Fact 1: Microbial fuel cells convert chemical energy into electrical energy.

Fact 2: Fuel cells are devices that directly convert hydrogen into electricity.

Given the two facts above, answer the question "What do microbial fuel cells transform hydrogen into?" with the following options: 
- Renewable energy
 - Electrical energy
 - kinetic energy
 - electromagnetic energy
 - an engine
 - transportation technology
 - Solar energy
 - Oil


 

  Electrical energy       