parallel plate capacitor doesn't have an anode or a cathode. MichelJullian 11:05, 18 June 2007 (UTC)
Having said that, it occurs to me that a symmetrical electrolytic cell (e.g. with both electrodes made of carbon) would be a non polarized device, although there is no doubt it has an anode and a cathode. So by your fault we now have to find a replacement for "polarized", which would fit a symmetrical electrolytic cell but wouldn't fit a resistor :-) Or we remove the "polarized" altogether, but then people may think a resistor features an anode and a cathode. I don't know which is best, what do you think? MichelJullian 11:21, 18 June 2007 (UTC)

I have read your last three entries, but for the moment I want to focus on the first. I don't know how what I am going to say relates to what you wrote; I just want to clarify a point. In rereading your first comment I realized that my conception of a spark gap being equivalent, in a certain sense, to a CRT, was wrong. Simply cutting a wire would give CRT behavior for both types of relative voltage between the two sides of the cut, if the two ends of the wire were identical. (If they were nearly the same, both would give CRT behavior, but the smaller tip would eject electrons at a higher rate, for a given applied voltage, because of the larger field at the tip.) To get an ART, one would have to make one of the sides very flat; solder a flat plate on the left end of the cut, to face the sharp tip of the cut wire on the right. If the tip is negative, then electrons will be ejected, at a certain rate for a given voltage. If the tip is positive, then positive ions (characteristic of the anode) will be ejected, but the same rate of ejection (assuming valence +1) would require a much higher voltage than for electrons. At any rate, I now realize that a CRT has to be more complex than my simple version of a wire with a symmetrical cut.

OK. A resistor or a parallel plate capacitor has neither an anode or a cathode (except perhaps at very large applied voltages, where physical inequivalence of the two sides might matter). Got it.

I agree that a symmetrical electrolytic cell presents a problem.

I would want to read what Faraday has to say about cathode and anode in his evacuated cell experiments. If he uses the same definition as you, then I would feel confident that I know the correct general definition. Would you know of an online source for that? What bothers me is that I was taught which was the "correct" cathode in a CRT, but I never got the proper reason. Where did you learn the definitions? It has taken me a long time to understand how chemists think, and it was painful to try to understand your points.

By the way, I get the impression that most younger chemists don't know how the definitions of oxidation and reduction came about. But see, which I looked up just before I sent this message off. Sandman42 00:01, 20 June 2007 (UTC)

I learned the definitions on Wikipedia actually, except they were in terms of electron flow at the time. As discussed on this page I put them in terms of current (i.e. the opposite direction) to allow for ionic current etc. I then found Faraday's original work (ref to copy at the bottom of the articles, where you may also find some of his work on vacuum devices), and found he had also defined A and C in terms of current (cf etymology sections of A and C). MichelJullian 13:38, 20 June 2007 (UTC)

bits and pieces[edit]

I added a bit about external to the cell vs. internal to the cell in anode to clear up some of the positive/negative confusion. I also added a bit about flow of electrons vs. electrical flow diagrams in the hopes of clearing the air a bit. Jonathan888 01:16, 26 October 2005 (UTC)

There was a recent edit which removed the mention of electrolytic solution from the main definition of anode... I reverted that edit and am noting here in case anyone wants to discuss it. I believe that it actually belongs in the definition because Faraday's naming convention was based on his original electrolytic cell.Jonathan888 (talk) 18:47, 6 December 2006 (UTC)

