Cobalt oxide CoO and Co3O4

spore: profile
id: cobalt-oxide
spore_version: 0.2
family: oxide-ceramics
name: Cobalt oxide
abbreviation: CoO and Co3O4
role: cobalt oxides used as battery cathode and anode precursors, catalysts, ceramic pigments and solar-selective paints
category: ceramics
type: oxides
summary: |
  Cobalt oxide is a family of two compounds: cobalt(II) oxide (CoO) and cobalt(II,III) oxide (Co3O4). CoO is a green-grey powder with a cubic structure; PubChem's record gives a density of 6.45 g/cm3 at 25 °C and a melting point of 1830 °C. Co3O4 is a black spinel with a density of 6.11 g/cm3 that decomposes at 1170 K. Co3O4 is studied as a lithium-ion anode with a theoretical capacity of 890 mAh/g, against 372 mAh/g for graphite. In a 2015 laboratory study, Co3O4 powder in an alkyd paint gave 93% solar absorptance on copper or aluminium, but thermal emittance above 90% because the films were thick. No flight or space-exposure result for a cobalt oxide coating was found.
best_for: Lithium-ion anode research on Co3O4, where the theoretical capacity (890 mAh/g) is more than twice that of graphite
weakest_at: Supply is concentrated. Congo (Kinshasa) mined an estimated 73% of world cobalt in 2025 (USGS), and cobalt is on the USGS 2025 critical-minerals list
identity:
  formula: CoO and Co3O4 (CoO is cobalt(II) oxide; Co3O4 is cobalt(II,III) oxide, a spinel)
  cas: 1307-96-6 (CoO); 1308-06-1 (Co3O4)
  crystal_system: cubic (both compounds)
  space_group: Fd-3m (Co3O4, normal spinel)
  source: pubchem-coo
  where: CAS 1307-96-6 and the Gray cubic crystals entry in the Color/Form section (PubChem CID 14786); CAS 1308-06-1 in the PubChem record CID 6432046; space group and normal spinel structure from the SOLID database entry for Co3O4 (sshade-co3o4)
tags:
  environments: []
  stresses: []
  applications:
    - batteries
    - thermal-control
properties:
  - benchmark: density
    label: Density, cobalt(II) oxide (Merck value quoted by PubChem)
    value: 6.45
    unit: g/cm3
    scope: material
    conditions:
      temperature: 25 °C
    method: Value printed in the PubChem density section, with the Merck Index as the underlying reference
    status: ground
    source: pubchem-coo
    where: Density section of PubChem CID 14786 (printed as 6.45 @25 °C)
  - benchmark: density
    label: Density range, cobalt(II) oxide, depends on preparation
    value: 5.7
    value_high: 6.7
    bound: range
    unit: g/cm3
    scope: material
    conditions:
      basis: range printed for the compound; the source says it depends on preparation
    method: Range printed in the PubChem density section (Merck Index entry)
    status: ground
    source: pubchem-coo
    where: Density section of PubChem CID 14786 (printed as 5.7-6.7 g/cm3)
  - benchmark: density
    label: Relative density, cobalt(II) oxide (ECHA registration)
    value: 6.66
    unit: '-'
    scope: material
    conditions:
      temperature: 21.3 °C
      test: OECD Guideline 109 (Density of Liquids and Solids)
    method: Relative density printed in the PubChem density section, citing the ECHA registration dossier
    status: ground
    source: pubchem-coo
    where: 'Density section of PubChem CID 14786 (printed as Relative density: 6.66 at 21.3 °C)'
  - benchmark: density
    label: Density, cobalt(II,III) oxide (Co3O4)
    value: 6.11
    unit: g/cm3
    scope: material
    conditions:
      form: synthetic Co3O4, normal spinel structure
    method: Value listed in the SOLID database entry for synthetic Co3O4
    status: ground
    source: sshade-co3o4
    where: Physical properties, Density line (printed as 6.11 g/cm^3)
  - benchmark: melting_point
    label: Melting point, cobalt(II) oxide (Merck value)
    value: 1830
    unit: °C
    scope: material
    conditions:
      basis: melting point printed in the PubChem record (Merck Index entry)
    method: Value printed in the PubChem melting point section; not measured for this entry
    status: ground
    note: The same PubChem record also prints 1935 °C for the same compound (see the next property); the two Merck entries differ.
