水伏科学与技术的召唤

水覆盖了约71%的地球表面,占人体重量约70%,在细胞里的含量可达80%。水与能量相生,维持着大至地球系统的能量循环,小至生物体的温度平衡,是天然的吸能器、储能器、换能器和传能器。水吸收了太阳辐射到达地表能量的近70%,在地球上动态吸纳释放能量的年平均功率高达60万亿千瓦(1015 瓦),比全人类目前年平均能量消耗功率高3个数量级。水以热能、动能的形式存储所吸收的热量,更以蒸发、凝结、形云布雨、兴风作浪的形式,把存储的太阳能转化成机械能等多种形式的能量。更为重要的是,水在热处将太阳能吸收,经过蒸发、对流等过程在冷处凝结释放,再经沉降、径流而成川入海,无时无刻不在转移着巨大的能量。水因其能量过程主导全球气候变化,让地球成为生命的家园,如《道德经》云“上善若水,几近于道”。

从水的储能和换能过程中提取对人类有用的能量一直是人们的追求。人类利用水能的历史可追溯到春秋时期的水车或更早,随着电磁学诞生发展了水电技术。然而,传统技术主要利用水流的动能产生有用的机械能,并间接发电。纳米材料具有显著的量子效应和表面效应,可与各种形式的水发生耦合而输出显著的电信号,如石墨烯可通过双电层的边界运动将拖动和下落水滴的能量直接转化为电能(拖曳势)、也可将海水波动能转化为电能(波动势)。更具里程碑意义的发现是,廉价的碳黑等纳米结构材料可通过大气环境下无所不在的水的自然蒸发,持续产生伏级的电能。我们将这类直接转化水能为电能的现象称为“水伏效应”(hydrovoltaic effect)。水伏效应为全链条式捕获地球水循环的水能开辟了全新的方向,提升了水能利用能力。

水伏效应的理论与技术研究目前还处于萌芽期,但其发展势头、巨大潜力和应用前景,足以引起各学科领域的高度关注和大力探索。当前广泛研究的可再生能源,如太阳能、风能,其捕获不仅受时间、地域限制,而且需要晶体硅等光吸收能力好的半导体或特殊有机物等特种材料,其存储、并网更给相关储能技术提出了巨大挑战,而风能和太阳能本身的不稳定性也制约着产业的发展。与之相比,水蒸发无处不在,不受天气、时空的影响,而且可结合风能、太阳能、废热等显著提高蒸发发电量,使得蒸发能利用在理论上具有比光伏技术更大的发展空间。而且,大海深水储存的热能会以百年的长周期稳定地球表面水能的转化和分布,可谓取之不竭。

同步内容

最新研究进展 | Recent Highlights

Nov 6, 2019

Higher order J-Tz-AT solution for three-dimensional crack border fields in power-law hardening solids

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Higher order J-A2 solution has been developed to improve the HRR singular solution under ideal plane strain conditions in power-law hardening solids with the the second A2 being considered to take into account of the in-plane constraint effect, and the J-Tz singular solution has been obtained for three-dimensional (3D) cracked body by introducing the out-of-plane stress constraint factor Tz. Here a higher order J-Tz-AT solution is developed on the basis of the J-Tz and J-A2 solutions and validated against comprehensive 3D finite element (FE) analyses for specimens with through-thickness, surface, embedded and corner cracks. It is shown that better agreements are obtained between the higher order J-Tz-AT solution and 3D FE results in all simulated conditions than previously available two- or three-parameter solutions. For specimens of high in-plane constraint, such as the single-edge cracked tension specimen, compact specimen and single-edge-notched bending specimen under three-point bending,the J-Tz leading singular solution itself shows sufficient accuracy. This universal characterization of crack border stress fields confirms that the developed J-Tz-AT solution combines the advantages of the J-Tz and J-A2 solutions, which can service as a solid foundation of elastic-plastic fracture mechanics.Read more

