fuel cells

Q: What are the four main types of fuel cell losses?

A: Activation losses, Internal currents & fuel crossover, Ohmic losses, Concentration (mass-transport) losses.

What causes activation losses?

Slow electrode reaction kinetics. Energy is lost driving the chemical reaction that moves electrons.

Where do activation losses appear on the V–I curve?

At low currents — seen as the rapid initial voltage drop after OCV.

What are internal current and fuel crossover losses?

Losses due to fuel leaking through the electrolyte or electron conduction through the electrolyte.

What causes ohmic losses?

Resistance to electron flow in electrodes/interconnects and ion flow in electrolyte.

How do ohmic losses show on the V–I curve?

As a linear voltage drop with current density (straight downward slope).

What are concentration/mass-transport losses?

Losses from reactant concentration changes at the electrodes when fuel is consumed (limited diffusion).

Where do concentration losses appear on the V–I curve?

At high currents, where voltage begins to drop sharply.

Why is the actual OCV lower than the theoretical no-loss voltage?

Because of fuel crossover and internal currents.

What happens to the thermodynamic voltage E∘E∘ as fuel cell temperature increases?

It decreases because ΔG decreases ΔG=ΔH−TΔS

Why does the practical voltage increase with temperature?

Faster reaction kinetics (lower activation loss), better ion conductivity (lower ohmic loss), and improved mass transport.

How does increasing T affect activation losses?

Reduces them, because reactions at electrodes proceed faster.

How does increasing T affect ohmic losses?

Reduces them, because the electrolyte and electrode materials conduct ions/electrons better.

How does increasing T affect concentration losses?

Reduces them, because diffusion and transport of reactants are improved.

Overall, how does raising temperature affect cell efficiency?

Thermodynamic efficiency falls slightly (lower E∘E∘), but practical efficiency usually improves because real cell voltage rises.