アニオン交換膜直接アンモニア燃料電池の物質移動と電気化学的特性

Unofficial AI-generated summary based on the public title and abstract. Not an official translation.

🔬研究者:AEM-DAFCの物質移動と劣化機構に関する詳細な実験的知見を提供し、今後の高性能化研究の基礎となる。

🏢実務担当者:アンモニア燃料電池の実用化に向けた性能限界と劣化要因を理解し、システム設計に活かせる。

🏛政策担当者:アンモニア燃料電池技術の現状と課題を把握し、水素・アンモニア政策の技術ロードマップ策定に参考となる。

To keep global warming below 1.5°C, decarbonization of various sectors in our economy is urgent for achieving global carbon neutrality by 2050. Following this, there will be an overwhelming demand for carbon-free fuels to replace carbon-intensive fossil fuels. Ammonia (NH₃), as a zero-carbon fuel that can be produced from renewable energy sources, has attracted ever-increasing attention in recent years. Direct ammonia fuel cells (DAFCs), which can directly convert the chemical energy stored in ammonia into electrical energy with a high efficiency and only emit nitrogen and water, are widely investigated. Especially, the anion-exchange membrane based direct ammonia fuel cells (AEM-DAFCs), which can operate at low temperatures (below 120°C), offer several promising features, such as fast start-up and zero-gap configurations. Despite some experimental and numerical studies of AEM-DAFCs have been conducted in terms of operating conditions, the overlook of mass transfer and degradation characteristics has limited the comprehensive and in-depth understanding of AEM-DAFCs. Therefore, the primary objective of this study is to investigate the mass transfer characteristics of AEM-DAFCs, with a specific focus on the crossover behaviours of ammonia and water, and the resulting challenges of mixed potential and water flooding that impede cell performance. Furthermore, this study aims to elucidate cell degradation mechanisms by decoupling overlapping electrochemical polarization processes that govern poor durability (lifetime < 80 h). To further address these limitations, a novel hybrid cell configuration is proposed to enhance cell performance. Finally, a three-dimensional numerical model is established to investigate the anode diffusion layer design parameters. In this study, firstly, the general performance of an AEM-DAFC is examined under various operating conditions. It achieves a maximum peak power density (PPD) of 160.8 mW cm⁻² and an open circuit voltage (OCV) of 0.65 V under the optimized conditions. Secondly, an in-situ observation method is developed to quantitatively characterize the rates of ammonia and water crossover. The effects of operating conditions (such as ammonia concentration and cell temperature) and membrane electrode assembly (MEA) design parameters (such as membrane thickness and cathode wettability) on behaviours of ammonia and water crossover are thoroughly examined. The findings show that ammonia crossover can be substantially reduced by using a low-concentration ammonia solution or a thicker membrane. Thirdly, to investigate the degradation mechanisms of AEM-DAFCs, the electrochemical impedance spectroscopy (EIS) combined with distribution of relaxation times (DRT) analysis is employed. DRT is a non-parametric model that effectively interprets EIS spectra by translating them from the frequency domain to the time domain, allowing for the distinction of overlapping polarization processes. Operating conditions assist in identifying the characteristic peaks obtained by DRT, which correspond to the kinetics of the ammonia oxidation reaction (AOR), the kinetics of the oxygen reduction reaction (ORR), and ionic transport. During a 50-hour stability test, in addition to interpreting EIS spectra with DRT, a reference electrode is used to separate the overpotential losses of the anode and cathode. Post-characterization tests are also conducted to examine changes in the electrode microstructure and composition before and after the stability test. The results indicate that cell performance decay primarily stems from the deterioration of AOR kinetics, specifically due to the dissolution (particularly of iridium), migration, and agglomeration of the PtIr/C catalyst, as well as poisoning by adsorbed species such as *N and *NOₓ. Fourthly, a novel hybrid direct ammonia fuel cell, incorporating an alkaline anode, a cation exchange membrane, and an acidic cathode, is proposed to significantly enhance cell performance. The hybrid design elevates the theoretical cell voltage from the standard 1.17 V to 2.55 V, thereby enabling an OCV of 1.42 V and a PPD over 600 mW cm⁻². Finally, a three-dimensional numerical model is developed to explore the effects of anode gas diffusion layer design parameters on cell performance and mass transport characteristics.

• openalex http://hdl.handle.net/10397/121952first seen 2026-11-10 04:46:27 · last seen 2026-11-14 04:44:45