What Is a Phosphate Fuel Cell?
A phosphate fuel cell is a type of fuel cell that employs an aqueous solution of phosphoric acid as its electrolyte. This technology uses hydrogen, often derived from reforming city or LP gas, to generate electricity. Developed in the 1970s, phosphate fuel cells stand out for their performance and reliability among various fuel cell types.
However, they face challenges such as lower efficiency per unit volume compared to other fuel cell technologies and higher costs due to platinum catalyst usage. Moreover, operating at temperatures around 200°C, phosphate fuel cells must be monitored for carbon monoxide poisoning at lower temperatures.
Uses of Phosphate Fuel Cells
Known for their reliability and durability, phosphate fuel cells have found applications in hospitals, hotels, office buildings, and sewage treatment plants, serving primarily as stationary power sources. These systems, comprising the fuel cell stack, an inverter, a reformer, a cooling system, and a control unit, efficiently convert reformed hydrogen from city gas or industrial byproducts into electricity.
Benefitting from high-temperature operation, many systems integrate cogeneration to utilize waste heat for heating purposes, promising further cost reductions by leveraging hydrogen byproducts from various plants. Notably, their ability to switch gas sources enhances resilience against supply disruptions during disasters.
Principle of Phosphate Fuel Cells
Phosphate fuel cells generate electricity by converting the chemical reaction of hydrogen oxidation into water. This process involves:
1. Reforming Natural Gas
High-purity hydrogen is produced from city gas through desulfurization, steam reforming, and carbon monoxide oxidation, using catalysts to facilitate reactions and heat from excess hydrogen combustion to drive the endothermic reforming process. Despite carbon monoxide’s potential to poison the platinum catalyst, the operation temperature around 200°C allows a higher tolerance for carbon monoxide than in polymer electrolyte fuel cells.
2. Power Generation
Hydrogen is oxidized at the fuel electrode under a platinum catalyst, producing hydrogen ions and electrons. The electrons travel through an external circuit to the air electrode, where they combine with oxygen and hydrogen ions to form water, generating electric power. To achieve the voltage levels necessary for practical applications, multiple cells are stacked.
Composition of Phosphate Fuel Cells
The fuel electrode consists of porous carbon, resistant to phosphoric acid corrosion and permeable to gases. The phosphoric acid solution serves as the electrolyte, sandwiched between fuel and air electrodes, each laden with a platinum catalyst and separated by a separator.