An experimental investigation of fuel assisted electrolysis as a function of fuel and reactant utilization

Abstract

In this paper we describe and analyze the results of experiments on a Solid Oxide ElectrolyzerCell with and without the supply of a fuel to the oxygen producing electrode. In theexperiments a 5 x 5 cm2 Solid Oxide Fuel Cell is used operating in electrolyzer mode. Wehave tested the influence of varying reactant utilization (i.e. steam utilization) and fuelutilization in fuel assisted electrolysis. In particular the effect of insufficient fuel supplywas studied experimentally as well as theoretically. In doing so we defined a turning pointat which all the fuel is utilized. It was shown that by supplying not enough fuel all the fuelis oxidized and as in conventional electrolysis, oxygen production will start and oxygen isleaving the cell. Moreover the cell performance approaches conventional electrolysis andthe effect of adding fuel on reducing the necessary amount of electric power almost vanishes.As in conventional high temperature steam electrolysis conversion efficiencies ofmore than hundred percent can be achieved also with fuel assisted electrolysis, under thecondition that sufficient fuel is supplied i.e. fuel utilization must be lower than hundredpercent.We have put the concept of fuel assisted electrolysis in the framework of multisourcemultiproduct energy systems (MSMP's) and emphasized for example the benefits of usingbio(syn)gas as the fuel in fuel assisted electrolysis. When using bio(syn)gas, the gas is defacto upgraded to pure hydrogen. This is an additional benefit next to the lowering of theelectric power consumption for producing the same amount of hydrogen in the fuelassisted electrolysis process. Furthermore the suitability of these flexible MSMP systems ina market with volatile electricity prices due to increasing penetration of intermittentrenewable energy sources is highlighted.