Technology atlas / Photochemical conversion

Photocatalytic CO₂ reduction

Semiconductor photocatalysts use sunlight to drive CO₂ reduction with water directly, without a separate electrolyser.

Technical reference · Updated 2026-10-10 · No current-news claim

CO₂ + 2 H₂O → CH₄ + 2 O₂ (overall, 8-electron)

CO₂ → CO + ½ O₂ (overall, 2-electron)

Where the carbon goes

Most target products (CO, methane, methanol) are fuels or fuel precursors, so carbon is typically re-released at use.

Conceptual process flow · left to right

01CO₂ + water feed
02Illuminated photoreactor
03Gas separation
04Product purification

From chemistry to process

Feedstocks: CO₂, Water, Sunlight
Products: CO, methane, methanol or formate (catalyst-dependent), Oxygen
Catalysts: Semiconductors such as TiO₂ with co-catalysts; molecular and hybrid systems
Conditions: Near-ambient temperature under illumination. Report light source, spectrum, irradiance, quantum yield, product rates and control experiments together.

Performance & demonstrated scale

Predominantly laboratory research; solar-to-fuel efficiencies reported so far are generally low.

8 mol e⁻/mol CH₄ theoretical
Reaction stoichiometry. Electrons transferred per methane formed; sets the charge-carrier demand, not the efficiency.

Pathway TRL: not assigned. Project-specific evidence is required.

Economics

No credible plant economics yet; reactor area per unit output is the key cost driver.

Climate considerations

Lifecycle data is limited to early-stage estimates; materials and large reactor area dominate.

CCU Reality Check · pathway assessment

What remains to be demonstrated?

This initial assessment separates process knowledge from the evidence needed for a commercial conclusion. Missing information is left unresolved.

Dimension	Assessment and evidence gap
CO₂ feedstock availability	No site-specific supplier, volume, purity guarantee or delivery contract has been verified.
Capture and delivered cost	Not quantified. Capture, conditioning, compression and transport need separate boundaries.
Energy and hydrogen demand	Theoretical stoichiometric or thermodynamic values are shown above. Actual process energy and feed losses remain scenario assumptions.
Catalyst and reactor performance	Semiconductors such as TiO₂ with co-catalysts; molecular and hybrid systems. No plant lifetime or sustained performance is verified here.
Product separation	The process flow identifies separation stages where relevant; a quantified separation duty and cost remain unavailable.
CAPEX and OPEX	No plant-specific capital estimate or complete operating-cost dataset is attached.
Minimum selling price	Not calculated. Capital recovery, utilization, financing and a complete operating boundary are required.
Fossil benchmark competitiveness	No verified regional benchmark comparison. Calculator benchmark values, where shown, are illustrative.
Climate performance	Lifecycle data is limited to early-stage estimates; materials and large reactor area dominate.
Scale-up bottlenecks	Low solar-to-fuel efficiency; Product separation from mixed, dilute streams; Catalyst stability under illumination; Carbon contamination artefacts in measurements.
Customer and offtake readiness	No qualified-customer or executed-offtake evidence is attached to this pathway profile.
Policy dependence	Not assessed for a specific project or jurisdiction. Do not assume subsidies or certification eligibility.

Source references

Original diagrams and explanatory text. References support process context; no numerical commercial performance has been extrapolated.