Hi Jonathan, thanks let's discuss the current definition: "An anode (from the Greek anodos = 'going up') is the electrode in a device that electrons flow out of to return to the circuit. Literally, it is the path through which the electrons ascend out of an electrolyte solution. The other charged electrode in the same cell or device is the cathode." In Greek, Anodos is 'the way up' actually. An electrode being literally an 'electron way', anode thus means 'the way up for electrons'. The way up in Faraday's beakers was the way out of course, so what he meant was indeed the above. However electrons are only one of the many possible charge carriers for electric current. Also, it could be understood from this definition that an electrolyte is necessarily involved. Therefore I suggest: "Anode: electrode through which electric current flows into a device. For example in a galvanic cell the anode is the negative electrode (cf drawing: electrons flow out i.e. current flows in), in an electrolytic cell the positive one, in a diode the terminal where current is allowed in. Faraday originally coined the word from Greek 'anodos' (ana hodos, the way up) for the electrode (elektron hodos, electron way) in an electrochemical cell where electrons flow up, i.e. out of the cell considering the device geometry. The other charged electrode in the same cell or device is the cathode." Comments/critics welcome of course, I will do the change in a few days if there are no objections. For the record I had proposed that mnemonic I found useful (ACID, Anode Current Into Device) but it was edited out on the grounds of it being an original creation rather than encyclopedic knowledge, oh well now people can find it at least in this discussion page :) MichelJullian 01:01, 10 December 2006 (UTC)

Hi Michael, I am very concerned based on my experiences editing and helping with this page that changing the definition to be based on electrical current will make it almost impossible to understand... read through this talk page and you should see what I mean. The problem is basically that electricians treat electricity as a positive force that flows from the positive terminal or contact. The physics reality is that negative electrons are drawn to a positive charge. The only way I've found to unobsfucate this confusion is to follow the teaching lead of some physics instructors and talk about the actual direction of flow of the electrons.Jonathan888 (talk) 18:38, 11 December 2006 (UTC)
Also, we should haul up user User:Heron and get his input... he's done a lot of work here.Jonathan888 (talk) 18:40, 11 December 2006 (UTC)

Being a physicist I would agree if the physics reality was as you suggest, but reality is more varied than that: an electric current (flow of charge) can be carried by all varieties of charged particles not just electrons and not just negatively charged particles, cf [[1]]. For example the Zn++ ions flowing from the anode into the electrolyte in the drawing are the charge carriers for that part of the current loop, no electrons involved there. Even the external part of the current loop could use positive charge carriers only instead of the electrons in the drawing, e.g. if the load of the galvanic cell was a point to plane corona discharge in Argon with the cell's anode as the plane, the carriers would be Ar+ ions flowing in from the positive point. I hope I have convinced you that electric current is more general than electron flow, and that the main definition should be as general as possible, and as simple as possible (but not simpler!). Electron flow should be mentioned also, if only for the origin of the word (the way up for electrons). Note the Columbia Electronics Encyclopedia, among others, also defines the anode more generally in terms of current flow: [2]. I'll wait for objections for another few days before implementing the changes MichelJullian 01:05, 12 December 2006 (UTC)

Micheal, the special case electrical carriers ONLY happen within the device with the electrodes - for the rest of the metallic circuit it is electron flow. Please don't make the article unreadable for anyone without a physics degree. All of the special cases are mentioned in the subarticles, it doesn't negate the fact that electrons are the carriers from the contacts to the circuit.Jonathan888 (talk) 18:12, 12 December 2006 (UTC)
Please check the current edit and see if you can live with it.Jonathan888 (talk) 21:28, 12 December 2006 (UTC)

Thanks Jonathan and Heron for the improvements, but some things are still wrong: "path through which the electrons ascended out of an electrolyte solution". A closer look at the galvanic cell drawing will show you that no electrons whatsoever ascend out of the solution, instead one Zn++ descends into the solution. It generates the same current(direction included) as the two electrons sent out to the external circuit mind you, which BTW leaves no room for negative ion involvement in the internal current, this will have to be corrected too. The etymology must be based on electrons rising _out of the cell_. Also the "oppositely charged" thing needs fixing, a cathode being defined as a terminal through which current flows the other way rather than in terms of polarity. Shall I let you do the rewording? MichelJullian 14:05, 13 December 2006 (UTC)