    source: pubchem-coo
    where: Melting Point section of PubChem CID 14786 (printed as 1830 °C)
  - benchmark: melting_point
    label: Melting point, cobalt(II) oxide (other Merck value)
    value: 1935
    unit: °C
    scope: material
    conditions:
      basis: Merck Index entry printed as About 1935 °C
    method: Value printed in the PubChem melting point section
    status: ground
    source: pubchem-coo
    where: Melting Point section of PubChem CID 14786 (printed as 1935 °C and About 1935 °C)
  - benchmark: water_solubility
    label: Solubility in water, cobalt(II) oxide
    value: 4.88
    unit: mg/L
    scope: material
    conditions:
      temperature: 20 °C
      method: column elution method
    method: Value printed in the PubChem solubility section
    status: ground
    source: pubchem-coo
    where: Solubility section of PubChem CID 14786 (printed as 4.88 mg/L at 20 °C, column elution method)
  - benchmark: neel_temperature
    label: Néel temperature, bulk cobalt(II) oxide (value quoted in a 2023 paper)
    value: 293
    unit: K
    scope: material
    conditions:
      basis: bulk CoO value quoted in the introduction, citing earlier work
    method: Stated in the introduction of an open-access paper on NixCo1-xO films, which cites its own reference 11 for the value
    status: ground
    source: arxiv-nico-2023
    where: Introduction, first paragraph (printed as Their Néel temperatures are 525 K and 293 K respectively)
  - benchmark: decomposition_temperature
    label: Decomposition temperature, cobalt(II,III) oxide
    value: 1170
    unit: K
    scope: material
    conditions:
      basis: listed on the database page as decomposes at 1170K; the same page also lists 1168K (895°C) under another temperature
    method: Value printed in the SOLID database entry for synthetic Co3O4
    status: ground
    source: sshade-co3o4
    where: Temperature lines of the SOLID entry (printed as decomposes at 1170K)
  - benchmark: theoretical_capacity
    label: Theoretical capacity, Co3O4 as a lithium-ion anode (conversion reaction)
    value: 890
    unit: mAh/g
    scope: material
    conditions:
      reaction: Co3O4 + 8Li+ + 8e- to 3Co + 4Li2O
      electrode: lithium-ion anode
    method: Value quoted in a 2016 research article for the conversion reaction
    status: calculated
    source: pmc-sci-rep-2016
    where: Introduction, paragraph on Co3O4 as an anode material (printed as 890 mAhg-1)
  - benchmark: theoretical_capacity
    label: Theoretical capacity, graphite (comparison value in the same paper)
    value: 372
    unit: mAh/g
    scope: material
    conditions:
      material: graphite, anode
    method: Value quoted in the same paper for comparison
    status: ground
    source: pmc-sci-rep-2016
    where: Introduction, same sentence as the Co3O4 value (printed as 372 mAhg-1)
  - benchmark: solar_absorptance
    label: Solar absorptance, Co3O4 pigment in alkyd paint on copper or aluminium
    value: 93
    unit: '%'
    scope: material
    conditions:
      substrate: copper or aluminium
      binder: alkyd resin
      film: thick coating; the authors attribute the high emittance to the film width
      wavelength: 300 to 2500 nm, integrated
    method: Measured by the authors from reflectance spectra; the paper reports the value for both surfaces
    status: ground
    source: sedici-procedia-2015
    where: Abstract and conclusions (printed as solar absorptance values were 93%)
  - benchmark: thermal_emittance
    label: Thermal emittance, same Co3O4 alkyd films (lower bound)
    value: 90
    bound: lower
    unit: '%'
    scope: material
    conditions:
      substrate: copper or aluminium
      binder: alkyd resin
      film: thick coating
    method: Measured by the authors; printed as higher than 90 percent, so 90 is a lower bound
    status: ground
    note: A selective surface needs low emittance. These thick films do not meet that requirement in this study.
