Energy Storage II

Energy Density of Some Materials (KHW/kg)

So potentially, Hydrogen wins big but the main problem is that there are no naturally occurring sources of hydrogen so it must be made and that has an energy cost associated with it.

Note: the actual fire on the Hindenburg was the result of a spark that ignited the outer skin and not the spontaneous explosion of hydrogen

Hydrogen as a Secondary Fuel:

While hydrogen is the most abundant element in the Universe on the Earth its mostly found as water.

Hydrogen can be easily separated from Oxygen in water via Electrolysis. This process is about 67% efficient

Burning hydrogen combines with oxygen to form water --> no other combustion products (except for small amounts of nitrogen oxides formed around high temperature combustion zone)

For use as a secondary fuel, Hydrogen needs to be stored as a liquid. (20 K; -253 C).

As a liquid its energy density per unit volume is 1000 times higher.

For a given stored energy requirment, a cryogenic hydrogen facility is much less expensive than a pumped hydro facility

But overall efficiency is 25% cryogenic storage is energy intensive

But, one can make a hydgrogen-oxygen fuel cell Using a catalyst, hydrogen combines with oxygen to make water plus electricity. In the lab, such cells can acheive 85% efficiency but large scale value is unknown and untested although there have been some recent breakthroughs:

Hydrogen Fuel Cells

This animation shows the process that goes on inside an individual fuel cell. The red Hs represent hydrogen molecules (H2) from a hydrogen storage tank. The orange H+ represents a hydrogen ion after it's electron is removed. The yellow e- represents an electron moving through a circut to do work (like lighting a light bulb or powering a car). The green Os represent an oxygen molecule (O2) from the air, and the blue drops at the end are for pure water--the only byproduct of hydrogen power.


Advantages of Hydrogen technology and fuel cells

Good overview of different kinds of Fuel Cells

Basic Chemisty of a Fuel Cell:

Anode: 2H2 --> 4H+ + 4e-
Cathode: 4e- + 4H+ + O2 --> 2H2O

Overall: 2H2 + O2 --> 2H2O

What about fuel cell yield? This information is hard to find, but GM announced in October 2001 the following specifications: