Researchers from Lawrence Berkeley National Laboratory (LBNL) and Nissan Research Center report on their investigation of the internal reforming of ethanol fuel on high-performance metal-supported solid-oxide fuel cells (MS-SOFCs) with infiltrated catalysts in a paper in the Journal of Power Sources.

Dogdibegovic et al.

Nissan’s public interest in ethanol-fueled solid-oxide fuel cells stretches back several years to its announcement of the e-Bio Fuel cell system in 2016. (Earlier post.) The e-Bio Fuel Cell system featured an an SOFC stack and an on-board reformer to convert 100% ethanol or ethanol-blended water (55% water, 45% ethanol) to hydrogen. At the time, Nissan said it planned commercialization of the technology in 2020.

In 2018, Ceres Power entered into a new partnership with Nissan further to develop solid-oxide fuel cell technology for EV applications. (Earlier post.)

In the new paper, the LBNL-Nissan team noted that currently, reforming of hydrocarbon fuels for use with SOFCs is mainly performed external to the SOFC stack.

However, for small-scale and portable applications the complexity, size and weight of the system can be reduced by eliminating the external reformer and annex units, and performing internal reforming of the fuels inside the SOFC stack. This approach would be practical and cost-effective for vehicular applications due to size and weight restrictions for the SOFC system.

In this work, ethanol is considered as a renewable transportation fuel for use in MS-SOFC range extenders in vehicles. Dilution of ethanol with water increases safety, and is expected to suppress anode coking by increasing the steam-to-carbon ratio.

… To improve internal reforming of ethanol fuel in conventional SOFCs, the primary approach has been to augment or replace the Ni anode electrocatalyst. …The majority of these studies reported low performance with ethanol (peak power <0.3 W cm􏰀^-2 at 600–800 ˚C), due to the use of inherently low-performing cells, incomplete reforming, or both.

… It is also imperative to note that a simple comparison of SOFC performance with hydrogen and ethanol fuel is commonly reported in literature. Such approach does not address the large range of derating factors. Individual effects that should all be taken into consideration include: (1) hydrogen concentration (lower hydrogen content in reformed fuel and concentration polarization across the thickness of the anode), (2) internal reforming (chemical catalytic activity towards fuel reforming), and (3) coking (deposition of solid carbon that can block the reforming or electrochemical catalysts active sites). Separation of these effects would inform development of cell architecture and catalyst compositions for ethanol internal reforming.

—Dogdibegovic et al.

The researchers evaluated hydrogen concentration and internal reforming effects in a symmetric-architecture metal-supported solid-oxide fuel cell (MS-SOFC) with different fuels including hydrogen, simulated reformate, anhydrous ethanol, ethanol water blend, and hydrogen-nitrogen mixtures. They isolated the impact of electrocatalytic, internal reforming, hydrogen concentration, mass transport, and coking limitations in button cells under low fuel utilization.

Comparison of cell performance under ethanol internal reforming conditions. (Bottom grey region) Summary of previous performance of conventional SOFCs with internal reforming of ethanol fuel (dry or steam reforming). (Top white region) Performance obtained in present work for MS-SOFCs with 2xNi-SDCN₄₀ anode operating with anhydrous ethanol (red) and ethanol-water blend (blue). Dogdibegovic et al.

Symmetric-architecture MS-SOFCs have been optimized for high performance and longevity with internal reforming of ethanol fuel. Performance of baseline MS-SOFC was determined to be limited by both hydrogen concentration and internal reforming. Addition of extra Ni to the MS-SOFC anode resulted in excellent performance in the presence of internal reforming, and the remaining decrease in peak power density, when compared to hydrogen fuel, was attributed solely to decrease in hydrogen concentration.

Simple infiltration of high-surface area Ni nanoparticles over the fuel-side metal support and anode layers lead to unprecedented peak power density between 1.0 and 1.4 W cm^􏰀-2 at 650–700 ˚C, with internal reforming of ethanol-water blend and anhydrous ethanol fuel. Stable electrochemical operation in ethanol-water blend was observed after 25 h at 700 ˚C and 0.7 V.

—Dogdibegovic et al.

The work was funded in part by Advanced Research Projects Agency - Energy (ARPA-E).

Resources

• Emir Dogdibegovic, Yosuke Fukuyama, Michael C. Tucker (2020) “Ethanol internal reforming in solid oxide fuel cells: A path toward high performance metal-supported cells for vehicular applications,” Journal of Power Sources, Volume 449, doi: 10.1016/j.jpowsour.2019.227598.