Electrochemical Preparation of Tungsten Bronzes

At IREQ, besides the participation in the field tests run by the engineers of Hydro-Quebec (12), the main effort has been to tackle fundamental problems in the field of electrocatalysis (18-22) and of anodic oxidation of different potential fuels (23-26). A careful and extensive study of the electrochemical properties of the tungsten bronze has been carried out (18-20) the reported activity of these materials in acid media for the oxygen reduction could not be reproduced and this claim by other workers has been traced back to some platinum impurities in the electrodes. Some novel techniques in the area of electrode preparation are also under study (21,22) the metallic deposition of certain metals on oriented graphite show some interesting catalytic features for the oxygen reduction and also for the oxygen evolution reaction. 

The hydrogen molybdenum and tungsten bronzes H MoOj and H WOj, where X = 0.6, may be prepared by electrochemical reduction of WO3 or M0O3. They violate the condition that the metal must be a hydride former, but they cannot be prepared by direct reaction of the oxide with Hj, and they differ from other compounds because the hydrogen prefers to bond with oxygen rather than the metal. 

Tungsten and molybdenum bronzes, AxW03 and AxMo03 (As k, Rb, Cs) are generally prepared by reaction of the alkali metals with the host oxide. Electrochemical methods are also employed for these preparations. A novel reaction that has been employed to prepare bronzes which are otherwise difficult to obtain involves the reaction of oxide host with anhydrous alkali iodides [49] ... 

Oxides of the type A O- (A = alkali metal) are known as tungsten oxide bronzes. These are readily prepared by the insertion of the alkali metal into WO3. The corresponding molybdenum bronzes are more difficult to prepare. High pressures and electrochemical methods are generally employed to synthesize some of them. A simple solid-state reaction between an alkali iodide and M0O3 or Moj j Wj 03 (under dry conditions) has been found to yield such molybdenum oxide bronzes [11]. The following reaction represents a simple means of making these bronzes ... 

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