anode
An electrode, of a cell or other electrically polarized device, through which a positive current of electricity flows inwards (and thus, electrons flow outwards). It can have either a positive or a negative voltage with respect to cathode of the same polarized device (depending on whether the device is a load or a source, respectively).
anode: where electrons leave and current enters
The anode is the electrode in an electrochemical cell or electrical device where oxidation occurs and electrons depart. In a galvanic cell (battery), it is the negative terminal, where chemical reactions liberate electrons. In an electrolytic cell, it is the positive terminal, connected to the positive lead of an external power source. The confusion arises because the anode's electrical polarity reverses between these two cases, but its electrochemical role remains constant: it is always the site of oxidation.
In practical terms, conventional current (positive charge flow) enters the anode from the external circuit, while electrons flow out of it into the external circuit. This definition holds regardless of the device type. A battery's anode supplies electrons to your load; a plating tank's anode is where metal dissolves or where oxygen evolves, depending on the electrolyte and applied voltage. Steel anodes in cathodic protection systems corrode sacrificially to shield buried pipelines or offshore structures.
Material selection and wear
Anode materials are chosen for their ability to withstand oxidation. In galvanic cells, the anode is often the less noble metal (zinc in a zinc-carbon battery, for example). In electroplating, copper anodes dissolve slowly and uniformly to supply ions to the bath. In arc welding, some electrode types function as anodes when used in AC; the anode tip melts and oxidizes faster than the cathode, producing asymmetric wear patterns. Graphite and lead are common sacrificial anodes in industrial applications because they oxidize predictably.
The term itself derives from Greek, meaning 'the way up' (from ana-, up, and hodos, way). Early researchers chose it because cations (positively charged ions) were observed to migrate toward this electrode in electrolytic cells, though the etymology reflects their motion rather than electron flow. In modern electrochemistry, this migration still occurs, but understanding the anode as the electron-departure point is more mechanically useful for troubleshooting and design.
Anode performance degrades over time. In batteries, the anode may develop surface films that increase internal resistance. In plating operations, anode impurities can contaminate the bath. In cathodic protection, anode consumption is predictable and planned: a zinc anode in seawater corrodes at roughly 20 kg per amp-year, so system designers size anodes to last the design life of the structure. Monitoring anode voltage and consumption rates is essential for maintaining system function.