Come on, please consider it: it's a net equation... Zn++ and (-)(-) all the ionic flow is INTERNAL to the device. Talking about electrical current and direction consistently obsfucates and confuses to the point that people cry; this talk page is a case in point. Jonathan888 (talk) 20:43, 13 December 2006 (UTC)

Let's agree to disagree on this current vs electrons issue for now, and let's discuss the other points one at a time, do electrons ascend _out of the electrolyte solution_ Jonathan? MichelJullian 01:34, 14 December 2006 (UTC)

Apparently Faraday chose to describe it that way... thus the greek work he used to describe the process. Electrons are freed from the zinc anode and flow into the circuit - is the zinc anode part of the device? I would consider it part of the device with the electrodes but it's kind of semantics isn't it? Jonathan888 (talk) 16:40, 14 December 2006 (UTC)

Part of the device yes indeed, part of the solution (the liquid), no :) The 'ana hodos' 'elektron hodos' means the electrons ascend _out of the device_, no need to say they ascend _out of the electrolyte solution_, which they don't. As a matter of fact no electrons flow from the cathode to the anode internally as incorrectly stated in the 'electron flow' section, not even carried by negative ions, not a single one. The Zn++ ions must do the entire charge carrying job to satisfy Faraday's law. I see Heron has now come down on the conventional current side.I have already proposed a practice definition in my first post above, maybe we could elaborate on that? MichelJullian 00:41, 15 December 2006 (UTC)

The talk of electrons rising from the solution (which is the net effect of the device, but seems to be a real sticking point in discussing this) is limited to Faraday's device from whence the names came. Re-read the opening paragraph and it has been disambiguated to the point where a junior high student like my 11 year old son is able to understand it. The article does clearly state that it is a NET movement of electrons, not electrons themselves moving through the solution. I'm not sure where you are drawing the conclusion that Heron decided upon conventional current as being the way to describe this... please elaborate. Jonathan888 (talk) 20:00, 16 December 2006 (UTC)
Having read further down on the talk page and agreeing generally with all of Heron's points, and being out of time and patience... I'm throwing up my hands and walking away, feel free to bugger up the articles however suits your needs. In my experiences, electronically, chemically and physically the only way I've been able to keep things sorted out was following electron flow but that's just me... Jonathan888 (talk) 21:40, 16 December 2006 (UTC)

Implemented changes in anode article, as discussed. MichelJullian 13:34, 17 December 2006 (UTC)

Which is right? is anode negative? or positive? does the anode attract anions or cations? i thought that the negative electrode was ALWAYS the cathode, and I have textbooks that say so, but there's enough confusion here to twiddle anyone up. What's the right answer?

Quote:As it stands now, on the one page:

  • "In an electrolytic cell the anode is positively charged",
  • "In an electrolytic cell the cathode is positively charged";
  • "in a galvanic cell the anode is negatively charged",
  • "in a galvanic cell the cathode is negatively charged".

That didn't really help much, yet. -- JohnOwens 09:59 Mar 26, 2003 (UTC)

Someone's mixed up their definitions a bit. Here's the candy: A galvanic cell is one where chemical energy is converted to electrical energy. The anode is negatively charged, as the metal forming it attracts the positive ions. An electrolytic cell is one where electrical energy is converted to chemical energy - It's the other way round. The anode is still in the same place, but as the metal is now converting atoms to positive ions, it is positively charged.

""In a galvanic cell, the cathode is positive while the anode is negative, while in an electrolytic cell, the cathode is negative while the anode is positive.""

I hope this helps clear the confusion!

