Inorganic chemistry for renewable energy conversion and storage

The supply of readily available and inexpensive energy is becoming a significant issue for humanity, concerning both environmental sustainability and the world economy in terms of available natural resources. The future lines of development of both factors will profoundly affect the life of you, me and everybody else. Thus, the identification of reliable, inexpensive and available techniques for renewable energy conversion is one of the challenges facing humanity. Unfortunately, the mere existence of a readily available and inexpensive source of energy, such as fossil fuels, retards the development of alternatives, although the long-term effects of today's dependence on fossil fuels appear to be grim. Thus, any source of renewable energy conversion must also be able to take up the cost challenge of existing techniques in order to offer not only an environmentally benign alternative, but also an economically feasible and competitive one.

Closely associated with the challenge of renewable energy conversion is the challenge of energy storage, since most renewable energy sources produce energy in a non-continuous way, possibly with the exception of geothermal energy. Thus, direct or indirect energy conversion by wind, waves, tides, solar radiation etc. requires both energy buffering and intermittent energy storage methods that allow multiple, high efficiency, energy conversion steps.

The energy conversion and storage challenges fundamentally represent a knowledge and materials challenge; we need to know how to do it and to identify materials that can meet the demands required. At the centre of such efforts you find inorganic chemistry, both with respect to fundamental knowledge and new materials and molecular coordination entities, such as catalysts or the building blocks of materials. In addition, its links to other scientific areas, in particular physical, surface and organic chemistry, are of profound importance. The related field of “Contributions of inorganic chemistry to energy research” was the topic of a themed issue in Dalton Transactions in 2011. This current themed issue, devoted to renewable energy conversion and storage, embraces just over 20 contributions to the diverse field of renewable energy.

In the contributions to this themed issue, the solar alternative receives significant attention, highlighting components in both dye-sensitized solar cells (DSSCs) and catalysts for photoreactions and solar fuel production. The papers communicate fundamental understanding regarding both surface adsorption (Gray and co-workers, DOI: 10.1039/c4dt01149j), and the photochemistry of sensitizers (Gorun, Van Doorslaer, and co-workers, DOI: 10.1039/c4dt00621f) and devices (De and co-workers, DOI: 10.1039/c4dt01926a). New ruthenium-based sensitizers for dye-sensitized solar cells are presented in two articles (Kong, Malapaka and co-workers, DOI: 10.1039/c4dt01598c; Nazeeruddin, Torres and co-workers, DOI: 10.1039/c4dt01357c). Also, quantum-dot-sensitized DSSCs are discussed (Pan, Zhu and co-workers, DOI: 10.1039/c4dt01276c). Photocatalysis and the usage of catalysts for small-molecule activation with the ambition to form solar fuels are closely related fields of research. In this issue nanoparticles as co-catalysts in photocatalysis are discussed (Besenbacher, Hutchings and co-workers, DOI: 10.1039/c4dt01309c), as well as catalysts for carbon dioxide reduction (Ott and co-workers, DOI: 10.1039/c4dt01591f) and water oxidation (La Ganga, Natali, Licciardello, Campagna and co-workers, DOI: 10.1039/c4dt01785d).

In terms of energy storage, two devices dominate the contributions to this issue; lithium-ion batteries and fuel cells. The papers on lithium-ion batteries focus on electrode materials of quite different types. The materials investigated involve silicates (Bresser, Passerini and co-workers, DOI: 10.1039/c4dt01325e), manganates (Brummerstedt Iversen and co-workers, DOI: 10.1039/c4dt01307g), carbon materials (Pan and co-workers, DOI: 10.1039/c4dt01223b), and germanide-based materials (Fässler and co-workers, DOI: 10.1039/c4dt00743c). The fuel cell work involves several different aspects, such as carbon electrode materials and their potential use in other electrochemical devices (Chattopadhyay and co-workers, DOI: 10.1039/c4dt01258e), the effects of perovskite-based catalysts (Staniforth and co-workers, DOI: 10.1039/c4dt01288g), and proton conduction in electrolyte materials (Rahman and co-workers, DOI: 10.1039/c4dt01280Aa). It is notable that the combination of materials for many devices of interest to energy conversion and storage can also be modified to operate in the ‘opposite’ direction. For instance, solar cells can be run in reverse mode by modification of the materials and their combination for light-emitting devices (LEDs) or light-emitting electrochemical devices (LEEDs), both which have significant importance with respect to energy housekeeping. Likewise, fuel cells can be operated in reverse mode as electrolyser cells, converting, for instance, excess energy from renewable sources into energy-rich substances to be re-converted to electricity at a later stage. One contribution to this issue focuses on the ageing of the electrolyte in such devices (Kiebach and co-workers, DOI: 10.1039/c4dt01053a).

Finally, the themed issue contains four contributions with a clear materials emphasis, three of which are directed towards thermoelectrical materials based on silicides and their composites with carbon nanotubes (Kleinke and co-workers, DOI: 10.1039/c4dt01177e; Gascoin and co-workers, DOI: 10.1039/c4dt01441c) and borocarbides (Mori and co-workers, DOI: 10.1039/c4dt01303d). In addition, one article describes superconducting materials, having implicit importance in the storage aspects of energy, in the iron–arsenide family of materials (Saparov and Sefat, DOI: 10.1039/c4dt01068j).

In summary, the themed issue on renewable energy conversion and storage highlights several areas where inorganic chemistry, involving both new knowledge, and potential coordination compounds and materials for energy applications, has a central and important role to play. Enjoy the reading!

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