Researchers at SASTRA Deemed University have developed and patented a method for converting spent activated carbon from household water filters into manganese oxide/carbon nanocomposites for energy-storage and electrocatalytic applications. The process gives discarded carbon a second life as electrode material for supercapacitors and components relevant to rechargeable zinc-air batteries, linking waste recycling with energy-storage technology.

Turning Waste Carbon Into a Battery Material

Carbon is already one of the most important materials used in energy-storage technologies, particularly because its electrical conductivity, surface area and tunable structure can make it useful in electrodes.

Researchers are now looking at whether carbon that would otherwise become waste can be processed into useful energy-storage materials.

A team led by Dr. S. Devaraj at SASTRA Deemed University, Thanjavur, has developed a method for recovering spent activated carbon from exhausted household water filters and converting it into a functional nanocomposite. The process has been protected through Indian patent application 202441032753, according to India’s Department of Science and Technology.

The development is part of a broader research effort focused on making rechargeable zinc-air batteries more practical while reducing dependence on expensive materials.

How Waste Carbon Is Converted

The researchers begin with spent activated carbon, a porous carbon material that has already been used in household water-purification systems.

Instead of treating the material as waste, the team uses a hydrothermal conversion process to produce an MnO₂/C nanocomposite — a material combining manganese dioxide with carbon.

The resulting material has two potential roles. It can function as a bifunctional electrocatalyst, helping drive the oxygen reactions required in rechargeable zinc-air batteries, and it can also serve as an electrode material for supercapacitors.

This approach effectively changes the value of the waste stream: rather than requiring fresh carbon-based raw material, an existing waste material becomes a component for another energy technology.

Why Zinc-Air Batteries Matter

Zinc-air batteries use oxygen from the surrounding air as part of their electrochemical reaction and can use a water-based electrolyte.

They have attracted interest for applications where safety, cost and material availability are important, including stationary energy storage.

However, rechargeable zinc-air systems face technical challenges.

At the zinc electrode, unwanted hydrogen evolution can consume energy and contribute to corrosion. At the air electrode, oxygen-reduction and oxygen-evolution reactions can be relatively slow, traditionally creating pressure to use catalysts based on expensive metals such as platinum or ruthenium.

The SASTRA research addresses several of these challenges through a combination of electrolyte development, earth-abundant catalysts and waste-derived electrode materials.

Waste Carbon Becomes Part of the Energy-Storage Chain

The significance of the patented process extends beyond simply recycling a household waste product.

Activated carbon has a highly porous structure, giving it a large surface area that can be useful in electrochemical systems. By modifying spent carbon rather than discarding it, researchers can potentially create a higher-value material for energy technologies.

The SASTRA team also investigated another waste stream: used surgical face masks.

The masks were chemically converted into activated carbon with a high surface area. According to India’s Department of Science and Technology, the resulting material demonstrated oxygen-reduction performance comparable to platinum in the reported experiments.

These findings suggest that different carbon-containing waste streams could potentially become feedstocks for electrode and catalyst production, although each waste source requires its own processing and performance assessment.

The Other Half of the Battery Equation

The waste-derived carbon work was developed alongside a separate innovation in the same research programme: a nanofluid electrolyte for rechargeable zinc-air batteries.

The researchers dispersed small quantities of silica and zinc oxide nanoparticles into the electrolyte. The reported objective was to suppress unwanted hydrogen evolution and zinc corrosion while improving oxygen-reaction performance at the air electrode.

That technology has received Indian Patent IN570691 and was described by the Department of Science and Technology as ready for use.

The combination is notable because it approaches the battery from multiple directions: improving the electrolyte, developing lower-cost catalysts and finding useful electrode materials from waste.

From Waste Management to Circular Energy Materials

The idea fits into a wider movement toward a circular materials economy, where industrial and consumer waste is treated as a potential source of raw materials rather than simply something to dispose of.

Research published in 2026 has similarly examined waste-derived carbon and other industrial residues for energy-storage applications. Studies have reported the conversion of waste carbon black and activated carbon into hard-carbon materials for sodium-ion batteries, demonstrating that discarded carbon materials can be structurally modified for electrochemical storage.

Other research has explored systems that combine carbon capture with energy storage, showing how carbon-management technologies and energy technologies can increasingly overlap.

The emerging field is therefore not limited to capturing carbon and storing it permanently. Researchers are also investigating whether carbon-containing waste can become a useful feedstock for new products.

What the Patent Actually Shows

The patent filing protects a method for synthesising nanocomposites from spent activated carbon for supercapacitor and electrocatalysis applications. It does not mean that household waste can simply be placed into a battery and converted directly into electricity.

The waste material must first undergo chemical processing to achieve the desired structure and composition.

Likewise, laboratory performance does not automatically establish commercial-scale battery performance. Manufacturing costs, consistency of waste feedstocks, long-term cycling, environmental impacts of processing and scale-up will all influence whether the approach becomes commercially competitive.

These distinctions are important when evaluating waste-to-energy technologies: a promising material transformation is an engineering step, not necessarily a finished energy-storage product.

Could Carbon Waste Become an Energy Resource?

The SASTRA work illustrates a different way of thinking about carbon waste.

Instead of treating discarded carbon solely as an environmental burden, researchers are investigating whether its chemical and physical properties can be recovered and redirected into useful technologies.

For energy storage, that could create a link between two traditionally separate problems: waste management and demand for new battery materials.

The patented SASTRA process is still one piece of that larger research landscape. But by converting spent activated carbon into functional electrode and catalyst materials, it demonstrates how waste streams can potentially become part of the material supply chain for next-generation energy technologies.

FAQs

What is waste carbon?

Waste carbon refers to discarded carbon-containing materials such as spent activated carbon, industrial carbon residues or other carbon-rich waste streams that can potentially be processed into useful materials.

How is waste carbon being used for energy storage?

Researchers can chemically or thermally modify waste carbon to create electrode materials with useful electrical and surface properties for batteries and supercapacitors.

What did the SASTRA researchers patent?

The researchers filed Indian Patent Application 202441032753 for a method of synthesising nanocomposites from spent activated carbon for supercapacitor and electrocatalysis applications.

Can waste carbon replace conventional battery materials?

Not necessarily. Waste-derived carbon can potentially replace or supplement certain electrode and catalyst materials, but commercial adoption depends on performance, consistency, processing costs and large-scale manufacturing.

Why is waste-derived carbon important for sustainable batteries?

It can create a secondary source of functional carbon materials while reducing the amount of waste sent for disposal, potentially supporting a more circular supply chain for energy-storage technologies.