Editorial: Nanoconfined Fluids in Energy Applications

Nanoconfined Fluids in Energy ApplicationsNanoconfined fluids (NCFs) (Sun et al., 2020) exhibit a rich array of physical and chemical phenomena.Formally, a fluid is nanoconfined if it is situated in an environment in which the distance between solid boundaries is of nanometer scale in at least one spatial dimension.NCFs can be confined within a diversity of geometries, including those with cross-sections that are planar [e.g., nanochannels (Neek-Amal et al., 2016)], circular (e.g., nanotubes), or irregular [e.g., various nanopores (Thiruraman et al., 2020; Hassani et al., 2021a; Hassani et al., 2021b)].NCFs are remarkable for a number of reasons.Chief among these (potentially interconnected) phenomena are surface effects [owing to the high surface-area-to-volume ratios typical of NCF systems (Wang et al., 2019; Wang and Hadjiconstantinou, 2019)], finite-size effects [owing to the comparability of the confining length scale with the fluid internal length scale (Wang and Hadjiconstantinou, 2015)], and even quantum-mechanical effects [owing to the rough comparability of the confining length scale with the thermal de Broglie wavelength (Tocci et al., 2014)].As a consequence of these effects, NCFs may exhibit many distinctive characteristics in their mass, momentum, and energy transport as compared to their unconfined (bulk) counterparts.Research on NCFs presents a number of new challenges and opportunities, ranging from experimental design, to simulation methodology, to approaches for uncertainty quantification for material and transport properties of fluids under nanoconfinement (Li and Wang, 2022).Such work is critical for advancing fundamental physics and chemistry; from an engineering perspective, this work can also promote the development of novel energy-related technologies, with applications ranging from energy storage [e.g., supercapacitors (Yoo et al., 2011;Salanne, 2017)], to energy harvesting [e.g., solar evaporation (Liu et al., 2018;Chen et al., 2019) or electricity generation via reverse electrodialysis (Vanoppen et al., 2018;Zhu et al., 2021)], to enhanced oil and gas recovery (Lee et al., 2016), to membrane-based separation processes (Gong et al., 2021).A schematic illustration of energy applications of NCFs is presented in Figure 1.In this Research Topic, we aim to present Frontier research in experimental, computational, and theoretical approaches to thermodynamics; mass, momentum, and energy transport; flow physics; and phase behavior of NCFs, especially in energy-related applications.We also aim to discuss and identify research challenges in the field, worthy of the community's broader attention.The main topics of interest in this Research Topic include 1) reviews on recent developments in the field of NCFs, 2) novel experimental and theoretical investigations of NCFs, 3) novel computational studies of NCFs, and 4) NCFs in energy-related applications.In this Research Topic, four high-quality papers were accepted for publication, which we briefly summarize below.Cui et al. study diffusion of nanoconfined fluids as motivated by problems of shale gas production.In particular, the authors investigate the diffusivity of high-temperature and high-pressure CH 4 gas