ABSTRACT
Chapter 1 described the motivations for developing a hydrogen-based energy infrastructure. Here, we discuss the hydrogen-based power technologies that convert hydrogen into electricity and useful heat or shaft power and provide the context for the need for improved hydrogen storage materials. Ultimately, hydrogen power technology seeks to take advantage of the following chemi-
cal reaction:
2H2 + O2 → 2H2O + Q (2.1)
That’s it. All of hydrogen power technology we are about to describe aims to implement that chemical reaction in the lowest-cost and most efficient manner possible. It turns out, however, that if you put hydrogen and oxygen in a balloon and let it sit at room temperature, the mixture will remain unreacted essentially indefinitely. The reaction as written in Reaction 2.1 does not proceed because the activation energy for the reaction is too high at room temperature for the reaction to take place-nothing happens. However, if you do something that either changes the activation barrier of the reaction
(add a catalyst) or provides an external source of energy (like an electric spark) to enable the reaction to surmount the activation barrier, the reaction proceeds to the right, forming
CONTENTS
Introduction ................................................................................................................................... 31 Hydrogen Internal Combustion Engines: Spark Ignition Engines ........................................ 32 Hydrogen Internal Combustion Engines: Gas Turbines .........................................................40 Hydrogen Fuel Cells .....................................................................................................................44 H2 PEM Fuel Cell........................................................................................................................... 47 Operational Effects on PEM Fuel Cells ......................................................................................50 Membrane Degradation ...............................................................................................................53 Stability of the Catalyst ................................................................................................................54 Gas Diffusion Layer ......................................................................................................................56 Automotive OEM View of Fuel Cell Attractiveness ................................................................58 Future Generations .......................................................................................................................60 Acknowledgments ........................................................................................................................ 61 References ....................................................................................................................................... 62
water and releasing heat (denoted as Q). If you fill a balloon with a stoichiometric mix of hydrogen and oxygen (as in Equation 2.1) and hold a match under it, the reactants will be excited above the activation energy, and the reaction then proceeds to the right, producing water and heat. Overcoming the activation energy barrier of Reaction 2.1 is the basis for extracting heat (Q) to perform useful work. This heat can be transformed into shaft power using a heat engine such as a reciprocating internal combustion engine, a turbine, or a sterling engine, for example. Alternatively, if one places a catalyst in the balloon, like a piece of Pt metal, one changes
the reaction pathway such that the activation energy is lowered, and the reaction proceeds rapidly at room temperature. This catalytic acceleration is the basis for hydrogen catalytic heaters and hydrogen fuel cells. Hydrogen internal combustion engines (ICEs) (turbines and reciprocating engines) [1] and hydrogen fuel cells [2] are two of the primary means of converting the reaction energy of Equation 2.1 into useful shaft power and electrical energy, respectively. These energy conversion devices are described in more detail in this chapter. Hydrogen is an attractive fuel for ICEs [1]. Hydrogen has physical and chemical
properties that enable conversion devices such as ICEs that are more efficient than their hydrocarbon counterparts. Both H2 ICEs and hydrogen fuel cell systems, when designed properly, produce near-zero emissions, with the only substantial emission being water vapor.
