text: A variety of nanoparticle materials have been demonstrated to promote various electrochemical reactions, although none have been commercialized. These catalysts can be tuned with respect to their size and shape, as well as the surface strain.
  Also, higher reaction rates can be achieved by precisely controlling the arrangement of surface atoms: indeed, in nanometric systems, the number of available reaction sites is a better parameter than the exposed surface area in order to estimate electrocatalytic activity. Sites are the positions where the reaction could take place; the likelihood of a reaction to occur in a certain site depends on the electronic structure of the catalyst, which determines the adsorption energy of the reactants together with many other variables not yet fully clarified.
  According to the TSK model, the catalyst surface atoms can be classified as terrace, step or kink atoms according to their position, each characterized by a different coordination number. In principle, atoms with lower coordination number (kinks and defects) tend to be more reactive and therefore adsorb the reactants more easily: this may promote kinetics but could also depress it if the adsorbing species isn't the reactant, thus inactivating the catalyst. Advances in nanotechnology make it possible to surface engineer the catalyst so that just some desired crystal planes are exposed to reactants, maximizing the number of effective reaction sites for the desired reaction.
  To date, a generalized surface dependence mechanism cannot be formulated since every surface effect is strongly reaction-specific. A few classifications of reactions based on their surface dependence have been proposed but there are still many exceptions that do not fall into them.