interface_current method and accompanying test added

interfaces/cython/cantera/kinetics.pyx

@@ -6,6 +6,7 @@ import warnings
 cimport numpy as np
 import numpy as np
 
+from .constants import *
 from .reaction cimport *
 from ._utils cimport *
 from . import _utils
@@ -880,6 +881,14 @@ cdef class InterfaceKinetics(Kinetics):
         """
         return self.net_production_rates[self._phase_slice(phase)]
 
+    def interface_current(self, phase):
+        """
+        The interface current is useful when charge transfer reactions occur at
+        an interface. It is defined here as the net positive charge entering the
+        phase ``phase`` (Units: A/m^2).
+        """
+        return sum(self.get_net_production_rates(phase)*phase.charges)*faraday
+
     def write_yaml(self, filename, phases=None, units=None, precision=None,
                    skip_user_defined=None):
         """

test/python/test_kinetics.py

@@ -1065,6 +1065,29 @@ def cathode_current(phi_s, phi_l, X_Li_cathode):
         ref = np.genfromtxt(self.test_data_path / "lithium-ion-battery-test.csv")
         assert np.allclose(data, ref, rtol=1e-7)
 
+    def test_interface_current(self):
+        file = "lithium_ion_battery.yaml"
+
+        # The 'elde' electrode phase is needed as a source/sink for electrons:
+        anode = ct.Solution(file,"anode")
+        elect = ct.Solution(file,"electron")
+        elyte = ct.Solution(file,"electrolyte")
+        anode_int = ct.Interface(file,"edge_anode_electrolyte",[anode,elect,elyte])
+
+        anode.X = [0.9, 0.1]
+        elyte.X = [0.4, 0.3, 0.15, 0.15]
+
+        anode.electric_potential = 0.
+        elyte.electric_potential = 3.
+
+        species_productions = anode_int.get_net_production_rates(elyte)
+        species_charges = elyte.charges
+
+        method = anode_int.interface_current(elyte)
+        manual = sum(species_productions*species_charges)*ct.faraday
+
+        self.assertEqual(method,manual)
+
 
 class TestDuplicateReactions(utilities.CanteraTest):
     infile = 'duplicate-reactions.yaml'