Radiative Cooling Paints

Radiative cooling is a passive cooling technology to promise significant cooling power saving and alleviate climate change, by reflecting sunlight and emitting radiation in the sky window. We focus on developing the paint format to enable wide range of residential and commercial applications, with full daytime sub-ambient cooling and low-cost scalable fabrication.

• The Best Inventions of 2023, TIME Magazine

• Guinness World Record of “World’s Whitest Paint”.

• Finalist for 2021 R&D 100 Awards.

• More than 1000 worldwide media appearances, including BBC, CNN, USA TODAY, Wall Street Journal, Washington Post, Guardian, Science Magazine. 

Publication and Patent:

[1] Peoples, J., Li, X., Lv, Y., Qiu, J., Huang, Z., & Ruan, X. (2019). A strategy of hierarchical particle sizes in nanoparticle composite for enhancing solar reflection. International Journal of Heat and Mass Transfer, 131, 487-494.

[2] Li, X., Peoples, J., Huang, Z., Zhao, Z., Qiu, J., & Ruan, X. (2020). Full daytime sub-ambient radiative cooling in commercial-like paints with high figure of merit. Cell Reports Physical Science, 1(10), 100221.

[3] Li, X., Peoples, J., Yao, P., & Ruan, X. (2021). Ultrawhite BaSO4 paints and films for remarkable daytime subambient radiative cooling. ACS Applied Materials & Interfaces, 13(18), 21733-21739.

[4] Ruan, X., Li, X., Huang, Z., & Peoples, J. A. (2021). U.S. Patent Application No. 17/282,958.

[5] Peoples, J., Hung, Y. W., Li, X., Gallagher, D., Fruehe, N., Pottschmidt, M., ... & Ruan, X. (2022). Concentrated radiative cooling. Applied Energy, 310, 118368.

[6] Tong, Z., Peoples, J., Li, X., Yang, X., Bao, H., & Ruan, X. (2022). Electronic and phononic origins of BaSO4 as an ultra-efficient radiative cooling paint pigment. Materials Today Physics, 24, 100658.

[7] Zhang, C., Gao, G., Guo, Y., Liu, Y., Liu, Y., & Wu, G. (2024). Structural optimization model of oil-natural air-natural transformer radiator based on data-model hybrid-driven. Applied Thermal Engineering, 125016.

[8] Bu, K., Huang, X., Li, X., & Bao, H. (2023). Consistent assessment of the cooling performance of radiative cooling materials. Advanced Functional Materials, 33(51), 2307191.

Water Adsorption and Harvesting

Due to high affinity with water molecules, adsorbent materials can capture water vapor and release it under low humidity or high temperature. Such effect enables atmospheric water harvesting even under extremely low humidity, beyond the traditional dewing and fog harvesting processes. Additionally, the high adsorption enthalpy also translates to high energy density when adopted for thermal energy storage units. 

Publication and Patent:

[1] Li, A. C., Zhang, L., Zhong, Y., Li, X., El Fil, B., Fulvio, P. F., ... & Wang, E. N. (2022). Thermodynamic limits of atmospheric water harvesting with temperature-dependent adsorption. Applied Physics Letters, 121(16).

[2] Liu, X., Zhang, L., El Fil, B., Díaz‐Marín, C. D., Zhong, Y., Li, X., ... & Wang, E. N. (2023). Unusual temperature dependence of water sorption in semicrystalline hydrogels. Advanced Materials, 35(22), 2211763.

[3] El Fil, B., Li, X., Díaz-Marín, C. D., Zhang, L., & Jacobucci, C. L. (2023). Significant enhancement of sorption kinetics via boiling-assisted channel templating. Cell Reports Physical Science, 4(9).

[4] Guo, H., Luo, Q., Liu, D., Li, X., Zhang, C., He, X., ... & Qin, X. (2024). Super Moisture‐Sorbent Sponge for Sustainable Atmospheric Water Harvesting and Power Generation. Advanced Materials, 2414285.

[5] Zhang, X., Qu, H., Li, X., Zhang, L., Zhang, Y., Yang, J., ... & Tan, S. C. (2024). Autonomous Atmospheric Water Harvesting over a Wide RH Range Enabled by Super Hygroscopic Composite Aerogels. Advanced Materials, 2310219.

[6] Zhong, Y., Zhang, L., Li, X., El Fil, B., Díaz-Marín, C. D., Li, A. C., ... & Wang, E. N. (2024). Bridging materials innovations to sorption-based atmospheric water harvesting devices. Nature Reviews Materials, 1-18.

[7] Li, X., El Fil, B., Li, B., Graeber, G., Li, A. C., Zhong, Y., ... & Lin, E. (2024). Design of a compact multicyclic high-performance atmospheric water harvester for arid environments. ACS Energy Letters, 9(7), 3391-3399.

