- Reversible operation of solid oxide cells will significantly increase market penetration capability of the solid oxide fuel cells (SOFC) due to the production of hydrogen and electricity at different operating modes. It can potentially address the energy storage grand challenge by leveraging hydrogen as the energy carrier medium. The protonic ceramic electrochemical cell (PCEC) is an emerging and attractive technology that allows such conversion from the conventional high temperature (>800o C) to intermediate temperatures (400-650o C). Reduced operating temperatures can significantly improve the cell/stack durability, minimize stack sealing problems, enable the use of less expensive materials (e.g., ferritic stainless steels for interconnect), and improve response to rapid startup and repeat thermal cycling needs. Furthermore, when operated for hydrogen production, the PCECs can overcome the problems that the conventional oxygen-ion conducting electrolysis cells face, including the mixture of hydrogen and steam, severe delamination of electrodes at high current densities, and partial oxidation of the Ni-based electrode.

• With reduced operating temperatures, highly active, robust and durable electrodes are needed for both electrolysis and fuel cell operation. Researchers at INL have discovered a new electrode material that has excellent electrocatalytic activity toward water oxidation and oxygen reduction reactions, which are dominating factors for these two modes of operation, respectively.
• The new INL electrode material demonstrates remarkable triple conductivity (H+-O2--e-), confirmed by a series of experiments (e.g., hydration/dehydration measurement, thermogravimetric analysis, hydrogen/oxygen permeation test, Fourier transform infrared spectrometry, oxygen nonstoichiometric characterization) and modeling (density function theory), thus resulting in good electrochemical performance. In electrolysis mode, the high current density of 1.18 A cm2 is achieved at electrolysis voltage of 1.3 V and 600° C when water is supplied as the reactant. The hydrogen generated in electrolysis mode can be instantaneously converted into electricity by switching to the fuel cell working mode.

Illustration 1: A schematic of a reversible proton-conducting electrochemical cell (r-PEC) operating under both fuel cell and electrolysis cell modes.