Effect of proton-conduction in electrolyte on electric efficiency of multi-stage solid oxide fuel cells

Abstract

Solid oxide fuel cells (SOFCs) are promising electrochemical devices that enable the highest fuel-to-electricity conversion efficiencies under high operating temperatures. The concept of multi-stage electrochemical oxidation using SOFCs has been proposed and studied over the past several decades for further improving the electrical efficiency. However, the improvement is limited by fuel dilution downstream of the fuel flow. Therefore, evolved technologies are required to achieve considerably higher electrical efficiencies. Here we present an innovative concept for a critically-high fuel-to-electricity conversion efficiency of up to 85% based on the lower heating value (LHV), in which a high-temperature multi-stage electrochemical oxidation is combined with a proton-conducting solid electrolyte. Switching a solid electrolyte material from a conventional oxide-ion conducting material to a proton-conducting material under the high-temperature multi-stage electrochemical oxidation mechanism has proven to be highly advantageous for the electrical efficiency. The DC efficiency of 85% (LHV) corresponds to a net AC efficiency of approximately 76% (LHV), where the net AC efficiency refers to the transmission-end AC efficiency. This evolved concept will yield a considerably higher efficiency with a much smaller generation capacity than the state-of-the-art several tens-of-MW-class most advanced combined cycle (MACC).

Modified Energy Efficiencies of Proton‐conducting SOFCs with Partial Conductions of Oxide‐ions and Holes

“…The u f dependence of the voltage can be approximately calculated by logarithmic mean of the EMF s of the inlet and outlet of the cell, EMF (average) . …”

Proton Conduction in Grain-Boundary-Free Oxygen-Deficient BaFeO2.5+δ Thin Films

“…Proton migration pathways are most often characterized by lower activation barriers within solid oxides as compared to oxygen ions (protons possess smaller mass, lower radius, have no electron cloud and their transport behavior can be roughly described via a Grotthuss-related mechanism [5]) and therefore proton-conducting materials can in principle show increased ionic conductivity especially at intermediate temperatures [1,6]. Additionally, devices, employing proton conductors have attracted attention due to potentially higher electrical efficiency as has been found before [7,8,9]. A limiting factor for the application of these electrolytes is the lack of suitable electrode catalysts, which are conductive for both electrons and protons.…”

Decomposition reaction of BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_{3−δ} in carbon dioxide atmosphere with nickel sintering aid

“…1) Acceptor-doped-perovskite-type oxide such as barium zirconate, barium cerate and similar composites are wellknown as proton conducting oxide materials, following the report by Iwahara et al…”