A bifunctional electrochemical flow cell integrating ammonia production and electricity generation for renewable energy conversion and storage |
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Affiliation: | 1. Department of Mechanical Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR, China;2. Institute of Acoustics, School of Physics Science and Engineering, Tongji University, Shanghai, 200092, China;3. Key Laboratory of Low-grade Energy Utilization Technologies and Systems (Chongqing University), Ministry of Education, Chongqing, 400030, China;4. Institute of Engineering Thermophysics, Chongqing University, Chongqing 400030, China;5. The Hong Kong Polytechnic University Shenzhen Research Institute, Shenzhen 518057, China |
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Abstract: | Renewable energy has rapidly advanced in the global energy system, triggering the visible development of energy storage technologies in recent decades. Among them, the electricity-fuel-electricity approach is an effective way for the storage and utilization of renewable power. In this work, a bifunctional electrochemical flow cell integrating both ammonia production and electricity generation modes is developed for renewable energy conversion and storage. Ammonia, a hydrogen carrier having a high hydrogen content of 17.6 wt %, is relatively easier to convert to liquid phase for large-scale storage. The long-distance ammonia transport can reliably depend on the established infrastructure. In addition, as a carbon-free fuel beneficial for achieving the goal of carbon-neutrality, ammonia is considered as an environmentally benign and cost-effective mediator fuel. This flow cell is able to operate via two modes, i.e., an ammonia-production mode for energy storage in the form of ammonia (via nitrogen reduction reaction) and an electricity-generation mode for energy conversion in the form of electricity (via ammonia oxidation reaction). This flow cell is constituted by a PtAu/C-coated nickel-foam electrode for nitrogen and oxygen reduction reactions, a Pt/C-coated nickel-foam electrode for water and ammonia oxidation reactions, and an alkaline anion exchange membrane for charge-carrier migration. Charging this flow cell with the supply of nitrogen results in a Faradaic efficiency of 2.70% and an ammonia production rate as high as 9.34 × 10?10 mol s?1 cm?2 at 23 °C. Moreover, energizing this flow cell with ammonia results in an open-circuit voltage of 0.59 V and a peak power density of 3.31 mW cm?2 at 23 °C. A round-trip efficiency of 25.7% is realized with the constant-electrode mode. |
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Keywords: | Renewable energy Energy conversion and storage Electrochemical flow cell Ammonia mediator Operation mode |
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