Electrocatalytic Performance

In addition to the proton conductivity of the electrolyte, the performance of a fuel cell is largely dependent on the electrocatalytic activity of the anodic and cathodic interface. This depends both on the structure of the gas-electrocatalyst-electrolyte three phase boimdaries and on the electrocatalytic activity of the charge transfer reaction that takes place along the electrochemical interface. The former case determines the extent of the electrochemical surface area (ESA), while the latter is directly related to the physicochemical properties of the Pt based catalyst and the extent to which its catalytic properties are affected by its contact /interaction with the polymer electrolyte. 

The stmcture of the electrochemical interface depends on the particle size, the loading and the active surface area of the caibon supported Pt particles. In addition for the case of HT PEMFCs the amount of H3PO4 plays a predominant role on the performance by affecting both the stmcture and the catalytic properties of the electrochemical interface. 

Too mnch phosphoric acid within the catalytic layer stmcture induces a flooding effect over the Pt particles thns resrrlting in the irrhibition of reacting gases and especially O2 to reach the catalyst srrrface, given the low permeability of oxygen in phosphoric ac- 

In general the Nyquist plots of Fig. 27 can be simulated by two semicycles which rather correspond to the anodic (high frequencies arc) and cathodic (low frequencies arc) electrocatalytic processes (Table 5) 8,119,120 anodic H2 oxidation reaction being faster than the cathodic O2 reduction reaction appears at higher frequencies and with lower polarization resistance. 

The Ionic Resistance of the Electrolyte Rei and the Polarization Resistances Ri and R2 Based on the Fitting of the Niquist Plots 

---

Mao and Mao invented a method for synthesizing supported metal catalysts with small metal nanoparticles (1-3 nm) even at high metal loadings (30-50 wt.%) [25]. The obtained metal catalysts exhibited superior electrocatalytic performance in fuel cells. In this invention, the unprotected metal nanocluster colloids prepared according... 

Rondinini, S., Mussini, P.R., Specchia, M. and Vertova, A. (2001a) The electrocatalytic performance of silver in the reductive dehalogenation of bromophenols. J. Electrochem Soc. 148, D102-D107. 

Ding, H.Y., Feng, Y.J. and Liu, J.F. (2007) Comparison of electrocatalytic performance of different anodes with cyclic voltammetry and Tafel curves. Chin. J. Catal. 28(7), 646-650 (in Chinese). 

Part V addresses the critical issues of particle size effects, alloying, spillover, classic and electrochemical promotion, and metal-support interactions on the catalytic and electrocatalytic performance of nanoparticles. Recent experimental evidence is presented on the functional similarities and operational differences of promotion, electrochemical promotion, and metal-support interactions. 

As a result, the reduction potential of Cu(II) centers becomes significantly shifted. The electrocatalytic performance of MOFs is illustrated in Figure 5.17, where... 

Many efforts have been undertaken to enhance the electrocatalytic performance of catalytic reactions that have technological importance. The case of organic fuel electrooxidation is a major point for study, especially the possibility of achieving long-term, less-polluting fuel cells. In the case of methanol electrooxidation, the reaction occurs by a self-poisoning mechanism, so it is clear that the catalysts performances must be improved to impede the formation of carbon... 

For use as PAFC catalysts a trimetallic colloidal (3.8 nm) precursor of composition Pt5oCo3oCr2o was prepared by co-reduction of the corresponding metal saks. " ] XRD examination showed that the particles consist of a trimetallic alloy with an ordered fee structure. In a standard half-cell test the electrocatalytic performance was compared with that of an industrial standard catalyst manufactured by co-precipitation and subsequent annealing to 900 °C, giving 5.7 nm trimetallic crystallites. Preliminary results have shown that the trimetallic colloid catalysts have advantages in respect of long-term stability - essential for PAFC catalysts. The decay of the potential after 22 h was found to be less than 10 mV. Further work is in progress. l... 

