•Platinum Metals Rev., 2011, 55, (3), 175–179• 9th International Frumkin Symposium “Electrochemical Technologies and Materials for 21st Century” doi:10.1595/147106711X579074 http://www.platinummetalsreview.com/ Reviewed by Alexey Danilov Introduction A. N. Frumkin Institute of Physical Chemistry and The 9th International Frumkin Symposium was held Electrochemistry of the Russian Academy of Sciences, at the Conference Hall of the Russian Academy of Moscow, Russia Sciences in Moscow, Russia, between 24th–29th Email: [email protected] October 2010. The event was organised jointly by the A. N. Frumkin Institute of Physical Chemistry and Elec- trochemistry of the Russian Academy of Sciences (IPCE RAS) and the Chemical Department of Lomono- sov Moscow State University. The Symposium was sponsored by the Russian Academy of Sciences and the International Society of Electrochemistry. The fi rst symposium of this series, held in 1979, was dedicated to the memory of Russian electrochemist Alexander Frumkin (1895–1976). Since then, the Sym- posia have been held every 3–5 years to discuss cur- rent understanding of fundamental electrochemistry and its applications. The 9th Frumkin Symposium included 4 plenary lectures, 112 oral and 131 poster presentations. Scien- tists from the Russian Federation, Ukraine, Belarus, the USA, Canada, Austria, the UK, Germany, Spain, Denmark, Poland, Serbia, Switzerland, Finland, France, Italy, Iran and Taiwan took part in fi ve ‘microsympo- sia’ which made up the conference, including ‘Electri- cal Double Layer and Electrochemical Kinetics’, ‘New Processes, Materials and Devices for Successful Elec- trochemical Transformation of Energy’, ‘Corrosion and Protection of Materials’, ‘Electroactive Composi- tion Materials’ and ‘Bioelectrochemistry’. Platinum group metals (pgms) are widely used by electrochemists as electrode materials for studies of adsorption, nucleation, electrodeposition, electro- catalytic reactions and many other electrochemical processes used in applications such as fuel cells. About 30 presentations focused on pgm studies at the Symposium. This short review highlights a selection of the work presented. Electrochemistry of PGM Single Crystals The Symposium was opened with a plenary lecture by Juan Feliu (University of Alicante, Spain). He dis- cussed models for the estimation of potential zero 175 © 2011 Johnson Matthey doi:10.1595/147106711X579074 •Platinum Metals Rev., 2011, 55, (3)• total charge (pztc) and potential zero free charge The main problem in carbon monoxide displace- (pzfc), experimental results on anion adsorption and ment experiments (3) is oxygen interference. Without displacement of the adsorbed species by carbon this, the pztc and the pzfc almost coincide at 0.37 V vs. monoxide and the thermodynamic analysis of the reversible hydrogen electrode (RHE) for the Pt(111) temperature dependence of interfacial properties of electrode. The potential of the maximum entropy of platinum single crystal electrodes (basal faces and double layer formation, obtained from laser pulsed stepped surfaces). experiments, also coincides with this value (4). The For the three basal planes of Pt, both the entropy results of CO displacement experiments for stepped of formation of the interface and the entropy of surfaces Pt(S)[n(111) (111)] (n atomic width (111) adsorbed hydrogen and hydroxyl species are struc- terraces separated by parallel steps of monoatomic ture sensitive magnitudes. These results can be ana- height with (111) orientation) are shown in Figure 1. lysed using statistical thermodynamic calculations, It can be seen that an increase in the step density revealing that adsorbed hydrogen is rather mobile leads to a negative shift in the pztc. on Pt(111) and Pt(100), while adsorbed hydroxyl is Several reports by Alexey Danilov and colleagues rather immobile. Interestingly, adsorbed hydrogen on (IPCE RAS and University of Alicante) were devoted Pt(110) is rather immobile at low coverages but to the kinetics and mechanism of nitrate anion reduc- becomes very mobile at near saturation coverage. tion on Pt single crystals and copper modifi ed elec- Using cyclic voltammetry (CV), it has also been shown trodes (5, 6). Modifi cation of the Pt surface with Cu that some anions are not adsorbed on Pt. For instance, adatoms or a small amount of 3D Cu crystallites was trifl uoromethane sulfonic acid and perchloric acid performed using potential cycling in solutions with a both show the same voltammetry on basal plane low concentration of Cu2 ions. This allowed the sur- electrodes and no adsorbate bands were observed face coverage of Cu, Cu, to be varied smoothly. It was by spectroscopy (2). also found that nitrate reduction in sulfuric acid 200 200 j, Pt(n n n–2) Pt(10 10 9) Pt(554) Pt(S)[n(111) (111)] 100 n = 20 n = 10 150 –2 Pt(S)[(n–1)(111) (110)] 0 100 A cm C cm Pt(775) –2 –100 50 j, –200 0 0.2 0.4 0.6 0.8 0.2 0.4 0.6 0.8 Pt(775) Pt(221) 100 150 q, n = 7 n = 4 –2 A cm C cm 0 100 –2 –100 50 –200 0 q, 0.2 