Platinum spontaneous hydrogen reaction

The assumption is still made here as previously that the spontaneous hydrogen reaction on iron is negligible compared to that on platinum. 

It is quite impossible to determine the absolute potential difference across a sin e met /solution interface, and the potential must be evaluated indirectly from the e.m.f. of a cell comprising the interface under consideration and another electrified interface. The e.m.f. of the cell can be determined readily by a suitable measuring device such as a potentiometer, vacuum-tube voltmeter or an electrometer, which are capable of measuring the e.m.f. with the minimum passage of electrical charge. This is essential since if a significant current is allowed to pass, the electrodes (electrified interfaces) become polarised and the e.m.f. will be less than the equilibrium value. Consider the determination of the interfacial potential at the surface of a zinc electrode in equilibrium with Zn ions in solution. In order to determine the potential it is necessary to couple it with another electrode, and for the purpose of this discussion the equilibrium between ions in solution and gas will be chosen, i.e. the reversible hydrogen electrode in which the equilibrium between and H takes place at a platinised-platinum surface. The spontaneous cell reaction will be... 

RG. 7—Spontaneous passivation of an active-passive metal, such as titanium, by galvanically coupling to a noble metal such as platinum. The noble metal has a high rale constant for the proton-hydrogen reaction thus, the corrosion potential of the system Is near to the reversible potential for this reaction [7]. 

Sometimes anodic protection is used, in which case the metal s potential is made more positive. The rate of spontaneous dissolution will strongly decrease, rather than increase, when the metal s passivation potential is attained under these conditions. To make the potential more positive, one must only accelerate a coupled cathodic reaction, which can be done by adding to the solution oxidizing agents readily undergoing cathodic reduction (e.g., chromate ions). The rate of cathodic hydrogen evolution can also be accelerated when minute amounts of platinum metals, which have a stroug catalytic effect, are iucorporated iuto the metaf s surface fayer (Tomashov, 1955). 

SAFETY PROFILE Poison by inhalation and ingestion. A corrosive irritant to skin, eyes, and mucous membranes. Inhalation may cause pulmonary edema and hemorrhage. Potentially explosive reaction with acetone + platinum. Mixtures with hydrogen + oxygen ignite spontaneously. When heated to decomposition it emits very toxic fumes of CT and NO. ... 

In 1823, Dobereiner published a paper entitled Concerning Newly Discovered, Highly Remarkable Properties of Platinum, wherein he reported the spontaneous reaction of hydrogen and oxygen in the presence of platinum. 

Thus the cell reaction is spontaneous under standard-state conditions. Note that the reaction is the same as the hydrogen combustion reaction, but the oxidation and reduction are carried out separately at the anode and the cathode. Like platinum in the standard hydrogen electrode, the electrodes have a twofold function. They serve as electrical conductors, and they provide the necessary surfaces for the initial decomposition of the molecules into atomic species, prior to electron transfer. They are electrocatalysts. Metals such as platinum, nickel, and rhodium are good electrocatalysts. 

The H2/O2 fuel cell uses inert electrodes (porous graphite containing platinum as a catalyst, for example). A solution of phosphoric acid, or some other acid, serves as electrolyte. The reaction between oxygen and hydrogen is spontaneous and the fuel cell therefore provides electric power. The current is directly proportional to the number of moles of H2 and O2 that react at the electrodes, with n = 4 and n = 2 for oxygen and hydrogen, respectively ... 

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