A first full cell: two half-cells and a proton-exchange membrane

docs/api/electrochemistry.md

@@ -64,6 +64,9 @@
 
 .. autoclass:: SchloeglFlow
    :members:
+
+.. autoclass:: MembraneProtonFlux
+   :members:
 ```
 
 ## Half-cells
@@ -75,3 +78,16 @@
 .. autoclass:: RedoxHalfCell
    :members:
 ```
+
+## Full cells
+
+```{eval-rst}
+.. autoclass:: FullCell
+   :members:
+
+.. autoclass:: HalfCellSpec
+   :members:
+
+.. autoclass:: MembraneSpec
+   :members:
+```

docs/api/symbolic.md

@@ -56,6 +56,8 @@
 
 .. autofunction:: input_or_parameter
 
+.. autofunction:: expression_or_parameter
+
 .. autoclass:: Residual
    :members:
 

src/sumfem/electrochemistry/__init__.py

@@ -11,9 +11,13 @@
   on :class:`ElectrodeReaction`, with the Butler-Volmer equation
   :func:`~sumfem.models.butler_volmer`.
 - Membranes: :class:`ProtonExchangeMembrane`, with the flow of water of
-  :class:`SchloeglFlow`.
+  :class:`SchloeglFlow`, whose current the protons of an electrode carry
+  through its face, :class:`MembraneProtonFlux`.
 - Half-cells of a redox flow battery: :class:`RedoxHalfCell`, negative or
   positive, of any :class:`RedoxCouple` and electrolyte.
+- Full cells: :class:`FullCell`, two half-cells, each a
+  :class:`HalfCellSpec`, and a membrane between them, a
+  :class:`MembraneSpec`.
 
 The package imports from the core of :mod:`sumfem`, and never the other
 way around.
@@ -22,6 +26,7 @@
 from .charge import ElectrolyteConduction
 from .couple import RedoxCouple
 from .electrolyte import Electrolyte, Ion
+from .full_cell import FullCell, HalfCellSpec, MembraneSpec
 from .half_cell import RedoxHalfCell
 from .kinetics import (
     ButlerVolmer,
@@ -30,7 +35,7 @@
     MassTransferButlerVolmer,
     PistonVelocityButlerVolmer,
 )
-from .membrane import ProtonExchangeMembrane, SchloeglFlow
+from .membrane import MembraneProtonFlux, ProtonExchangeMembrane, SchloeglFlow
 from .porous import PorousElectrode, Region
 from .transport import NernstPlanck, TransientNernstPlanck
 
@@ -44,8 +49,12 @@
     "TransientNernstPlanck",
     "ProtonExchangeMembrane",
     "SchloeglFlow",
+    "MembraneProtonFlux",
     "RedoxCouple",
     "RedoxHalfCell",
+    "FullCell",
+    "HalfCellSpec",
+    "MembraneSpec",
     "ButlerVolmer",
     "ElectrodeReaction",
     "ExchangeCurrentButlerVolmer",

src/sumfem/electrochemistry/electrolyte.py

@@ -10,7 +10,14 @@
 import sympy.physics.units as syu
 import ufl
 
-from sumfem.symbolic import FARADAY, GAS_CONSTANT, Domain, Field, Parameter
+from sumfem.symbolic import (
+    FARADAY,
+    GAS_CONSTANT,
+    Domain,
+    Field,
+    Parameter,
+    expression_or_parameter,
+)
 from sumfem.symbolic.si import to_si
 
 __all__ = ["Electrolyte", "Ion"]
@@ -219,16 +226,8 @@ def __init__(
             unit=syu.joule / (syu.mol * syu.kelvin),
             doc="Universal gas constant",
         )
-        self._T = (
-            temperature
-            if isinstance(temperature, ufl.core.expr.Expr)
-            else Parameter(
-                f"{name}.T",
-                domain,
-                default=temperature,
-                unit=syu.kelvin,
-                doc="Temperature",
-            )
+        self._T = expression_or_parameter(
+            f"{name}.T", temperature, domain, unit=syu.kelvin, doc="Temperature"
         )
         self._floor = Parameter(
             f"{name}.floor",
@@ -237,27 +236,15 @@ def __init__(
             unit=CONCENTRATION,
             doc="Regularization of positive concentrations",
         )
-        self._density = (
-            density
-            if isinstance(density, ufl.core.expr.Expr)
-            else Parameter(
-                f"{name}.density",
-                domain,
-                default=density,
-                unit=syu.kg / syu.m**3,
-                doc="Density",
-            )
+        self._density = expression_or_parameter(
+            f"{name}.density", density, domain, unit=syu.kg / syu.m**3, doc="Density"
         )
-        self._viscosity = (
-            viscosity
-            if isinstance(viscosity, ufl.core.expr.Expr)
-            else Parameter(
-                f"{name}.viscosity",
-                domain,
-                default=viscosity,
-                unit=syu.pascal * syu.second,
-                doc="Dynamic viscosity",
-            )
+        self._viscosity = expression_or_parameter(
+            f"{name}.viscosity",
+            viscosity,
+            domain,
+            unit=syu.pascal * syu.second,
+            doc="Dynamic viscosity",
         )
         self._ions = types.MappingProxyType({ion.name: ion for ion in ions})
         self._diffusivities = {