Influence of Pressurisation on SOFC Performance and Durability: A Theoretical Study

Abstract

Hybrid power plants consisting of a solid oxide fuel cell (SOFC) and a gas turbine show high electrical efficiencies, however require pressurisation of the SOFC to several bar. This paper presents a theoretical investigation of the pressure influence on SOFC performance and durability. A two‐dimensional elementary kinetic model is used to predict the performance of a single cell in the pressure range of 1–20 bar. The influence of pressure on thermodynamics, reaction kinetics, porous electrode diffusion, channel transport and efficiency is assessed. It was found that polarisation resistance decreases with increasing pressure due to increased diffusion through porous electrodes and a higher electrode surface coverage with reactant species. Furthermore, open‐circuit voltage increases slightly with pressure. As a consequence, power density and efficiency increase upon pressurisation with the strongest increase at low pressures between 1 and 5 bar. The influence of pressure on two typical degradation mechanisms, nickel oxidation and carbon deposition, is assessed using thermodynamic simulations. Pressurisation facilitates nickel oxidation whereas its effect on carbon deposition strongly depends on temperature.

A validated multi‐scale model of a SOFC stack at elevated pressure

“…This effect is rather strong compared with concentration overpotentials. Activation overpotentials are reduced due to increased reactant adsorption rates at the electrode surfaces [11]. These results are in good agreement with the impedance spectra shown in Fig.…”

“…The legend indicates the operating conditions according to Table 1. [11]. However, other significant effects exist.…”

“…For the safe operation of such power plant the behavior of the SOFC stacks has to be well known and understood. The authors have previously published experimental and theoretical research results [11][12][13] which showed an increase in SOFC performance with increasing pressure. Pressure effects were found to be strongest at low pressure and weaker towards higher pressure.…”

“…Calculated values, however, show a behavior qualitatively comparable to anode concentration overpotentials. The reduction in concentration overpotential is due to improved diffusion through the electrodes which is caused by a change from Knudsen diffusion to ordinary diffusion mechanism [11].…”

Pressurized solid oxide fuel cells: Experimental studies and modeling

“…The model is based on physical equations and is applicable to elevated pressures [19]. The results presented here are based on a model of anode-supported cells that was previously validated at ambient pressure [20].…”