If we can capture CO₂, the next prize is to use it. Electrochemical CO₂ reduction (CO₂RR) uses renewable electricity to convert CO₂ into valuable products — carbon monoxide, formate, ethylene, ethanol and more — effectively running combustion in reverse and storing clean energy in chemical bonds.
Working principle
In an electrolyser, CO₂ is reduced at the cathode while water is oxidised to O₂ at the anode. The catalyst determines the product: silver and gold favour CO, tin favours formate, and notably copper is uniquely able to form multi-carbon products (ethylene, ethanol). The reaction competes with the unwanted hydrogen-evolution reaction, so selectivity (Faradaic efficiency) is the central metric. Gas-diffusion electrodes feed CO₂ as gas to reach industrially relevant current densities.
| Catalyst | Main product | Note |
|---|---|---|
| Silver / gold | CO | High selectivity |
| Tin / bismuth | Formate | Low cost |
| Copper | C₂H₄, ethanol | Only metal for C–C coupling |
| — | H₂ (parasitic) | Competing side reaction |
Key challengeThe hard part is achieving high selectivity at high current density with long catalyst life — especially for multi-carbon products on copper, where many pathways compete.
Applications
- Power-to-X: storing renewable energy as synthetic fuels
- Sustainable production of ethylene and other chemical feedstocks
- On-site CO production for industry
References & further reading
- Nitopi et al., “Progress and Perspectives of Electrochemical CO₂ Reduction on Copper,” Chemical Reviews, 2019.
- De Luna et al., “What would it take for renewably powered electrosynthesis to displace petrochemical processes?,” Science, 2019.
- Burdyny & Smith, “CO₂ reduction on gas-diffusion electrodes,” Energy & Environmental Science, 2019.