Chemistry, a science often unloved in France, plays a key role in most energy sectors. On the occasion of the International Year of Chemistry in 2011, chemists have identified the themes that will structure the chemical research in the next ten years and are all important for energy. In the vast field of energy transition, chemistry is working on five fronts : – the relationship between the properties (eg  electrical conductivity) and structures of materials (including battery electrodes) – synthesis of materials to find new properties or to improve their performance (this is the case for solar cells ) – the kinetics of reactions via catalysis (to produce hydrogen for example) – the alliance with biology for the synthesis of genomes of bacteria or algae from nucleotides (to produce biofuels) – new reactions using less energy or to extract materials by recycling rare earths or nuclear fuels (to extract plutonium from  nuclear fuels, for example) .

If we limit ourselves to renewable energy and energy storage, recent literature illustrates the potential of chemistry. As far as the solar photovoltaic electricity production is concerned, the lowering the cost of cells and finding new materials with good yields (for most of silicon cells it is in a range between 15% and 20%) are priorities. Materials chemistry has recently offered a new solution with a semiconductor of the perovskite family materials (usually metal oxides) which is an organometallic compound of an halogen (chlorine, bromine or iodine) and a metal such as lead or tin realized by vapor deposition on a support (M. Liu et al. « Efficient perovskite planar heterojunction solar cells by vapor deposition » Nature, vol. 501, p. 395, 19 September 2013, www.nature.com ). The efficiency of these cells is 15% which deliver a higher voltage than silicon cells. It is a new technology that is being tested with the advantage of being easy to use possibly in tandem with silicon because they do not absorb the same photons. Plastic materials which are semiconductors (such as trans-polyacetylene) are another area for cells with an efficiency which presently does not exceed 10 %, but their cost is far lower than that of silicon. A major objective is to increase the mobility of electrons in these materials in order to raise their performance (by avoiding, for example the presence of microcrystals or aggregates in the material with long-chain polymers), polythiophenes (containing sulfur) which are long rigid chains may also open interesting perspectives ( R.A. Street  » Unraveling load transportation in conjugated polymers, » Science , vol. 341, p. 1072, 6 September 2013, www.sciencemag.org). The light-emitting diode (LED) usually made ​​of electroluminescent semiconductor material are very interesting from the energy point of view (their light output is very high), and again plastic materials offer interesting perspectives, such as superposed layers of plastic semiconductors constituting diodes emitting white light which would be a considerable advantage (C.Groves  » Bright design, » Nature Materials, vol. 12, p. 597, July 2013).

Structures of materials (electrodes and electrolyte) play also an important role in batteries and fuel cells. This is the case for lithium-ion batteries which are a recent breakthrough (for electric vehicles or the « mass » storage for intermittent electricity sources). Materials chemistry, again, should improve the performance of electrochemical batteries, especially their energy density and their ability to undergo numerous cycles of charge and discharge. One possibility on which chemists are working is to develop new structures of oxides layers in which lithium ions will be inserted, a new generation of lithium oxides and manganese, cobalt and nickel (or a lithium oxide of ruthenium and tin) and provides an interesting perspective (M. Shatiya  » Reversible anionic redox chemistry in high – capacity layered oxide electrodes », Nature Materials ,vol. 12, p. 827, September 2013, www.nature.com/naturematerials). Other types of batteries might be envisaged with performance higher than those with lithium-ion: the oxygen – metal systems (oxygen forms an oxide during discharge which is decomposed when charging) as couples like lithium-air, zinc-air, or a super- oxide sodium, the couple lithium-sulfur might be also a good candidate for large storage capacity of electricity (energy density being five times higher than current lithium-ion batteries). Carbon chemistry probably has not said its last word in the field of batteries (the anodes of several battery systems are made of graphite) or solar cells. Graphene consists of monoatomic carbon layers, it is a very light porous material and an excellent conductor that could be used to produce electrodes for lithium / air batteries, we might achieve the same performance with a fullerene cage electrode constituted by sixty carbon atom, which is a kind of anchor to which a lithium ion is attached. Superimposed layers of graphene and of transition metals compounds such as molybdenum, are possible candidates for solar cells but until now the yields obtained are rather low.

The rate of chemical reactions is often a key point in the operation of energy systems. This is particularly the case for hydrogen fuel cell electric motors that operate at room temperature but using platinum as a catalyst (it accelerates hydrogen oxidation at the anode) and chemistry has to be mobilized to find an alternative to platinum group metals, which are expensive, organic alternatives may be of interest (eg phthalocyanine with cobalt or iron) . Meanwhile the issue of hydrogen production remains open (presently it is realized via water electrolysis or thermochemical process from natural gas). An alternative to natural gas is methanol, the simplest alcohol, with which one can produce hydrogen using a catalyst such as an organic ruthenium compound. Photochemistry, using solar electricity to split water vapor (as plants are doing) is a possibility, but again you need a good catalyst (molybdenum and tin are possible candidates as well as organic compounds). A Swiss laboratory of EPFL in Lausanne showed that one could get very good yields with photoelectrodes consisting of iron oxide nanoparticles. The alternative is to use solar heat in an oven for example, a U.S. laboratory has recently developed a new catalyst consisting of a manganese oxide to decompose water vapor and working within a cycle 1000-1400 ° C (C.L. Muhich and al., « Efficient generation of H2 by splitting water with an isothermal cycle, » Science, vol.341, p. 540, 2 August 2013, www.sciencemag.org) .

Chemistry is involved in other energy sectors. An alliance with biology, including synthetic « biology », can open interesting perspectives to produce biofuel either from biomass (cellulose, for example) or from genetically modified microorganisms. The production of simple alkanes by engineered bacteria was thus reported recently by two Korean laboratories(Y.J. Choi, S.Y.Lee, “Microbial production of short-chain alkanes, Nature, Vol. 502, p; 571, 24 October 2013, www.nature.com ) Similarly, metal recycling (effective for platinum) in particular rare earths (dysprosium magnets constituting the wind turbines and electric motors of hybrid cars being one of them) would be crucial.

Finally, in our penultimate blog we reported a possible breakthrough : the use of a new kind of titanium catalyst for reacting hydrogen with nitrogen at room temperature and ordinary pressure, a possible step towards a synthesis of ammonia consuming much less energy (now between 1% to 2% of world energy consumption). Chemistry, often underestimated by strategies for energy research, is a critical point for several energy transition routes.