Mechanistic Studies of Liquid Metal Anode SOFCs I. Oxidation of Hydrogen in Chemical - Electrochemical Mode

Liquid metal anode (LMA) solid oxide fuel cells (SOFCs) are a promising type of high temperature fuel cell suitable for the direct oxidation of gaseous or solid fuel. Depending upon the operating conditions they can be run in four different modes. In this first of a series of studies concerning the mechanism of reaction and species transport in LMA SOFCs, the oxidation of hydrogen fuel in a liquid tin anode has been investigated. An electrochemical model is developed based upon fast dissolution of hydrogen in a molten tin anode, slow, rate-determining homogeneous reaction of hydrogen with oxygen dissolved in the liquid tin, followed by anodic oxygen injection under diffusion control to replace the oxygen removed by reaction (so-called Chemical - Electrochemical mode or CE mode). Experimentally-generated data are used to validate the model. The model has introduced a new key parameter, (z) over bar, which takes a value between zero and unity; its value is determined by geometric and convective factors in the cell as well as the partial pressure of the supplied hydrogen fuel. Current output of the cell is proportional to the value of (z) over bar. (C) 2015 The Electrochemical Society. All rights reserved.