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 Electrolyzer Cell with and without the supply of a fuel to the oxygen producing electrode. In the experiments a 5 × 5 cm2 Solid Oxide Fuel Cell is used operating in electrolyzer mode. We have tested the influence of varying reactant utilization (i.e. steam utilization) and fuel utilization in fuel assisted electrolysis. In particular the effect of insufficient fuel supply was studied experimentally as well as theoretically. In doing so we defined a turning point at which all the fuel is utilized. It was shown that by supplying not enough fuel all the fuel is oxidized and as in conventional electrolysis, oxygen production will start and oxygen is leaving the cell. Moreover the cell performance approaches conventional electrolysis and the effect of adding fuel on reducing the necessary amount of electric power almost vanishes. As in conventional high temperature steam electrolysis conversion efficiencies of more than hundred percent can be achieved also with fuel assisted electrolysis, under the condition that sufficient fuel is supplied i.e. fuel utilization must be lower than hundred percent.We have put the concept of fuel assisted electrolysis in the framework of multisource multiproduct energy systems (MSMP's) and emphasized for example the benefits of using bio(syn)gas as the fuel in fuel assisted electrolysis. When using bio(syn)gas, the gas is de facto upgraded to pure hydrogen. This is an additional benefit next to the lowering of the electric power consumption for producing the same amount of hydrogen in the fuel assisted electrolysis process. Furthermore the suitability of these flexible MSMP systems in a market with volatile electricity prices due to increasing penetration of intermittent renewable energy sources is highlighted.