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Sensor surfaces with micron- and nano-gap scales possess high surface-to-volume ratio which greatly affects their contribution towards water adsorption and condensation. However, the quantitative relationship between adsorbed water molecules and condensed water droplets remains unclear. In this study, we used the humidity-based detected galvanic current within the micron gaps of our newly developed moisture sensor chip (MSC) to emphasize the quantitative relationship between adsorbed water molecules and condensed water droplets. The mass of adsorbed water molecules was detected using a quartz-crystal-microbalance electrode (QCM) whereas the mass of condensed water droplets was estimated microscopically based on their occupying volumes at MSC surface. Experimental results demonstrated that the minimum detection limit of MSC under these experimental conditions was ~150 ng/cm2 for adsorbed water molecules and ~700 ng/ cm2 for condensed water droplets. The detected-response galvanic current arises when a water bridges between two adjacent arrays is found to be linearly correlated to the adsorbed and/or the condensed water’s mass. Such correlation is believed to provide a feasible long-range sensor that can distinguish the status of its surface-existing water either in adsorbed molecular or condensed droplet-wise regimes.

Solar-driven, sorption-based atmospheric water harvesting (AWH) offers a cost-effective solution to freshwater scarcity in arid areas. Creating AWH devices capable of performing multiple adsorption–desorption cycles per day is crucial for increasing water production rates matching human water requirements. However, achieving rapid-cycling AWH in passive harvesters has been challenging due to sorbents’ slow water adsorption–desorption dynamics. Here we report an MOF-derived nanoporous carbon, a sorbent endowed with fast sorption kinetics and excellent photothermal properties, for high-yield AWH. The optimized structure (40% adsorption sites and ~1.0 nm pore size) has superior sorption kinetics due to the minimized diffusion resistance. Moreover, the carbonaceous sorbent exhibits fast desorption kinetics enabled by efficient solar-thermal heating and high thermal conductivity. A rapid-cycling water harvester based on nanoporous carbon derived from metal–organic frameworks can produce 0.18 L kgcarbon−1 h−1 of water at 30% relative humidity under one-sun illumination. The proposed design strategy is helpful to develop high-yield, solar-driven AWH for advanced freshwater-generation systems.A metal–organic-framework-derived nanoporous carbon with intrinsically fast sorption kinetics and excellent photothermal properties enables high-yield, solar-driven atmospheric water harvesting in arid areas.

Crashed or dimensional rocks have been used as natural construction material, decoration stone or as material for artistic sculptures. Especially old historical towns not only in Slovakia have had experiences with use of stones for construction purposes for centuries. The whole buildings were made from dimensional stone, like sandstone, limestone or rhyolite. Pavements were made especially from basalt, andesite, rhyolite or granite. Also the most common modern construction material - concrete includes large amounts of crashed rock, especially limestone, dolostone and andesite. However, rock as any other material if exposed to exogenous processes starts to deteriorate. Especially mechanical weathering can be very intensive if rock with unsuitable rock properties is used. For long it had been believed that repeated freezing and thawing in relation to high absorption is the main reason of the rock deterioration. In Slovakia for many years the high water absorption was set as exclusion criterion for use of rocks and stones in building industry. Only after 1989 the absorption was accepted as merely informational rock property and not exclusion. The reason of the change was not the understanding of the relationship between the porosity and rock deterioration, but more or less good experiences with some high porous rocks used in constructions exposed to severe weather conditions and proving a lack of relationship between rock freeze-thaw resistivity and water absorption. Results of the recent worldwide research suggest that understanding a resistivity of rocks against deterioration is hidden not in the absorption but in the structure of rock pores in relation to thermodynamic properties of pore water and tensile strength of rocks and rock minerals. Also this article presents some results of research on rock deterioration and pore structure performed on 88 rock samples. The results divide the rocks tested into two groups - group N in which the pore water does not freeze even when the temperature decreases to -20 ºC, and the second group F in which the pore water freezes. It has been found that the rocks from group N contain critical portion of adsorbed water in pores which prevents freezing of the pore water. The presence of adsorbed water enables thermodynamic processes related to osmosis which are dominantly responsible for deterioration of rocks from group N. A high correlation (R = 0.81) between content of adsorbed water and freeze-thaw loss was proved and can be used as durability estimator of rocks from group N. The rock deterioration of group F is caused not only by osmosis, but also by some other processes and influences, such as hydraulic pressure, permeability, grain size, rock and mineral tensile strength, degree of saturation, etc., and the deterioration cannot be predicted yet without the freeze-thaw test. Since the contents of absorbed water and ratio between adsorbed and bulk water (of which the absorbed water consists) is controlled by the porosity and pore structure, it can be concluded that the deterioration of some rocks is strongly related to rock pore structure.