Pete, Jan 21, 2005

I'm getting really confused by this article, it really needs to be cleared up. a lot. -- lommer 23:32 May 12, 2003 (UTC)

Wikipedia is correct. The words anode and cathode cannot be assigned fixed polarities. Some textbooks make such assignments, but they are talking about a specific type of electrochemical cell, and are not correct in the general sense. -- Heron
Ok, thanks for the info. However, in an electrochemical (primary) cell, my textbook (Green + Danje Chemistry, 2nd Ed.), it lists the Cathode as (-) and the anode as (+), in contradiction to what is written here. As well, this would make sense since cations (+, agreed on by wikipedia) are attracted to the cathode AND reduction (which happens at the cathode) is the gain of electrons (which should happen at the negative electrode). This should apply equally well when an electrolytic cell is discharging, but be reversed when it it being charged. Given this, it seems that wikipedia has the signs mixed up all the way through the article!!! Should Someone change this? I won't b/c i'm not 100% sure, but I do *think* that I am right and wikipedia is wrong on this... -- lommer 23:28 15 May 2003 (UTC)

This web page, a battery primer from Analog Devices, agrees with Wikipedia: Other web sites I have found from battery manufacturers also agree. Or how about this web page from NASA: ? (Not that NASA is infallible, of course!) -- Heron

I think I see the error in your explanation, Lommer. As you say, reduction happens at the cathode. The cathode material gains electrons, which it sucks from the external circuit, making that electrode positive, not negative as you say. The anode material is oxidized, meaning that it loses electrons, emitting them into the external circuit, making that electrode negative, not positive as you say. Perhaps an example will illustrate this. In a Leclanché cell:

At the anode the zinc is oxidized, releasing electrons which travel into the external circuit, making this the negative terminal. At the cathode the reaction consumes electrons, making this the positive terminal. -- Heron

Ahhhh! There is my confusion - I thought that the reduction/oxidation bit referred to the ions in solution, not the electrode. I'm gonna spend some time puzzling over all of this and see if I can eventually get everything straight, cuz I'm still a bit muddled on other things - but I've been effectively convinced that wikipedia is right! -- lommer 01:52 17 May 2003 (UTC) :-)

one DOES NOT say FROM WHENCE!!!! One says, quite simply, WHENCE, not FROM WHENCE, for that is absurd in english grammar!!!!!

Actually, this is Wikipedia, which means that instead of saying, quite simply, "whence", one just goes and sticks it in the article. -- John Owens

Anode and Cathode seem to me to be overly-specialized articles, I think all of this stuff should be merged into Electrode as subheaders. Any objections before I proceed? Bryan Derksen

I'm not sure, but the cathode article has a short notice about the ray tubes, so maybe there's more to tell (though it could be at cathode ray tube, of course). So I'd say these articles are not harming anybody, but: do what you think best. jheijmans

I may have moved too fast -- I saw Anode on the most wanted stubs list and proceeded in spinning it off the electrode article. The blurb on the cathode ray tube didn't seem appropriate for the unbiased electrode. -- Prefect

This page and cathode both describe themselves as fulfilling the same row in both kinds (electrolytic and galvanic) of cells, which is obviously wrong. On the other hand, I'm not sure which is which between the cells, so, anyone else know which should be which? -- JohnOwens 09:42 Mar 26, 2003 (UTC)

*cough* As it stands now, on the one page:

  • "In an electrolytic cell the anode is positively charged",
  • "In an electrolytic cell the cathode is positively charged";
  • "in a galvanic cell the anode is negatively charged",
  • "in a galvanic cell the cathode is negatively charged".

That didn't really help much, yet. -- JohnOwens 09:59 Mar 26, 2003 (UTC)

Well, at least we have the self-contradiction all in one place, so we can fix it once and for all. The Anome 10:02 Mar 26, 2003 (UTC)
OK, when does this "we" you speak of show up? ;) -- JohnOwens
We just did. Now we need to sort out the anion/cation business: the whole "attracted to" tratment in that article clearly needs changing. Over to you. The Anome 10:17 Mar 26, 2003 (UTC)
Thanks, we... err, I mean, Heron! :) -- JohnOwens
The modern definition, based on oxidation and reduction, has superseded Faraday's original definition, based on the attraction of anions and cations. Faraday's def. applied only to electrolytic cells and not to generalized reversible cells. I think the coexistence of old and new defs was causing the confusion in the article. To avoid this problem, I just scrapped the old definition, but perhaps it could be mentioned in an historical footnote, and not in the main text where it might cause more confusion. -- Heron

