A Feasibility Study of Integrating CO2 Capture and Light-Driven CO2 Conversion to a Fuel

Junwang Tang,^1* Zhengxiao Guo² and Kimfung Li¹

1. Chemical Engineering, UCL. Email: junwang.tang@ucl.ac.uk
2. Chemistry, UCL

The upward spiral of CO₂ concentration in the atmosphere triggered by industrialization, rising commercial and domestic use of energy coupled with rapid rate of deforestation could result in further increase in the global average temperature followed by rising sea levels and other dire consequences

Photocatalytic conversion of CO₂ to a more stable energy carrier like methanol using sunlight energy offers a sustainable solution to address unnatural rise in CO₂ level. However, to be viable commercially, photocatalysts (or photocatalyst systems) involved need to tap more of the sunlight’s energy. This can only be achieved if the photocatalysts/photocatalyst systems involved are sensitive to the visible wavelength range and have high energy conversion efficiency.

Fig. 1: (a) Baseline of sample before light irradiation. (b) GC results show methanol and CO production when the Ta-based photocatalyst is exposed to light in one hour.

We have previously demonstrated facile synthesis of nanostructured films that are sensitive to UV light irradiation via solution growth process. In this project, we tested the UV sensitive nanostructured films, and found that they could actively reduce CO₂ to fuel (CO and methanol), albeit under UV light irradiation (Fig 1). Currently, the absolute amount of detected gaseous methanol is low. This is due to difficulties to quantify reaction products that are soluble and unoptimized measurement and reaction conditions that can be overcome with continuous efforts.

The next target within this project is to tap into the most intense of the sunlight radiation in the visible wavelength range. We are convinced that the way forward is to develop visible light sensitive material by selecting materials system with suitable band energy, low enough for visible light excitation, but straddling CO₂ reduction and water oxidation.

Fig. 2. Nanostructured visible light-driven Cu2O film. (a) SEM observation and (b) pictures.

One of our approaches is by using copper based nanostructures. We focused on copper based materials because of its appropriate bandgap in principal meeting the requirement of CO₂ reduction under visible light excitation. Cuprous oxides (CuO, Cu₂O) were investigated for water photolysis under visible light irradiation. However, reports of CO₂ reduction to fuel using copper based photocatalyst have been seldom reported. Cu₂O films have been successfully grown on glass substrate using simple and reproducible solution growth method (Fig 2). The Cu₂O films grown show significant absorption well above 500nm wavelength, which makes it suitable to capture the visible light radiation of the sun. It is underway to assess the activity of the copper based films under visible light irradiations with and without bias. If successful, it will be the first report on visible-driven CO₂ photoreduciton and the results will be filed.