Fuel cells producing *liquid* water?

Robert Clark wrote:
...
A material that might be able to reach these criteria is "tetrahedral
amorphous diamond" if used in the form of microspheres.
This report gives an average tensile stength of 7.3 GPa when tested on
micron-scale samples:

Young’s modulus, Poisson’s ratio and failure properties of
tetrahedral amorphous diamond-like carbon for MEMS devices.
J. Micromech. Microeng. 15 (2005) 728–735
doi:10.1088/0960-1317/15/4/009
http://ej.iop.org/links/q03/3NXzoBo,...jmm5_4_009.pdf

The thickness to radius ratio of a spherical pressurized tank is given
by:

h/r = Δp/(2σ)

where h is the wall thickness, r the radius of the sphere, Δp the
overpressure, and σ the tensile strength of the material.

This page gives properties of hydrogen at various pressures and
temperatures (there is deviation from the ideal gas law at very high
pressures):

Hydrogen Properties Package.
http://www.inspi.ufl.edu/data/h_prop_package.html

At a temperature of 300 K, a pressure of 6000 bar gives a density of
72 kg/m^3, or .072 kg/l.
Using a tensile strength of 7.2 GPa = 72,000 bar for the tetrahedral
amorphous diamond and 6000 bar pressure for the hydrogen, the thickness
to radius ratio for a spherical tank would be h/r = 1/24.
The volume for a sphere is V = (4/3)Pi*r^3. For a wall thickness small
compared to the radius, we can take the volume of the wall to be 4*h*
Pi*r^2, which equals (1/6)*Pi*r^3, when h/r = 1/24.
Since the volume of the tank and the wall both have r to the third
power, the radius will cancel when calculating the ratio of the
hydrogen mass to the mass of the tank wall material. So I'll take r =
1. Then the mass of the hydrogen in the tank would be 72*(4/3)*Pi =
301.6 kg.
I'll take the density of tetrahedral amorphous diamond to be that of
diamond, 3500 kg/m^2. Then the mass of the container would be:
3500*(1/6)*Pi = 1885 kg. Then the ratio of the mass of hydrogen to the
container wall mass would be 301.6/1885 = 0.16.
The tetrahedral amorphous diamond is amorphous as is glass. So it may
be that heat and laser irradiation could also allow hydrogen to be
infused and/or released.


Bob Clark

I should have calculated the mass of hydrogen to the total weight. The
total weight is 1885+301.6 = 2186.6 kg. So the weight of the hydrogen
to the total weight is 301.6/2186.6 = .138.


Bob Clark