Thermal storage units, components thereof, and methods of making and using them

A method of forming carbon nanotubes on a carbon substrate, comprising:

• a. depositing a buffer layer on the carbon substrate by atomic layer deposition;
• b. depositing a catalyst on the carbon substrate and/or buffer layer;
• and
• c. contacting the carbon substrate with a working gas at an elevated temperature to thereby form carbon nanotubes on the carbon substrate.

A thermal storage unit comprising:

• a heat exchange path through which a heat exchange medium flows;
• and
• a thermal storage medium in thermal contact with the heat exchange path;
• wherein the thermal storage medium comprises a composite which comprises a porous thermally conductive matrix and a phase change material disposed within the porous thermally conductive matrix.