Energy-Efficient and Self-Powered Green Ammonia Synthesis by Electrochemical Nitrate Reduction Combined with Hydrazine Oxidation

Chaeeun Lim; Hyogyun Roh; Eun Ho Kim; Hangyeol Kim; Taiho Park; Donghwa Lee; Kijung Yong

doi:10.1002/smll.202304274

Energy-Efficient and Self-Powered Green Ammonia Synthesis by Electrochemical Nitrate Reduction Combined with Hydrazine Oxidation

Small. 2023 Dec;19(50):e2304274. doi: 10.1002/smll.202304274. Epub 2023 Aug 25.

Authors

Chaeeun Lim^{1

2}, Hyogyun Roh^{1

2}, Eun Ho Kim³, Hangyeol Kim^{2

4}, Taiho Park^{2

4}, Donghwa Lee³, Kijung Yong^{1

2}

Affiliations

¹ Surface Chemistry Laboratory of Electronic Materials (SCHEMA), Department of Chemical Engineering, Pohang University of Science and Technology (POSTECH), Pohang, 37673, South Korea.
² Research Center for Carbon-zero Green Ammonia Cycling (RCCGAC), Pohang University of Science and Technology (POSTECH), Pohang, 37673, South Korea.
³ Computational Nano-Materials Design Laboratory (CNMD), Department of Material Science & Engineering, Pohang University of Science and Technology (POSTECH), Pohang, 37673, South Korea.
⁴ Polymer Chemistry & Electronics Lab (PCEL), Department of Chemical Engineering, Pohang University of Science and Technology (POSTECH), Pohang, 37673, South Korea.

PMID: 37626461
DOI: 10.1002/smll.202304274

Abstract

To achieve the global goal of carbon neutrality, recently, emphasis has been placed on developing green ammonia production method to replace the Haber-Bosch process. Nitrate reduction reaction (NO₃ RR) has received considerable attention, especially for electrochemically producing ammonia from nitrate and simultaneously purifying wastewater. This study first demonstrates that the combination of NO₃ RR with hydrazine oxidation reaction (HzOR) is an energy efficient green ammonia production method, which overcomes the sluggish water oxidation limitation. Tungsten phosphide (WP) nanowires (NWs) are prepared as cathode NO₃ RR electrocatalysts, which exhibit a high Faradaic efficiency in both neutral (≈93%) and alkaline (≈85%) media. Furthermore, they show a high bifunctional activity in anodic reactions and exhibit a low potential 0.024 V for generating a current density of 10 mA cm^-2 in HzOR. The overall NO₃ RR-HzOR required an impressively low potential of 0.24 V for generating a current density of 10 mA cm^-2 ; this potential is much lower than those required for NO₃ RR-OER (1.53 V) and NO₃ RR-UOR (1.31 V). A self-powered ammonia production system, prepared by assembling an NO₃ RR-HzOR with a perovskite solar cell, displays a high ammonia production rate of 1.44 mg cm^-2 h^-1 . A single PV cell provides enough driving voltage in the PV-EC due to low required potential. This system facilitates unassisted green ammonia synthesis with a low energy consumption and also allows upcycling of wastewater to produce useful fuel.

Keywords: ammonia production; hydrazine oxidation; nitrate reduction; photovoltaic-electrolysis; tungsten phosphide.

Abstract

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