I'm not sure exactly how to say this (or even if this is correct), but I think something should be said on how the "positive" terminal of a battery is the cathode and the "positive" terminal of an external device is the anode. -postglock 14:45, 8 February 2006 (UTC)

Error in anode article[edit]

Here is the official definition taken out of Merriam Webster's dictionary. It is conclusive that Anode is positive in an electolytic cell and negative in a galvanic cell. Based upon the front page article of an Anode here on Wikipedia, Wikipedia is half right and half wrong. Please correct the article.

Main Entry: an·ode Pronunciation: 'a-"nOd Function: noun Etymology: Greek anodos way up, from ana- + hodos way 1 : the electrode of an electrochemical cell at which oxidation occurs: as a : the positive terminal of an electrolytic cell b : the negative terminal of a galvanic cell 2 : the electron-collecting electrode of an electron tube -- compare CATHODE - an·od·ic /a-'nä-dik/ also an·od·al /-'nO-d&l/ adjective - an·od·i·cal·ly /-di-k(&-)lE/ also an·od·al·ly /-d&l-E/ adverb -- Anon.

I fixed the anode article. --Heron 19:20, 28 February 2006 (UTC)
Sorry, you broke it. M-W is confused, this is a confusing topic because polarity is relative. The only sane way to look at polarity of electrodes is in terms of current flow NOT voltage. physics of polarity of electrodes
I see your point and apologize for *my* confusion :) Thanks for the clarifications.Jonathan888 (talk) 21:53, 14 March 2006 (UTC)
What did I break? I wrote that "The anode [of a primary cell] is always the negative electrode". This agrees with the web page you cited, which says "batteries being discharged (anode=negative)". Please explain what you mean by "broke". Also, please note that it was not I who quoted M-W, it was an anonymous editor. I don't care what M-W says, since I wouldn't use it as a reference on electrochemistry. My edits were based on the redox definition of anode and cathode that all scientists have used since Faraday. --Heron 19:32, 14 March 2006 (UTC)
The current edit is good, I like the bit about ion flows in opposite directions... I'm going to label them anion and cation now.Jonathan888 (talk) 21:40, 14 March 2006 (UTC)
OK. We seem to be on the same wavelength now. :-) --Heron 09:51, 15 March 2006 (UTC)

The image[edit]

The image top right of the Cathode page shows a b+ sign, so I'm guessing it is connected to positive of a battery? If so, the current should be flowing from there to negative, yet the electrons (which have negative charge) are shown flowing in the same direction. I might be completely wrong here, but I think this might need addressing. /Mat 00:00, 1 October 2006 (UTC)

Hi Matt, there is a lot of confusion about polarity i.e. positive/negative charges and where the electrons are going. It is the most edited part of the article. The main reason for the confusion is that the polarity is referential - to one side of an electrode the charge is negative and to the other side of the same electrode the charge of the same electrode is positive. If you consider it strictly by electron flow it all sorts out.Jonathan888 (talk) 15:04, 10 October 2006 (UTC)

This page is dreadful[edit]

It hasn't helped me in the slightest with my biology thing I am even more confused than i was before i think it's irresponsable to make pages like this that only cause confusion, missery and upset to all who read them. What is anyone ment to do with this information. Reduce it to One sentance: A Cathode is (Negative) / (Posative) (ommit the right one somebody!!! :'(

