Record Atmospheric Fresh Water Capture and Heat Transfer with a Material Operating at the Water Uptake Reversibility Limit

Abstract

The capture of water vapor at low relative humidity is desirable for producing potable water in desert regions and for heat transfer and storage. Here, we report a mesoporous metal-organic framework that captures 82% water by weight below 30% relative humidity. Under simulated desert conditions, the sorbent would deliver 0.82 g_H2O g_MOF^-1, nearly double the quantity of fresh water compared to the previous best material. The material further demonstrates a cooling capacity of 400 kWh m^-3 per cycle, also a record value for a sorbent capable of creating a 20 °C difference between ambient and output temperature. The water uptake in this sorbent is optimized: the pore diameter of our material is above the critical diameter for water capillary action, enabling water uptake at the limit of reversibility.

Figure 1

Structure of 2 projected along the c axis: Co, purple; C, gray; N, blue; O, red; Cl, green. Hydrogen atoms are omitted for clarity. At low RH, water is absorbed at the open coordination sites of the Co atoms, decreasing the pore diameter from slightly above to slightly below the D_c of water, enabling water uptake by reversible continuous pore filling.

Figure 2

(A) Water vapor adsorption (closed symbols) and desorption (open symbols) at 298 K for 1 (red squares), 2 (blue triangles), and 3 (green pentagons). (B) Comparison of MOF and zeolites investigated for water sorption.^,, Materials that take up water between 10% and 30% RH are desirable for their strong affinity for water and their relative ease of regeneration. *This work.

Figure 3

Performance of 2 in AWGs. (A) Estimation of the deliverable capacity of water from 2 under simulated desert conditions: daytime 45 °C and 5% RH and nighttime 25 °C and 35% RH. (B) Percent change in weight while cycling 2 between 45 °C and 5% RH (day), and 25 °C and 35% RH (night).

Figure 4

Performance of 2 in AHPs. (A) Volumetric (left axis) and gravimetric (right axis) heat energy transferred from ambient per cycle as a function of the temperature lift. (B) Material-based coefficient of performance for AHP cooling applications with a 20 °C temperature lift for the water–2 working pair as a function of desorption temperature. (C) Temperature-swing water cycling of 2 at a constant water vapor pressure of 13 mmHg.