Seite - 137 - in Clean Water Using Solar and Wind - Outside the Power Grid

Handling variable production 137 10.5.2 Fuel cells Hydrogen that is stored will sooner or later be converted to electricity. This is done in a fuel cell, a device that converts the chemical energy from a fuel into electricity. Here the fuel is hydrogen that will react with oxygen or another oxidising agent. In a battery the chemical energy comes from chemicals present in the battery. In a fuel cell there must be a continuous supply of fuel (hydrogen) and oxygen (usually from the air) to sustain the chemical reaction. Fuel cells can produce electricity continuously for as long as fuel and oxygen are supplied. They are not new inventions; the first was invented in 1838. All fuel cells contain an anode, a cathode and an electrolyte: see Figure 10.4. There are many types, classified by the type of electrolyte and different start-up times. Oxygen from the air Cathode Load H+ Anode Hydrogen fuel e- Electrolyte Figure 10.4 Electrode reactions and electric circuit flow for an electrolyte fuel cell. Note that the negative electrons move from anode to cathode, while the “conventional current” flows from cathode to anode. Modified from Larminie and Dicks (2003). At the anode a catalyst breaks down the fuel (hydrogen gas) into electrons and ions. The catalyst speeds the reactions at the electrodes. The anode catalyst often consists of fine platinum powder: 2H2 → 4H+ + 4e− The hydrogen ions travel through the electrolyte from the anode to the cathode. The electrons from the anode are led to the cathode via an external electrical circuit, thus producing a DC current. Oxygen from the air enters the cell at the cathode. Downloaded from https://iwaponline.com/ebooks/book-pdf/520710/wio9781780409443.pdf by IWA Publishing user