May 28, 2019

美国化学学会会刊(JACS)发表纳米科学研究所团队最新研究成果

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Synthetic two-dimensional (2D) materials without layered bulk allotropes are approaching a new frontier of materials flatland, one with properties richer than those of graphene-like materials. This is the case even as only a few chemical elements and blends have shown synthetic 2D forms. While hydrogen and metals are earth-abundant and form numerous compounds, rarely are 2D materials with only robust metal–hydrogen bonds. Here, a large new family of 2D materials is found from metal hydrides by high-throughput computational search augmented with first-principles calculations. There are 110 thermally and dynamically stable 2D materials that range from metallic materials to wide-gap semiconductors. A subgroup of these materials even varies from topological insulators to nodal-loop semimetals as well as from antiferromagnetic semiconductors to ferromagnetic half-metals. Unexpectedly, these monolayers resemble graphene in an ability to form weak interlayer interaction due to the variable multicenter bonding of hydrogen that eliminates the otherwise prevalent dangling bonds, rather than the covalent bonds between stacked layers as in previously reported synthetic 2D materials. This feature will favor potential experimental synthesis of these metal hydride monolayers.Read more

Apr 12, 2019

Waving potential at volt level by a pair of graphene sheets

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Electricity generated from liquid flow on graphene has triggered great interests and shown its prospect in harvesting mechanical water energy. However, most attention so far has just been paid to voltage induced in graphene, little is paid for the energy induced by ions movement on liquid side. Here, by employing a pair of graphene sheets, we report the electricity generation in liquid. An open circuit voltage up to 1 V can be obtained as graphene moves across electrolyte solution. Molecular dynamics simulations indicate that the underlying mechanism is due to potential difference generated between solutions near graphene surface and that in the bulk. Experimental results show that the generated voltage has a close relation with moving speed of graphene, ion concentration and species. This work of considering ion motion in solution should provide new ideas for the development in harvesting water energy with graphene.Read more

Apr 12, 2019

Novel nonlinear coarse-grained potentials of carbon nanotubes

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Centimetres-long carbon nanotube (CNT) bundles with tensile strength over 80 GPa have been fabricated and tested recently [Nat. Nanotechnol. 13, 589–595 (2018)], but it is still a tremendous challenge to predict their nonlinear mechanical behaviors by full-atom molecular dynamics (MD) due to the huge computational cost, particularly for carbon nanotube networks. We completely established here the explicit expressions of the chirality-dependent higher-order nonlinear coarse-grained stretching and bending potentials based on the full-atom Reactive Empirical Bond-Order interatomic potential of second generation (REBO potential). In particular, the coarse-grained non-bonded potentials are improved by using the 18–24 Lennard-Jones potential. By comparison with available experimental results and full-atom MD simulations as well as our analytical results, the present nonlinear coarse-grained potentials have high accuracy. The obtained nonlinear coarse-grained potentials can be used to efficiently characterize the nonlinear mechanical behaviors and understand the failure mechanism of the CNT bundles and networks with 2∼5 orders of magnitude reduction in computing time, which should be of great help for designing and assembling CNT-based flexible microdevices.Read more

Feb 1, 2019

Graphynes for Water Desalination and Gas Separation

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Selective transport of mass through membranes, so-called separation, is fundamental to many industrial applications, e.g., water desalination and gas separation. Graphynes, graphene analogs yet containing intrinsic uniformly distributed pores, are excellent candidates for highly permeable and selective membranes owing to their extreme thinness and high porosity. Graphynes exhibit computationally determined separation performance far beyond experimentally measured values of commercial state-of-the-art polyamide membranes; they also offer advantages over other atomically thin membranes like porous graphene in terms of controllability in pore geometry. Here, recent progress in proof-of-concept computational research into various graphynes for water desalination and gas separation is discussed, and their theoretically predicted outstanding permeability and selectivity are highlighted. Challenges associated with the future development of graphyne-based membranes are further analyzed, concentrating on controlled synthesis of graphyne, maintenance of high structural stability to withstand loading pressures, as well as the demand for accurate computational characterization of separation performance. Finally, possible directions are discussed to align future efforts in order to push graphynes and other 2D material membranes toward practical separation applications.Read more

