The Electrochemical Reduction of Oxygen on Electrodes Partially Immersed in Phosphoric Acid

Diffusion-controlled currents for the reduction of oxygen in phosphoric acid for partial ly immersed electrode structures which have an intrinsic meniscus and thin film extending over their surface can be predicted from a general rate equation. For plat inum black electrodes, and temperatures rang-ing from 25 ~ to 170 ~ the l imiting current varies l inearly with the square root of electrolyte conductivity, electrode polarization, and oxygen partial pressure. The increased current obtained on partial ly immersed electrodes has been shown to be associated with a very narrow region starting approxi-mately 0.28 cm (the height of the meniscus) above the bulk of the electrolyte solution. Approximate calculations of the activation energy of diffusion using parameters from the rate equation give values which are close to those ex-pected for a diffusional process. Good agreement is obtained between theo-retical and experimental ly determined values of the l imiting current at 25~ Equations have been derived to describe the interracial iquid-gas geometr