    source: sedici-procedia-2015
    where: Abstract and conclusions (printed as thermal emittance value was over 90%)
  - benchmark: solar_absorptance
    label: Solar absorption, Co3O4 powder pigment (stoichiometric route)
    value: 86
    unit: '%'
    scope: material
    conditions:
      form: powder pigment
      route: stoichiometric combustion route
    method: Measured by the authors on the powder
    status: ground
    source: sedici-procedia-2015
    where: Results, paragraph on optical properties (printed as solar absorption value was 86%)
corrosion:
  - environment: Water at room temperature
    headline: Cobalt(II) oxide is only slightly soluble in water.
    effect: PubChem prints 4.88 mg/L at 20 °C and 3.27 mg/L at 37 °C by column elution, so only small amounts of cobalt pass into water.
    rating: low
    conditions:
      temperature: 20 °C and 37 °C
      method: column elution method
    source: pubchem-coo
    where: Solubility section of PubChem CID 14786
  - environment: Strong acids and alkalis
    headline: Cobalt(II) oxide dissolves in acids and alkalis.
    effect: PubChem's solubility section says insoluble in ammonium hydroxide and soluble in acids and alkali hydroxides. No rate, concentration or temperature is given, so no corrosion rating is assigned.
    rating: unknown
    conditions:
      concentration: not stated
      temperature: not stated
    source: pubchem-coo
    where: Solubility section of PubChem CID 14786
  - environment: Heating (thermal ageing of Co3O4)
    headline: Co3O4 decomposes when heated to 1170 K.
    effect: The SOLID database entry gives a decomposition temperature of 1170 K. The page does not state the atmosphere or the decomposition product, so this is a thermal limit, not a corrosion rate.
    rating: unknown
    conditions:
      atmosphere: not stated on the source page
    source: sshade-co3o4
    where: Temperature lines of the SOLID entry
risks:
  hazards:
    - text: PubChem's GHS record for cobalt(II) oxide lists several supplier notifications, and they do not agree. Notified statements include H301 (toxic if swallowed), H317 (skin sensitisation), H330 (fatal if inhaled), H334 (respiratory sensitisation), H351 (suspected of causing cancer), H360F, H372 and H410. One notification reads Not Classified.
      ghs:
        - H301
        - H317
        - H330
        - H334
        - H351
        - H360F
        - H372
        - H410
      source: pubchem-coo
      where: GHS Classification section of PubChem CID 14786 (several notifications, not one agreed classification)
    - text: PubChem's GHS record for cobalt oxide (CID 6432046, CAS 1308-06-1) prints Not Classified and states Reported as not meeting GHS hazard criteria by 7 of 7 companies. Other notifications on the same page list H301, H317, H330 and H334.
      ghs: []
      source: pubchem-co34
      where: GHS Classification section of PubChem CID 6432046
  failure_risks:
    - mode: Decomposition of Co3O4 on heating
      trigger: Heating to about 1170 K
      consequence: The compound decomposes at that temperature, so Co3O4 cannot be used above this point as the same material.
      severity: moderate
      source: sshade-co3o4
      where: Temperature lines of the SOLID entry
    - mode: Dissolution in strong acid or alkali
      trigger: Exposure of cobalt(II) oxide to acids or alkali hydroxides
      consequence: The oxide dissolves; no rate is given in the source.
      severity: low
      source: pubchem-coo
      where: Solubility section of PubChem CID 14786
  side_effects:
    - text: Under the PubChem notifications for cobalt(II) oxide, the powder can cause skin sensitisation (H317) and respiratory sensitisation (H334).
