No abstract

No abstract

Ammonia is a very attractive carbon-neutral fuel due to its low cost, high energy density, and existing transportation infrastructure. However, the viable commercial application of direct ammonia fuel cells (DAFC) has not been realized, largely due to materials challenges. Generally, DAFCs either use low temperature polymer electrolytes, which are limited by low reaction rates, or use high temperature solid oxide electrolytes, which suffer from severe material thermal degradation. We have developed an intermediate temperature alkaline electrolyte-based DAFC that operates at 400-600 °C, enabling high reaction rates while limiting thermal degradation. This DAFC is based on our innovative molten hydroxide electrolyte impregnated in a porous ceramic matrix, which has conductivity as high as 0.4 S/cm at 350 °C, enabling rapid hydroxide transport. The DAFCs use state-of-the-art ammonia oxidation catalysts and ammonia-tolerant ORR catalysts developed in-house and by our collaborators at SUNY Buffalo and University of Delaware. Our DAFC has demonstrated an OCV of 1.2 V and can achieve 300 mA/cm2 at 0.86 V, or >250 mW/cm2 power from pure humidified ammonia. It is stable for days without loss of activity and has very low ammonia crossover, enabling the high OCV and high power density without catalyst poisoning. Further work on catalyst development and cell design is underway to achieve higher power densities and reduce PGM catalyst loading and operation temperature, making this a more commercially viable technology. Acknowledgements: This work is financially supported by the Department of Energy’s ARPA-E under the award# DE_AR000814

Hydrogen production from water electrolysis for mobile and energy storage applications is attractive due to its high efficiency, fast ramp rates, and potential for the clean energy economy. However, current hydrogen production from electrolysis comprises only a small fraction of the global hydrogen market due to the high cost associated with expensive stack materials (membrane, catalyst, and bipolar plates) and electricity consumption of the commercial electrolysis systems. We have developed a high temperature alkaline electrolyte-based water electrolyzer (HTAWE) that operates at 350-550 °C, enabling high reaction rates while limiting thermal degradation compared to solid oxide cells operating above 700 °C. This water electrolyzer is based on our innovative molten hydroxide electrolyte impregnated in a porous ceramic matrix, which has conductivity as high as 0.4 S/cm at 350 °C, enabling rapid hydroxide transport. This HTAWE can simultaneously reduce the electrolyzer cost (by adopting cheap material) and improve energy efficiency (by enabling high-temperature operation). Using an innovative new SrZrO3-based matrix, we have demonstrated exceptional water electrolysis performance using both single and binary hydroxide mixtures. We successfully achieved sustained cell performance of 1.35 V at a current density of 1,000 mA/cm2 with area specific resistance (ASR) 0.1 Ohm-cm2 across the cell at furnace temperature 500 °C. We were also able to demonstrate cell performance of 1.45 V at a current density of 1,000 mA/cm2 with ASR of <0.2 Ohm-cm2 across the cell at a furnace temperature 400 °C. Furthermore, we have demonstrated stable cell performance for >1000 h of continuous operation at 1 A/cm2 with ASR of 0.2 Ohm∙cm2 across the cell.

Ammonia is a very attractive carbon-neutral fuel due to its low cost, high energy density, and existing transportation infrastructure. However, the viable commercial application of direct ammonia fuel cells (DAFC) has not been realized, largely due to materials challenges that lead to poor cell performance. Generally, DAFCs either use low temperature polymer electrolytes, which are limited by low reaction rates and severe ammonia crossover, or use high temperature solid oxide electrolytes, which suffer from severe material thermal degradation. We have developed an intermediate temperature alkaline electrolyte-based DAFC that operates at 400-600 °C, enabling high reaction rates while limiting thermal degradation. This DAFC is based on our innovative molten hydroxide electrolyte impregnated in a porous ceramic matrix, which has conductivity as high as 0.4 S/cm at 350 °C, enabling rapid hydroxide transport. The DAFCs uses state-of-the-art ammonia oxidation catalysts and ammonia-tolerant oxygen reduction reaction catalysts. Our DAFC has demonstrated an OCV of 1.2 V and can achieve 300 mA/cm2 at 0.86 V at 550 ⁰C, and 0.98 V at 600 ⁰C, or >450 mW/cm2 power from pure humidified ammonia. It has low ammonia crossover, thus enabling the high OCV and high power density without catalyst poisoning. Further work on catalyst development and cell design is underway to achieve higher power densities and reduce PGM catalyst loading and operation temperature, making this a more commercially viable technology.