Molybdenum disulfide is naturally inert for alkaline hydrogen evolution catalysis, due to its unfavorable water adsorption and dissociation feature originated from the unsuitable orbital orientation. Herein, we successfully endow molybdenum disulfide with exceptional alkaline hydrogen evolution capability by carbon-induced orbital modulation. The prepared carbon doped molybdenum disulfide displays an unprecedented overpotential of 45 mV at 10 mA cm −2 , which is substantially lower than 228 mV of the molybdenum disulfide and also represents the best alkaline hydrogen evolution catalytic activity among the ever-reported molybdenum disulfide catalysts. Fine structural analysis indicates the electronic and coordination structures of molybdenum disulfide have been significantly changed with carbon incorporation. Moreover, theoretical calculation further reveals carbon doping could create empty 2p orbitals perpendicular to the basal plane, enabling energetically favorable water adsorption and dissociation. The concept of orbital modulation could offer a unique approach for the rational design of hydrogen evolution catalysts and beyond. Technologies allowing for sustainable hydrogen production will contribute to the decarbonization of the future energy supply. Here the authors report that carbon induced orbital modulation can facilitate the otherwise inert MoS 2 electrocatalyst superior alkaline hydrogen evolution reactivity.

We present detailed measurements of the double-layer capacitance of the Pt(111)–electrolyte interface close to the potential of zero charge (PZC) in the presence of several different electrolytes consisting of anions and cations that are considered to be nonspecifically adsorbed. For low electrolyte concentrations, we show strong deviations from traditional Gouy–Chapman–Stern (GCS) behavior that appear to be independent of the nature of the electrolyte ions. Focusing on the capacitance further away from PZC and the trends for increasing ion concentration, we observe ion-specific capacitance effects that appear to be related to the size or hydration strength of the ions. We formulate a model for the structure of the electric double layer of the Pt(111)–electrolyte interface that goes significantly beyond the GCS theory. By combining two existing models, namely, one capturing the water reorganization on Pt close to the PZC and one accounting for an attractive ion–surface interaction not included in the GCS model, we can reproduce and interpret the main features the experimental capacitance of the Pt(111)–electrolyte interface. The model suggests a picture of the double layer with an increased ion concentration close to the interface as a consequence of a weak attractive ion–surface interaction, and a changing polarizability of the Pt(111)–water interface due to the potential-dependent water adsorption and orientation.

The development of cost-effective hydroxide exchange membrane fuel cells is limited by the lack of high-performance and low-cost anode hydrogen oxidation reaction catalysts. Here we report a Pt-free catalyst Ru 7 Ni 3 /C, which exhibits excellent hydrogen oxidation reaction activity in both rotating disk electrode and membrane electrode assembly measurements. The hydrogen oxidation reaction mass activity and specific activity of Ru 7 Ni 3 /C, as measured in rotating disk experiments, is about 21 and 25 times that of Pt/C, and 3 and 5 times that of PtRu/C, respectively. The hydroxide exchange membrane fuel cell with Ru 7 Ni 3 /C anode can deliver a high peak power density of 2.03 W cm −2 in H 2 /O 2 and 1.23 W cm −2 in H 2 /air (CO 2 -free) at 95 °C, surpassing that using PtRu/C anode catalyst, and good durability with less than 5% voltage loss over 100 h of operation. The weakened hydrogen binding of Ru by alloying with Ni and enhanced water adsorption by the presence of surface Ni oxides lead to the high hydrogen oxidation reaction activity of Ru 7 Ni 3 /C. By using the Ru 7 Ni 3 /C catalyst, the anode cost can be reduced by 85% of the current state-of-the-art PtRu/C, making it highly promising in economical hydroxide exchange membrane fuel cells. Development of hydroxide exchange membrane fuel cells (HEMFCs) requires high-performance and low-cost catalysts for hydrogen oxidation reaction at the anode. Here the authors report Ru 7 Ni 3 /C as anode catalysts, delivering high power density and good durability in alkaline media for HEMFCs.

