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Energy harvesting devices that prosper in harsh environments are highly demanded in a wide range of applications ranging from wearable and biomedical devices to self-powered and intelligent systems. Particularly, over the past several years, the innovation of triboelectric nanogenerators (TENGs) that efficiently convert ambient kinetic energy of water droplets or wave power to electricity has received growing attention. One of the main bottlenecks for the practical implications of such devices originates from the fast degradation of the physiochemical properties of interfacial materials under harsh environments. To overcome these challenges, here we report the design of a novel slippery lubricant-impregnated porous surface (SLIPS) based TENG, referred to as SLIPS-TENG, which exhibits many distinctive advantages over conventional design including optical transparency, configurability, self-cleaning, flexibility, and power generation stability, in a wide range of working environments. Unexpectedly, the slippery and configurable lubricant layer not only serves as a unique substrate for liquid/droplet transport and optical transmission, but also for efficient charge transfer. Moreover, we show that there exists a critical thickness in the liquid layer, below which the triboelectric effect is almost identical to that without the presence of such a liquid film. Such an intriguing charge transparency behavior is reminiscent of the wetting transparency and van der Waals potential transparency of graphene previously reported, though the fundamental mechanism remains to be elucidated. We envision that the marriage of these two seemingly totally different arenas (SLIPS and TENG) provides a paradigm shift in the design of robust and versatile energy devices that can be used as a clean and longer-lifetime alternative in various working environments.

The recent back-to-back findings of low-density porous ice XVI and XVII have rekindled the century-old field of the solid-state physics and chemistry of water. Experimentally, both ice XVI and XVII crystals can be produced by extracting guest atoms or molecules enclosed in the cavities of preformed ice clathrate hydrates. Herein, we examine more than 200 hypothetical low-density porous ices whose structures were generated according to a database of zeolite structures. Hitherto unreported porous EMT ice, named according to zeolite nomenclature, is identified to have an extremely low density of 0.5 g/cm 3 and the largest internal cavity (7.88 Å in average radius). The EMT ice can be viewed as dumbbell-shaped motifs in a hexagonal close-packed structure. Our first-principles computations and molecular dynamics simulations confirm that the EMT ice is stable under negative pressures and exhibits higher thermal stability than other ultralow-density ices. If all cavities are fully occupied by hydrogen molecules, the EMT ice hydrate can easily outperform the record hydrogen storage capacity of 5.3 wt % achieved with sII hydrogen hydrate. Most importantly, in the reconstructed temperaturepressure (T-P) phase diagram of water, the EMT ice is located at deeply negative pressure regions below ice XVI and at higher temperature regions next to FAU. Last, the phonon spectra of empty-sII, FAU, EMT, and other zeolite-like ice structures are computed by using the dispersion corrected vdW-DF2 functional. Compared with those of ice XI (0.93 g/cm 3 ), both the bending and stretching vibrational modes of the EMT ice are blue-shifted due to their weaker hydrogen bonds. porous ice | ultralow density | EMT ice | reconstructed temperaturepressure phase diagram | record hydrogen storage capacity W ater is a unique form of matter with many intriguing properties. One such physical property is its wide variety of stable and metastable crystal structures. To date, 18 different crystalline ice phases have been established experimentally (1-3). Many more ice phases ranging from 1D to 3D have been predicted from computer simulations (4-10). Another known ice form is ice clathrate hydrates with large internal cavities that can host guest molecules. Clathrate natural gas hydrates have received considerable attention because they are an enormous energy source on Earth. Indeed, the amount of carbon in natural gas hydrates is estimated to be at least twice that in all other fossil energies combined (11). Clathrate hydrogen hydrates have also received growing attention as they are a renewable and carbon-free energy source (12).In previous computer simulation studies, guest-free clathrate hydrates of type sII were independently predicted to be a stable phase at negative pressures by Jacobson et al. (13), Conde et al. (14), and Huang et al. (8). Remarkably, the guest-free clathrate hydrate of type sII was recently produced in the laboratory by Falenty et al. (2) by pumping off guest Ne atoms from the cavities of sII clathrate hydrate, confirming earlier ...

In contrast to the rich knowledge of water and 17 experimentally confirmed crystalline phases of solid water under positive pressures, water under negative pressure has been poorly explored. In this study, a new crystalline phase of ice with ultralow density (0.6 g cm), named "clathrate ice sL", is constructed by nano water cage clusters, and it is predicted to be stable under a lower negative pressure than the experimentally confirmed sII phase by first-principles phase diagram computations, thereby extending the phase diagram of water to negative pressure regions below -5170 bar at 0 K and below -4761 bar at 300 K. In addition, according to our theoretical prediction, the optimal hydrogen storage mass density in the new clathrate ice sL is 7.7 wt% (larger than the 2017 DOE target of 5.5 wt%), which would set a new record of hydrogen storage capacity in clathrate hydrates. The finding of clathrate ice sL not only proposes a new type of crystalline ice under negative pressure but also explores the potential applications of the ultralow density ice phases while extending the water phase diagram and enriching the knowledge of people about water.