Fuel cells can use hydrogen directly, or they can obtain hydrogen from another fuel, like liquid methanol (wood alcohol), which is renewable and can be transported more easily than hydrogen. With hydrogen fuel, heat and water are the only byproducts. With methanol fuel, heat and water are still the major byproducts, along with only a fraction of the carbon dioxide and none of the other pollutants produced by a gasoline-burning engine.

The Gemini spacecraft, which preceded the Apollo spacecraft, carried two hydrogen-oxygen fuel cell battery sections in its adapter/equipment section.

Each battery section contains three stacks of fuel cells with plumbing. The stacks are connected in parallel and can be switched in and out of use individually. Each stack has 32 individual cells connected in series and produces about 490 amperes at 23 to 26 volts. Maximum power output per battery section is about one kilowatt. 

The fuel cell models displayed here contain many individual fuel cells along with the plumbing and sensors required to supply reactants and keep the cell at the proper temperature. The reactants were stored in separate tanks in liquid form to reduce space. This required keeping the oxygen at -173°C (-280°F) and at a pressure of 63.26 kilograms per square centimeter (245 pounds per square inch). Waste heat from the fuel cells was used to bring the reactants to gaseous form before they entered the cell. The Apollo fuel cell operated at a temperature of about 206°C (400°F) and the Gemini cell at about 65°C (150°F).

An Apollo spacecraft carried three hydrogen-oxygen fuel cells in the service module. Each unit contains 31 individual fuel cells connected in series and operates at 27 to 31 volts. Normal power output is 563 to 1420 watts, with a maximum of 2300 watts. Primary construction materials are titanium, stainless steel, and nickel.

 For space applications, fuel cells have another advantage over conventional batteries: they produce several times as much energy per equivalent unit of weight. When oxygen and hydrogen combine to form water, energy is released because the electrons in the water molecule are in a lower energy state than those in the gas molecules. In a combustion reaction, as in a rocket engine, the energy appears as heat. In a fuel cell some of it —about 50-60%—is converted directly to electrical energy. As fuel cells operate, oxygen and hydrogen combine to produce water as well as electrical power. Apollo crews used this water for drinking. 

A phase-one proton exchange membrane fuel cell design for space exploration developed by Teledyne. Credit: NASA

In recent years, the Department of Energy (DOE) and private industry have made significant advances in the development of Proton Exchange Membrane (PEM) fuel cells using hydrogen and air as the fuel and oxidant for ground-transportation applications. Additionally, the DOE and the ground power industries are working on emerging Solid Oxide Fuel Cells (SOFC) for ground-based power generation. NASA is building upon these PEM and SOFC developments to dramatically advance fuel cell technologies, providing reliable, compact and high-energy renewable power sources for aerospace applications. 

With the aid of industry and universities, NASA is addressing aerospace challenges that include reduced gravity, low or no atmospheric pressure, extreme temperatures, dynamic vibration, shock loads and extended duration operations. For airless space applications, the focus is on closed-cycle regenerable PEM technology. The targeted space systems feature power outputs of 1 to 10 kilowatt systems (eventually scalable up to 100 kilowatts), compact sizing (250 to 350 watts per kilogram), and high reliability for long lives (10,000 hours). With the appropriate investments and collaborations, NASA intends to revolutionize aerospace power generation to enable new capabilities. Experts at Glenn, the Jet Propulsion Laboratory, the Johnson Space Center and Kennedy are leading these fuel cell efforts

 

Friedrich Wilhelm Ostwald (1853–1932), one of the founders of physical chemistry, provided a significant portion of the theoretical understanding of fuel cells. In 1893, Ostwald experimentally determined the roles of many fuel cell components.

 

Ludwig Mond (1839–1909) was a chemist that spent most of his career developing soda manufacturing and nickel refining. In 1889, Mond and his assistant Carl Langer performed numerous experiments using a coal-derived gas. They used electrodes made of thin, perforated platinum, and had many difficulties with liquid electrolytes. They achieved six amps per square foot (the area of the electrode) at 0.73 volts.

 

Charles R. Alder Wright (1844–1894) and C. Thompson developed a similar fuel cell around the same time. They had difficulties in preventing gasses from leaking from one chamber to another. The leaking and a few other design flaws prevented the battery from reaching voltages as high as 1 volt. Wright and Thompson felt that if they had more funding, they could create a more robust cell that would provide adequate electricity for many applications.

 

The French team of Louis Paul Cailleteton (1832–1913) and Louis Joseph Colardeau came to a similar conclusion, but thought the fuel cell electrochemical process was not practical due to needing “precious metals.” Also, many papers published during that period said that coal was extremely inexpensive so that a new system with a higher efficiency would not decrease the prices of electricity drastically.

 

William W. Jacques (1855–1932), an electrical engineer and chemist, did not pay attention to these critiques and startled the scientific world by constructing a “carbon battery” in 1896. Air was injected into an alkali electrolyte to react with a carbon electrode. He thought he was achieving an efficiency of 82 percent but obtained only an 8-percent efficiency.

 

Emil Baur (1873–1944) of Switzerland and several of his students conducted many experiments on different types of fuel cells during the early 1900s. He worked on high-temperature devices, and a unit that used a solid electrolyte of clay and metal oxides.

 

O. K. Davtyan of the Soviet Union did many experiments to increase the conductivity and mechanical strength of the electrolyte in the 1940s. Many of the designs did not yield his desired results, but Davtyan’s and Baur’s work contributed to the necessary preliminary research for today’s current Molten Carbonate Fuel Cell (MCFC) and Solid Oxide Fuel Cell (SOFC) devices.

 

Fuel cells are used in the space shuttle as one component of the electrical power system. Three fuel cell power plants, through a chemical reaction, generate all of the electrical power for the vehicle from launch through landing rollout. 

Before launch, electrical power is provided by ground power supplies and the onboard fuel cell power plants. Each fuel cell power plant consists of a power section, where the chemical reaction occurs, and a compact accessory section attached to the power section, which controls and monitors the power section's performance. 

This is one of the three fuel cells that make up the generating system that provides electrical power to the space shuttle orbiter. The unit is a little more than a foot high and weighs approximately 200 pounds. Credit: NASA

The three fuel cell power plants are individually coupled to the reactant (hydrogen and oxygen) distribution subsystem, the heat rejection subsystem, the potable water storage subsystem, and the electrical power distribution and control subsystem. The fuel cell power plants generate heat and water as by-products of electrical power generation. 

The excess heat is directed to fuel cell heat exchangers, where the excess heat is rejected to Freon coolant loops. The water is directed to the potable water storage subsystem.