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Adsorption-driven heat transfer technology using water as working fluid is a promising eco-friendly strategy to address the exponential increase of global energy demands for cooling and heating purposes. Here we present the water sorption properties of a porous aluminum carboxylate metal-organic framework, [Al(OH)(C6H3NO4)]·nH2O, KMF-1, discovered by a joint computational predictive and experimental approaches, which exhibits step-like sorption isotherms, record volumetric working capacity (0.36 mL mL−1) and specific energy capacity (263 kWh m−3) under cooling working conditions, very high coefficient of performances of 0.75 (cooling) and 1.74 (heating) together with low driving temperature below 70 °C which allows the exploitation of solar heat, high cycling stability and remarkable heat storage capacity (348 kWh m−3). This level of performances makes this porous material as a unique and ideal multi-purpose water adsorbent to tackle the challenges of thermal energy storage and its further efficient exploitation for both cooling and heating applications.

The development of new water adsorbents that are hydrothermally stable and can operate more efficiently than existing materials is essential for the advancement of water adsorption-driven chillers. Most of the existing benchmark materials and related systems in this field suffer from clear limitations that must be overcome to meet global requirements for sustainable and green energy production and utilization. Here, we report the energy-efficient water sorption properties of three isostructural metal-organic frameworks (MOFs) based on the simple ligand pyridine-2,4-dicarboxylate, named M-CUK-1 [M3(3-OH)2(2,4-pdc)2] (where M = Co 2+ , Ni 2+ or Mg 2+). The highly hydrothermally-stable CUK-1 series feature step-like water adsorption isotherms, relatively high H2O sorption capacities between P/P0 = 0.10-0.25, stable cycling, facile regeneration, and most importantly, benchmark coefficient of performance (COP) values for cooling and heating at low driving temperature. Furthermore, these MOFs are prepared under green hydrothermal conditions in aqueous solutions. Our joint experimental-computational approach revealed that M-CUK-1 integrates several optimal features, resulting in promising materials as advanced water adsorbents for adsorption-driven cooling and heating applications.

For ex-situ co-doping methods, sintering at high temperatures enables rapid diffusion of Sn4+ and Be2+ dopants into hematite (α–Fe2O3) lattices, without altering the nanorod morphology or damaging their crystallinity. Sn/Be co-doping results in a remarkable enhancement in photocurrent (1.7 mA/cm2) compared to pristine α–Fe2O3 (0.7 mA/cm2), and Sn4+ mono-doped α-Fe2O3 photoanodes (1.0 mA/cm2). From first-principles calculations, we found that Sn4+ doping induced a shallow donor level below the conduction band minimum, which does not contribute to increase electrical conductivity and photocurrent because of its localized nature. Additionally, Sn4+-doping induce local micro-strain and a decreased Fe-O bond ordering. When Be2+ was co-doped with Sn4+-doped α–Fe2O3 photoanodes, the conduction band recovered its original state, without localized impurities peaks, also a reduction in micro-strain and increased Fe-O bond ordering is observed. Also the sequence in which the ex-situ co-doping is carried out is very crucial, as Be/Sn co-doping sequence induces many under-coordinated O atoms resulting in a higher micro-strain and lower charge separation efficiency resulting undesired electron recombination. Here, we perform a detailed systematic characterization using XRD, FESEM, XPS and comprehensive electrochemical and photoelectrochemical studies, along with sophisticated synchrotron diffraction studies and extended X-ray absorption fine structure.

Adsorption-based heat transfer (AHT) devices are promising alternatives for green energy production and (re)­usage; however, they are still limited by the low performance of their benchmark adsorbent materials. Metal–organic frameworks (MOFs) have been ranked among the most promising water adsorbents for this application owing to their potential superior water uptake and moderate hydrophilicity. However, there is still a need to rationalize and understand at the microscopic scale the water adsorption performances of this family of materials to further guide the selection of the next-generation water adsorbents. In this context, a full understanding of the water adsorption mechanism in the most promising MOFs containing coordinated unsaturated sites is still highly challenging. Here, we explore the water adsorption in the mesoporous MOF MIL-100­(Fe) containing coordinated unsaturated Fe­(III) sites by combining advanced modeling and experimental tools. As a first stage, density functional theory calculations are performed to derive an accurate force field to describe the specific interactions between water and the coordinated unsaturated Fe­(III) sites. This force field is further implemented in a grand canonical Monte Carlo scheme to simulate the water adsorption isotherm and enthalpy in the whole range of relative pressures. A validation of the microscopic models and force field parameters is gained from a very good agreement between the experimental and simulated water adsorption data. As a further step, we provide an unprecedented description of the water adsorption microscopic mechanism in this very promising AHT water adsorbent by a careful analysis of the MIL-100­(Fe)/H2O interactions at low and intermediate relative pressures as well as the hydrogen bond network and cluster formation at higher relative pressure.

Adsorption-driven heat transfer devices incorporating an efficient “adsorbent–water” working pair are attracting great attention as a green and sustainable technology to address the huge global energy demands for cooling and heating. Herein, we report the improved heat transfer performance of a defective Zr fumarate metal–organic framework (MOF) prepared in a water solvent (Zr-Fum HT). This material exhibits an S-shaped water sorption isotherm (P/P 0 = 0.05–0.2), excellent working capacity (0.497 mLH2O mL–1 MOF) under adsorption-driven cooling/chiller working conditions (T adsorption(ads) = 30 °C, T condensation (con) = 30 °C, and T desorption(des) = 80 °C), very high coefficient of performances for both cooling (0.83) and heating (1.76) together with a relatively low driving temperature at 80 °C, a remarkable heat storage capacity (423.6 kW h m–3 MOF), and an outstanding evaporation heat (343.8 kW h m–3 MOF). The level of performance of the resultant Zr-Fum HT MOF is above those of all existing benchmark water adsorbents including MOF-801 previously synthesized in the N,N-dimethylformamide solvent under regeneration at 80 °C which is accessible from the solar source. This is coupled with many other decisive advantages including green synthesis and high proven chemical and mechanical robustness. The microscopic water adsorption mechanism of Zr-Fum HT at the origin of its excellent water adsorption performance was further explored computationally based on the construction of an atomistic defective model online with the experimental data gained from a subtle combination of characterization techniques.

To minimize the huge global energy consumption for cooling and heating, adsorption-based heat allocation devices operating with an "adsorbent−water" working pair have received great interest over the last decades. Herein, we report scalable green synthesis of an Al-based metal−organic framework (Al-MOF) in water built from the assembly of inorganic Al helix chains linked to pyridine dicarboxylate linkers that delimits a three-dimensional structure proven to be isoreticular to CAU-10H and denoted as CAU-10pydc. This channel-like MOF exhibits attractive water sorption properties with an S-shaped adsorption isotherm associated with a major water uptake in the range of P/P°= 0.015−0.17 and a good working capacity (0.31 mL H2O mL −1 MOF ) under lowtemperature cooling conditions of the adsorption-driven heat allocation system (T evaporator(ev) = 5 °C, T adsorption(ads) and T condensation(con) = 30 °C, and T desorption(des) = 80 °C), along with exceptional coefficient of performances for both cooling (0.79) and heating (1.72) together with a useful and sustainable heat source accessible from a solar source and good specific heat capacity (212.9 kWh m −3 MOF ) and heat storage capacity (273.5 kWh m −3 MOF ). The molecular adsorption mechanism was finally investigated computationally demonstrating the predominant role played by the formation of hydrogen-bonding between water molecules and the hydroxyl functionality of the MOF.