Sep 27, 2018

Toward a more scientific science

Climb atop shoulders and wait for funerals. That, suggested Newton and then Planck, is how science advances (more or less). We've come far since then, but many notions about how people and practices, policies, and resources influence the course of science are still more rooted in traditions and intuitions than in evidence. We can and must do better, lest we resign ourselves to “intuition-based policy” when making decisions and investments aimed at driving scientific progress. Science invited experts to highlight key aspects of the scientific enterprise that are steadily yielding to empirical investigation—and to explain how Newton and Planck got it right (and Einstein got it wrong). —Brad Wible Read more

Jan 30, 2017

4 Water-evaporation-induced electricity with nanostructured carbon materials

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Water evaporation is a ubiquitous natural process that harvests thermal energy from the ambient environment. It has previously been utilized in a number of applications including the synthesis of nanostructures and the creation of energyharvesting devices. Here, we show that water evaporation from the surface of a variety of nanostructured carbon materials can be used to generate electricity. We find that evaporation from centimetre-sized carbon black sheets can reliably generate sustained voltages of up to 1 V under ambient conditions. The interaction between the water molecules and the carbon layers and moreover evaporation-induced water flow within the porous carbon sheets are thought to be key to the voltage generation. This approach to electricity generation is related to the traditional streaming potential, which relies on driving ionic solutions through narrow gaps, and the recently reported method of moving ionic solutions across graphene surfaces, but as it exploits the natural process of evaporation and uses cheap carbon black it could offer advantages in the development of practical devices.Read more

Nov 25, 2016

Hydroelectric generator from transparent flexible zinc oxide nanofilms

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Harvesting wave energy based on waving potential, a newly found electrokinetic effect, is attractive but limited mainly to monolayer graphene. Here we demonstrate that moving a transparent flexible ZnO nanofilm across the surface of ionic solutions can generate electricity. The generated electricity increases linearly with the moving velocity with an open-circuit voltage up to tens of millivolt and a short-circuit current at the order of microampere. The harvested electricity can be efficiently scaled up through series and parallel connections. Theoretical simulations show that it is the proper electrical property that endows the ZnO nanofilm with the outstanding capacity in harvesting the wave energy.Read more

Mar 15, 2016

Tunable electronic and magneticproperties of two-dimensionalmaterials and theirone-dimensional derivatives

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Low-dimensional materials exhibit many exceptional properties and functional-ities which can be efficiently tuned by externally applied force or fields. Here wereview the current status of research on tuning the electronic and magnetic prop-erties of low-dimensional carbon, boron nitride, metal-dichalcogenides, phos-phorene nanomaterials by applied engineering strain, external electric field andinteraction with substrates, etc, with particular focus on the progress of computa-tional methods and studies. We highlight the similarities and differences of theproperty modulation among one- and two-dimensional nanomaterials. Recent breakthroughs in experimental demonstration of the tunable functionalities intypical nanostructures are also presented. Finally, prospective and challenges forapplying the tunable properties into functional devices are discussed.Read more

Aug 25, 2015

Large-Area, Periodic, Hexagonal Wrinkles on Nanocrystalline Graphitic Film

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Sinusoidal wrinkles develop in compressively stressed film as a means to release stored elastic energy. Here, a simple way to fabricate large-area, periodic, hexagonal wrinkled pattern on nanocrystalline graphitic films grown on c-plane sapphire (<50 nm thick) by the spontaneous delamination–buckling of the as-grown film during cooling is reported. According to the continuum mechanics calculation, strain-relief pattern adopting the hexagonal wrinkled pattern has a lower elastic energy than that of the telephone cord wrinkle at thickness regime below 50 nm. A high-fidelity transfer method is developed to transfer the hexagonal wrinkled films onto arbitrary substrates. Nanoindentation studies show that hexagonal wrinkle film engineered this way may act as shock absorber. The hexagonal wrinkled carbon film is able to selectively promote the differentiation of human mesenchymal stem cell toward the osteogenic lineage in the absence of osteogenic inducing medium.Read more