Carbon Free Aluminum Production with Inert Electrodes for Clean Energy Storage and Production

According to the International Aluminium Institute, the worldwide primary aluminum industry produced around 72.7 million tonnes of aluminum in 2024. Production is expected to grow even further in the coming years in order to meet corresponding increases in demand. This presents an environmental challenge, because the industry emits significant CO₂ emissions — something it has been actively working to address over the past decade.

Arctus Aluminium, based in Iceland, has been focused on addressing direct emissions in the aluminum smelting process. The company is working on the development of a smelting process that utilizes inert anodes, which are able to produce oxygen instead of CO₂ as in the conventional smelting method. In addition, the company has joined the European REVEAL project, which aims to revolutionize energy storage by considering aluminum as a powerful energy carrier.

Development of Carbon Free Smelting

Conventional primary aluminum production utilizes the Hall-Héroult process, which is implemented in smelters around the world. The Hall-Héroult process uses a prebaked carbon anode in an electrolytic bath kept at 950°C (1,742°F). The bath dissolves the alumina and consumes the carbon anode, producing aluminum and carbon, according to the following formula:

2 Al₂O₃ + 3 C + Electricity  ⇒  4 Al + 3 CO₂

In other words, 2 tonnes of alumina combined with 0.5 tonnes of carbon anodes and 14 MWh of electricity will produce 1 tonne of aluminum and 1.5 tonnes of CO₂. The aluminum industry has been attempting to address the challenge of CO₂ emissions during electrolysis since the Hall-Héroult process was first developed. Over the decades, attempts have been made at producing inert anodes, without achieving the necessary results. However, in recent years, several companies have finally been making progress in the development of inert anodes, including ELYSIS (which is currently building an industrial-scale demonstration plant in Canada, with plans to be operational by 2027) and RUSAL (which is in the process of scaling up its development with the aim of starting operation by 2030).

Arctus Aluminium has also been developing its own inert anode technology in cooperation with IceTec, an Icelandic research organization, and its industrial partners, Nordural, a smelter in Iceland, and Trimet Aluminium, the largest primary aluminum producer in Germany. The Arctus technology involves the vertical electrode cell (VEC), which features vertical inert anodes and wettable inert cathodes (Figure 1). In the VEC, the electrolyte is kept at a relatively low temperature of 800°C (1,472°F). The inert anodes are made from a non-consumable metal alloy and the wettable inert cathodes are comprised of TiB₂ plates.

These inert anode cells have produced aluminum using this technology with a commercial purity of 99.8%, while emitting one tonne of oxygen for every tonne of aluminum, with no direct CO₂ emissions. The potential CO₂ savings of this technology, using Iceland as an example, are shown in Table I. Around 882,000 tonnes of aluminum were produced in Iceland in 2022. With this inert anode technology, around 1.7 million tonnes of CO₂ could be saved, which is about one-third of the total CO₂ emissions in Iceland.

The Arctus cells are also designed to reduce power consumption (by 20% compared to conventional smelting) due to the low-temperature electrolyte and placement of the anodes and cathodes. The vertical positioning allows for both sides of the anodes and cathodes to be exposed, and the short anode-cathode distance (3–4 cm) improves efficiency. The cell is also designed to allow for modular power feeding during peak hours to optimize power pricing.

In addition, the inert anode cells are one-third of the size of a Hall-Héroult cell, while producing the same amount of aluminum, reducing space requirements by 50%. The company also believes their inert anode design will require 40% less investment costs and 30% less operational cost.

With the initial testing completed, Arctus collaborated with Trimet to install a demonstration facility at the smelter’s Essen plant in Germany. In August 2024, Trimet began commissioning the 10 kA demonstration cells, which will test the inert anode technology at an industrial scale. If the demonstration goes well, then the smelter plans to scale up the technology at Essen in 2025, bringing the cells up to 40 kA. The aim is to be able to continue increasing the scale of the technology until commercialization can be achieved in 2030.

Aluminum as Energy Storage

Although the implementation of inert anodes in the electrolytic process is a key step forward, it does not reflect the full picture. The electrolytic production process only represents 12% of overall emissions, with the majority of emissions coming from the generation of electricity (62%). Aluminum companies have been attempting to address this issue by shifting their power consumption to renewable energy (hydro, solar, wind, etc.), but this comes with its own challenges — primarily in regard to energy storage.

One potential method of addressing this energy storage challenge is to use aluminum as an energy carrier. Trimet introduced the concept of using its smelter as a “virtual battery” in 2019, when the company began to retrofit its aluminum smelters in Germany and France to flexibly handle fluctuating amounts of electricity from wind and solar systems. This allowed Trimet to react to changes in the electricity supply, thus creating a huge power storage facility (with the capacity of medium-sized pumped electrical storage).

The REVEAL project, which includes Arctus, IceTec, SINTEF, and a number of other industrial and research partners, aims to take the concept of aluminum as an energy carrier even further, enabling it to be used to store renewable energy for months or longer periods at an affordable cost. The aim of the project is to combine the zero-carbon aluminum production process (through inert anodes) and renewable energy to create a long-term energy storage solution using aluminum (Figure 2). According to REVEAL, “The resulting aluminum acts as a compact, high-energy storage medium that can be utilized to generate on demand heat and hydrogen, or alternatively, heat and electricity, depending on the application. This approach offers key advantages, including a volumetric energy density more than twice that of [liquified natural gas], three times that of methanol, and over five times higher than liquid hydrogen.”

The project aims to close the material cycle. Thus, the aluminum that is introduced into the charging concept is expected to be able to cycle between the charging and discharging process multiple times, and it ideally will not have to be replaced with new alumina.

In November 2024, the REVEAL project achieved an important milestone, when Eastern Switzerland University of Applied Sciences (OST) demonstrated that a bulk energy density of 15 MWh/m³ could be achieved using aluminum granules. Repeated measurements have confirmed the bulk energy densities of the aluminum granulate, highlighting the potential of aluminum as a high-density energy carrier. The project partners are continuing to explore the potential of this technology by analyzing the technical aspects of the design, as well as the cost and environmental impact.

Editor’s Note: This article first appeared in the February 2025 issue of Light Metal Age. To receive the current issue, please subscribe.