      affects: Workers who handle powder and dust
      source: pubchem-coo
      where: GHS Classification section of PubChem CID 14786
  handling:
    - text: Notifications for cobalt(II) oxide include H330 (fatal if inhaled) and H334 (may cause allergy or asthma symptoms or breathing difficulties if inhaled). Avoid breathing the powder.
      source: pubchem-coo
      where: GHS Classification section of PubChem CID 14786
    - text: PubChem lists cobalt(II) oxide as stable under recommended storage conditions.
      source: pubchem-coo
      where: Stability/Shelf Life section of PubChem CID 14786
  mitigations:
    - text: Keep Co3O4 below its decomposition temperature of 1170 K if it must stay Co3O4.
      source: sshade-co3o4
      where: Temperature lines of the SOLID entry
uses:
  - application: batteries
    device: Lithium-ion anode in laboratory cells (research)
    example: A 2016 research article gives a theoretical capacity of 890 mAh/g for Co3O4 in the conversion reaction, more than twice the 372 mAh/g of graphite.
    source: pmc-sci-rep-2016
    where: Introduction
  - application: thermal-control
    device: Solar-selective paint for solar collectors (laboratory coating)
    example: A 2015 study made Co3O4 powder into alkyd paint films on copper or aluminium with 93% solar absorptance, but thermal emittance above 90% on thick films, so the coatings were not selective in that study.
    source: sedici-procedia-2015
    where: Abstract and conclusions
  - application: batteries
    device: Lithium-ion battery market (cobalt context)
    example: USGS reports that China was the world's leading consumer of cobalt in 2025, primarily for the lithium-ion battery industry.
    source: usgs-mcs2026-cobalt
    where: Events, Trends, and Issues
supply:
  - subject: Cobalt (feedstock for both oxides)
    producers:
      - country: Congo (Kinshasa)
        share_percent: 73
        year: 2025
      - country: Indonesia
        share_percent: 14
        year: 2025
    critical_lists:
      - list: USGS 2025 List of Critical Minerals (cobalt is listed; used in batteries and in metal alloys for extreme temperatures)
        listed: true
      - list: EU critical raw materials list (Regulation (EU) 2024/1252; the page summary read in this run lists cobalt, but the exact entry text was not quoted)
        listed: true
    recycling: 'USGS: cobalt content of purchased scrap represented 25% of estimated cobalt consumption in 2025.'
    substitutes:
      - 'USGS: the cobalt content of lithium-ion batteries, the leading global use for cobalt, was being decreased; cobalt-free substitutes that use iron and phosphorus held significant market share in China.'
    source: usgs-mcs2026-cobalt
    where: Events, Trends, and Issues (the 73% and 14% shares, printed as an estimate); World Mine Production and Reserves table (2025 column, world total 310,000 t); Recycling; Substitutes. The EU list entry is from the ec-crm page (summary only)
documents:
  - title: 'PubChem: Cobalt(II) oxide (CID 14786), GHS, density, melting point, solubility and uses'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/14786
    year: 2026
  - title: 'PubChem: Cobalt oxide (CID 6432046), Co3O4 GHS record and molecular weight'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/6432046
    year: 2026
  - title: 'SOLID database: synthetic Co3O4, physical properties'
    type: database
    url: https://sshade.eu/data/solid/SOLID_synthetic_Co3O4
    year: 2026
  - title: Mineral Commodity Summaries 2026, Cobalt (USGS)
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-cobalt.pdf
    year: 2026
  - title: Combustion synthesis of ultrafine powders of Co3O4 for selective surfaces of solar collectors (open access, Procedia Materials Science 9, 2015)
    type: paper
    url: https://sedici.unlp.edu.ar/bitstream/handle/10915/146314/Documento_completo.pdf?sequence=1
    year: 2015
  - title: Nanoparticle Decorated Ultrathin Porous Nanosheets as Hierarchical Co3O4 Nanostructures for Lithium Ion Battery Anode Materials (Scientific Reports, PMC)
    type: paper
    url: https://pmc.ncbi.nlm.nih.gov/articles/PMC4742879/
    year: 2016
  - title: 'Tuning the Néel temperature in an antiferromagnet: the case of NixCo1-xO microstructures (arXiv)'
    type: paper
    url: https://arxiv.org/pdf/2309.13721
    year: 2023
gaps:
  - No band gap found for CoO or Co3O4 in a source we could open. The searches returned only magnetic and catalytic results.
