Proton Exchange Membrane Water ElectrolysisPresentation by Rich SmithEE 295 Carbon Free Electric Power

Water Electrolysis

● Production of homonuclear diatomic molecules: hydrogen and oxygen gas.

● Requires H2O and electric energy inputs.

● Recent interest in production of hydrogen as an energy carrier.

Electrochemical Reactions

● Overall chemical equation:

● Oxygen Evolution Reaction(OER):

● Hydrogen Reduction Reaction(HRR):

Thermodynamics

The enthalpy of the overall reaction (ΔH) is a combination of the water dissociation reaction change of Gibbs free energy (ΔGd) and the resulting entropy (TΔS).

Overall Cell Reaction

The overall cell equation with the addition of the thermodynamic energy input is:

Thermodynamic Values of Water

Enthalpy ΔH = 285.8 kJ/mol

Entropy TΔS = 48.6 kJ/mol

Gibbs Free Energy ΔG = 237.2 kJ/mol

Required Cell Voltage

The minimum required cell voltage can be calculated considering all possible heat energy is provided. Though operational cell voltages need to accommodate for overpotentials.

PEM Electrolyzer

Bipolar Plates

Function: Mass Transport of ReactantsCollect CurrentThermal Stability

Gas Diffusion Layer (GDL)

Function:Mass Transport of ReactantsConductive Link between Electrode andBipolar plates.Balances liquid and gaseous H2O

Membrane Electrode Assembly (MEA)

Consists of two electrode layers on either side of a proton conductive membrane.

Location of electrochemical reactions.Electrocatalyst facilitate electrochemical reactions.

Electrocatalyst

Lower the reaction overpotential.

Anode: IrO2 and RuO2

Cathode: Pt

Proton Conductive Membrane

Allow movement of hydronium ion without conducting electrons.

Nafion Membranes 115, 117, 212

Hydrophilic sulfonated groups Hydrophobic teflon backbone

Nafion Membrane

Renewable Energy Storage Technology

Reversible Fuel Cell

Green Methanol Synthesis

Carbon Recycling International Inc. (CRI)Emission to liquid process