A preference for acidsWhen titanium dioxide surfaces are exposed to water under ambient conditions, an ordered overlayer forms. Balajka et al. studied this process with scanning tunneling microscopy and x-ray photoelectron spectroscopy for water adsorption under vacuum conditions and in air (see the Perspective by Park). The ordered overlayer was only formed in air, the result of the adsorption of organic acids (formic and acetic acids). Although other species such as alcohols were present in much higher concentrations in air, the bidentate adsorption and entropic effects favored acid adsorption.Science, this issue p. 786; see also p. 753Researchers around the world have observed the formation of molecularly ordered structures of unknown origin on the surface of titanium dioxide (TiO2) photocatalysts exposed to air and solution. Using a combination of atomic-scale microscopy and spectroscopy, we show that TiO2 selectively adsorbs atmospheric carboxylic acids that are typically present in parts-per-billion concentrations while effectively repelling other adsorbates, such as alcohols, that are present in much higher concentrations. The high affinity of the surface for carboxylic acids is attributed to their bidentate binding. These self-assembled monolayers have the unusual property of being both hydrophobic and highly water-soluble, which may contribute to the self-cleaning properties of TiO2. This finding is relevant to TiO2 photocatalysis, because the self-assembled carboxylate monolayers block the undercoordinated surface cation sites typically implicated in photocatalysis.

The electrocatalytic hydrogen evolution reaction (HER) is one of the most studied and promising processes for hydrogen fuel generation. Single-atom catalysts have been shown to exhibit ultra-high HER catalytic activity, but the harsh preparation conditions and the low single-atom loading hinder their practical applications. Furthermore, promoting hydrogen evolution reaction kinetics, especially in alkaline electrolytes, remains as an important challenge. Herein, Pt/C 60 catalysts with high-loading, high-dispersion single-atomic platinum anchored on C 60 are achieved through a room-temperature synthetic strategy. Pt/C 60 -2 exhibits high HER catalytic performance with a low overpotential (η 10 ) of 25 mV at 10 mA cm −2 . Density functional theory calculations reveal that the Pt-C 60 polymeric structures in Pt/C 60 -2 favors water adsorption, and the shell-like charge redistribution around the Pt-bonding region induced by the curved surfaces of two adjacent C 60 facilitates the desorption of hydrogen, thus favoring fast reaction kinetics for hydrogen evolution. The synthesis of high-loading Pt single-atom catalysts is important but challenging. Here, the authors use fullerene C 60 with electron-deficient C=C bonds to build Pt/C 60 catalysts with abundant Pt single atoms which exhibits high catalytic activity for electrochemical hydrogen evolution reactions

Efficient use of energy for cooling applications is a very important and challenging field in science. Ultra-low temperature actuated ( T driving  < 80 °C) adsorption-driven chillers (ADCs) with water as the cooling agent are one environmentally benign option. The nanoscale metal-organic framework [Al(OH)(C 6 H 2 O 4 S)] denoted CAU-23 was discovered that possess favorable properties, including water adsorption capacity of 0.37 g H2O / g sorbent around p / p 0  = 0.3 and cycling stability of at least 5000 cycles. Most importantly the material has a driving temperature down to 60 °C, which allows for the exploitation of yet mostly unused temperature sources and a more efficient use of energy. These exceptional properties are due to its unique crystal structure, which was unequivocally elucidated by single crystal electron diffraction. Monte Carlo simulations were performed to reveal the water adsorption mechanism at the atomic level. With its green synthesis, CAU-23 is an ideal material to realize ultra-low temperature driven ADC devices. Ultra-low-temperature-actuated adsorption-driven chillers that rely on water as the cooling agent are desirable for energy-efficient and environmentally benign cooling devices. Here the authors show that the metal–organic framework of composition [Al(OH)(C 6 H 2 O 4 S)] displays high water uptake capacity, high stability, and driving temperatures as low as 60 °C.

In situ/operando surface enhanced infrared and Raman spectroscopies are widely employed in electrocatalysis research to extract mechanistic information and establish structure-activity relations. However, these two spectroscopic techniques are more frequently employed in isolation than in combination, owing to the assumption that they provide largely overlapping information regarding reaction intermediates. Here we show that surface enhanced infrared and Raman spectroscopies tend to probe different subpopulations of adsorbates on weakly adsorbing surfaces while providing similar information on strongly binding surfaces by conducting both techniques on the same electrode surfaces, i.e., platinum, palladium, gold and oxide-derived copper, in tandem. Complementary density functional theory computations confirm that the infrared and Raman intensities do not necessarily track each other when carbon monoxide is adsorbed on different sites, given the lack of scaling between the derivatives of the dipole moment and the polarizability. Through a comparison of adsorbed carbon monoxide and water adsorption energies, we suggest that differences in the infrared vs. Raman responses amongst metal surfaces could stem from the competitive adsorption of water on weak binding metals. We further determined that only copper sites capable of adsorbing carbon monoxide in an atop configuration visible to the surface enhanced infrared spectroscopy are active in the electrochemical carbon monoxide reduction reaction. Infrared and Raman spectroscopies are often assumed to provide similar insights into heterogeneous reaction mechanisms. This study shows that these techniques provide similar data when CO is strongly bound to a surface, yet distinct subpopulations of CO are probed when binding is weaker.