Restructuring of an Ir(210) electrode surface by potential cycling
Summary This study addresses the electrochemical surface faceting and restructuring of Ir(210) single crystal electrodes. Cyclic voltammetry measurements and in situ scanning tunnelling microscopy are used to probe structural changes and variations in the electrochemical behaviour after potential cycling of Ir(210) in 0.1 M H2SO4. Faceted structures are obtained electrochemically as a function of time by cycling at a scanrate of 1 V·s−1 between −0.28 and 0.70 V vs SCE, i.e., between the onset of hydrogen evolution and the surface oxidation regime. The electrochemical behaviour in sulfuric acid solution is compared with that of thermally faceted Ir(210), which shows a sharp characteristic voltammetric peak for (311) facets. Structures similar to thermally-induced faceted Ir(210) are obtained electrochemically, which typically correspond to polyoriented facets at nano-pyramids. These structures grow anisotropically in a preferred direction and reach a height of about 5 nm after 4 h of cycling. The structural changes are reflected in variations of the electrocatalytic activity towards carbon monoxide adlayer oxidation.
Electrocatalysis on the nm scale
The past two decades have seen a renewed and rapidly growing interest in the fields of electrochemistry and electrocatalysis. This is on the one hand stimulated by applications in energy conversion and energy storage, where highly efficient electrochemical/electrocatalytic processes are considered to be an indispensable part of modern energy concepts based on the use of renewable energy sources. However, it is also pushed by the rapid development of modern in situ spectroscopy and microscopy tools, such as in situ vibrational spectroscopy, in situ X-ray spectroscopy/diffraction, and in situ scanning probe microscopy, just to name a few, as well as the enormous progress that has been made in the theoretical description of processes occurring at the electrochemical solid–liquid interface. The experimental methods provide, at least in principle, the opportunity to gain insight into the processes occurring at the solid–electrolyte interface on an unprecedented, atomic/molecular level. The theory has not only developed to a stage where a reliable description of complex surface structures and surface processes (at the solid–gas interface) is possible based on first-principles electronic structure theory (in particular, (periodic) density functional theory (DFT)), but it is also increasingly developing new approaches for a more realistic modeling of the electrochemical solid–liquid interface from first principles. Although there is still a long way to go, it is not unrealistic to assume that an atomic/molecular scale understanding of the elementary processes occurring at the electrochemical interface (similar to that developed for the solid–gas interface) is within reach, given the rapid progress in both theory and experiment. Furthermore, the employment of modern strategies from nanotechnology for the systematic fabrication of optimized, nanostructured electrodes and electrocatalysts sets the stage and provides the means for a systematic, knowledge-based optimization of electrochemical and electrocatalytic processes. This is unprecedented in this discipline and will hopefully allow us to satisfy the expectations from the technology side. 
 
These aspects are the topics of the present Thematic Series, “Electrocatalysis on the nm scale”. This work was initiated by and is largely based on a workshop organized by the Research Group, “Elementary Reaction Steps in Electrocatalysis: Theory meets Experiment”, which was held at Reisensburg Castle (close to Ulm, Germany) in 2013. As suggested by the name of the Research Group, the topics equally cover experiment and theory. They range from fundamental aspects of electrochemistry, such as anion adsorption [1] or potential induced restructuring of the electrode surface [2], to the presentation of new theoretical concepts, the mechanistic understanding [3], and the theoretical description of important electrocatalytic reactions, such as hydrogen evolution/water splitting [4–5] or electrocatalytic ammonia synthesis [6]. Additionally, mechanistic studies of electrocatalytic reactions, such as O2 reduction [7], CO oxidation [8] or the electrooxidation of small organic molecules [9], are presented. The potential of in situ microscopy [10] and in situ spectroscopy [8–9], in addition to electrochemical measurements for the characterization of electrode surfaces/electrocatalysts and for the mechanistic understanding of electrocatalytic reactions is illustrated. Finally, the systematic use of nanostructuring strategies is outlined, both for fundamental studies [8] and for the directed design of active and stable Pt/C fuel cell catalysts [11]. In summary, despite the limited number of contributions to this Thematic Series, it provides a broad perspective covering a variety of important topics in modern electrocatalysis research, with a clear focus on the nanoscale understanding of the relevant processes. 
 
I would like to thank all authors for their excellent contributions, as well as the referees for their valuable and prompt reports. Special thanks go to the team at the Beilstein Journal of Nanotechnology for their continuous support in the handling of this series. Finally, I would like to acknowledge the Beilstein-Institut for its support of open access policies, allowing colleagues from all over the world to freely access the contributions in this journal, as well as the financial support from the Deutsche Forschungsgemeinschaft (FOR 1376) for the initiating workshop and for part of the work. 
 
R. Jurgen Behm 
 
Ulm, March 2015
Experimental investigation of the geotechnical properties and microstructure of lime-stabilized saline soils under freeze-thaw cycling
Abstract The Song-Nen Plain in northeastern China holds one of the three largest expanses of soda saline-alkali soil in the world. Due to its disadvantageous geotechnical properties, the saline soil in this area is unable to meet the needs of construction projects. This study evaluates the stabilizing effect of adding lime to such soils. Specifically, it investigates how the physicochemical and mechanical properties and microstructure of soda saline-alkali soil are altered by lime and how these changes are affected by both freeze-thaw cycling and the duration of curing. The results reveal that adding lime to saline soil transforms clay particles into sand and silt particles and causes the pore size distribution (PSD) to become bimodal, with small-pore and macropore populations. An increase in lime content leads to an increase in the unconfined compressive strength (UCS) but a gradual decrease in both the cation exchange capacity (CEC) and plastic index. Freeze-thaw cycles break up coarse particles and aggregate finer particles, increasing the diameter of macropores and decreasing the USC; however, the effect on specimens with >9% lime is negligible. It is further shown that the geotechnical properties of the soil change immediately after the addition of lime, indicating that the cation exchange reaction takes place very quickly. Furthermore, the pozzolanic reaction leads to an increase in the percentage of sand-sized particles and a decrease in porosity after 28 days of curing. Overall, these results indicate that it is feasible to use lime to improve the engineering properties of soda saline-alkali soil in this area.