2D materials: ‘holy grail’ for photocatalytic CO2 reduction into solar fuels

Artificial photosynthesis: a ‘killing two birds with one stone’ approach for tackling energy and environmental challenges

   A research group led by Li-Chyong Chen and Kuei-Hsien Chen at the Center for Condensed Matter Sciences, National Taiwan University, has created a way to trigger a chemical reaction in a synthetic two-dimensional (2D) ., specifically, graphene oxides (GOs) and hybrid GOs that convert CO2 into solar fuels. This process is so-called artificial photosynthesis, mimicking the way plants convert CO2 and sunlight into glucose. Here, solar fuels and solar chemicals are produced utilizing solar energy in the gas phase.

Inspired by what Mother Nature has been doing for billions of years, fuels produced from sunlight through artificial photosynthesis can serve as future energy sources that are an environmental friendly alternative to fossil fuels. As per current global energy and clean environmental policies, the production of alternative green-energy sources while reducing CO2 emissions without affecting our energy demand is highly challenging. Taiwan’s geography and climate provide an abundance of solar light and water as free natural resources. Professors Li-Chyong Chen and Kuei-Hsien Chen believe that the conversion of CO2 and water into solar fuels via solar light is an approach capable of tackling both energy and environmental issues and addressing future prospects via efficient, cost-effective solar fuel production. Several semiconductor materials have been explored for photocatalytic CO2 reduction. However, all the previously explored photocatalysts are not suitable for commercial requirements due to their low quantum efficiencies and lack of product selectivity. As a main goal for the Academic Pioneering Research Project recently awarded to Li-Chyong Chen, the team has introduced several efficient novel materials and a breakthrough idea to this artificial photosynthesis research.

Graphene oxide (GO) is an atomically thin two-dimensional (2D) carbon nanostructured oxide of graphite. The isolated oxygenated functional groups on the basal plane, with a typical C/O ratio of ~3, make GO a wide band gap semiconductor material. This sufficiently large band gap and suitable band alignment to straddle the reduction and oxidation levels of CO2 and H2O make GO a potential candidate for photocatalytic CO2 reduction. To further improve the photocatalytic activity, several methods to modify GO have been developed. Among them, Cu-nanoparticle (NP)-modified GO was successfully synthesized by a simple microwave process, and CuNP/GO possessed an order-of-magnitude enhancement in solar fuel production. More recently, the team developed an in situ carbon-doped 2D tin disulfide material (C-SnS2), wherein strain was inherently induced. Under visible light, C-SnS2 exhibited a highly effective photocatalytic activity for CO2 reduction with a photochemical quantum efficiency exceeding 0.7 %, a world-record value reported for an inorganic catalyst. The US patent application for this technology was filed earlier this year.

1. “Carbon doped tin disulphide and methods for synthesizing the same”, 2017 (US Patent filing number O104-17001US)
2. Indrajit Shown, Hsin-Cheng Hsu, Yu-Chung Chang, Chang-Hui Lin, Pradip Kumar Roy, Abhijit Gangul, Chen-Hao Wang, Jan-Kai Chang, Chih-I Wu, Li-Chyong Chen*, and Kuei-Hsien Chen*. (2014). Highly Efficient Visible Light Photocatalytic Reduction of CO2 to Hydrocarbon Fuels by Cu-Nanoparticle Decorated Graphene Oxide, Nano Letters, 14 (11), 6097–6103. DOI: 10.1021/nl503609v.
3. Hsin-Cheng Hsu, Indrajit Shown,* Hsieh-Yu Wei, Yu-Chung Chang, He-Yun Du, Yan-Gu Lin, Chi-Ang Tseng, Chen-Hao Wang,* Li-Chyong Chen, Yu-Chuan Lin and Kuei-Hsien Chen*. (2013). Graphene oxide as a promising photocatalyst for CO2 to methanol conversion, Nanoscale, 5, 262-268. DOI:10.1039/C2NR31718D.

Dr. Li-Chyong Chen
Research Fellow and Director
Center for Condensed Matter Sciences