  - Néel temperature for Co3O4 (about 30 to 40 K in a porous-glass study) was seen in a search result only and was not read in this run.
  - Crustal abundance of cobalt not found in an opened source, so the abundance line is left out.
  - No space flight, vacuum, radiation or atomic-oxygen result for a cobalt oxide coating was found. The solar-absorber results are laboratory films on copper and aluminium.
  - 'The air temperature at which Co3O4 converts back to CoO is not given: the 1998 J. Materials Chemistry paper (Xu and Zeng) and the Catalysis Science and Technology review (Liotta et al., 2013) both returned HTTP 403 or were not readable.'
  - The Applied Sciences (MDPI) and Catalysts (MDPI) pages returned HTTP 403 and were not read, so no catalytic-performance value is given.
  - The PubChem record pages returned a verification screen to the browser tool; the values were read from the same record's JSON export (pug_view) for CID 14786 and CID 6432046.
  - The EU critical-list entry for cobalt was read only as a page summary, not as a quoted sentence. Check it before relying on the EU line.
  - The Co3O4 density of 6.11 g/mL at 25 °C from supplier listings (Sigma-Aldrich, Parchem) was seen in search results only and was not read. The SOLID database value (6.11 g/cm3) is used instead.
  - Hazard data are PubChem supplier notifications that disagree with each other. No agreed GHS classification and no supplier SDS was read for either oxide.
  - No quantitative corrosion or ageing test for CoO or Co3O4 was found, so the corrosion ratings are unknown except for the water solubility line.
  - 'Property names not in spores/property-canon.yaml: neel_temperature, water_solubility, decomposition_temperature, solar_absorptance, thermal_emittance. Used as snake_case names.'
sources:
  usgs-mcs2026-cobalt:
    title: Mineral Commodity Summaries 2026, Cobalt
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-cobalt.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  usgs-crit2025:
    title: About the 2025 List of Critical Minerals (USGS, final list of 60 minerals)
    id: Final 2025 List of Critical Minerals, November 2025
    url: https://www.usgs.gov/programs/mineral-resources-program/science/about-2025-list-critical-minerals
    year: 2025
    kind: web
    license: public domain (USGS)
  ec-crm:
    title: Critical raw materials (European Commission, list under Regulation (EU) 2024/1252)
    id: Regulation (EU) 2024/1252
    url: https://single-market-economy.ec.europa.eu/sectors/raw-materials/areas-specific-interest/critical-raw-materials_en
    year: 2024
    kind: web
    license: European Commission web page
  pubchem-coo:
    title: PubChem compound record, Cobalt(II) oxide (CID 14786)
    id: CID 14786; CAS 1307-96-6
    url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/14786/JSON
    year: 2026
    kind: database
    license: public domain (NCBI)
  pubchem-co34:
    title: PubChem compound record, Cobalt oxide (CID 6432046; CAS 1308-06-1)
    id: CID 6432046
    url: https://pubchem.ncbi.nlm.nih.gov/compound/6432046
    year: 2026
    kind: database
    license: public domain (NCBI)
  sshade-co3o4:
    title: SOLID database, synthetic Co3O4 (physical properties and structure)
    id: SSHADE solid entry, synthetic Co3O4
    url: https://sshade.eu/data/solid/SOLID_synthetic_Co3O4
    year: 2026
    kind: database
    license: database terms (cited, not reproduced)
  arxiv-nico-2023:
    title: 'Tuning the Néel temperature in an antiferromagnet: the case of NixCo1-xO microstructures'