Once again, there is not a simple answer to 'positive' / 'negative' because the voltage polarity is dependant upon where you are measuring from - external to the device a cathode appears positive as electrons are flowing into the device through the cathode and the charge to draw the electrons in must be positive. Inside the device the cathode appears negative since it is the source of the electrons to the device. Therefore, if you measure from the circuit to the device's cathode you get a a 'positive' polarity reading, if you measure from the cathode to the anode you get a 'negative' polarity reading. This page is not meant to be an easy crib sheet for your biology 'thing' but rather a technically accurate description of electrodes and their functions.Jonathan888 (talk) 22:00, 31 October 2006 (UTC)


I'm replying to a request that Jonathan888 made on my Talk page. There is no final answer, because there is no universal authority on what anode and cathode mean. Chemists define them in terms of redox; electronics engineers in terms of electrons; and physicists in terms of conventional current. Apparently, there are even some battery makers who ignore the science and assign them to fixed polarities. All of these definitions (except the battery makers') are equivalent, so what do we do?

I can see arguments for and against all three versions:

  • Redox
    • For: Avoids taking sides in the electrons/conventional current war. The clearest definition for electrochemists. A nice opportunity to mention Faraday.
    • Against: Not helpful for non-chemists who only want to know what to call the pointy end of a diode.
  • Electrons
    • For: Describes what is going on in metallic circuits, which are the most common type of conductor in everyday engineering.
    • Against: Ignores other conduction mechanisms, although the actual use of non-electronic conduction to a cell's electrodes is rare to non-existent
  • Current
    • For: The most general definition. Cannot be contradicted even by hair-splitting physicists. ;-) Will annoy those pesky electron current advocates. :-D
    • Against: As Jonathan888 points out, it divorces the definition from physical reality, and might lead students to think that conventional current actually flows in and out of electrodes. However, this criticism could be made of the use of conventional current in general, which is nevertheless pretty popular.

I'm reluctant to take sides. I think I can rule out the chemical definition, because it's too specific. Emotionally, I prefer the electron version, because I feel that I know where I am with electrons, and that's the version that I originally promoted. Rationally, I prefer the conventional current version, because it's the only one that doesn't exclude any possibilities that I can think of, even though it's based on an arbitrary convention. So I'm going to have to come down, weakly, on the side of conventional current. I am concerned, however, that the upheaval that this will cause to the article might make a mess of it in the short term, so let's be careful if we go down that route, please. How about a practice definition here on the talk page? --Heron 11:22, 13 December 2006 (UTC)

Faraday's original naming based on ascent/descent of sun, not of electrons :))[edit]

In retrospect, one thing tickled me in Wikipedia's attractive "way up for electrons" and "way down for electrons" explanation for Faraday's naming of the anode ('way up') and cathode ('way down') electrodes ('elektron ways'), which had made such perfect sense to me that I had reworded it without even questioning it in the new "Etymology" section of the Anode article. That thing was: had the electron already been discovered in the 1830's ???

When I found that the electron was only discovered about 40 years later (in 1874), I realized that 'elektron' in the etymology of 'electrode' must have meant electricity rather than electron and that the Wikipedia explanation was wrong, but then what was it that went up on the anode side and down on the cathode side in Faraday's mind, since it couldn't be electrons? I found the answer in Faraday's original paper: the sun, as ludicrous as this may seem! Here is the link to Faraday's original 1834 paper ('s html version) and a few relevant extracts, which BTW provide authoritative support to Wikipedia's new current-based definition:

