Heat Harvesting with Cellulosic Membranes

Elke Arenholz, CHESS

"Wood-based ionic conductors are flexible, lightweight, biocompatible and based on sustainable materials that can enable large-scale manufacture and suitable for low-grade thermal energy harvesting."

Left: The cellulose fibers are naturally aligned along the growth direction. Cellulose exhibits a hierarchical alignment, in which the nanofibres consist of aligned cellulose molecular chains. Right: Schematic of the ionic device after infiltrating electrolyte into the nanofluidic cellulosic membrane. Under a thermal bias, the surface charged nanofibres regulate ionic movement via nanofluidic effects (that is, the overall effect created by a high degree of confinement and the charged walls of the cellulose

Left: Cellulose fibers are naturally aligned along the growth direction. Cellulose exhibits a hierarchical alignment, in which the nanofibres consist of aligned cellulose molecular chains. Right: Schematic of the ionic device after infiltrating electrolyte into the nanofluidic cellulosic membrane. Under a thermal bias, the surface charged nanofibres regulate ionic movement via nanofluidic effects (that is, the overall effect created by a high degree of confinement and the charged walls of the cellulose nanochannels).

What did the Scientists Discover?
Converting low-grade heat into useful electricity requires a technology that is efficient and cost effective. Here researchers demonstrate a cellulosic membrane that relies on sub-nanoscale confinement of ions in aligned cellulose molecular chains to enhance selective ion diffusion under a thermal gradient. After infiltrating electrolyte into the cellulosic membrane and applying an axial temperature gradient, the ionic conductor exhibits a thermal gradient ratio (analogous to the Seebeck coefficient in thermoelectrics) of 24 mV K–1—more than twice the highest value reported until now.

Why is this important?
There are few processes that can convert low-grade heat to electricity, including electrolyte-based thermal energy conversion, which relies on the thermophoretic mobility difference between the negative and positive ions of an electrolyte. Infiltrating electrolyte into a cellulosic membrane leads to enhanced ionic selectivity in the charged molecular chains. The resulting wood-based ionic conductor is flexible, lightweight, biocompatible and based on sustainable materials that can enable large-scale manufacture. It is suitable for a range of applications, including temperature sensing and low-grade thermal energy harvesting.

characterization of the dry cellulosic membrane, showing mostly cellulose II

What are the broader impacts of this work?
The work demonstrates the feasibility of using abundantly available wood cellulose nanofibers for low-grade thermal energy harvesting, particularly in situations where sustainability and cost-effectiveness are necessary attributes. Future development include the optimization of electrodes for continuous operation, enhanced long-term stability in aqueous systems and the extension of the technique to the functional regulation of other ion species.

Why did this research need CHESS?
The wide angle X-ray scattering (WAXS) measurements were conducted at the A1 undulator station of CHESS. The data was collected in transmission through the sample using an X-ray beam of 19.9 keV photon energy and recorded using a large-field-of-view detector (ADSC, Quantum-210) placed at a distance of L = 504.7 mm from the sample.

Collaborators:

  • Tian Li, Department of Materials Science and Engineering, University of Maryland
  • Xin Zhang, Department of Materials Science and Engineering, University of Maryland
  • Steven D. Lacey, Department of Materials Science and Engineering, University of Maryland
  • Ruiyu Mi, Department of Materials Science and Engineering, University of Maryland
  • Xinpeng Zhao, Department of Mechanical Engineering, University of Colorado
  • Feng Jiang, Department of Materials Science and Engineering, University of Maryland
  • Jianwei Song, Department of Materials Science and Engineering, University of Maryland
  • Zhongqi Liu, Department of Wood Science, The University of British Columbia
  • Guang Chen, Department of Wood Science, The University of British Columbia
  • Jiaqi Dai, Department of Materials Science and Engineering, University of Maryland
  • Yonggang Yao, Department of Materials Science and Engineering, University of Maryland
  • Siddhartha Das, Department of Mechanical Engineering, University of Colorado
  • Ronggui Yang, Department of Wood Science, The University of British Columbia
  • Robert M. Briber, Department of Materials Science and Engineering, University of Maryland
  • Liangbing Hu, Department of Materials Science and Engineering, University of Maryland

Publication Citation:
Li, T., Zhang, X., Lacey, S.D. et al., “Cellulose ionic conductors with high differential thermal voltage for low-grade heat harvesting,” Nat. Mater., 8, 608–613 (2019) https://doi.org/10.1038/s41563-019-0315-6

How was the work funded?
X-ray experiment at CHESS were supported by NSF award DMR-1332208 and neutron scattering at the NIST Center for Neutron Research is supported through a partnership between NIST and NSF under agreement DMR-1508249.