Why are fuel cells more efficient than combustion engines?

They convert chemical energy directly to electricity electrochemically, so they are not bound by the Carnot limit that constrains heat engines, allowing higher efficiency, especially at partial load.

Why do hydrogen fuel cells need expensive platinum catalysts?

The oxygen reduction reaction at the cathode is kinetically very slow, and platinum-group metals provide the activity needed to keep overpotential acceptable; reducing or replacing this catalyst is a major research goal.

Fuel Cells

A fuel cell converts the chemical energy of a continuously supplied fuel and oxidant directly into electricity through spatially separated electrode reactions, without combustion.

Definition

An electrochemical device that produces electricity by continuously oxidizing an externally supplied fuel at the anode and reducing an oxidant, typically oxygen, at the cathode, with ions carried through an electrolyte.

Scope

This topic covers the operation of fuel cells: the anodic oxidation of a fuel such as hydrogen and the cathodic reduction of oxygen, the role of the ion-conducting electrolyte or membrane, the main cell types distinguished by electrolyte and temperature, the kinetic limitation of the oxygen reduction reaction, and efficiency relative to thermodynamic limits. It addresses why fuel cells are central to hydrogen-based energy systems.

Core questions

How does a fuel cell generate electricity directly from fuel without combustion?
What role does the ion-conducting electrolyte or membrane play in separating the half-reactions?
Why does the oxygen reduction reaction limit performance, and how does catalysis address it?
How do fuel cell types differ in electrolyte, operating temperature, and application?

Key theories

Continuous electrochemical oxidation: Unlike a battery, a fuel cell stores no reactants internally; fuel and oxidant flow continuously to spatially separated electrodes, so electricity is produced as long as supply continues, decoupling power from stored capacity.
Oxygen reduction overpotential: The sluggish kinetics of the multi-electron oxygen reduction reaction at the cathode imposes a large overpotential that dominates efficiency loss, motivating the development of platinum-group and alternative electrocatalysts.

Clinical relevance

Fuel cells offer clean, efficient power for vehicles, stationary generation, and portable systems, and are pivotal to hydrogen-economy strategies for decarbonizing transport and industry; their cost and durability hinge on catalyst and membrane advances.

History

Grove demonstrated the gaseous voltaic battery in 1839, building on Schönbein's observations; Bacon developed practical alkaline fuel cells in the mid-20th century, which powered the Apollo missions, and proton-exchange-membrane cells matured for transport from the 1990s onward.

Key figures

William Grove
Francis Thomas Bacon
Christian Friedrich Schönbein

Seminal works

winter2004
ohayre2016
newman2004

Frequently asked questions

Why are fuel cells more efficient than combustion engines?: They convert chemical energy directly to electricity electrochemically, so they are not bound by the Carnot limit that constrains heat engines, allowing higher efficiency, especially at partial load.
Why do hydrogen fuel cells need expensive platinum catalysts?: The oxygen reduction reaction at the cathode is kinetically very slow, and platinum-group metals provide the activity needed to keep overpotential acceptable; reducing or replacing this catalyst is a major research goal.