Design Principles and Experimental Progress of Novel Hydrocarbon Hydrogen Storage Materials

As the global energy landscape undergoes a profound transformation driven by the "Dual Carbon" goals, developing efficient and safe hydrogen storage solutions has emerged as a critical challenge in the energy sector. Among various potential media, hydrocarbon compounds stand out due to their abundant availability, low cost, and well-established industrial supply chains. However, traditional liquid hydrocarbons, such as gasoline and diesel, suffer from significantly lower volumetric hydrogen density compared to gaseous hydrogen, making them unsuitable for mobile applications. This limitation has spurred the development of novel solid-state and supercritical storage technologies based on engineered hydrocarbons. The core strategy lies in molecular design to maximize hydrogen capacity per unit mass or volume while maintaining material stability.

The design principles of hydrocarbon-based hydrogen storage materials revolve primarily around the tunability of molecular architecture. The hydrogen-to-carbon ratio (H/C ratio) is a decisive factor in determining storage density. By increasing the number of hydrogen atoms relative to the carbon skeleton—without compromising structural integrity—researchers can significantly enhance mass storage density. Strategies include introducing unsaturated bonds (such as double or triple bonds) or constructing cage-like frameworks that accommodate additional hydrogen atoms. Furthermore, optimizing pore structure is paramount. For porous hydrocarbon materials, the pore size must align with the kinetic diameter of hydrogen molecules to facilitate optimal adsorption. Additionally, leveraging hydrophobic effects or specific van der Waals interactions can strengthen the binding force between hydrogen molecules and the material surface.

Experimental progress in this field has shifted from simple liquid hydrocarbons to functionalized solid-state systems. Current research trajectories primarily focus on three key areas:

• Organic Framework Materials: Chemically cross-linked networks with permanent porosity, such as Covalent Organic Frameworks (COFs) and Metal-Organic Frameworks (MOFs), are extensively studied. These materials offer highly tunable pore structures, allowing scientists to "customize" the environment specifically for hydrogen molecules.
• Porous Polymers: Utilizing aromatic polyimides and other high-performance polymers, researchers adjust porosity by controlling polymerization degree and cross-linking density. This approach optimizes the balance between mechanical strength and hydrogen uptake capacity.
• Supercritical Fluid Technology: This method involves pressurizing liquid hydrocarbons into a supercritical state. In this phase, the fluid exhibits properties of both a gas (rapid diffusion) and a liquid (high solvating power), enabling dense physical adsorption of hydrogen.

It is worth noting that while alkanes, alkenes, alkynes, and aromatics possess distinct chemical properties, they are often integrated within a broader hydrocarbon framework for synergistic consideration. For instance, aromatic rings, with their planar geometry and $\pi$-electron clouds, serve as ideal building blocks for porous scaffolds. Conversely, the high unsaturation of alkenes and alkynes can introduce specific reactive sites to enhance hydrogen adsorption capabilities.

Recent experimental data reveals promising performance from novel hydrocarbon storage materials. Certain porous materials based on aromatic skeletons have achieved mass storage densities exceeding 5.5 wt% at 7 MPa, rivaling or surpassing some metal hydrides. However, practical applications face significant hurdles. Thermal stability remains a primary concern; many organic frameworks tend to depolymerize or oxidize at elevated temperatures, limiting their viability in vehicular environments. Furthermore, cycle life is a critical bottleneck, as repeated adsorption-desorption cycles can lead to pore collapse or structural degradation. Finally, the lack of low-cost, large-scale manufacturing processes continues to hinder commercialization.

Looking ahead, future research will prioritize a deeper understanding of the "structure-property" relationship. Combining high-throughput computational screening with rigorous experimental validation offers a powerful pathway to accelerate the discovery of new materials. Simultaneously, developing hydrocarbon materials with self-healing capabilities or enhanced anti-aging properties will be crucial for improving their engineering utility. With the ongoing convergence of materials science, chemical engineering, and computational chemistry, it is reasonable to anticipate that next-generation hydrogen storage technologies based on hydrocarbon compounds will achieve scalable application in the near future, providing a solid foundation for the rise of the hydrogen economy.