Solar Desalination

Recent advances in solar evaporation hold significant promise for vapor generation, seawater desalination, wastewater treatment, and medical sterilization. However, salt accumulation is one of the key bottlenecks for reliable adoption, especially for wicking materials commonly used. By leveraging natural convection enabled by the density gradient, highly efficient and salt rejecting solar evaporation can be simultaneously achieved by engineering the fluidic flow in a wick-free confined water layer. 

• Featured in MIT News, Nature Communications Editors’ highlights of “Materials science and chemistry” and “Devices".

Publication and Patent:

[1] Zhang, L.,† Li, X.,† (co-first author) Zhong, Y., Leroy, A., Xu, Z., Zhao, L., & Wang, E. N. (2022). Highly efficient and salt rejecting solar evaporation via a wick-free confined water layer. Nature communications, 13(1), 1-12.

[2] Chen, Y., Shen, L., Qi, Z., Luo, Z., Li, X., & Bao, H. (2025). Large-scale implementation of solar interfacial desalination. Nature Sustainability, 1-8.

High Temperature Heat Exchanger Design

The efficiency of a heat engine can be significantly improved by operating in a high-temperature and high-pressure environment, which is crucial for a wide range of applications such as aviation as well as power generation. A key challenge is the heat exchanger under such extreme operating conditions. Despite materials development such as super alloys and ceramics, using these materials in a traditional heat exchanger design requires high cost and yields low power density. We propose an ultrahigh power density ceramic heat exchanger enabled by a multiscale porous design, offering significant improvement to both heat transfer and structural strength with a negligible pressure drop penalty. 

 Publication and Patent:

[1] Li, X.,† Wilson, C. T.,† (co-first author) Zhang, L., Bhatia, B., Zhao, L., Leroy, A., ... & Wang, E. N. (2022). Design and modeling of a multiscale porous ceramic heat exchanger for high temperature applications with ultrahigh power density. International Journal of Heat and Mass Transfer, 194, 122996.

[2] Wang, E.N., Zhao, L. Bhatia, B., Li, X., Leroy, A., Wilke, K., Zhang, L., Youngblood, J., Trice, R., Wilson, C., Brandt, O., and Guerra, R. Devices and Methods for Fabrication of Components of A Multiscale Porous High-Temperature Heat Exchanger. U.S. Patent: 63/166,973, filed March 27, 2021.

Material and Composite Modeling and Characterization

Novel materials innovation and composite development enable significant performance enhancement and customization for thermal and mechancial properties, in applications such as electronic thermal management.

We adopt various simulation and modeling approaches to address the multiscale material challenges. Atomic level toolset includes GPUMD, which leverages GPU power with accurate first-principles methods available, to develop new interatomic potentials far superior to traditional empirical potentials. It is suitable for both thermal and mechanical property prediction and modeling, especially for complicated crystal structures, multi-element mixture, and large-scale simulations. Classical models include effective medium approximation (EMA), acoustic mismatch and diffuse mismatch models (AMM, DMM), Monte Carlo simulation.

 Publication and Patent:

[1] Park, W., Guo, Y., Li, X., Hu, J., Liu, L., Ruan, X., & Chen, Y. P. (2015). High-performance thermal interface material based on few-layer graphene composite. The Journal of Physical Chemistry C, 119(47), 26753-26759.

[2] Li, X., Park, W., Chen, Y. P., & Ruan, X. (2017). Effect of particle size and aggregation on thermal conductivity of metal–polymer nanocomposite. Journal of Heat Transfer, 139(2), 022401.

[3] Park, W., Li, X., Mandal, N., Ruan, X., & Chen, Y. P. (2017). Compressive mechanical response of graphene foams and their thermal resistance with copper interfaces. APL Materials, 5(3).

[4] Li, X., Park, W., Chen, Y. P., & Ruan, X. (2017). Absence of coupled thermal interfaces in Al2O3/Ni/Al2O3 sandwich structure. Applied Physics Letters, 111(14).

[5] Li, X., Park, W., Wang, Y., Chen, Y. P., & Ruan, X. (2019). Reducing interfacial thermal resistance between metal and dielectric materials by a metal interlayer. Journal of Applied Physics, 125(4).

[6] Peoples, J., Li, X., Lv, Y., Qiu, J., Huang, Z., & Ruan, X. (2019). A strategy of hierarchical particle sizes in nanoparticle composite for enhancing solar reflection. International Journal of Heat and Mass Transfer, 131, 487-494.

[7] Zhang, S., Chen, P., Wei, L., Zhang, P., Wang, X., Liu, B., ... & Du, T. (2025). Theoretical investigation on the dynamic thermal transport properties of graphene foam by machine-learning molecular dynamics simulations. International Journal of Thermal Sciences, 210, 109631.