Cobalt-Ion Superhygroscopic Hydrogels Serve as Chip Heat Sinks Achieving a 5 °C Temperature Reduction via Evaporative Cooling

Abstract

In the rapidly advancing semiconductor sector, thermal management of chips remains a pivotal concern. Inherent heat generation during their operation can lead to a range of issues such as potential thermal runaway, diminished lifespan, and current leakage. To mitigate these challenges, the study introduces a superhygroscopic hydrogel embedded with metal ions. Capitalizing on intrinsic coordination chemistry, the metallic ions in the hydrogel form robust coordination structures with non-metallic nitrogen and oxygen through empty electron orbitals and lone electron pairs. This unique structure serves as an active site for water adsorption, beginning with a primary layer of chemisorbed water molecules and subsequently facilitating multi-layer physisorption via Van der Waals forces. Remarkably, the cobalt-integrated hydrogel demonstrates the capability to harvest over 1 and 5 g g^-1 atmospheric water at 60% RH and 95% RH, respectively. Furthermore, the hydrogel efficiently releases the entirety of its absorbed water at a modest 40°C, enabling its recyclability. Owing to its significant water absorption capacity and minimal dehydration temperature, the hydrogel can reduce chip temperatures by 5°C during the dehydration process, offering a sustainable solution to thermal management in electronics.

Keywords: atmospheric water; chip cooling; energy conversion; hydrogel; water harvesting.

Figure 1

Synthesis Route and Morphology of Hydrogels. a) Schematic illustrating the cyclic adsorption and desorption processes. b) Flow diagram outlining the synthesis steps. c) Color changes and corresponding viscosity of the hydrogel under different water capacities, with inset depicting the water absorption/desorption model. d) SEM image showing the morphology of the hydrogel. e) HRTEM image of the hydrogel and f) corresponding Fourier transform data.

Figure 2

Structural Properties of Hydrogels. a) Photographs showing the hydrogel at different stages of water absorption over time, covering an area of ≈15 cm². b) In situ Fourier transform infrared spectra obtained after exposing the hydrogel to ambient air for various durations. c) X‐ray diffraction patterns of the hydrogel in dehydrated and hydrated states. d) Raman spectra of the hydrogel.

Figure 3

Moisture Sorption Performance of Hydrogels. a) Moisture harvesting rate comparison among Co hydrogel and control groups (CoCl₂ and ethanolamine) under 25°C and 90% RH; all samples weigh 0.2 g. b) Water uptake of hydrogels with varying cobalt‐ammonia ratios; testing conducted at 90% RH and 25 °C. c) Water absorption rate of hydrogel at 90% RH and 25 °C, with inset showing the structural model of hydrous hydrogel. d) Adsorption isotherms of hydrogels at temperatures ranging from 30% RH to 95% RH. e) ln(P) versus 1/T curves of the prepared hydrogel under different water contents. f) Enthalpy of adsorption of hydrogels at different water contents, with inset depicting the structure of Co(H₂O)_n.

Figure 4

Dehydration Properties of Hydrogels. a) Illustration of the water dehydration mechanism in the hydrogel. b) The water adsorption and desorption characteristics of the hydrogel in comparison with SiO₂ gel under 1 Sun illumination (AM 1.5G); all samples were tested at 70% RH and 25°C. c) IR thermographs showing surface temperature changes in the hydrogel under 1 Sun illumination. d) The dehydration rate of hydrogel at different temperatures (70% RH). e) Dehumidification rate achieved by the hydrogel in a confined space (20 × 10 × 10 cm³). f) Water uptake and desorption temperature of the hydrogel in comparison with other relevant commercial hygroscopic materials.

Figure 5

Chip Cooling with Hydrogels. a) Structure of the chip and hydrogel assembly. b) Schematic illustrating the use of hydrogel to lower chip temperature by capturing and releasing water. c) Measurement of chip surface temperature (with/without hydrogel) using an infrared imager. d) Temperature change curve of the assemblies, with the insets showing digital photographs of the chips (of area ≈4 cm²) with and without the hydrogel.

Figure 6

Illustration of the Water Binding Mechanism in Hydrogels. a) Co ions interact with N and O atoms in ethanolamine, increasing hydrophilicity by forming binding sites. b) The process of water capture by the hydrogel; water molecules adjacent to the binding site undergo chemisorption, while outer water molecules undergo physiosorption.