Platinum-free electrocatalysts

Platinum-free electrocatalysts for fuel cells could be designed when Pd on carbon electrocatalysts promoted with nanocrystal oxide particles like C03O4, Mn30 and NiO, were used [62], In terms of activity and poison tolerance, the latter were significantly superior. 

Bert, P. and Bianchini, C. (2006) Platinum-free electrocatalysts materials, European Patent EP 1 556 916 Bl. 

In addition to the above mentioned catalyst, Schmidt et al. [60] reported the superior activity and CO tolerance of PdAu/C (Vulcan XC-72) (platinum-free electrocatalysts) at 60 °C compared to PtRu/C. This enhanced CO tolerance was explained by the significantly reduced CO adsorption energy on the PdAu surface, resulting in very low effective CO coverage and therefore in high HOR rates [60, 61],... 

Yato K, Doi S, Ishihara A, Mitsushima S, Kamiya N, Ota KI. Effect of heat treatment of titanium oxynitride as platinum-free electrocatalyst on oxygen reduction reaction. Suiso Enerugi Shisutemu 2006 31 58-65. 

XPS or AES is extensively used not only to indicate the cleanliness of the sample before transfer, but also to indicate the presence of adsorbates and their oxidation states following electrochemical experiments and transfer back into the UHV environment. In the case of model platinum-based electrocatalysts, the electron spectroscopies have been used to estimate the coverage of the adsorbate metal atoms or the alloy composition. In the case of alloys, or the nucleation and growth of metal adsorbate structures, the techniques give only the mean concentrations averaged over a depth determined by the inelastic mean free path of the emitted electrons. Adsorption and reaction at surfaces often depend on the... 

Ohnishi R, Takahashi Y, Takagaki A, Kubota J, Domen K (2008) Niobium oxides as cathode electrocatalysts for platinum-free polymer electrolyte fuel cells. Chem Lett 37 838-839... 

Wang RF, Liao SJ, Fu ZY, Ji S (2008) Platinum free ternary electrocatalysts prepared via organic colloidal method for oxygen reduction. Electrochem Commun 10(4) 523-526... 

Examples of both approaches will be discussed below, starting with the so-called core shell catalysts, which mostly consist of non-noble metal cores covered by a noble metal such as platinum. Platinum-free materials, especially when based on non-noble components, have to fulfill the criterion of stability in acidic media. Recently, electrocatalysts including cobalt and iron proved then-suitability in fuel cell applications where the metal ion is incorporated in a nitrogen macrocycle comparable to the natural porphyrin ring system. 

Liu J, Hu WB, Zhong C, Cheng Y (2013) Surfactant-free electrochemical synthesis of hierarchical platinum particle electrocatalysts for oxidation of ammonia. J Power Sources 223 165-174... 

Because of the irreversible and not well-understood change of the electrocatalyst surface above 1.0 V, early mechanistic studies were conducted under ill-defined conditions. Thus, while anodic evolution of Oj takes place always in the presence of oxygen-covered electrodes, the cathodic reaction proceeds on either oxygen-covered or oxygen free surfaces with different mechanisms (77,158). The electrochemical oxide path, proposed for oxide-covered platinum metals in alcaline electrolytes (759,160), has been criticized by Breiter (7), in view of the inhibition of oxygen reduction by the oxygen layers. Present evidence points to the peroxide-radical mechanism (77,... 

Apart from platinum s intermediate nature on bonding, another point in platinum s favor is availability platinum can be purchased in various suitable forms at a reasonable price some noble metals are difficult to find and purchase. The word noble means here stable and of course that is a first point one wants in an electrocatalyst. It must be a catalyst, not enter into the reaction. It is meant to accelerate the reaction. It must itself be stable, thermally and electrochemically. On the last point, platinum is only fairly good because oxide-free platinum does start itself to dissolve around 1.0 V on the normal hydrogen scale. By using it in anodic reactions in a potential range anodic to 1.0 V, Pt(II) is likely to get into the solution and may be deposited on the cathode. 

Two types of EC-NMR experiments have been carried out electrode potential-dependent studies of an adsorbate ( CO, CN) at room temperature [6, 8, 24], and temperature-dependent studies of an adsorbate [5, 10] and of platinum electrocatalysts [7, 25], down 10 K. For all of the EC-NMR measurements, the electrode materials, either polycrystalline platinum black or carbon-supported commercial fuel cell grade platinum electrodes, were immersed in a supporting electrolyte, typically 0.5 M H2SO4. For temperature-dependence studies, EC-NMR samples are prepared in a conventional three-electrode flow cell with oxygen-free N2 or Ar as a protecting gas, then together with supporting electrolyte and under the protection of... 

Eor their exploitation at the anode of microbial BBSs, these compounds have to be oxidized at an electrocatalytic electrode surface. This anode concept has been used for the oxidation of hydrogen produced during glucose fermentation on a platinum polymer-based sandwich electrode. In a subsequent step, these noble metal-free materials were replaced by noble metal-free electrode electrocatalysts allowing the oxidation of not only H2 but also low-molecular organic acids such as formate and lactate [33-35]. furthermore, the exploitation of sulfur species [36-38] can be classified within this electron transfer concept, although it needs to be noted that sulfur species can be reversibly cycled over sulfide/sulfur in BESs [39]. 

Considerable improvement in the platinum tolerance of the electrocatalysts to carbon monoxide poisoning. Carbon monoxide is a major problem because trace amounts of CO in the H2 feed gas (more than 10 ppm) will poison the Pt anode electrocatalyst in PEMFCs operating at 80 C. A quantitative analysis of the free energy for H2 and CO adsorption as a function of temperature suggests that, by elevating the operating temperature of the cell to 145 °C, CO tolerance at the anode should increase by a factor of 20 (from 5-10 to 100-200 ppm). 

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