Pt-free catalysts

One-step facile hydrothermal methods can synthesize novel nanoporous Ptdr and Pt on RuO2(110) catalysts for ORR. Pt-free catalysts such as Pd-Co, Pd-Ni, Pd-Cr, Pd-Ta, Co-Ni, and CoPds metal alloys"" " as well as the chalcogenide Ru-S and Ru-Se catalysts" " are believed to be promising candidates. Modem studies on ORR electrocatalysts deal with nano-porous gold particles (10-20 nm) with large specific surface area that reduce... 

Simulations on P Pd clusters and Pd monolayers on different metal surfaces have provided insight into low-Pt and Pt-free catalysts. Calvo et al performed DFT calculations on finite PhPd clusters (with x + y = 10) focusing on the effects of geometry and local electronic structure on ORR. The PtsPdv cluster is thermodynamically most favorable for the ORR in terms of reaction energies of OOH and water formation. The activity of Pd monolayers deposited on Ru(OOOl), Rh(lll), Ir(lll), Pt(lll), and Au(lll) surfaces were investigated with periodic DFT calculations. From calculated -band center shifts, the following order in the ORR activity was proposed Pd/Ru(0001) < Pd/Ir(lll) < Pd/Rh( 111) < Pd/Au( 111) < Pd/Pt(l 11). 

Develop Pt-free catalysts by using transition-metal oxide mixtures that mimic Pt performance. Develop fuel-cell testing capabilities at the Naval Research Laboratory (NRL). 

The faster kinetics of alcohol oxidation and oxygen reduction reactions in alkaline direct alcohol fuel cells opens up the possibility of using less expensive Pt-free catalysts, as nickel, gold, palladium and their alloys [30]. Thus, the cost of ADAFC could be potentially lower compared to the acid DAFC technology if non-precious metal alloys are used for the alcohol electrooxidation, being the nanoparticulated Ni-Fe-Co alloys developed by Acta (Italy) with the trade name of HYPERMEC a good example. 

So far, kinetics of MOR were discussed throughout this chapter considering the acid medium, however the kinetics are, in average, halffold faster in alkaline medium. The same reads for ORR. Concisely, the enhanced activity in alkaline media results from the lack of specifically-adsorbed spectator ions in alkaline solutions, and the higher coverage of adsorbed OH at low potential [63]. The fastest kinetics allows to use low catalyst loadings and to select Pt-free catalysts. 

Meng H, Shen PK. Novel Pt-free catalyst for oxygen electroreduction. Electrochem Commun 2006 8(4) 588—94. 

On the other hand, according to Department of Energy (DOE), cost of catalyst (Pt) presents over 1/3 of the total cost of a fuel cell stack. Many approaches have been seriously considered in order to reduce the catalyst cost, especially by reducing Pt loadings on both electrodes in fuel cell systems, namely, using metal carbides [9], metal oxide-CNT composites [10], metal phosphides [11], transition metal-carbon composites [12], metal chalcogenides [13], Pt monolayers [14], and iron-based catalyst (called, nowadays, Pt-free catalysts) [15-17]. 

Moreover, Yin et al. [57] developed WC on carbon surface by intermittent microwave heating method to support other Pt-free catalyst, such as Pd-Fe (catalyst noted as Pd-Fe/WC/C). According to TEM images, a good dispersion was obtained with particle sizes in the range of 4 nm for Pd-Fe/WC/C and 2.8 nm for the... 

Meizougui B, Hachimi A, Akinpelu A, Bukola S, Shao M (2013) A Pt free catalyst for oxygen reduction reaction based on Fe—N multiwalled carbon nanotube composites. Eleetrochim Acta 107 126-132... 

Figure 7.5. (a) ORR on different catalysts in O2 saturated 1 mol dm KOH solution, and (b) ethanol oxidation on Pd-NiO/C catalyst in 1.0 mol dm ethanol/1.0 mol dm KOH [55, 56]. (Graph (a) reprinted from Electrochemistry Commununications, 8, Meng H, Shen PK. Novel Pt-free catalyst for oxygen electroreduction, 588-94, 2006 with permission from Elsevier. Graph (b) reprinted from Electrochemistry Commununications, 8, Alcohol oxidation on nanocrytaUine oxide Pd/C promoted electrocatalyst, 184-8, 2006 with permission from Elsevier.)... 

Shen s group focused on flie studies of the Pt-free catalysts preparation and the effect of the CL structure on fuel eell performance. They developed oxide-promoted Pd catalysts prepared by a novel intermittent microwave heating technique [56, 96, 97]. All flie oxide-Pd catalysts on carbon showed higher catalytic activities than those of Pt/C or Pt-Ru/C catalysts. The Pd-NiO/C eatalyst... 

In this chapter we present an overview of methods used to synthesize fuel cell catalysts, with a focus on catalysts for PEMFCs and direct methanol fuel cells (DMFCs). Examples for the synthesis of catalysts for other low-temperature fuel cells, such as formic acid, are not included in this ehapter. The synthesis of both Pt-based and Pt-free catalysts is discussed, and dedieated sections describe methods that allow control of catalyst size and composition. First, general catalyst synthesis methods are introduced. Subsequently, the reader is introduced to particle size and stracture control of fuel cell catalysts. 

Re search over several decades has found that platinum and platinum-eontaining catalysts are the most effective catalytic materials for PEMFCs nonetheless, platinum-based catalysts are expensive and have low durability (Borup et al, 2007 Thompsett, 2003 Rabis et al, 2012). Studies have been intensively conducted to significantly reduce the Pt loading in both electrodes and/or enhance the Pt electro-catalytic efficiency. Alternatively, Pt-free catalysts have been particularly studied to replace Pt (Chen, 2011). 

---