Cellulose ionic conductors with high differential thermal voltage for low-grade heat harvesting

Abstract

Converting low-grade heat into useful electricity requires a technology that is efficient and cost effective. Here, we demonstrate a cellulosic membrane that relies on sub-nanoscale confinement of ions in oxidized and aligned cellulose molecular chains to enhance selective 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. We attribute the enhanced thermally generated voltage to effective sodium ion insertion into the charged molecular chains of the cellulosic membrane, which consists of type II cellulose, while this process does not occur in natural wood or type I cellulose. With this material, we demonstrate a flexible and biocompatible heat-to-electricity conversion device via nanoscale engineering based on sustainable materials that can enable large-scale manufacture.

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Fig. 1: Schematic of the ionic conductor composed of high aspect ratio, aligned cellulose nanofibres.
Fig. 2: Characterization of the cellulosic membrane.
Fig. 3: Ion transport and regulation capability of the cellulosic membrane.
Fig. 4: Thermal charging behaviour of the electrolyte-infiltrated cellulosic membrane.

Data availability

The data that support the plots in this paper and other findings of this study are available from the corresponding author upon reasonable request.

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Acknowledgements

The work has no direct funding support. We acknowledge the constructive discussions with B. Dunn from the University of California, LA. We thank H. Jiang and D. Ji for the assistance with the BET analysis. We thank Y. Mao and C. Gagnon for the assistance with the SANS measurements. Access to the NGB-30 m SANS beamline at the NIST Center for Neutron Research was provided by the Center for High Resolution Neutron Scattering, a partnership between the National Institute of Standards and Technology and the National Science Foundation under agreement no. DMR-1508249. S. Stoupin’s assistance with the synchrotron WAXS experiment at the A1 beamline of Cornell High Energy Synchrotron Source (CHESS) was greatly appreciated. CHESS is supported by the NSF award no. DMR-1332208. We also acknowledge the support of the Maryland NanoCenter and its AIMLab.

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L.H. and T.L. conceived the idea and supervised the project. X.Z., T.L. and R.M.B. contributed to the structural characterization. T.L., R.M., F.J., J.S., J.D. and Y.Y. contributed to material preparation and characterization. T.L., S.D. and G.C. contributed to the analysis of the ionic transport. F.J. and Z.L. determined the charge density. T.L., X.Z. and R.Y. contributed to the thermal analysis. T.L., S.D.L. and L.H. contributed largely to writing, while all authors participated.

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Correspondence to Liangbing Hu.

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Competing interests

L. Hu and T. Li are the inventors of a patent currently pending with the University of Maryland (no. 62/789325, filed 7 January 2019). All the other authors declare that they have no competing interests.

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Supplementary Information

Supplementary Figures 1–26, Supplementary Tables 1,2, Supplementary References 1–6.

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Li, T., Zhang, X., Lacey, S.D. et al. Cellulose ionic conductors with high differential thermal voltage for low-grade heat harvesting. Nat. Mater. 18, 608–613 (2019). https://doi.org/10.1038/s41563-019-0315-6

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