Natural Science Foundation of China [20673091, 20433060, 20503023, 20873113, 20833005]; Mnistry of Science and Technology of China [2009CB220102, 2007DFA40890]

Platinum Metal Catalysts of High-Index Surfaces: From Single-Crystal Planes to Electrochemically Shape-Controlled Nanoparticles

Tuning reaction rates by lateral strain in a palladium monolayer.

Structural effects in electrocatalysis: oxygen reduction on platinum low index single-crystal surfaces in perchloric acid solutions

Catalytic activity of low-index platinum single-crystal faces, Pt(111), Pt(100), and Pt(110), and polycrystalline platinum toward methanol electrooxidation was enhanced by controlled amounts of electrodeposited ruthenium. Platinum surface structure affects all factors involved in the oxidation process:  (i) ruthenium coverage corresponding to the highest methanol oxidation rate, (ii) rate of oxidation current decay, (iii) Tafel slopes and reaction turnovers, and (iv) apparent activation energy. We found a unique methanol oxidation reactivity at the Pt(111) surface covered by 0.2 monolayer of ruthenium. The turnover number from such a surface at 80 °C is approximately 1 order of magnitude higher than that from the industrial platinum/ruthenium catalyst. Therefore, the Pt(111)/Ru electrode is the best laboratory scale fuel cell anode for methanol oxidation. We conclude that crystallographic variables should be exploited in syntheses of novel metal-alloy catalysts for fuel cell use.

Surface Structure Effects in Platinum/Ruthenium Methanol Oxidation Electrocatalysis

Reactivity towards methanol and formic acid electrooxidation on Pt nanoparticles with well characterised surfaces were studied and compared with the behaviour of single crystal electrodes with basal orientations. Polyoriented and preferential (100), (111) and (100)–(111) Pt nanoparticles were synthesised, cleaned preserving its surface structure, characterised and employed to evaluate the influence of the surface structure/shape of the Pt nanoparticles on these two relevant electrochemical reactions. The results pointed out that, in agreement with fundamental studies with Pt single crystal electrodes, the surface structure of the electrodes plays an important role on the reactivity of both oxidation processes, and thus the electrocatalytic properties strongly depend on the surface structure/shape of the nanoparticles, in particular on the presence of sites with (111) symmetry. These findings open the possibility of designing new and better electrocatalytic materials using decorated shape-controlled Pt nanoparticles as previously described with Pt single crystal electrodes.

Shape-dependent electrocatalysis: methanol and formic acid electrooxidation on preferentially oriented Pt nanoparticles

Studies of chemical reactions on well-defined surfaces provide fundamental data on surface reactivity and guidelines for the understanding and design of catalytic materials but few such studies have been done in electrocatalysis. We report here a study of the oxidation kinetics of HCOOH, CH3OH and CH2O on single crystal platinum electrodes with (100), (110) and (111) orientations. Pronounced dependence of the kinetics of these reactions on the crystallographic orientation of the surface has been found. The potential regions where reactions take place, the peaks of voltammetry curves, and the magnitude of currents at the peaks are different for each plane. These differences are explained on the basis of adsorption of a strongly bound intermediate, which shows a pronounced dependence on the symmetry of the single crystal planes. This intermediate completely blocks the Pt (100) surface; the smallest adsorption is at the (111) plane. On activation, the (100) surface shows the highest activity. These results suggest that electrocatalytic reactions exhibit structural sensitivity. They also provide guidelines for designing catalysts for the oxidation of small organic molecules to be used in electrochemical energy conversion.

W. E. O'Grady

Papers

Structural effects in electrocatalysis