Harvesting renewable energy with chemistry

Worldwide efforts to decouple energy and production from fossil fuel consumption have lead to an increasing instalment of energy systems based on renewable resources.¹ Renewable energies are becoming available, yet their deployment in current infrastructures presents significant challenges.

Renewable energies are diverse in nature, characterized by the strongly fluctuating availability of primary energy sources as well as large regional differences. This imposes major challenges on the flexibility and storage capacity of the energy grid as well as the efficiency of the distribution system. At the same time, integrating renewable energies also opens novel opportunities for energy intensive production industries, if they can react in an adaptive way to the availability of “surplus” energy at peak times.

The chemical sector, in particular, might take advantage of such scenarios, as the chemical bond is probably the most fundamental pivot between the energy and materials worlds.² Key vector molecules such as H₂ and CO₂ can be combined through chemo- or biocatalytic transformations for the synthesis of products ranging from simple hydrocarbons to complex biologically-active structures.^3,4 Exploiting the synthetic power of nature in photosynthesis can help to provide additional building blocks from biomass for tailor-made products or fuels.⁵ The direct use of green electrons opens new routes and disruptive technologies for chemical production.⁶ We believe that the direct, selective routes from renewable energies to targeted added-value chemicals are a crucial token of the necessary paradigm shift, providing attractive harvesting technology towards the “defossilization” of the anthropogenic value chain.

The contributions in this special issue highlight recent developments and innovative concepts that illustrate the challenges and opportunities resulting from new degrees of freedom at the interface between the renewable energy and chemical sectors. Future directions related to the conversion of solar energy into hydrogen will be presented in contributions by the groups of Bonchio, Fornasiero, Misawa, Neese, and Saracco. The inter-conversion of CO₂ and H₂ to C1 chemicals and energy vectors is discussed in the papers of Laurenczy and Prechtl. Using CO₂ as a carbon source for electrocatalytic transformations is featured in the contributions from Saracco, and Centi and Perathoner, and its photocatalytic reduction is considered in the paper by Beller. The necessity to explore the interface with biomass-derived (by)products and their role in this energy-driven scenario is explicitly treated in contributions by Palkovits, Pérez-Ramirez, and Poliakoff. Finally, thermal storage systems for solar energy will be discussed from a green chemistry and engineering perspective in the paper of Maravelias.

In summary, we are most grateful to the authors of this Green Chemistry collection to showcase representative examples for current molecular approaches in this important field. We hope that this will help to define the state of the art in research, to identify future directions, and to stimulate the creativity of many scientists in one core area of green chemistry: contributing to the transition towards a closed anthropogenic carbon cycle.

References

1. International Renewable Energy Agency (IRENA), REmap: Roadmap for A Renewable Energy Future, 2016 edition, IRENA, Abu Dhabi, 2016. http://www.irena.org/DocumentDownloads/Publications/IRENA_REmap_2016_edition_report.pdf, accessed April 10th, 2017.
2. (a) Chemical Energy Storage, ed. R. Schlögl, Walter de Gruyter GmbH, Berlin/Boston, 2013; (b) R. Schlögl, Angew. Chem., Int. Ed., 2015, 54, 4436–4439.
3. (a) J. Klankermayer and W. Leitner, Harnessing renewable energy with CO₂ for the chemical value chain: challenges and opportunities for catalysis, Philos. Trans. R. Soc. London, Ser. A, 2016, 20150315,  DOI:10.1098/rsta.2015.0315; (b) J. Klankermayer, S. Wesselbaum, K. Beydoun and W. Leitner, Angew. Chem., Int. Ed., 2016, 55, 7296–7343.
4. G. Centi, E. A. Quadrelli and S. Perathoner, Catalysis for CO₂ conversion to introduce renewable energy in the value chain of chemical industries, Energy Environ. Sci., 2013, 6, 1711–1731.
5. W. Leitner, J. Klankermayer, S. Pischinger, H. Pitsch and K. Kohse-Höinghaus, Advanced Biofuels and Beyond: Chemistry Solutions for Propulsion and Production, Angew. Chem., Int. Ed., 2017, 56 DOI:10.1002/anie.201607257 , available online.
6. E. A. Quadrelli, Green Chem., 2016, 18, 328.

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