1st TYC workshop on energy materials

Reducing our dependency on fossil fuels is an urgent and essential step in ensuring energy security as well as preventing climate change. This requires the design and development of new materials for alternative and sustainable means of energy generation, storage, distribution and supply. As theoretically minded scientists, we are particularly interested in how theory and computation can contribute to this ambitious goal. It becomes increasingly clear that modelling will play an important role in the rational design of materials with desired properties. However, in many areas of computational research, the predictive power of existing methods is still limited. In this respect, the recent surge of funding in the Energy sector provides a great opportunity for computational scientists to improve existing methods, and to develop entirely new approaches that have the potential to significantly reduce the gap between experiments and numerical predictions.

Computational energy materials research is one of the cornerstones of the Thomas-Young Centre (TYC, http://www.thomasyoungcentre.org/). The TYC is a London-wide interdisciplinary community of research groups working to address challenges of society and industry through the theory and simulation of materials. With about 80 participating groups, and ambitious programmes of events, the TYC is a supportive community for research students and young researchers, a source of new collaborations for visiting scientists, and a long-term partner for business and government.

In September 2010, the TYC organised the first workshop on energy materials that brought together internationally leading computational and experimental scientists, across a broad area of energy materials research. Recent advances in the development of energy converting materials for a green economy—one of the scientific priorities of University College London, King's College London and Imperial College London—were presented. This special issue is a collection of papers that were presented at this workshop. It can be roughly divided into three areas: photo-induced energy conversion (Furman et al., Guo et al., Böckmann et al., Nadeem et al.), hydrogen & energy storage (Sorby et al., Shevlin et al., Liu et al.), and electrochemistry & fuel cells (Piccinin et al., Mamatkulov et al., H. Wang et al., Sun et al., Di Paola et al. and P. Wang et al.)

One way to reduce our energy demand is to make lighting more efficient, for example by use of solid state white light emitting diodes rather than fluorescent lighting sources. Furman et al. report on three novel inorganic–organic compounds as phosphor materials for solid state lighting. The efficient conversion of light to electricity is a key issue in organic solar cells. Of particular importance is the reduction of charge recombination reactions that occur at the organic–organic interface. Guo et al. propose two novel donor–acceptor co-polymers that, according to electronic structure calculations, preferentially form the charge-separated rather than the exciton-bound state upon photo-excitation. A novel multi-scale modelling approach for soft photoactive materials is presented in the perspective article of Böckmann et al. The method, bridging quantum mechanical, classical and coarse-grained simulation techniques, is applied to the light-induced phase transition in liquid crystalline azobenzene. The photo-catalytic production of hydrogen is envisaged as a viable route for providing large fractions of our future energy needs. Nadeem et al. combine experiments and density functional theory (DFT) calculations to investigate the reaction mechanism of photo-catalytic hydrogen production from ethanol adsorbed on TiO₂.

Hydrogen storage is a pressing issue in a hydrogen economy. Recently the use of metal-ammine halides combined with an ammonia decomposition catalyst was suggested as a possible hydrogen storage system. Sorby et al. report on the crystal structure and dynamics of Mg(ND₃)₆Cl₂ using powder neutron diffraction and molecular dynamics simulation. Another related class of hydrogen storage materials is investigated in the work of Shevlin et al. Using DFT calculations, the thermodynamics and reaction mechanism for dehydrogenation of metal amido-boranes is reported, showing the role of light metal as hydrogen carrier. A new strategy for designing electrodes for energy storage applications is presented by Cao et al. The authors report on the synthesis of a new sandwich-type functionalised graphene sheet-sulfur nanocomposite for rechargeable lithium-sulfur batteries. The new cathode material displays a high reversible capacity and good cycling stability.

Oxidation-reduction reactions in homogeneous or heterogeneous phases are at the heart of most energy converting processes. The efficient four-electron oxidation of water to oxygen can probably be considered as the holy grail of contemporary (photo)-electrochemistry. In their contribution, Piccinin et al. investigate the mechanism of a recently synthesised water splitting catalyst based on a tetra-ruthenium oxo-core using DFT calculations. Some of the challenges associated with the modelling of an explicit electrochemical interface are highlighted in the contribution of Mamatkulov et al. A new method for correction of the unphysical effects of the neutralising background counter charge is scrutinised using CO adsorbed on Pt(111) as a test case. The energetics for electron detachment/attachment from negatively charged/neutral transition metal clusters of Rh and Co atoms is reported by H. Wang et al. in their joint photoelectron/theoretical study.

Fuel cells are expected to play an important role in the future power supply. A major issue determining the performance of solid oxide fuel cells (SOFC) is the proton conductivity. In their contribution Sun et al. report on a new Li-based sintering additive to lower the grain boundary resistance to proton conduction in BaZr_0.8Y_0.2O_3−δ electrolytes. Proton exchange membrane fuel cells (PEMFC) are a very promising tool in automotive applications due to their low operational temperature. However, the slow oxygen reduction reaction and the high cost of Pt as a cathode material still hinder their widespread commercialisation. A possible solution is the use of bimetallic nanoparticles, thanks to their optimal surface/volume ratio. The topic has been presented in the contribution of Di Paola et al., where, by means of DFT simulations and basin hopping techniques, the alloy and size effects on O₂ chemisorption have been addressed through the comparison between the case of pure Pt and PtNi nanoparticles. Finally, departing from inorganic electrode catalysts, P. Wang et al. report on a novel simulation method for gas diffusion in a [NiFe]-hydrogenase, an enzymatic catalyst for hydrogen splitting and generation in biofuel cells.

This collection of articles should be seen as a snapshot of current experimental and computational activities in the many sub-areas of energy materials research. It was our intention to remain broad and to attract a diverse audience. Arguably, this makes our collection of papers somewhat less coherent than a themed issue on a specific sub-topic. That said, we certainly miss a contribution on dye-sensitised photovoltaic cells, which may be covered in a future TYC workshop. We hope that this collection provides some stimulation for fruitful future collaborations of computational and experimental scientists in the field.

We wish to thank all the authors for their contributions to this special Issue. We are particularly indebted to Philip Earis for giving us the opportunity to publish this collection of workshop papers in PCCP, and to Yuandi Li and the other editorial staff for the excellent coordination of the reviewing process.

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