This is a guest editorial by Suljo Linic, professor of chemical engineering at the University of Michigan, Ann Arbor.
It was my privilege to lead the American Chemical Society delegation at the 7th Chemical Sciences & Society Summit (CS3) held in Dalian, China, Sept. 5–8, 2017. The CS3 meeting series is hosted by the funding agencies and chemical societies of the U.S., Germany, China, Japan, and the U.K. CS3 brings together leading researchers from those countries to discuss how the chemical sciences can tackle some of the most daunting societal challenges and to inform agencies and policy stakeholders that could address those challenges about recent progress in emerging fields. The 2017 topic was “Solar Energy & Photonics for a Sustainable Future,” which focused on photocatalysis for water splitting, photovoltaic (PV) materials, artificial photosynthesis for CO2 reduction, photonic materials, and photon upconversion. Our goal was to assess the current state of solar energy science and technology and make recommendations about the future directions of the field. The summit attendees highlighted reducing atmospheric CO2 as one of the most critical challenges for the current generation of scientists and engineers. CO2 in the atmosphere has been increasing, recently reaching 400 ppm. This increase is leading to changes in our environment, manifested in coral reef bleaching, glacier melting, and extreme weather events.
In the area of PV development, the challenges relate to the development of less energy-intensive methods to prepare thinner silicon films without compromising the electronic quality of the material. Summit presenters saw replacing expensive components of the PV cell and boosting efficiencies by employing dual or triple absorber cells as worthy technological objectives. They also argued that manipulating light by the use of photonic devices (solar concentrators, plasmonic materials, metamaterials, and up- and downconverters) can lead to improvements in PV performance. Developing the know-how to integrate these photonic materials with conventional semiconductor PV materials should lead to further improvements in efficiency. Attendees acknowledged that chemical catalysis plays the central role in many of the proposed solutions. Scientists should put significant efforts in CO2 capture and solar water splitting to form abundant, affordable, and clean H2. Developments in these areas would open up avenues for the use of classical thermal catalytic approaches to form fuels and chemicals from CO2 and H2 via the use of conventional Fischer-Tropsch or Sabatier reactions. These approaches would not require significant changes in current infrastructure, as the nature of the end-use fuels and chemicals would not be different. Direct photochemical CO2 reduction is a longer-term, higher-risk objective because of the severe constraints on product selectivity, with the H2 evolution reaction being the critical competing reaction. A number of overarching issues cut across the above-mentioned areas. New materials should be based on abundant elements that offer stability under functioning conditions and relevant timescales. Rational and systematic integration of materials that bring different features into multifunctional operating devices is an area that will require investment and development. The summit also stressed the need for standardizing the ways in which the results of various studies are reported in terms of performance, stability, and reproducibility. Emerging computational tools are critical to increasing the rate of discovery. Over the past 15 years, we have made incredible strides in pursuit of sustainable, solar-powered technologies. These include significant increases in the efficiencies of PV devices—reaching over 20% efficiency—and water-splitting devices—reaching lab-scale solar-to-hydrogen conversion efficiency of 15%—as well as improved control over synthesis approaches that allow us to manipulate light through the use of photonic devices. The coming years will see amplified efforts in this space, eventually leading to a sustainable economy where all the required ingredients are derived from air, water, and sunlight.
Views expressed on this page are those of the author and not necessarily those of C&EN or ACS.