# CO₂ electrolyzers: gas-diffusion electrodes

> In an H-cell, CO₂ must dissolve before it reaches the catalyst, and that caps the current. Flow electrolyzers feed CO₂ as a gas through a gas-diffusion electrode right up to the catalyst, reaching more than 200 mA cm⁻². On copper at an abrupt interface in hydroxide, CO₂ became ethylene with 70% efficiency for 150 hours.

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- Updated: 2026-10-14
- Category: Electrocatalysis
- Method: Flow electrolyzer
- Starting materials: A copper catalyst on a gas-diffusion layer, CO₂ gas, a hydroxide or bicarbonate electrolyte, a membrane and an anode
- Product: CO₂ reduced at high current: ethylene and other products from the gas and liquid streams
- Key result: Current densities and ethylene results from the abstracts of Weekes et al. (2018) and Dinh et al. (2018); cells, interface and the stability trace are schematic
- Figure: 1920 × 1080 px, 70 editable layers (4 generated objects with settings)

## Steps

1. **H-cell**: Good for screening catalysts, but dissolved CO₂ limits mass transport and current (Weekes et al. 2018)
2. **Flow cell**: CO₂ goes to the cathode as a gas through a gas-diffusion electrode; flow cells and microfluidic reactors both exceed 200 mA cm⁻²
3. **Membrane**: Cation-exchange, anion-exchange or bipolar: it sets the ions that cross and the electrolytes you can use
4. **Abrupt interface**: Copper in hydroxide at a sharp gas–catalyst–electrolyte interface: 70% ethylene efficiency held for 150 h (Dinh et al. 2018)

## Strengths

- High current densities
- Gas-phase CO₂ avoids its low solubility in water

## Limitations

- Water management: the cell must stay hydrated
- CO₂ reacts with hydroxide to bicarbonate
- Long-term stability of the electrode

## Uses

- Ethylene, CO and formate from CO₂ at scale

## References

1. Weekes, Salvatore, Reyes, Huang & Berlinguette, “Electrolytic CO2 Reduction in a Flow Cell”, Acc. Chem. Res. 2018. https://doi.org/10.1021/acs.accounts.8b00010 (review)
2. Dinh, Burdyny, Kibria, Seifitokaldani, Gabardo, García de Arquer, Kiani, Edwards, De Luna, Bushuyev, Zou, Quintero-Bermudez, Pang, Sinton & Sargent, “CO2 electroreduction to ethylene via hydroxide-mediated copper catalysis at an abrupt interface”, Science 2018. https://doi.org/10.1126/science.aas9100 (primary)
3. Nitopi et al., “Progress and Perspectives of Electrochemical CO2 Reduction on Copper in Aqueous Electrolyte”, Chem. Rev. 2019. https://doi.org/10.1021/acs.chemrev.8b00705 (further reading)

Credit: After Weekes et al., Acc. Chem. Res. 2018 (doi:10.1021/acs.accounts.8b00010) and Dinh et al., Science 2018 (doi:10.1126/science.aas9100). Cells and interface schematic; stability trace drawn after the paper, not its data.

## Questions

**What does the “CO₂ electrolyzers: gas-diffusion electrodes” template show?** In an H-cell, CO₂ must dissolve before it reaches the catalyst, and that caps the current. Flow electrolyzers feed CO₂ as a gas through a gas-diffusion electrode right up to the catalyst, reaching more than 200 mA cm⁻². On copper at an abrupt interface in hydroxide, CO₂ became ethylene with 70% efficiency for 150 hours.

**What are the steps shown in “CO₂ electrolyzers: gas-diffusion electrodes”?** 1. H-cell: Good for screening catalysts, but dissolved CO₂ limits mass transport and current (Weekes et al. 2018). 2. Flow cell: CO₂ goes to the cathode as a gas through a gas-diffusion electrode; flow cells and microfluidic reactors both exceed 200 mA cm⁻². 3. Membrane: Cation-exchange, anion-exchange or bipolar: it sets the ions that cross and the electrolytes you can use. 4. Abrupt interface: Copper in hydroxide at a sharp gas–catalyst–electrolyte interface: 70% ethylene efficiency held for 150 h (Dinh et al. 2018).

**What are the starting materials and the product?** Starting materials: A copper catalyst on a gas-diffusion layer, CO₂ gas, a hydroxide or bicarbonate electrolyte, a membrane and an anode. Product: CO₂ reduced at high current: ethylene and other products from the gas and liquid streams.

**Which papers is “CO₂ electrolyzers: gas-diffusion electrodes” based on?** Weekes, Salvatore, Reyes, Huang & Berlinguette, “Electrolytic CO2 Reduction in a Flow Cell”, Acc. Chem. Res. 2018 (doi:10.1021/acs.accounts.8b00010); Dinh, Burdyny, Kibria, Seifitokaldani, Gabardo, García de Arquer, Kiani, Edwards, De Luna, Bushuyev, Zou, Quintero-Bermudez, Pang, Sinton & Sargent, “CO2 electroreduction to ethylene via hydroxide-mediated copper catalysis at an abrupt interface”, Science 2018 (doi:10.1126/science.aas9100); Nitopi et al., “Progress and Perspectives of Electrochemical CO2 Reduction on Copper in Aqueous Electrolyte”, Chem. Rev. 2019 (doi:10.1021/acs.chemrev.8b00705).

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