Hydrogen Carriers

Ammonia Synthesis & Decomposition

Ammonia (NH₃) is considered one of the most effective hydrogen carriers and clean energy resources, which can be liquefied by mild compression for easy transport. The key issue for NH₃ synthesis and decomposition is the development of non-noble metal-based, highly active, and stable catalysts that can be operated under mild conditions. Recent progress in nanomaterials synthesis enables us to assess materials with ubiquitous elements because they essentially have high surface area and enormous active sites for catalysis. Our group conducted a systematic analysis to develop novel catalysts and design highly efficient reactors for the ammonia synthesis & decomposition processes for future renewable energy conversion technologies. In this context, the characterization of intermediate products and the surface of catalysts provide interesting information that helps to elucidate the true rate-controlling step for controlling reaction conditions for efficiency improvement. Notably, these developed materials for NH₃ synthesis/decomposition can serve as new types of catalysts for various catalytic reactions, including hydrogen evolution, CO₂ absorption, & oxygen evolution reactions.

Selected Publications

• Recent Advances in Ammonia Synthesis over Ruthenium Single-atom-embedded Catalysts: A Focused Review
• Material Discovery and High Throughput Exploration of Ru-based Catalysts for Low Temperature Ammonia Decomposition

Methylcyclohexane Dehydrogenation

Among the various homocyclic Liquid Organic Hydrogen Carriers (LOHCs) subjected to extensive investigation—namely, cyclohexane (CH), methylcyclohexane (MCH), and decalin (DEC)—MCH emerges as the most promising candidate. This is attributed to its strong compatibility with existing conventional transport, storage, and distribution systems, despite its slightly lower hydrogen storage capacity (6.2 wt.% or 47.3 kgH₂∙m⁻³) in comparison to CH (7.2 wt.%) and DEC (7.3 wt.%). The drawbacks of benzene (BEN, a product from CH) with carcinogenic toxicity and the solid phase of naphthalene (NAP, a product from DEC) at ambient conditions introduce additional challenges in storage and handling. MCH's distinct advantages include its very low freezing temperature (-126.6 °C) and that of its dehydrogenated form toluene (TOL) (-95 °C), surpassing the freezing temperatures of CH (6.5 °C) and benzene (5.5 °C). This characteristic facilitates convenient storage and handling, even in subzero temperature conditions. Furthermore, MCH and TOL's high boiling temperatures (>100 °C) contribute to their lower volatility, making them safer to handle at normal temperature and pressure, as indicated by recent thermal hazard studies. However, it is crucial to acknowledge the environmental concerns associated with MCH, such as its high aquatic toxicity and poor biodegradability, as well as the reproductive toxicity of TOL. These factors suggest that the LOHC system, while efficient for hydrogen storage and transportation, may pose significant hazards to both human health and the environment, rendering them less preferable compared to current diesel oil-based energy systems. MCH, with its petroleum-like characteristics, stands out as an efficient carrier for hydrogen, surpassing the capabilities of hydrogen gas. Notably, in industrial settings, dehydrogenation catalysts predominantly consist of Pt/Al₂O₃. The development of highly efficient catalysts for hydrogenation holds great promise for advancing hydrogen storage technologies, offering both economic and ecological benefits. In our research group, our focus revolves around the design, development, synthesis, and evaluation of catalysts in reactors. We systematically characterize the properties of these catalysts to identify the most efficient ones, contributing to the ongoing efforts to enhance hydrogen storage technologies.