Platinum monolayers

Zhang J, Mo Y, Vukmirovic MB, Klie R, Sasaki K, Adzic RR. 2004. Platinum monolayer electrocatalysts for O2 reduction Pt monolayer on Pd(lll) and on carbon-supported Pd nanoparticles. J Phys Chem B 108 10955-10964. 

Zhang J, Vukmirovic MB, Xu Y, Mavrikakis M, Adzic RR. 2005b. Controlling the catalytic activity of platinum-monolayer electoocatalysts for oxygen reduction with different substrates. Angew Chem Int Ed 44 2132-2135. 

Vukmirovic MB, Zhang J, Sasaki K, Nilekar AU, Uribe E, Mavrikakis M, Adzic RR. 2007. Platinum monolayer electrocatalysts for oxygen reduction. Electrochim Acta 52 2257-2263. 

Zhang, J. et al., Platinum monolayer on nonnoble metal-noble metal core-shell nanoparticle electrocatalysts for O2 reduction, J. Phys. Chem. B, 109, 22701, 2005. 

Zhang J, Lima FHB, Shao MH, Sasaki K, Wang JX, Hanson J, Adzic RR (2005) Platinum monolayer on non-noble metal-noble metal core-shell nanoparticle electrocatalysts for 0-2 reduction. J Phys Chem B 109 22701... 

E25.17 Electrocatalysts are compounds that are capable of reducing the kinetic barrier for electrochemical reactions (barrier known as overpotential). While platinum is the most efficient electrocatalyst for accelerating oxygen reduction at the fuel cell cathode, it is expensive (recall Section 25.18 Electrocatalysis). Current research is focused on the efficiency of a platinum monolayer by placing it on a stable metal or alloy clusters your book mentions the use of the alloy PtsN. An example would be a platinum monolayer fuel-cell anode electrocatalyst, which consists of ruthenium nanoparticles with a sub-monolayer of platinum. Other areas of research include using tethered metalloporphyrin complexes for oxygen activation and subsequent reduction. 

Nilekar AU, Mavrikakis M (2008) Improved oxygen reduction reactivity of platinum monolayers on transition metal surfaces. Surf Sci 602 L89-L94... 

The activity for the ORR of Pt monolayers, deposited on different single-crystal surfaces, using the Cu UPD technique [14], were investigated in acid and in alkaline electrolytes [7, 8]. Figure 5.1a show the typical ORR curves obtained for pure Pt/C and Pt monolayer on Pd/C nanoparticles, and Fig. 5.1b shows the plot of ORR activity versus Pt d-band center on different surfaces [7]. As can be seen, the ft monolayer electrocatalysts exhibited support-induced tunable activity by arising either by structural and/or electronic effects. It can be observed that the most active of all surfaces is PtML/Pd(lll), and the least active is PtML/Ru(0001). The plots of the kinetic current on the platinum monolayers on various substrates at 0.8 V as a function of the calculated d-hznA center, e, generated a volcano-like curve, with PtML/Pd(lll) showing the maximum activity (Fig. 5.1a). 

Regarding the geometric effect, compressive strain tends to down-shift ej in energy, whereas tensile strain has the opposite effect, as revealed by DFT studies [7, 15, 16]. The platinum monolayers on Ru(OOOl), Rh(lll), and Ir(lll) are compressed compared with Pt(lll), whereas PtML/Au(lll) is stretched by more than 4 %. However, the position of the eelectronic effect, in which the magnitude of the Cd shift depends on the intensity of the electronic interaction between the platinum monolayer and its substrate [19]. This indicates that PtMc/Ru (0001), PtMi/lr(lll), and PtML/Rh(lll) are less active for O2 reduction than platinum because breaking the 0-0 bond is more difficult on their surfaces than on Pt(lll), while the kinetics of hydrogenation of the oxygen atoms may be... 

Galvanic displacement method is also often used for synthesizing catalysts. By this method, low Pt-content electrocatalysts can be obtained. For example, a carbon-supported core—shell structured electrocatalyst with bimetallic IrNi as the core and platinum monolayer as the shell has been successfully synthesized using this method. In this synthesis, IrNi core supported on carbon was first synthesized by a chemical reduction and thermal annealing method and a Ni core and Ir shell structure could be formed finally. The other advantage of this method is that the Ni can be completely encased by Ir shell, which will protect Ni dissolve in acid medium. Secondly, IrNi PtML/C core—shell electrocatalyst was prepared by depositing a Pt monolayer on the IrNi substrate by galvanic displacement of a Cu monolayer formed by under potential deposition (UPD). 

Kuttiyiel KA, Sasaki K, Choi Y, Su D, Liu P, Adzic RR. Bimetallic IrNi core platinum monolayer shell electrocatalysts for the oxygen reduction reaction. Energy Environ Sci 2012 5(1) 5297. 

Figure 7.4 (A) Polarization curves for O2 reduction on platinum monolayers (PIml) on Ru(OOOI), lr(111), Rh(111), Au(111), and Pd(111) surfaces in 02-saturated 0.1 M HCIO4 solution on a disk electrode. The rotation rate is 1600 rpm, and the sweep rate is 20 mV s (50 mV s for R(111)) y= current density, RHE = reversible hydrogen electrode. (Reprinted with permission from Ref. 6) (B) kinetic currents (yi< square symbols) at 0.8 V for O2 reduction on the platinum monolayers supported on different single-crystal surfaces in 02-saturated 0.1 M HCIO4 solution and calculated binding energies of atomic oxygen (BEO filled circles) as functions of calculated d-band center (fd cp relative to the Fermi level) of the respective clean Pt monolayers. Labels (1) PtMi/Ru(0001),(2) RMi/lrOU). (3) PtMi/Rh(111),(4) PtMi/Au(111), (5) Pt(111), (6) PtML/Pd(111). Reprinted with permission from Ref. 22.

The electrocatalytic ORR activity of platinum monolayers supported onAu(lll),Rh lll), Pd lll), Ru(OOOl), andlr lll) surfaces in a 0.1 M HCIO4 were also studied, as shown in Figure 7.4(A). There was a volcano-type dependence of monolayer catalytic activity on the substrate, and the most active was PtML/Pd lH), as shown in Figure 7.4(B). The weighted center of the d-band (cd) was believed to play a decisive role in determining a surface reactivity. The positions of the cd of the Pt monolayers depend both on the strain (geometric effects) and on the electronic interaction between... 

Kongkanand A, Kuwabata S. Oxygen reduction at platinum monolayer islands deposited on Au(lll). J Phys Chem B 2005 109(49) 23190—5. 

Li M, Liu P, Adzic RR (2012) Platinum monolayer electrocatalysts for anodic oxidation of alcohols. J Phys Chem Lett 3 3480-3485... 

Adzic RR, Lima EHB (2009) Platinum monolayer oxygen reduction electrocatalysts, Chapter 1. In Vielstich W, Yokokawa H, Gasteiger HA (eds) Handbook of fuel cells, fundamentals, technology and applications. Advances in electrocatalysis, materials diagnostics and durability, vol 5, part 1. Wiley, West Sussex... 

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