What Is a Carbon Anode?

M.J. Casey

A carbon anode is a positively charged receptor on a carbon electrode. It attracts electrons, which are charged molecular particulates, and usually works in conjunction with a cathode, a negatively charged receptor. Together the anode and cathode carry an electrical or electrochemical charge, which is useful in a number of different applications. Some of the earliest batteries used carbon electrodes, and anodes played a crucial role in helping those batteries retain and conduct energy. In modern times carbon-based elements are more common in electrical capacitors, as well as in industry when it comes to the large-scale production of chlorine and certain other chemicals. These sorts of components are also really important in fuel cell functioning.

A piece of carbon, which is used to make carbon anodes.
A piece of carbon, which is used to make carbon anodes.

Understanding Carbon Electrodes Generally

In a very general sense, an “electrode” is any surface over which electrical charges are carried, trapped, or conducted. Electrodes are the solid surface at which fluid electrochemical reactions occur. The anode has a positive charge and attracts electrons, while the cathode has a negative charge and attracts the positive ions. In most cases it’s the exchange of electrons from the cathode to the anode that establishes an electrical current.

A carbon anode can be used in large-scale production of silicon.
A carbon anode can be used in large-scale production of silicon.

A specifically carbon electrode is usually one that is made of elemental carbon, or that uses carbon as its primary conductor. Electrochemical reactions involve the transport of electrons from one place to another and, if configured appropriately, yield useful electrical currents as a result. Electricity may be stored, produced, or consumed in the reactions. Carbon can serve as both an anode or cathode; however, in both applications, carbon is usually combined with other elements to increase its natural conductivity.

Electrochemical Properties

In organic chemistry, carbon is often thought of in terms of its hydrocarbon molecules, the key compounds of living and previously living matter. Electrochemists think of carbon in its solid states of graphite and other almost pure carbon forms. Carbon that is bonded almost exclusively to other carbon atoms achieves a high degree of delocalized electrons that make it a good conductor. An anode made of or with carbon is also a favored choice in electrochemistry for other reasons including non-toxicity, low cost, and flexibility.

Electronic capacitors made of carbon store electrical charge between double carbon electrodes of immense surface area. One side of the double layer acts as a carbon cathode and the other as an anode. The positively charged ions cling to the cathodic side, and negatively charges cling to the anodic side. When discharged, electrons are released to the circuit.

Early Uses

The first documented use of carbon as a cathodic material occurred in 1792, when graphite successfully replaced metals in some experimental early batteries. In a battery, energy is stored in the electrochemical potential of the reactants and released as necessary. Most modern batteries don’t rely on carbon, and those that include the element typically do so with so many other materials and compounds that the anodes couldn’t properly be called “carbon.”

Role in Chlorine Production

A molded anode made from artificial graphite is often used in the large-scale production of chlorine, aluminum, and silicon. Production of calcium carbide, yellow phosphorus, and ferroalloys uses carbon anodes. These processes require energy. The carbon anode is gradually consumed in the process, losing carbon as carbon dioxide. The anodes lose efficiency as they degrade, prompting the use of metal oxide anodes in modern chlorine manufacturing plants.

Fuel Cells

Fuel cells are another increasingly common place to find carbon-based anodes. In fuel cells, electricity is drawn directly from the anode of the electrochemical reaction — a very efficient conversion when compared to energy generated indirectly through combustion of fuels to drive mechanical equipment. The fuel is usually hydrogen gas, and the oxidant is oxygen from the air. The anode-electrolyte mix-cathode cell is very thin and is packaged in blocks of more than 400 cells arranged in series. The carbon anode performs an electrochemical function, but also serves as a way to disperse expensive metallic catalysts.

The anode has a positive charge and attracts electrons.
The anode has a positive charge and attracts electrons.

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