[3] : <<...In place of the term pole, I propose using that of Electrode (footnote:"[Greek: elektron], and [Greek: -odos] a way.")...The surfaces at which, according to common phraseology, the electric current enters and leaves a decomposing body, are most important places of action... Wishing for a natural standard of electric direction to which I might refer these, ..., I have thought it might be found in the earth. If the magnetism of the earth be due to electric currents passing round it, the latter must be in a constant direction, which, according to present usage of speech, would be from east to west, or, which will strengthen this help to the memory, that in which the sun appears to move. If in any case of electro-decomposition we consider the decomposing body as placed so that the current passing through it shall be in the same direction, and parallel to that supposed to exist in the earth, then the surfaces at which the electricity is passing into and out of the substance would have an invariable reference, and exhibit constantly the same relations of powers. Upon this notion we purpose calling that towards the east the anode (footnote:"[Greek: ano] upwards, and [Greek: -odos] a way; the way which the sun rises."), and that towards the west the cathode (footnote:"[Greek: kata] downwards, and [Greek: -odos] a way; the way which the sun sets."); ... The anode is therefore that surface at which the electric current, according to our present expression, enters... The cathode is that surface at which the current leaves the decomposing body...>>

Some rewriting of the various articles is in order I am afraid, who volunteers? ;-) MichelJullian 16:15, 22 December 2006 (UTC)

A very interesting article on the genesis of the terms before they were finally adopted, with transcripts of the many mails Faraday exchanged with friends on the subject: Faraday Consults the Scholars: The Origins of the Terms of Electrochemistry [4] in which we learn the many alternative terms which have been considered for anode and cathode, some of which are very strange :) Faraday's initial idea was by far the best as is often the case IMHO: eisode (way in [for current]) and exode (way out), unfortunately he was talked out of it by Whewell who suggested anode and cathode instead. It seems to me that Faraday wanted to please Whewell for some reason and designed the sunrise and sunset story as a circumvoluted way to reconcile in and up, and out and down. MichelJullian 18:19, 22 December 2006 (UTC)

Great work, Michel. I have changed the etymology in anode to reflect the Faraday-Whewell letters, which are fascinating reading. Luckily there wasn't much in cathode that needed rewriting. If there are any more articles that need attention, just let me know and I will be happy to help - unless you want to edit them yourself, of course. --Heron 19:22, 22 December 2006 (UTC)

Thanks Heron, I like your edits and I am quite happy to let you do the writing up, your English is much better than mine. Still, I think Faraday's original paper and naming scheme should be mentioned, and the current pages still don't explain what it is that goes up (ana) and down (kata). Maybe something like: Faraday explained the naming scheme in the original paper (ref) as follows: if the cell is so placed that electric current (which had the same direction convention as today) traverses the cell in the same direction as the sun traverses the sky (from East to West), the anode is on the East side (where the sun rises) and the cathode on the West side (where the sun sets). IOW the anode is where current enters the cell and the cathode is where current leaves the cell. MichelJullian 13:46, 23 December 2006 (UTC) I modified the etymology section in 'anode' accordingly. Also tweaked the intro a bit, cf edit summaries. Your comments/corrections welcome. MichelJullian 16:01, 27 December 2006 (UTC)

P.S. The royalsoc papers ref'd in anode may not remain freely accessible beyond the end of 2006 according to [[5]], in which case will it be OK to upload the pdf files to wikipedia commons? MichelJullian 17:03, 27 December 2006 (UTC)

Reading the papers in more detail I realized that I was wrong in my comment above, the 'East' for 'In' indirection was Faraday's idea, not Whewell's, and it was quite justified at the time. I have completed the etymology section of anode accordingly. Also added the Gutenberg ref for the Faraday paper since the RoyalSoc full text papers are now locked (had considered uploading the "Faraday consults..." paper to Wikipedia commons but found it's still copyrighted, until 1961+50=2011 in fact). MichelJullian 03:28, 11 January 2007 (UTC)

Anonymous edits[edit]

