Theoretical modeling of a pressurized tubular reversible solid oxide cell for methane production by co-electrolysis

Abstract

Power-to-syngas using a reversible solid oxide cell (R-SOC) can efficiently store intermittent renewable energy in the form of syngas. R-SOC functions in both solid oxide electrolysis cell (SOEC) mode for renewable energy storage and solid oxide fuel cell (SOFC) mode for converting syngas back to electricity. R-SOC thus can be used as a fuel cell or as an electrolysis cell, depending on the renewable energy outputs and user loads. Pressurized R-SOC is able to remarkably improve the cycle efficiency and reduce the system size. In this paper, we report a pressurized R-SOC reactor designed to test micro-tubular R-SOCs. We perform experiments in a pressurized R-SOC at 650 °C at pressures of 1–4 atm on a Ni-YSZ/ScSZ/LSM-ScSZ tubular cell; and develope a multi-scale and multi-physics two-dimensional (2D) micro-tubular R-SOC model. The experimental data obtained are used to validate the model. We conclude that the model is able to offer reliable guidance for micro-tubular R-SOCs at various operating conditions. We discuss in detail the effects of pressure on the cell performance and methane production and also consider the methanation reaction-rate distribution at pressures of 1 to 10 atm. The CH4 mole ratio reaches a maximum of 10% at OCV and 25% at 1.3 V at 10 atm. Competition between the methanation reaction and electrolysis is found to control the overall methane production.