Question

Hydrogen fuel has been used in fuel cells or internal combustion engines. Determine the heat of combustion, energy capacity, and carbon footprint of the fuel.

ΔHf H2O(l) = -285.8 kJ/mol

Answer 1

Fuel cell is a galvanic cell in which chemical energy is converted to electrical energy. Anodic and cathodic reactions of fuel cell are-

Anode: H2 2H+ +2e-

Cathode: 1/2O2 + 2H+ +e- H2O

Thus,

Overall Reaction is-

H2 + 1/2O2 H2O + Heat

Now, heat of combustion = Heat of product - Heat of reactants

= Hf (H2O) - Hf (H2) -Hf (O2)

For gases Hf =0

Thus, Heat of combustion=-285.8-0-0

=-285.8KJ/mol

Energy capacity of the cell is defined as the amount of energy that is stored in the cell.

Energy Capacity = Voltage provided by the battery * Current provided by the battery in one hour

Unit: V*A*h = Wh

Usually fuel cell have energy capacity of 33.6kWh.

Talking about the carbon foot print of hydrogen fuel, it produces only water vapours on burning which results in carbon free process with no carbon foot print. However, the process of production of hydrogen used in the cell results in production carbon dioxide gas. Thus, in a way tjhe hydrogen fuel cell is also ading up to the carbon foot print.