SOFC Anode Process Characterization By Means of a Novel Spot-Sampling Set-up for in-Operando Gas Analysis

Abstract

The development and operation of an innovative experimental setup is presented for in-depth, in-operando characterization of anode processes of Solid Oxide Fuel Cells.The idea behind this project is to realize a setup enabling the measurement of temperature and gas compositions using eleven points of sampling distributed over the anode surface. Simultaneous temperature measurement and gas chromatography are employed to detect the variation of thermodynamic and chemical conditions across the anode surface in steady state and in real time. The particular location of each sampling point is chosen in such a way as to minimize interference in the flow pattern across the anode but maximizing the spatial information of the measurements taken. Thus, it is possible to investigate the evolution of chemical reactions occurring during the operation of the cell, identified with a spatial resolution covering the whole surface of the anode in order to distinguish edge effects from bulk processes. Sampling settings are tailored to analyse representative specimens of anode gas without altering local conditions. Moreover, the novel housing allows for full simultaneous (bulk) electrochemical characterization through polarization curves and electrochemical impedance spectroscopy (EIS), maximizing the data output from a given experiment without significantly affecting the cell response during the characterization.This experimental setup is particularly important for the direct fuelling of SOFCs with natural gas, biogas or syngas, where the dynamic processes of internal reforming can create severe local gradients of temperature and gas compositions, inducing stresses and possible carbon deposition. Single cell tests have been carried out on intermediate-temperature, commercial SOFCs fed with simple hydrogen and selected syngas compositions to assess the thermochemical response of the SOFC at different current densities and create a detailed spatial mapping of critical hotspots correlated with operating conditions and inlet gas compositions. It is thus possible to identify areas within the operational space that are conducive to better uniformity of conditions, presumed to enhance SOFC durability, allowing to provide recommendations for fuel pre-conditioning processes as well as SOFC operation modes. Ultimately, it is envisaged to establish simplified but effective control algorithms based upon the correlation of the detailed, real-time spatial mapping with key parameters that are easily monitored in a real SOFC system.Experimental data will be useful to investigate phenomena occurring on the cell plane also with the help of a model based on finite element method that can simulate locally the behavior of the cell in order to validate the experimental map of temperature and composition of gases on the cell.