Electrochemical Cells#

An electrochemical cell is the fundamental unit in which an electrochemical reaction occurs. It converts chemical energy into electrical energy (or vice versa) through oxidation and reduction at two electrodes separated by an electrolyte.

An electrochemical cell is conceptually distinct from an electrochemical device:

  • A cell is the functional unit of reaction, composed of electrodes, electrolyte, and separator.

  • A device is a practical assembly that contains one or more cells, plus mechanical housing, terminals, casing, or other supporting systems.

Electrochemical Cell vs. Electrochemical Device

ElectrochemicalCell Represents the active system where charge transfer and ionic conduction occur. It includes electrodes, electrolyte, and separator, but not external casing or packaging.

ElectrochemicalDevice Represents a complete product or engineered object — such as a coin cell, pouch cell, battery module, fuel cell stack, or supercapacitor. It includes mechanical structures, safety components, and interfaces to the environment.

In other words, a device contains one or more cells, but a cell is the level at which the electrochemistry happens.

Conceptual Structure#

Every electrochemical cell consists of three core components:

  • Positive Electrode — the electrode at higher potential during discharge (cathode).

  • Negative Electrode — the electrode at lower potential during discharge (anode).

  • Electrolyte — the ionic conductor between the electrodes.

Many cells also include a Separator, Current Collectors, and Casing (when modeled as part of a device).

Structure of an electrochemical cell

Generic architecture of an electrochemical cell.#

Guidelines for Use#

Follow these steps to describe an ElectrochemicalCell in the ontology.

1. Identify the Cell#

Start with the ElectrochemicalCell class or one of its subclasses such as:

  • GalvanicCell — a spontaneous reaction generating electricity

  • ElectrolyticCell — a driven reaction consuming electrical energy

  • HalfCell — a single electrode–electrolyte interface (for measurement)

  • ReferenceCell — a standardized potential reference system

{
  "@context": "https://w3id.org/emmo/domain/electrochemistry/context",
  "@type": "ElectrochemicalCell"
}

2. Define the Main Parts#

Use domain-specific part relations, all of which are subproperties of emmo:hasPart, to describe composition.

  • hasElectrode

  • hasElectrolyte

  • hasSeparator

  • hasCase (optional, if modeling physical structure)

Example: generic two-electrode cell

{
  "@context": "https://w3id.org/emmo/domain/electrochemistry/context",
  "@type": "ElectrochemicalCell",
  "hasElectrode": [
    { "@type": "PositiveElectrode" },
    { "@type": "NegativeElectrode" }
  ],
  "hasElectrolyte": { "@type": "LiquidElectrolyte" },
  "hasSeparator": { "@type": "Separator" }
}

3. Define Electrode Composition#

Each electrode can itself be modeled using hasCoating, hasCurrentCollector, and related relations. This maintains hierarchical structure and reasoning consistency.

Example: lithium-ion half-cell electrodes

{
  "@context": "https://w3id.org/emmo/domain/electrochemistry/context",
  "@type": "ElectrochemicalCell",
  "hasElectrode": [
    {
      "@type": "PositiveElectrode",
      "hasCoating": {
        "@type": "ElectrodeCoating",
        "hasActiveMaterial": { "@type": "LiNi0.8Mn0.1Co0.1O2" },
        "hasBinder": { "@type": "PVDF" },
        "hasAdditive": { "@type": "CarbonBlack" }
      },
      "hasCurrentCollector": { "@type": "AluminiumFoil" }
    },
    {
      "@type": "NegativeElectrode",
      "hasCoating": {
        "@type": "ElectrodeCoating",
        "hasActiveMaterial": { "@type": "Graphite" },
        "hasBinder": { "@type": "PVDF" },
        "hasAdditive": { "@type": "CarbonBlack" }
      },
      "hasCurrentCollector": { "@type": "CopperFoil" }
    }
  ],
  "hasElectrolyte": {
    "@type": "OrganicElectrolyte",
    "hasSolvent": { "@type": "EthyleneCarbonate" },
    "hasSolute": { "@type": "LiPF6" }
  },
  "hasSeparator": { "@type": "MicroporousPolymerSeparator" }
}

4. Assign Cell Properties#

Cells have measurable properties describing electrochemical performance and physical configuration. These are modeled as quantities or conventional properties via hasProperty.

