Electrochemical Promotion of Ammonia Synthesis in Electrolysis Cells with High Conversion Efficiency

2022 Fiscal Year Final Research Report

• Project/Area Number: 20H02521
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 27030:Catalyst and resource chemical process-related
• Research Institution: Hokkaido University (2022); The University of Tokyo (2020-2021)
• Principal Investigator: Kikuchi Ryuji 北海道大学, 工学研究院, 教授 (40325486)
• Co-Investigator(Kenkyū-buntansha): 久保田 純 福岡大学, 工学部, 教授 (50272711)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: アンモニア / 電解合成 / プロトン伝導体 / 赤外分光 / 過渡応答法 / 鉄触媒 / 固体リン酸塩電解質 / バリウムジルコネート

Outline of Final Research Achievements

An electrochemical cell using a phosphate-based electrolyte was fabricated, and NH3 was synthesized electrochemically from N2 and water vapor in a temperature range around 200°C under atmospheric pressure. It was found that NH3 is not produced in Fe-based cathodes unless a voltage is applied, but NH3 is produced by applying a voltage and supplying H+, and N2H4 is also produced in addition to NH3. In situ infrared spectroscopic measurements of the developed electrode surface confirmed that N2Hx species were generated by applying voltage at 220°C, and the peak intensity increased with applied voltage. A response study in which the current is interrupted from the polarized state suggests that the decrease in the NH3 formation rate under high current densities is due to the decrease in the number of adsorbed nitrogen atoms and hydrogen atoms/H+ on the electrode surface.

Free Research Field

工学

Academic Significance and Societal Importance of the Research Achievements

NH3は燃焼時にCO2を排出せず、ゼロカーボン社会構築に向けたエネルギーキャリアとして注目されており、特に再生可能エネルギーを利用して合成されるNH3合成は、グリーンNH3として注目を集めている。本電解合成法は、常圧200℃付近でNH3を直接合成する方法で、再生可能エネルギーの利用に好適である。得られた研究成果は、本電解合成法でのN2の還元機構を明らかにするもので、窒素による電極の被覆率を高めることがNH3生成速度向上につながることを過渡応答法により明らかにした成果や、220℃におけるNH3合成において分極状態で電極上の中間体を赤外分光により初めて捕らえた成果は、学術的な意義が極めて高い。