16.

(a) Explain the principle difference between a fuel cell and an electrochemical cell.

(b) Explain what happens at the anode and the cathode of a hydrogen fuel cell.

(c) Palladium is a very expensive metal. Palladium hydride is metallic palladium that contains a substantial quantity of hydrogen within its crystal lattice. At r.t.p. palladium can absorb up to 900 times its own volume of hydrogen. Explain why:

(i) palladium hydride is not a compound but a mixture.

(ii) forming palladium hydride would be an excellent way of storing hydrogen.

(iii) palladium is not widely used for hydrogen storage.