Electrocatalysts noble-metal-free

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]. 

Alkaline Fuel Cell. The electrolyte ia the alkaline fuel cell is concentrated (85 wt %) KOH ia fuel cells that operate at high (- 250° C) temperature, or less concentrated (35—50 wt %) KOH for lower (<120° C) temperature operation. The electrolyte is retained ia a matrix of asbestos (qv) or other metal oxide, and a wide range of electrocatalysts can be used, eg, Ni, Ag, metal oxides, spiaels, and noble metals. Oxygen reduction kinetics are more rapid ia alkaline electrolytes than ia acid electrolytes, and the use of non-noble metal electrocatalysts ia AFCs is feasible. However, a significant disadvantage of AFCs is that alkaline electrolytes, ie, NaOH, KOH, do not reject CO2. Consequentiy, as of this writing, AFCs are restricted to specialized apphcations where C02-free H2 and O2 are utilized. 

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. 

This explains the higher methanol tolerance of the alloy material in relation to that of pure Pt/C. For Pt-free electrocatalysts, PCI4C01/C showed to be very active for the ORR even at a high concentration of methanol. The addition of noble metal such as Au, Ag and Pt onto the PdCo material, in order to increase their stability in acid electrolyte, conducts to a lowered MOR activity and high ORR kinetics. For the RuSe/C and RhS/C materials, the former presents a considerable tolerance to the presence of methanol. However, the observed loss of selenium from the surface, observed upon exposure to potentials greater than 0.85 V, indicates a detrimental effect on the implementation of RuSe/C as a cathode material in fuel cell applications. The commercially available rhodium sulphide underperforms and exhibits higher susceptibility to methanol compared to RuSe/C, but it is more stable under similar testing conditions. 

Since Pt is a scarce and expensive metal, in 2002, the US Department of Energy (DOE) set targets for the maximum quantity of Pt to be used in H2/O2 (Air) PEM fuel cells. Initially, the 2015 target was set to 0.2 g Pt/kWe (with kWe for the rated electric power) for total anode and cathode Pt content combined. However, due to the considerable rise in Pt price, a new target—0.125 g Pt/kWe—was recently set for 2017 [5]. At around 1,700-1,800 per Pt Troy ounce (31.1 g), 0.125 g Pt/kWe would represent a Pt raw material cost of around 7 Pt/kWe. Meanwhile, the DOE also sets the cost target for the entire membrane electrode assembly to 9/kWe There is, therefore, a strong case for replacing Pt with a lower cost non-noble metal-based electrocatalyst (or a metal-free electrocatalyst). 

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. 

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