Electrified surface chemistry

Chemistry at interfaces became of significant importance in the early 20th century with the start of the large-scale industrial production of ammonia in 1913 using a multi-component iron-based catalyst developed by A. Mittasch et al. (1910). Almost one hundred years ago (1911) another milestone was the foundation of the Kaiser-Wilhelm Institut für Physikalische Chemie und Elektrochemie, now the Fritz-Haber-Institut der Max-Planck-Gesellschaft.

The synthesis of ammonia from the elements, which started out with a production capacity of roughly 1000 tons per year in a single plant, now takes place world-wide on a scale of well over 100 million t annum⁻¹. While most ammonia is used to produce fertilizer, it also forms the basis of practically all nitrogen-containing chemical products. The market for catalysts continues to expand, not only in the chemical and petroleum industry, but also in pollution control (such as automotive exhaust systems). Electrochemistry plays a key role in a number of applications such as the production of chemicals (chlorine, aluminium), corrosion control, galvanization, but the hottest topic these days is the production and storage of electrical energy in fuel cells and batteries. The direct conversion of chemical into electrical energy and vice versa offers significantly higher efficiency than conventional power sources (heat engines). While solid oxide fuel cells combined with a gas turbine can already achieve about 90% conversion, there is still a lot of room for improvement of low-temperature fuel cells, where the high overvoltages for oxidation of small organic molecules and above all oxygen reduction severely limit performance.

Chemical reactions at interfaces thus play a crucial role for food production, pollution control and energy conversion, which are probably the most important problems facing the still increasing world population. A determined world-wide scientific effort will be necessary to provide answers to these pressing issues. Understanding interface reactions and the controlled manufacture and optimization of (electro)catalysts is therefore expected to be one of the key technologies of this century.

This Themed Issue of PCCP grew out of the First Ertl Symposium on Electrochemistry and Catalysis, held at the Gwangju Institute of Science and Technology (GIST) in S. Korea in April 2010 to celebrate the foundation of the Ertl Center for Electrochemistry and Catalysis at GIST in 2009. The objective of this center, as well as the meeting, is to bring together scientists working on different aspects of interfacial chemistry, in particular to encourage and enhance the cooperation and cross-fertilisation between basic research and technological applications. Consequently the topics range from basic studies to the development of specific applications.

Heterogeneous catalysis can still offer surprises as shown in the review by Kim et al. (DOI: 10.1039/c0cp00467g). While gold was for a long time regarded as inactive, very small Au clusters exhibit very interesting catalytic properties (in contrast e.g. to Pt where bulk properties are responsible for the activity). The authors describe how the catalytic properties can vary on an atom-to-atom basis using mass-selected Au clusters.

While the (electro)chemical properties of soft interfaces are of utmost importance in biology (such as in the physiology of excitable cells), such interfaces can also be used for molecular electrocatalysis as described in the review article by Girault et al. (DOI: 10.1039/c0cp00590h): with a molecular catalyst at the interface, electron acceptor and donor can be fed into the hydrophilic and lipophilic phase, respectively. Liquid/gel interfaces can also be used as sensors as exemplified in the paper by Lee et al. (DOI: 10.1039/c0cp00750a). Interfaces between immiscible electrolytes form a simplified, yet successful model system for biological membranes and can therefore be used for the characterization of biomolecules (DOI: 10.1039/c0cp00751j).

In electrochemistry the use of well-defined single crystal electrodes continues to be important for a thorough understanding of the elementary steps of reactions such as adsorption of H and OH (DOI: 10.1039/c0cp00104j and DOI 10.1039/c0cp00659a) or sulfate (DOI: 10.1039/c0cp00860e), but also the evolution of hydrogen (DOI: 10.1039/c0cp00780c). The electro-oxidation of small organic molecules (and CO) poses interesting and important challenges for mechanistic studies, not only for an identification of the active sites (in particular on multi-component material) (DOI: 10.1039/c0cp00593b and DOI: 10.1039/c0cp00394h), but also for an understanding of complex kinetics (DOI: 10.1039/c002574g). Obviously such studies are of fundamental importance for the use of organic molecules in fuel cells, which leads to the next topic, namely the improvement of the performance of the latter. Currently a large number of groups worldwide are working on various aspects in this field, such as the development of better, cheaper and more abundant (i.e. non-noble) electrode materials, improved support, better membranes and optimization of the membrane electrode assembly in direct membrane fuel cells (DMFC) and polymer electrolyte membrane fuel cells (PEMFC) (DOI: 10.1039/c0cp00609b, DOI: 10.1039/c0cp00698j, DOI: 10.1039/c0cp00767f, DOI: 10.1039/c0cp00370k and DOI: 10.1039/c0cp00662a).

One of the biggest challenges in electrochemistry remains the understanding and control of multi-step processes, which typically require a high overvoltage (and corresponding loss of efficiency) due to the difficulty of achieving a comparable (and low) activation energy of all elementary processes on a single electrode. The reactions most studied in this context are water splitting (oxygen evolution) and the oxygen reduction reaction (ORR), crucial for a high performance of fuel cells (DOI: 10.1039/c0cp00104j, DOI: 10.1039/c0cp00609b and DOI: 10.1039/c0cp00698j,). A solution to this problem will most likely involve basic research (such as measurement of the binding energies of O-species on various sites) and the manufacture and testing of new multi-component materials which offer different active sites.