Common examples:

  • NominalVoltage

  • RatedCapacity

  • InternalResistance

  • ElectrodeArea

  • SeparatorThickness

Example: adding cell-level properties

{
  "@type": "ElectrochemicalCell",
  "hasProperty": [
    {
      "@type": "NominalVoltage",
      "hasNumericalPart": { "@type": "RealData", "hasNumberValue": 3.7 },
      "hasMeasurementUnit": "emmo:Volt"
    },
    {
      "@type": "RatedCapacity",
      "hasNumericalPart": { "@type": "RealData", "hasNumberValue": 4.8 },
      "hasMeasurementUnit": "emmo:AmpereHour"
    }
  ]
}

5. Specialized Cell Types#

Several subclasses are available for specific electrochemical contexts.

Class | Description | Example |

|--------|--------------|----------| | GalvanicCell | Spontaneous discharge cell | Zinc–manganese dioxide (alkaline) | | ElectrolyticCell | Driven electrolysis | Water electrolysis, metal plating | | HalfCell | Single-electrode test cell | Li/Li⁺ reference or working electrode | | ReferenceCell | Stable potential reference | Ag/AgCl electrode | | ThreeElectrodeCell | Laboratory setup with reference electrode | Common in electrochemical testing |

Example: three-electrode configuration

{
  "@context": "https://w3id.org/emmo/domain/electrochemistry/context",
  "@type": "ThreeElectrodeCell",
  "hasWorkingElectrode": { "@type": "PlatinumElectrode" },
  "hasCounterElectrode": { "@type": "GraphiteElectrode" },
  "hasReferenceElectrode": { "@type": "SilverChlorideElectrode" },
  "hasElectrolyte": { "@type": "AqueousElectrolyte", "hasSolute": { "@type": "PotassiumChloride" } }
}

Reasoning and Hierarchy#

Because all part relations such as hasElectrode, hasElectrolyte, and hasSeparator are subproperties of `emmo:hasPart`, the ontology supports transitive reasoning:

::

If Cell hasElectrode Electrode, and Electrode hasCoating Coating, then Cell hasPart Coating.

This allows queries like “find all cells containing a given material” to retrieve results across multiple structural layers.

Best Practices#

  • Use ElectrochemicalCell for the functional reacting system, and ElectrochemicalDevice for encapsulated or engineered units.

  • Always define both electrodes and the electrolyte for completeness.

  • Use domain-specific subproperties (hasElectrode, hasElectrolyte, etc.) instead of hasPart directly.

  • For laboratory setups, use HalfCell or ThreeElectrodeCell depending on the measurement configuration.

  • Attach measurable quantities as hasProperty relations.

  • Avoid including mechanical casings, connectors, or packaging elements — those belong to the device level.

Summary#

Electrochemical cells represent the active domain of electrochemistry — the space where electrons, ions, and matter interact through redox reactions.

Concept | Relation | Example |

|----------|-----------|----------| | ElectrochemicalCell | hasElectrode, hasElectrolyte, hasSeparator | basic two-electrode configuration | | GalvanicCell | subclass of ElectrochemicalCell | zinc–manganese dioxide | | ElectrolyticCell | subclass of ElectrochemicalCell | water electrolysis cell | | HalfCell | part of a larger setup | lithium half-cell | | ThreeElectrodeCell | hasWorkingElectrode, hasCounterElectrode, hasReferenceElectrode | potentiostatic test cell |

By describing cells using these relations, EMMO enables structured, machine-interpretable representations of electrochemical systems — linking materials, structure, and performance under one consistent semantic framework.