Lead alloys protonation

The old design of cell is based on a lead-lined tank filled with aqueous sulphuric acid, and the spent chromic acid solution in porous ceramic pots was placed in the tank. The anodes were lead rods dipped into the ceramic pots and the cathode was the lining to the tank. The plant was obviously operated totally as a batch process. More modern and economic cells are now available they are often based on a bipolar filterpress concept with lead alloy anodes, steel cathodes and a Nafion proton-conducting membrane. The energy consumption and space-time yields with such cells are clearly likely to be superior. Moreover, such cells can be operated as continuous or semi-continuous processes. 

The stability and durability of Pt alloys, especially those involving a >d transition metal, are the major hurdles preventing them from commercial fuel cell applications. "" The transition metals in these alloys are not thermodynamically stable and may leach out in the acidic PEM fuel cell environment. Transition metal atoms at the surface of the alloy particles leach out faster than those under the surface of Pt atom layers." The metal cations of the leaching products can replace the protons of ionomers in the membrane and lead to reduced ionic conductivity, which in turn increases the resistance loss and activation overpotential loss. Gasteiger et al. showed that preleached Pt alloys displayed improved chemical stability and reduced ORR overpotential loss (in the mass transport region), but their long-term stability has not been demonstrated. " These alloys experienced rapid activity loss after a few hundred hours of fuel cell tests, which was attributed to changes in their surface composition and structure." ... 

The membrane conducted protons and therefore sulphuric acid was a natural choice for the anolyte. The anode was a lead-silver alloy, the silver reducing the oxygen overpotential and increasing the corrosion r itaiioe,... 

Of the two electrodes, the anode, although made of a less stable Pt-Ru alloy, suffers lower performance loss over time than the cathode. The anode is, however, the source of mobile ruthenium species, either neutral or ionic, capable of permeating the proton-conducting membrane (ruthenium crossover) and depositing at the cathode, leading to a decrease in ORR activity of the platinum catalyst. 

A much weaker attraction of water molecules to the electrode in comparison with HsO ions should lead to a larger distance between the initial and the final positions of a proton and, as a consequence, to a lower tunneling probability. This conclusion was experimentally verified in [294], where the temperature dependences of the hydrogen overpotential were determined for alkaline solution at cathodes made of gallium and liquid In-Ga alloy. In contrast to mercury cathodes and those made of some solid metals, e.g. lead, the... 

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