CO₂, water, and sunlight to hydrocarbon fuels: A sustained sunlight to fuel (Joule-to-Joule) photoconversion efficiency of 1%

If we wish to sustain our terrestrial ecosphere as we know it, then reducing the concentration of atmospheric CO₂ is of critical importance. An ideal pathway for achieving this would be the use of sunlight to recycle CO₂, in combination with water, into hydrocarbon fuels compatible with our current energy infrastructure. However, while the concept is intriguing such a technology has not been viable due to the vanishingly small CO₂-to-fuel photoconversion efficiencies achieved. Herein we report a photocatalyst, reduced blue-titania sensitized with bimetallic Cu-Pt nanoparticles that generates a substantial amount of both methane and ethane by CO₂ photoreduction under artificial sunlight (AM1.5): over a 6 h period 3.0 mmol g^-1 methane and 0.15 mmol g^-1 ethane are obtained (on an area normalized basis 0.244 mol m^-2 methane and 0.012 mol m^-2 ethane), while no H₂ nor CO is detected. This activity (6 h) translates into a sustained Joule (sunlight) to Joule (fuel) photoconversion efficiency of 1%, with an apparent quantum efficiency of φ = 86%. The time-dependent photoconversion efficiency over 0.5 h intervals yields a maximum value of 3.3% (φ = 92%). Isotopic tracer experiments confirm the hydrocarbon products originate from CO₂ and water.