Interviews with Faculty Researchers

– Interview with Prof. Molly Li Mengjung
Assistant Professor, Department of Applied Physics

As decarbonisation accelerates, hydrogen is a key clean energy carrier, but its storage and transport remain challenging. Prof. Molly Li Mengjung ’s research explores ammonia as an alternative hydrogen carrier, focusing on efficient hydrogen release and practical integration into real-world energy systems.

Unlike hydrogen, which requires high-pressure or cryogenic storage, ammonia can be liquefied under mild conditions and transported using existing infrastructure. Although toxic and requiring careful handling, ammonia provides a more practical and scalable hydrogen carrier. The main challenge is ammonia cracking—the decomposition of ammonia into hydrogen and nitrogen.

Ammonia does not readily release hydrogen, and conventional cracking requires temperatures around 500°C, making the process energy-intensive. To address this, Prof. Li’s team has developed nanostructured cobalt-based catalysts with a core-shell design, where cobalt nanoparticles are coated with a metal-oxide layer. This structure enhances performance by preventing particle aggregation at high temperatures and by providing a dynamic surface that improves ammonia adsorption and facilitates efficient hydrogen and nitrogen release.

These catalysts also exhibit dynamic nanoscale behaviour, allowing their surfaces to adapt to reaction conditions. This improves ammonia adsorption and product desorption, enabling more efficient hydrogen production at lower temperatures.

Beyond catalyst design, Prof. Li emphasizes system integration. A key challenge is bridging the temperature gap between high-temperature ammonia cracking and fuel cells, which operate at 80–150°C, to minimise energy losses and ensure efficient operation.

Hydrogen purity is another critical factor. Ammonia cracking produces a mixture of hydrogen and nitrogen, and applications vary in their requirements. Fuel cells need high-purity hydrogen, necessitating additional purification, while combustion-based uses can tolerate lower purity. System design must therefore be tailored to specific applications.

The technology has already advanced beyond the laboratory. Prof. Li’s prototypes include ammonia-powered golf carts, minibuses and charging stations, demonstrating the potential for decentralised energy supply and transportation.

Mainstream adoption depends on scalable, cost-effective green ammonia production, advances in catalysts and reactor design to improve cracking efficiency, and optimised system-level engineering for reliable, high-performance operation. Together, these advances demonstrate how ammonia can become a practical, potentially zero-carbon hydrogen carrier.

加以氨作為氫能載體：開啟零排放能源新機遇

– 李孟蓉教授專訪
應用物理學系助理教授

在全球邁向低碳環境下，氫能被視為重要的清潔能源載體，但其儲存與運輸一直面對不少挑戰。李孟蓉教授的研究以「氨」作為替代性氫能載體，以探索如何高效地釋放氫氣，並實際應用於能源系統之中。

與氫氣需要高壓或低溫儲存不同，氨可在較溫和條件下液化，並可利用現有基礎設施進行運輸。雖然氨具毒性，需要謹慎處理，但整體仍是一種可行的氫能載體。當中的核心技術為將氨分解為氫氣和氮氣的「氨裂解」過程。

氨本身並不容易釋放氫氣，傳統裂解技術需要約500°C的高溫，且能耗較高。為此，李教授的團隊研發出納米結構的鈷基催化劑，其「核殼結構」設計以金屬氧化物包覆鈷納米粒子，防止粒子在高溫下聚集，同時提供具動態特性的表面，提升氨的吸附能力，令氫氣與氮氣更容易被釋放。

這類催化劑具備納米動態特性，其表面能隨反應條件調整，有助提升氨的吸附與釋放效率，能在較低溫度下更高效地產生氫氣。

此外，李教授亦強調系統整合的重要性。其中一大關鍵，是解決高溫裂解與低溫燃料電池（約80–150°C）之間的溫差問題，以減少能耗。

氫氣純度亦是重要因素。氨裂解後會產生氫氣與氮氣的混合物，而不同應用對純度要求各異。例如燃料電池需要高純度氫氣，需進一步淨化；燃燒用途則可容許較低純度。因此，系統設計必須因應不同應用場景作出調整。

對此，李教授團隊已開發出以氨為動力的高爾夫球車、小型巴士及充電站原型，充份展示當中的應用潛力。

未來要推動技術廣泛應用，仍需在綠色氨生產、催化技術及系統工程等方面持續突破。隨着技術逐步成熟，氨有望成為一種具成本效益、可大規模應用，甚至接近零碳排放的氫能載體，為全球能源轉型注入新動力。