Poss470FC, the first stainless steel to be used for the core components of fuel cell electric vehicles

The bipolar separator provides a channel for oxygen and air, connects electricity created at each cell and provides mechanical support. For this application, stainless steel1) which can withstand harsh conditions is commonly used. Compared to graphite, which is expensive and vulnerable to impacts, POSCO’s Poss470FC2) is reasonably priced, rigid and easy to form. Most of all, it contains chromium, thus defying rust and featuring high conductivity.

1. 1) Stainless steel: An alloy steel that contains 10.5-12wt% of chromium and defies rust. Such an anti-rust capability is thanks to Cr2O3, a 2nm thick passive film, that can block oxygen from penetrating into the substrate.
2. 2) Poss470FC : POSCO Stainless Steel 470 Fuel Cell

Comparison of the oxide film between stainless steel and carbon steel

Comparison of the oxide film between stainless steel and carbon steel

Stainless steel	Carbon steel
The film is so thin and intense that oxygen can hardly penetrate It defies rust in the regular atmosphere	The film is so thick and porous that it is vulnerable to oxygen penetration Apt to rust in a regular atmosphere

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Ferritic series(400 series)

How Does a Fuel Cell Work

Reaction at the anode: H2 → 2H+ + 2e-
Reaction at the cathode: ½ O₂ + 2H+ + 2e- → H₂O
Total reaction: H₂ + ½ O₂ → H₂O + electricity + thermal energy