= Electrolytic cell
{wiki}
An <electrolytic cell> uses an external source of electrical <work> to drive <electrode> <chemical reactions>. In the ordinary two-terminal driven mode, its positive <anode> supports <oxidation> and its negative <cathode> supports <reduction>. The source removes <Electrons> from the <anode> and supplies <Electrons> to the <cathode>; through the <electrolyte>, net <conventional current> goes from <anode> toward <cathode>. Terminal signs refer to the driven cell's terminals relative to each other. The source supplies electrical <power> to the cell. See <Chemistry 2e by Paul Flowers and others/17.7 Electrolysis> (§17.7: electrolysis and electroplating).
For example, transferring <copper> from a soluble <copper> <anode> onto a conducting object at the <cathode> has the ideal <half-reactions>
$$
\begin{aligned}
\text{positive anode:}\quad&\mathrm{Cu}(s)\longrightarrow\mathrm{Cu}^{2+}(aq)+2e^-,\\
\text{negative cathode:}\quad&\mathrm{Cu}^{2+}(aq)+2e^-\longrightarrow\mathrm{Cu}(s).
\end{aligned}
$$
Their sum transfers <copper> between surfaces. For identical bulk states, this transfer need not have a positive bulk <Gibbs free energy> change; finite <electric current> still needs applied drive to overcome losses. Thus "consumes electrical <work>" does not mean every <electrolytic cell> stores all that <work> as chemical <Gibbs free energy>. <Electrolysis> can instead redistribute material. The charge-to-amount relation remains $\xi=Q/(2F)$ when only these <half-reactions> carry the <electric current>; competing <water> reactions would change the deposited amount. The electroplating principle and charge accounting are described in <Chemistry 2e by Paul Flowers and others/17.7 Electrolysis> (§17.7: electroplating and quantitative aspects).
The University of Washington's teaching demonstration makes this material transfer visible with a <copper> <electrode> and a stainless-steel <electrode> in a glass cell containing $0.5\,\mathrm{mol\,L^{-1}}$ $\mathrm{CuSO_4}$. The external source connects its positive lead to <copper> and negative lead to steel; the reported observation is a <copper> coating on the steel. Reversing the source polarity removes the deposited <copper> again: the coated surface now supports <oxidation> and acts as the <anode>. This polarity reversal changes the drive, unlike swapping the measurement leads in the <Daniell cell voltage and load experiment>. Coating appearance alone does not measure charge efficiency or exclude competing <chemical reactions>. See https://chem.washington.edu/lecture-demos/electroplating-copper-stainless-steel[University of Washington, Electroplating Copper on Stainless Steel: apparatus and reversible coating demonstration].
The <copper> <cathode> in this driven example is negative, while the <copper> <cathode> of a discharging <Daniell cell> is positive: both support exactly the same <reduction> <half-reaction>. Likewise, an <anode> need not lose material if its conducting surface is absent from its net <half-reaction>. Neither terminal sign nor a universal mass-change rule defines an <anode> or <cathode>.
Back to article page
