With the escalating severity of global warming and environmental degradation, reducing carbon emissions and transitioning to clean energy sources have become imperative. Hydrogen (H2) has emerged as one of the most promising alternative energy carriers, owing to its high energy density and zero carbon emission during utilization, and its combustion only produces water as a byproduct, which makes it compatible with the global carbon neutrality goal. Currently, methane steam reforming coupled with water-gas shift reactions dominates industrial hydrogen production processes, where carbon dioxide (CO2) is the primary byproduct. To obtain high-purity hydrogen meeting industrial standards, efficient separation of H2/CO2 mixtures is a critical prerequisite, which also falls into the typical pre-combustion carbon capture scenario and holds great significance for advancing low-carbon energy systems. Conventional separation technologies for H2/CO2 mixtures include distillation, adsorption, extraction, and crystallization. However, these methods are often plagued by high energy consumption, complex operational procedures, and large spatial footprints, severely limiting their sustainability in large-scale industrial applications. In contrast, membrane-based separation technology, especially the emerging nanofluidic membrane separation, has garnered extensive attention due to its inherent advantages of high selectivity, low energy requirements, compact equipment, and simple operation. Nanofluidic membranes have designable nanoporous structures and tunable physicochemical properties, making them an ideal platform for precise molecular/ionic sieving and efficient mass transport in separation processes. Specifically, the pore size of nanofluidic membranes can be tailored to match the kinetic diameters of H2 and CO2 molecules, while their surface charge properties, pore structure parameters, and chemical microenvironments can be accurately regulated. Such precise structural and chemical modulations enable selective permeation of target gas molecules (e.g., H2) and effective rejection of impurities (e.g., CO2), thereby achieving high-efficiency separation. Nevertheless, the practical application of nanofluidic membranes still faces a pivotal challenge in fabricating membranes that exhibit high selectivity, high permeability, and long-term operational stability simultaneously. To address this issue and provide systematic guidance for the development of advanced separation membranes, this review comprehensively summarizes the recent progress of nanofluidic membranes in gas separation, focusing specifically on their application in hydrogen purification. First, the cutting-edge fabrication strategies of nanofluidic membranes are elaborated, including in-situ growth, vacuum filtration, and spin-coating techniques, with a focus on the advantages and limitations of each method in regulating membrane structure and performance. Second, we systematically examine the design principles of nanofluidic membranes for selective separation, focusing on precise structural regulation through size exclusion, surface charge design, and specific adsorption mechanisms. Third, recent breakthroughs in nanofluidic membranes, particularly for high-purity hydrogen recovery, are analyzed. This analysis highlights the established structure-performance relationships and the underlying separation mechanisms, which collectively demonstrate the potential of these membranes to overcome traditional limitations and achieve superior separation performance. Finally, we delve into the practical potential of nanofluidic membranes and provide critical perspectives on the key scientific and technological challenges that must be addressed to advance their industrial application. These challenges include developing scalable and reproducible fabrication processes, enhancing membrane stability under harsh operating conditions, and optimizing the balance between selectivity and permeability. Addressing these challenges holds the promise of revolutionizing gas separation technologies and significantly contributing to the global transition towards sustainable energy solutions. Overall, this review serves as a comprehensive guide for developing next-generation separation membranes through rational nanofluidic engineering strategies. It highlights the importance of interdisciplinary research and collaborative efforts in advancing the field of nanofluidic membranes, ultimately paving the way for their widespread adoption to address pressing environmental and energy challenges.
Wang et al. (Thu,) studied this question.