    id: arXiv:2309.13721
    url: https://arxiv.org/pdf/2309.13721
    year: 2023
    kind: paper
    license: arXiv (author licence)
  sedici-procedia-2015:
    title: Combustion synthesis of ultrafine powders of Co3O4 for selective surfaces of solar collectors
    id: doi:10.1016/j.mspro.2015.04.029 (Procedia Materials Science 9, 230-238)
    url: https://sedici.unlp.edu.ar/bitstream/handle/10915/146314/Documento_completo.pdf?sequence=1
    year: 2015
    kind: paper
    license: CC BY-NC-ND 4.0
  pmc-sci-rep-2016:
    title: Nanoparticle Decorated Ultrathin Porous Nanosheets as Hierarchical Co3O4 Nanostructures for Lithium Ion Battery Anode Materials
    id: Scientific Reports 2016 (PMC4742879)
    url: https://pmc.ncbi.nlm.nih.gov/articles/PMC4742879/
    year: 2016
    kind: paper
    license: CC BY 4.0
license: CC-BY-4.0
updated: '2026-10-26'
review:
  status: draft
  method: assistant
  checked_values: 14
  unreachable: 3
  caveats: 4
  note: 'Read by an AI assistant on 2026-10-26 from the pages and PDFs fetched in that run. PubChem''s HTML pages returned a verification screen, so values were read from the PubChem JSON export of the same CIDs. MDPI and RSC pages returned HTTP 403 and were not read. Caveats: Co3O4 solar results are for thick, non-selective films; the cobalt supply shares are USGS estimates; hazard notifications disagree; the EU list entry was read as a summary.'
story:
  recipe:
    line: Cobalt(II) oxide (CoO) combines one cobalt atom with one oxygen atom. Cobalt(II,III) oxide (Co3O4) combines cobalt and oxygen in a 3:4 ratio and has a normal spinel structure, in which cobalt sits in two different sites in a cubic oxide lattice.
    parts:
      - name: Cobalt
        symbol: Co
        atoms: 1
        atomic_weight: 58.933
        role: The metal centre. In CoO it is in the 2+ state. In Co3O4 it is split between 2+ and 3+ states, which is what makes the spinel possible.
      - name: Oxygen
        symbol: O
        atoms: 1
        atomic_weight: 15.999
        role: Forms the oxide lattice. In Co3O4 there are four oxygen atoms for every three cobalt atoms.
  risk_groups:
    - title: For people
      level: 0
      verdict: Classification varies by supplier
      lead: PubChem lists several supplier notifications for cobalt(II) oxide. They disagree, and some say the powder is toxic, a sensitiser or a suspected carcinogen.
      points:
        - label: Sensitisation
          line: Several notifications list H317 (skin sensitisation) and H334 (respiratory sensitisation).
        - label: Inhalation
          line: Some notifications list H330 (fatal if inhaled). Avoid breathing the powder.
        - label: Cancer statement
          line: Some notifications list H351 (suspected of causing cancer).
        - label: Co3O4
          line: For cobalt oxide (CID 6432046), the PubChem record says it is reported as not meeting GHS hazard criteria by 7 of 7 companies, while other notifications on the same page list H301, H317, H330 and H334.
    - title: Heating
      lead: These points come from the thermal data, not from incidents.
      points:
        - label: Decomposition
          line: The SOLID database entry for Co3O4 gives a decomposition temperature of 1170 K.
        - label: Stability
          line: PubChem lists cobalt(II) oxide as stable under recommended storage conditions.
    - title: Handling and storage
      points:
        - label: Water
          line: 'Cobalt(II) oxide is only slightly soluble in water: 4.88 mg/L at 20 °C in PubChem''s column elution measurement.'