I have a BS in Physics and a MS in electrical engineering but I've never known there was so much confusion over the meaning of cathode and anode until today. Good work to those of you who have really looked into this. I would add that there is no such thing as a cathode or an anode unless you provide a conduction path between two metals with different electron affinities(or there might be other elements too that are capable of sustaining a current, I'm not sure.) And before the current begins flowing, neither one of the metals (which constitute the electrodes) are net positive or negatively charged. And also, due to the electrolytic solution, or whatever other method might be used in batteries to keep the electrodes both with net neutral charge by use of ion flow, NEITHER ELECTRODE IS ACTUALLY EVER NET POSITIVE OR NEGATIVE (to all most practical approximations.) So I think that really it's a flaw in the convention to call either positive or negative. But, the way I like to think of it is that of course the electrons will flow through the circuit to the positive. And that a cation is a positively charged ion (I don't believe there's any argument by anyone over that term), so the electron flow is TO the CATHODE. And I think it would be worth looking at whether the term "cation" for a net positively charged ion was instituted before the term cathode. I always assumed that cation had come first. Also, the anode article starts out just by describing current flow as electron flow. This is a major problem to me, as I have always in both physics and EE read in all texts, and been instructed by every professor, that current flow is positive charge flow unless you specify otherwise. I'm going to edit that now.

Dear anonymous, please open an account, read carefully both the articles and the talk page, and discuss your planned changes here prior to making major edits. Current flow is indeed positive charge flow, but you should be aware that it is also negative charge flowing in reverse. You replaced "current flow into the device/cell" by "electron flow into the external circuit", which is the same thing except it's less general as discussed above. Plus it shifts the focus from the device comprising the electrode to the external circuit which is a bad idea. I will therefore revert your edits now. MichelJullian 12:15, 23 December 2006 (UTC)
BTW cation was named after cathode, not the other way round, cf original paper in [6], Seventh Series. MichelJullian 10:09, 11 January 2007 (UTC)

this has really confused me....i think you need to look at as this states that the cathode is negatively charged Jamie

Look again, it's negative in some devices and positive in some others. It's a very common mistake to try and define anode and cathode from polarity. The true universal definition is based on current direction, as correctly stated in Wikipedia. MichelJullian 21:21, 25 February 2007 (UTC)


Memory helpers for the general defs of anode and cathode were cruelly missing IMHO, especially with the complex etymologies, so I added the following mnemonics, right after the defs for max effectiveness: ACE Anode Current Enters CCD Cathode Current Departs Critics welcome but I submit making up silly mnemonics can hardly be considered as "original research", so please don't remove them MichelJullian 23:18, 28 February 2007 (UTC)

Also: "Cats have POS" (paws). —Preceding unsigned comment added by (talk) 22:28, 14 October 2007 (UTC)

Diode Device Physics[edit]

Hi all, first time using Wiki so apologies if I miss some kind of convention...

On the Cathode page, it appears to me that the description of device physics for diodes is backwards. It states that holes are supplied from the N type layer and electrons are supplied from the P type layer. Last time I checked N stood for excess Negative charge carriers (electrons) while P type has excess Positive charge carriers (holes).

Jackjtang 18:53, 11 September 2007 (UTC)

Electrode Tracks?[edit]

Read an article referencing the "tracks" of an electrode. I have no idea what they are...I was hoping this page would reference them but it doesn't. If anyone knows, please add. —Preceding unsigned comment added by (talk) 03:29, 12 October 2007 (UTC)

intermediate electrodes[edit]

It seems to me that the common usage of the word electrode has been extended beyond the scope of this articles discussion, but in a way which still remains within the scope of the definition the article claims to discuss.

For instance, the usage of electrode extends to other elements in vacuum tubes, and this generality possibly extends to other realms as well. More specifically, amplifier vacuum tubes contain a number of grid elements that are categorized as electrodes. I just came here from the photomultiplier article, which describes a dynode as a kind of electrode. There is also a photocathode article. I see that there are a great many articles that link to the electrode article, including the ones mentioned. I think this means that electrode is a key concept.

Perhaps this article could extend its discussion of electrode to encompass other uses of the term beyond anode and cathode or provide links to these other kinds of electrode. --AJim (talk) 14:09, 12 May 2009 (UTC)


how about some images? —Preceding unsigned comment added by (talk) 08:29, 29 January 2010 (UTC)