As decarbonisation accelerates, hydrogen is a key clean energy carrier, but its storage and transport remain challenging. The research from Prof. Molly Li Mengjung, Assistant Professor of the Department of Physics and Materials at The Hong Kong Polytechnic University, 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 emphasises 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.
Source: Faculty of Science Newsletter (June 2026)