        - label: Acids
          line: PubChem says cobalt(II) oxide is soluble in acids and alkali hydroxides. No rate is given.
  why: Cobalt oxides are ceramic oxides of cobalt that come in two common forms. CoO is a green-grey powder used for ceramic pigments and enamels. Co3O4 is a black spinel that has been studied as a lithium-ion anode, where it stores far more lithium per gram than graphite on paper, and as a dark absorber in solar coatings. In 2025 cobalt was mined mainly in Congo (Kinshasa), which the USGS estimates supplied 73% of world output, so supply is a central concern.
  uses:
    - where: Lithium-ion anode research
      line: A 2016 research article gives a theoretical capacity of 890 mAh/g for Co3O4 in the conversion reaction, more than twice the 372 mAh/g of graphite. The paper is laboratory work.
    - where: Solar-selective paint research
      line: A 2015 study made Co3O4 powder into alkyd paint films on copper and aluminium. The films reached 93% solar absorptance, but thermal emittance was above 90% because the films were thick, so they were not selective.
    - where: Battery market context
      line: USGS reports that China was the world's leading consumer of cobalt in 2025, primarily for the lithium-ion battery industry. Cobalt-free substitutes using iron and phosphorus held significant market share in China.
  can_do:
    - label: Capacity
      benchmark: theoretical_capacity
      line: Co3O4 has a theoretical capacity of 890 mAh/g in the conversion reaction, more than twice the 372 mAh/g of graphite.
    - label: Density
      benchmark: density
      line: CoO has a density of 6.45 g/cm3 at 25 °C in the PubChem record. Co3O4 has a density of 6.11 g/cm3 in the SOLID database.
    - label: Solar absorptance
      benchmark: solar_absorptance
      value: 93%
      line: In a 2015 lab study, Co3O4 alkyd films reached 93% solar absorptance, but their thermal emittance was above 90%.
    - label: Thermal limit
      value: 1170 K
      line: Co3O4 decomposes at 1170 K, according to the SOLID database entry.
  compare: Co3O4 has a high theoretical capacity for an anode, about 890 mAh/g against 372 mAh/g for graphite. The density of the two oxides is similar, with CoO at 6.45 g/cm3 and Co3O4 at 6.11 g/cm3. Both are dark, high-absorptance materials, but the 2015 films had too much thermal emittance to count as selective surfaces. The table below compares the three figures.
  compare_rows:
    - label: Ideal capacity per gram
      benchmark: theoretical_capacity
    - label: Density
      benchmark: density
    - label: Solar absorptance in a lab film
      benchmark: solar_absorptance
  handling:
    - Avoid breathing cobalt oxide dust. PubChem notifications for cobalt(II) oxide include H330 (fatal if inhaled) and H334 (respiratory sensitisation).
    - Keep the powder in a sealed container. PubChem lists the compound as stable under recommended storage conditions.
    - Keep Co3O4 below 1170 K if it must stay as Co3O4.
  good_for:
    - Lithium-ion anode research on Co3O4, where the theoretical capacity is 890 mAh/g against 372 mAh/g for graphite.
    - Ceramic pigments and enamels with CoO, where the oxide has long been used for colour (PubChem, HSDB).
  watch_out:
    - 'Supply: the USGS estimates that Congo (Kinshasa) mined 73% of world cobalt in 2025, and cobalt is on the USGS 2025 critical-minerals list.'
    - 'Hazards: supplier notifications for CoO disagree, and some list fatal inhalation hazard and sensitisation.'
    - 'Solar coatings: the 2015 Co3O4 films had 93% solar absorptance but thermal emittance above 90%, so they are not selective thermal-control coatings.'
  verdict: 'Cobalt oxides are useful as lithium-ion anode precursors and as dark pigments. For spacecraft thermal control they are unproven: the one lab study we read gave high emittance, and no flight data were found.'