Anodes are made of different materials depending on the application, but the most common include graphite, zinc, lead, lithium metal, platinum, and sacrificial metals like magnesium and aluminum. The anode is the electrode where oxidation happens, meaning it releases electrons. Because of that job, anode materials need to be good electrical conductors, chemically stable under operating conditions, and efficient at giving up electrons.
Lithium-Ion Battery Anodes
The rechargeable batteries in your phone, laptop, and electric car almost universally use graphite as the anode material. A typical lithium-ion anode is about 92% graphite powder by weight, with small amounts of carbon black for conductivity and a polymer binder to hold everything together. This mixture is coated onto thin copper foil, which acts as the current collector.
Graphite works because of its layered crystal structure. When the battery charges, lithium ions slip between the graphite sheets and nestle into the gaps, a process called intercalation. At full charge, one lithium ion sits between every six carbon atoms. When you use the battery, those lithium ions release and flow back to the other electrode, generating current. Graphite provides a theoretical capacity of about 372 milliamp-hours per gram, which has been the industry standard since Sony commercialized the first lithium-ion battery in 1990.
Silicon is the leading candidate to replace or supplement graphite. It can theoretically store about 4,200 milliamp-hours per gram, roughly 11 times more energy than graphite. The catch is that silicon swells dramatically as it absorbs lithium, expanding up to 300%, which cracks the electrode and degrades battery life. Current commercial batteries sometimes blend a small percentage of silicon into graphite anodes to boost capacity without sacrificing too much durability.
Solid-State Battery Anodes
Solid-state batteries, still largely in development, aim to use pure lithium metal as the anode. Lithium metal offers far higher energy density than graphite because you’re using the lightest metal on the periodic table in its pure form rather than storing lithium inside another material. Prototype designs use lithium foil as thin as 20 micrometers, roughly one-fifth the thickness of a human hair. One of the biggest engineering challenges is preventing lithium from forming needle-like structures during charging that can short-circuit the cell, which is why solid-state batteries replace the liquid electrolyte with a solid one that physically blocks those growths.
Lead-Acid Battery Anodes
The battery under your car hood uses a much older chemistry. Lead-acid batteries use spongy lead as the anode (negative electrode). “Spongy” describes the porous, high-surface-area form of lead that maximizes contact with the sulfuric acid electrolyte surrounding it. The other electrode is made of lead dioxide. Both electrodes use lead-based current collectors, which is one reason these batteries are so heavy. Despite their weight, lead-acid batteries remain dominant in vehicles for starting engines because they deliver high bursts of current cheaply and reliably.
Alkaline Battery Anodes
The disposable AA and AAA batteries in your remote control and flashlight are alkaline cells, and their anodes are made of zinc powder. Using powdered zinc rather than a solid piece dramatically increases the surface area available for the chemical reaction, which lets the battery deliver more consistent power. The zinc powder is typically suspended in a gel along with an alkaline electrolyte (potassium hydroxide), giving it the paste-like consistency you’d see if you ever cut one open.
Fuel Cell Anodes
Hydrogen fuel cells, the type used in fuel cell vehicles, use platinum as their anode catalyst. Platinum is extraordinarily effective at splitting hydrogen molecules into protons and electrons, but it’s expensive and rare. Engineers have been working for decades to reduce the amount needed. One approach coats a thin layer of platinum over ruthenium nanoparticles on a carbon support. Department of Energy research demonstrated that this type of catalyst could operate with as little as 18 micrograms of platinum per square centimeter while maintaining stable performance for over 870 hours with no voltage loss. That’s a fraction of what earlier designs required.
Water Electrolyzer Anodes
Electrolyzers split water into hydrogen and oxygen, and the anode is where oxygen forms. In proton-exchange membrane (PEM) electrolyzers, the anode catalyst traditionally relies on iridium oxide, one of the rarest and most expensive metals on Earth. Iridium is necessary because the oxygen-producing side of electrolysis is extremely corrosive, and few materials survive those conditions for long.
Recent research has found ways to stretch iridium further by mixing small amounts into ruthenium oxide. A catalyst using an iridium-to-ruthenium ratio of just 1:6 ran continuously for over 1,500 hours at high current density without significant degradation. This approach could reduce iridium use by 80% compared to current commercial electrolyzers, a critical step for scaling up green hydrogen production.
Sacrificial Anodes for Corrosion Protection
Not all anodes produce electricity. Sacrificial anodes are chunks of metal deliberately attached to boats, pipelines, water heaters, and offshore platforms so they corrode instead of the structure they’re protecting. They work because they’re more chemically reactive than the steel or other metal they’re bolted to. The three main materials are zinc, aluminum, and magnesium, and the right choice depends on the environment:
- Zinc corrodes slowly and evenly in saltwater, making it the traditional choice for ocean-going vessels, propellers, and offshore structures.
- Aluminum works across saltwater, brackish water, and mixed environments. It lasts longer than zinc and is lighter, making it the most versatile option.
- Magnesium produces the strongest protective current, which makes it ideal for freshwater where electrical conductivity is low. However, it depletes quickly in saltwater because it’s so reactive.
A typical boat owner in coastal waters would choose zinc or aluminum anodes and replace them every one to two years as they dissolve. A home water heater almost always comes with a magnesium anode rod inside the tank, slowly sacrificing itself to protect the steel lining.
Electroplating Anodes
In industrial electroplating, where a thin metal coating is deposited onto a surface, the anode is often made of the same metal being plated. A copper plating bath uses a copper anode. A silver plating process uses a silver anode. As current flows, the anode slowly dissolves, releasing metal ions into the solution, which then deposit onto the object being plated at the other electrode. This “soluble anode” approach conveniently replenishes the plating solution as it’s used up.
When a soluble anode isn’t practical, inert anodes made of platinum or graphite are used instead. These don’t dissolve during the process, so the metal ions in the plating bath must be replenished by adding chemicals directly.