PROTEON ENERGY Contact
The case for the chemistry

Why iron-air

Long-duration storage is a materials problem before it is an engineering one. Iron is the cheapest electroactive metal available at grid scale, it is mined and processed in India today, and its reaction with oxygen is reversible in a water-based electrolyte. That combination is what makes multi-day storage affordable.

01 / MATERIAL
Iron, not a critical mineral
The active material is commodity iron and water. No lithium, cobalt or nickel, and no exposure to constrained global supply.
02 / COST
Cost scales with duration
Adding hours means adding iron, not another power stack. Commodity materials and a simple stack architecture keep CAPEX low.
03 / DURATION
Hours to days of backup
Deep discharge windows that carry a site through an evening peak, a cloudy stretch or an outage.
04 / SAFETY
Non-flammable by design
An aqueous electrolyte with no thermal runaway pathway, which simplifies siting, fire protection and permitting.
05 / LIFECYCLE
Benign at end of life
Iron and hydroxide recover into existing metals recycling streams. Nothing toxic to strand at decommissioning.
06 / SUPPLY
India-first supply chain
Built on abundant domestic iron and an established steel industry, so sourcing stays local and resilient.

Loose powder becomes a pressed electrode

Iron enters the process as a fine powder. Compaction consolidates it into a porous brick that holds its shape while leaving the internal surface open to electrolyte, which is where the capacity actually lives. Scroll through the three stages below.

01 / Iron molecules 02 / Iron pellets 03 / Pressed slab
01
It starts as iron
One element, the 26th. Commodity iron and water carry the whole charge: nothing scarce, nothing toxic.
02
Broken into pellets and powder
The metal is reduced to pellets and fine particles, multiplying the surface the electrolyte can reach.
03
Pressed into a slab
Compaction consolidates the powder into a porous slab that holds its shape while staying open inside.

From one cell to a field system

The same electrode sandwich repeats at every scale. Plates are stacked into a series string, strings are sealed into a module with its air and electrolyte management, and modules are arrayed into a system sized to the site.

CURRENT COLLECTOR POROUS IRON ELECTRODE SEPARATOR AIR ELECTRODE CURRENT COLLECTOR
01 / CELL
Five layers, one reaction

Iron electrode and air electrode share an aqueous electrolyte, held apart by a separator and tapped by collectors on both faces.

SERIES STRING
02 / STACK
Plates in series

Cells repeat between end plates under compression, adding voltage without changing the chemistry.

AIR + ELECTROLYTE MANAGEMENT
03 / MODULE
Sealed and serviced

A module carries the stacks plus the air feed, electrolyte loop and monitoring the chemistry needs to run.

TO GRID
04 / SYSTEM
Arrayed to the site

Modules are grouped and tied to a common bus, so capacity scales by adding units rather than redesigning them.

See the reaction that makes rust reversible
Back to the technology