Electrolyzer

Inputs

• Primary specification: select one capacity specification (Water Conversion, Current, or DC Power) and provide its value.
• Heat Mode: adiabatic or isothermal.
• Temperature: Required when Heat Mode is isothermal.
• Faradaic Efficiency: Must be in (0, 1].
• Overvoltage: Must be >= 0.
• Anode Pressure Drop and Cathode Pressure Drop: Must be >= 0.
• H2 Crossover Fraction and O2 Crossover Fraction: Must be in [0, 1].

Connections

The anode, which produces oxygen, is on the left side. The cathode, which produces hydrogen, is on the right side.

• Inlets:
  • AnodeInlet (bottom-left)
  • CathodeInlet (bottom-right)
• Outlets:
  • AnodeOutlet (top-left)
  • CathodeOutlet (top-right)

Voltage model

Cell voltage is calculated as:

• V_cell = V_rev + overvoltage

Where V_rev is rigorously calculated from the equation of state based on outlet activities. In this sense, the current model represents a 0D, continuously stirred electrolyzer.

Fluid package requirements

The connected inlet streams must use fluid packages that include these required components: H2O, H2, O2.

Additional components, for example inert gases like N2, are allowed. If anode and cathode inlet streams use different fluid packages, they must use identical component ordering. Otherwise, the solver will throw an informative error.

Water conversion specification

This is one of the ways to specify electrolyzer capacity. Water conversion a number in (0,1) indicating the fraction of water converted on the water-consuming side of the given technology.

• AlkalineElectrolyzer: water consumed at cathode -> conversion basis is cathode inlet water
• PEMElectrolyzer: water consumed at anode -> conversion basis is anode inlet water
• SOElectrolyzer: water consumed at cathode -> conversion basis is cathode inlet water

Outputs

After calculation, the electrolyzer reports solved properties such as:

• reaction_extent: extent of the overall electrolysis reaction.
• water_conversion_achieved: achieved water conversion (may differ from requested conversion in constrained cases).
• current_requested: current implied by the selected specification.
• current_used: current effectively used for hydrogen production.
• current_wasted: current not contributing to the target reaction.
• electrical_power_requested: electrical power implied by the selected specification.
• electrical_power_used: electrical power effectively used by the stack.
• electrical_power_wasted: electrical power not converted to useful electrochemical work.
• reversible_voltage: thermodynamic reversible cell voltage (V_rev).
• cell_voltage: effective cell voltage (V_cell).
• overvoltage_effective: effective overvoltage contribution (V_cell - V_rev).
• stack_lhv_efficiency: stack efficiency on hydrogen lower-heating value basis, calculated as (molar H2 production rate) * LHV_H2_molar / electrical_power_used.