Pd nanoparticles supported on PANI-NFs are efficient semi-heterogeneous catalysts for Suzuki coupling between aryl chlorides and phenylboronic acid, the homocoupling of deactivated aryl chlorides, and for phenol formation from aryl halides and potassium hydroxide in water and air [493], PANl-NF-supported FeCl3 as an efficient and reusable heterogeneous catalyst for the acylation of alcohols and amines with acetic acid has been presented [494]. Vanadate-doped PANI-NFs and PANI-NTs have proven to be excellent catalysts for selective oxidation of arylalkylsulfides to sulfoxides under nuld conditions [412]. Heterogeneous Mo catalysts for the efficient epoxidation of olefins with ferf-butylhydroperoxide were successfully synthesized using sea urchin-Uke PANI hollow microspheres, constructed with oriented PANI-NF arrays, as support [495]. Pt- and Ru-based electrocatalyst PANI-NFs—PSSA—Ru—Pt, synthesized by the electrodeposition of Pt and Ru particles into the nanofibrous network of PANI-PSSA, exhibited an excellent electrocatalytic performance for methanol oxidation [496]. A Pt electrode modified by PANI-NFs made the electrocatalytic oxidation reaction of methanol more complete [497]. Synthesis of a nanoelectrocatalyst based on PANI-NF-supported... 

C.W. Kuo, L.M. Huang, T.C. Wen, and A. Gopalan, Enhanced electrocatalytic performance fro methanol oxidation of a novel Pt-dispersed poly(3,4-ethylenedioxythiophene)-poly (styrene sulfonic acid) electrode, J. Power Sources, 160, 65-72 (2006). 

Whichever the synthesis route and the electrocatalytic performance, a certain lack of consistency between different electrocatalysts has been pointed out, suggesting the coexistence of a number of metal and/or oxidized phases in those systems. On the other hand, most reports fail to give the actual metallic loading of the final catalysts, or the Pt to Sn stoichiometry of the particles, or, more importantly for the sake of reproducibility of the methods, the target metal loading and Pt Sn atomic ratio. 

KCl, and HCl. The process is controllable by varying the electrochemical deposition conditions. The PB-Graphene/GCE had admirable electrocatalytic performance towards both the reduction of H2O2 and the oxidation of hydrazine. 

Gasparotto LHS, Garcia AC, Gomes JF, Tremiliosi G (2012) Electrocatalytic performance of environmentally friendly synthesized gold nanoparticles towards the borohydride electrooxidation reaction. J Power Sources 218 73-78... 

Ding J, Chan K-Y, Ren J, F-s X (2005) Platinum and platinum-ruthenium nanoparticles supported on ordered mesoporous carbon and their electrocatalytic performance for fuel cell reactions. Electrochim Acta 50 3131-3141... 

Fang B, Luo J, Njoki PN, Loukrakpam R, Wanjala B, Htnig J, Yin J, Hu X, Last J, Zhong CJ (2010) Nano-engineered PtVFe catalysts in proton exchange membrane fuel cells electrocatalytic performance. Electrochim Acta 55 8230-8236... 

Yan SH, Zhang SC, Lin Y, Liu GR (2011) Electrocatalytic performance of gold nanoparticles supported on activated carbon for methanol oxidation in alkaline solution. J Phys Chem C 115 6986-6993... 

The high dispersion of the Pd clusters and the presence of single Pd sites in Pd-(Ni-Zn)/C and Pd-(Ni-Zn-P)/C have been suggested to be important factors in boosting the electrocatalytic performance of these materials. On the other hand, although independent CV experiments in KOH solution with Ni-Zn/C and Ni-Zn-P/C electrodes, prior and after alcohol addition, have excluded any direct role of the Ni support,the existence of a co-catalytic effect of Ni on the Pd-catalyzed oxidation reaction of alcohols cannot be disregarded. In fact, several researchers have reported that the co-presence of nickel or nickel oxide may have a... 

Abe H, Matsumoto F, Alden FR, Warrai SC, Abmha HD, DiSalvo FJ (2008) Electrocatalytic performance of fuel oxidatimi by Pt3Ti nanoparticles. J Am Chem Soc 130 5452-5458... 

---