0.4 0.6 0.8 0.2 0.4 0.6 0.8 E, vs. RHE E, vs. RHE Fig.1. Potential dependences of total charge and positive-going sweeps of cyclic voltammograms for stepped surfaces of platinum single crystals (Courtesy of Professor Juan Feliu) 176 © 2011 Johnson Matthey doi:10.1595/147106711X579074 •Platinum Metals Rev., 2011, 55, (3)• solutions at E 0.05 V on Cu modifi ed electrodes was surface than for the disordered surface. This differ- hindered due to enhanced adsorption of sulfate ani- ence was attributed to the blocking of surface defect ons on a positively charged Cu adlayer. The effect sites by (bi)sulfate anions. However, at a low Cu con- was less pronounced for the Pt(100) surface where centration in the solution (1.2 106 M), the adsorption sulfate adsorption was weaker. of Cu adatoms occurred at lower potentials, where the In perchloric acid solutions, a strong catalytic effect interaction of anions with the Pt surface was weaker. In was observed at low potentials, due to induced this case the defects act as the preferential adsorption adsorption of nitrate anions. Nitrate reduction on Cu sites for UPD Cu. The Cu UPD process seems to be modifi ed electrodes was much faster as compared more sensitive to crystalline defects in the Pt(100) sur- to pure Pt; the current density was higher by 2 to 4 face than CO electrooxidation, and can be used as a orders of magnitude. Structure-sensitive competitive monitoring reaction to estimate the degree of order- adsorption of background electrolyte and nitrate ani- ing of a Pt(100) surface. ons largely determined the kinetics of nitrate reduc- tion both on the faces of Pt single crystals and on the PGMs as Electrocatalysts epitaxial 2D and 3D deposits of Cu. The maximal rate Jean-Pol Dodelet (National Research Institute of of the process was observed for the Cu modifi ed Energy, Materials and Telecommunications, Varennes, Pt(100) electrodes. The origin of intermediate prod- Canada) in his plenary lecture compared the behav- ucts of the nitrate reduction was discussed on the iour of platinum- and iron-based electrocatalysts basis of CV and Fourier transform infrared (FTIR) for the reduction of oxygen in proton exchange spectroscopy data. membrane (PEM) fuel cells. The catalytic activity of Results of electrochemical and in situ scanning new Fe/N/C electrocatalysts (Figure 2) was signifi - tunneling microscopy (STM) studies of the Pt(100) cantly improved by using a new synthesis procedure surface structure as dependent on the cooling atmos- (10). Cell current densities were comparable to those phere after fl ame annealing were presented by Alex- of Pt catalysts in the kinetic region and in the mass ander Rudnev (IPCE RAS) and Thomas Wandlowski transport region of the polarisation curve. However, all (University of Bern, Switzerland). The following cool- Fe/N/C catalysts produced thus still lack necessary sta- ing conditions were applied: a mixture of hydrogen bility. The catalyst should be stable at least for 5000 and argon (reducing atmosphere), argon (inert gas) hours at the current density and potential practically and air (oxidising atmosphere). Previous in situ STM used in fuel cells. Solving this problem is in progress. experiments revealed that a Pt(100) surface as pre- A highly active catalyst based on organometallic pared by fl ame annealing and subsequent slow cool- clusters was designed and tested for low temperature ing in a H2 fl ow exhibits atomically fl at terraces (7). fuel cells, as reported by Vitaly Grinberg and col- Cooling in an Ar atmosphere led to a reconstructed leagues (IPCE RAS and Kurnakov Institute of General Pt(100)-hex-R0.7° surface, where R0.7° means rotated and Inorganic Chemistry, RAS, Moscow). A new by 0.7°. However, the reconstruction was lifted after approach to the synthesis of electrocatalysts has been electrosorption of H2 and/or in the presence of traces suggested. Individual heterometallic clusters were sub- of O2 in the electrochemical system (8). Because of jected to thermal destruction on highly dispersed car- the excess of Pt surface atoms originating from the bonaceous supports at the temperatures of 250–500ºC. lifting of the hexagonally reconstructed Pt(100)-hex- The distinguishing feature of these catalysts was their R0.7° electrode, a (1 1) surface with many islands of good reproducibility with respect to composition, as monatomic height was generated (9). Cooling in air well as uniformity of the catalyst distribution over the led to a disordered surface structure characterised by support, which results in stability and reproducibility a large number of defects. of the catalyst characteristics (11). A bimetallic plati- The infl uence of defect density and of long range num-tin catalyst (Pt:Sn atomic ratio in the surface surface order of the Pt(100) electrode on the kinetics layer 2:1) and fl uoro-containing nickel-ruthenium cat- of CO electrooxidation and Cu underpotential deposi- alyst (Ni:Ru atomic ratio in the surface layer 8.6:1) tion (UPD) was demonstrated.