Besides topics related to fuel cells, electrochemistry offers a large variety of other important applications only a few of which are treated in the current issue. Of great current interest is the production (DOI: 10.1039/c0cp00586j) and performance enhancement (DOI: 10.1039/c0cp01754j) of solar cells. The production of sol–gel films with tunable physicochemical properties (DOI: 10.1039/c0cp00601g) provides valuable tools for biomedical applications. A special application of electrodeposited nanowires for thermoelectric use is treated in (DOI: 10.1039/c0cp00749h).

A number of the mentioned studies put emphasis on the support of the (electro)catalyst which can in most cases not be regarded as inert carrier material, but can have significant influence on the activity.

A recurring theme in both electrochemistry and heterogeneous catalysis is the emphasis on the nanostructure of the materials. The last few decades have seen ever improving techniques of the production, control and characterization of nanostructured (electro)catalysts, using stepped or doped surfaces as model systems (DOI: 10.1039/c0cp00104j and DOI: 10.1039/c0cp00780c), nanoparticles (DOI: 10.1039/c0cp00467g and DOI: 10.1039/c0cp00593b), small carbon particles (DOI: 10.1039/c0cp00593b, DOI: 10.1039/c0cp00609b and DOI: 10.1039/c0cp00698j), nanopores (DOI: 10.1039/c0cp01754j and DOI: 10.1039/c0cp00749h) as well as multi-component nanostructures and defects (DOI: 10.1039/c0cp00394h). A thorough understanding of the active sites is particularly important for processes in which several different steps are to take place on the same surface. The mentioned studies offer the hope that instead of systematically testing very large numbers of multi-component systems, we will soon be able to tailor catalysts for specific purposes. Control of the nanostructures should enable the manufacture of different active sites in very close vicinity, and possibly solve the problem of multi-electrode transfer (such as oxygen reduction).

Finally, we express our deep gratitude to all contributors to the First Ertl Symposium, to the members of the Ertl Center and above all to all authors who submitted their work to the current Themed Issue of PCCP.

We also thank the staff of the journal for their help and patience.

Jaeyoung Lee, Ertl Center for Electrochemistry and Catalysis, GIST, Gwangju, Korea

Markus Eiswirth, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany

Table 1

Category	Papers in this issue	Description
a This article can be found in issue 42 of vol. 12 (2010). This issue can be found from the PCCP homepage http://www.rsc.org/pccp.
Heterogeneous catalysis and soft interfaces	D.-C. Lim et al. (DOI: 10.1039/c0cp00467g)	Au nanoparticles (Perspective)
	M. A. Méndez et al. (DOI: 10.1039/c0cp00590h)	Electrocatalysis at soft interfaces (Perspective)
	S. N. Faisal et al. (DOI: 10.1039/c0cp00750a)	Proton sensors with liquid/gel interface
	J. A. Ribeiro et al. (DOI: 10.1039/c0cp00751j)	Biomolecules at water/dichlorohexane interface
Basic electrochemistry	K. J. P. Schouten et al. (DOI: 10.1039/c0cp00104j)	H and OH adsorption on Pt single crystals
	H. Matsushima et al. (DOI: 10.1039/c0cp00659a)^a	H-induced reconstruction of Cu(100)
	Z. Su et al. (DOI: 10.1039/c0cp00860e)	IR study of (Bi)sulphate adsorption on Pt(111)
	J. Schäfer and L. A. Kibler (DOI: 10.1039/c0cp00780c)	Hydrogen evolution Pd in Au(111)
	P. S. Ruvinskiy et al. (DOI: 10.1039/c0cp00593b)	CO oxidation on Pt nanoparticles
	A. Ko et al. (DOI: 10.1039/c0cp00394h)	Nanostructured electrodes for methanol oxidation
	E. Sitta et al. (DOI: 10.1039/c002574g)	Complex kinetics of glycol oxidation
Applied electrochemistry	F. Hasché et al. (DOI: 10.1039/c0cp00609b)	ORR of Pt on carbon nanotubes
	J.-H. Kim and J.-S. Yu (DOI: 10.1039/c0cp00698j)	Hollow carbon capsules in PEMFC, ORR
	J.-S Yu et al. (DOI: 10.1039/c0cp00767f)	Methanol fuel cell with non-noble metals
	J. H. Liu et al. (DOI: 10.1039/c0cp00370k)	Optimization of all components in fuel cells
	S.-J. Seo et al. (DOI: 10.1039/c0cp00662a)	Impedance study in membrane electrode assembly
	S. J. Yoo et al. (DOI: 10.1039/c0cp00737d)	Multilayered Pt/Ru nanorods for methanol oxidation
	M. Harati et al. (DOI: 10.1039/c0cp00586j)	CIGS films for solar cells
	H. Choi et al. (DOI: 10.1039/c0cp01754j)	Nanoporous titania solar cells
	R. Okner et al. (DOI: 10.1039/c0cp00601g)	Sol-gel films for biomedical implants
	J. M. Lee et al. (DOI: 10.1039/c0cp00749h)	Electrodeposited thermoelectric nanowires

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