The International Journal of Energy Research (IJER) recognized early on the potential and opportunities of nanomaterials and nanotechnology for energy applications. In the past, several special issues on this theme have been published and separate papers in this category have been regularly published [1, 2]. Through improved physical and chemical properties such as increased catalytic activity, large specific surface area, or new functionalities, nanomaterials have shown their applicability for a range of energy technologies such as solar cells, batteries, hydrogen technologies, among others. Nanotechnology is becoming a standard tool to improve the performance or to reduce the cost of novel energy systems. New nano energy devices such as energy harvesting are also emerging.
While IJER has launched specific calls for papers in nanotechnology for energy in the past, this time we have chosen extended papers from the 7th International Conference on Surfaces, Coatings & Nanostructured Materials (NANOSMAT 7) which was held in Prague, The Czech Republic, in autumn 2012. A few other paper submissions of interest are also included here. The NANOSMAT conferences have traditionally included several sessions on nanomaterials for energy showing an increasing interest among the science community in this research topic. NANOSMAT conferences have been running since 2005 and due to their great success NANOSMAT-USA and NANOSMAT-Asia have been launched.
The papers in this IJER Special Issue on nanotechnology for energy applications deal with solar cells, light-emitting diodes, Li-ion batteries, hydrogen storage, fuel cells, hydrogen production, and energy harvesting. A range of different nanomaterials are also covered such as carbon nanospheres, carbon nanotubes, nanoparticles, nanocomposites, etc. Altogether 14 papers are included in the special issue. A short summary of each paper is presented in the next to introduce the readers of the journal into this special issue.
Tsai et al.  investigated CuInS2 thin film solar cells in their paper. They looked on the effects of sulfurization and the Cu/in-ratio on the film quality and morphology, which depend very much on the processing conditions. A solar cell with an efficiency of 6.29% was produced.
Pimanpang et al.  fabricated dye-sensitized solar cells on plastics and stainless steel. The stainless steel was coated with a film of TiO2 nanoparticles and the plastic was made conductive through deposition of Pt-nanoparticles. This fully flexible DSSC solar cell showed an efficiency of 2.72%.
Su et al.  used ZrO2 nanoparticles to improve the light transmission for a natural pigment-sensitized solar cell in a water-based electrolyte. The nanoparticles improved the light transmission by a factor of eight. An environmentally friendly solar cell with an efficiency of 0.688 % was produced.
Ray et al.  studied the effect of nitrogen functionalization on the structure of carbon spheres which can potentially be used for energy applications such as solar cells and capacitors.
Kasdorf et al.  investigated resonant cavity-enhanced light-emitting diodes. Their sandwiched LED design consisted of an electroluminescent liquid crystal between a Bragg mirror deposited on a silicon substrate and a semitransparent top electrode, which enhanced the maximum electroluminescence intensity by a factor of 3–4.
Abdel-Hameed et al.  investigated a crednerite glass-ceramic material (CuMnO2) for the first time as for hydrogen storage. The average gravimetric capacity was ~50 g H2/ kg (T = 573 K, P = up to 20 bar). The hydrogen adsorbed increased with increasing temperature, but a drawback is the irreversibility of the material requiring improvement of the desorption properties.
Attia et al.  used a new nanoporous polypyrrole material for hydrogen storage. The material has permanent mesopores on the surface, internal pores, and pockets with sponge-like structures. The maximum reversible hydrogen adsorption capacity was 2.2 wt.% at 77 K.
Koultoukis et al.  studied high-temperature activated AB2 nanopowders for metal hydride hydrogen compression. The hysteresis in the absorption-desorption cycle was negligible. The maximum pressure in the measurements was 100 bar, but the alloy should enable values even above 150 bar.
Three papers dealt with Li-ion batteries discussing the electrode structure with different nanostructures. Guler et al.  produced a multiwall carbon nanotube (MWCNT) based buckypaper via vacuum filtration and coated the paper with tin oxide. The resulting structure was used as anode for a Li-ion battery. Cevher et al.  employed a nanocomposite substrate for an anode consisting of a SnO2:Sb coating on Cr-coated stainless steel and multiwall carbon nanotube (MWCNT). The nanocomposites showed reversible discharge capacities of 701-753 mAh g−1 after 100 cycles. Guler & Akbulut et al.  synthesized nanocrystalline LiMn2O4 cathode materials by a facile sol–gel method and alloyed these mechanically with MWCNTs. Compared with bare LiMn2O4, a composite cathode material with MWCNT (15.0 wt.%)/LiMn2O4 (85.0 wt.%) shows enhanced specific capacity of 136.5 mAh g−1 and improved cycling stability.
Abbas et al.  studied a low-temperature solid oxide fuel cell employing a Zn-based nanostructured Ba0.05Cu0.25Fe0.10Zn0.60O (BCFZ) oxide electrode material. The cell was fabricated by sandwiching a NK-CDC electrolyte between BCFZ electrodes. A maximum power density of 741.87 mW cm−2 was achieved at 550°C.
Raza et al.  synthezied a nanocomposite Zr/Sm-co-doped ceria electrolyte coated with K2CO3/Na2CO3 for a solid oxide fuel cell. The fuel cell power density with this material is 700 mWcm-2 and an open-circuit voltage of 1.00 V is achieved at low temperatures (400–550°C).
Kwon et al.  demonstrated an energy harvesting system using reverse electrodialysis with nanoporous polycarbonate track-etch membranes. In this technique electrical energy is converted from the concentration gradient between a concentrated and a diluted solution.
Finally, we would like to extend our thanks to the authors for their valuable contributions to the Special Issue on Nano Energy Technologies.