Stretchable and biodegradable plant-based redox-diffusion batteries.

The redox-diffusion (RD) battery concept introduces an environmentally friendly solution for stretchable batteries in autonomous wearable electronics. By utilising plant-based redox-active biomolecules and cellulose fibers for the electrode scaffold, separator membrane, and current collector, along with a biodegradable elastomer encapsulation, the battery design overcomes the reliance on unsustainable transition metal-based active materials and non-biodegradable elastomers used in existing stretchable batteries. Importantly, it addresses the drawback of limited attainable battery capacity, where increasing the active material loading often leads to thicker and stiffer electrodes with poor mechanical properties. The concept decouples the active material loading from the mechanical structure of the electrode, enabling high mass loadings, while retaining a skin-like young's modulus and stretchability. A stretchable ion-selective membrane facilitates the RD process, allowing two separate redox couples, while preventing crossovers. This results in a high-capacity battery cell that is both electrochemically and mechanically stable, engineered from sustainable plant-based materials. Notably, the battery components are biodegradable at the end of their life, addressing concerns of e-waste and resource depletion.

The enhanced ionic thermal potential by a polarized electrospun membrane.

Inspired by thermally sensitive ion channels in human skin, a polarized membrane composed of a ferroelectric polymer fiber matrix is used to double the heat-induced potential in ionic thermoelectric devices. The comparison of the thermal potentials between different directions of polarization and temperature gradient indicates the importance of cation-dipole interactions for the enhancement.

Switchable Broadband Terahertz Absorbers Based on Conducting Polymer-Cellulose Aerogels.

Terahertz (THz) technologies provide opportunities ranging from calibration targets for satellites and telescopes to communication devices and biomedical imaging systems. A main component will be broadband THz absorbers with switchability. However, optically switchable materials in THz are scarce and their modulation is mostly available at narrow bandwidths. Realizing materials with large and broadband modulation in absorption or transmission forms a critical challenge. This study demonstrates that conducting polymer-cellulose aerogels can provide modulation of broadband THz light with large modulation range from ≈ 13% to 91% absolute transmission, while maintaining specular reflection loss < -30 dB. The exceptional THz modulation is associated with the anomalous optical conductivity peak of conducting polymers, which enhances the absorption in its oxidized state. The study also demonstrates the possibility to reduce the surface hydrophilicity by simple chemical modifications, and shows that broadband absorption of the aerogels at optical frequencies enables de-frosting by solar-induced heating. These low-cost, aqueous solution-processable, sustainable, and bio-friendly aerogels may find use in next-generation intelligent THz devices.

The Origin of Thermal Gradient-Induced Voltage in Polyelectrolytes.

Ionic thermoelectric materials can generate large thermal voltages under temperature gradients while also being low-cost and environmentally friendly. Many electrolytes with large Seebeck coefficients are reported in recent years, however, the mechanism of the thermal voltage is remained elusive. In this work, three types of polyelectrolytes are studied with different cations and identified a significant contribution to their thermal voltage originating from a concentration gradient. This conclusion is based on studies of the loss and gain of water upon temperature changes, variations in conductivity with water content and temperature, and the voltages induced by changes in water content. The results are analyzed by the "hopping mode" dynamics of charge transport in electrolytes. The hydration of different cations influences the water concentration gradient, which affects the barrier height and ion-induced potential in the electrodes. This work shows that the hydro-voltage in ionic thermoelectric devices can be one order of magnitude larger than the contribution from thermodiffusion-induced potentials, and becomes the main contributor to energy harvesting when implemented into ionic thermoelectric supercapacitors. Together with the rationalized theoretical discussion, this work clarifies the mechanism of thermal voltages in electrolytes and provides a new path for the development of ionic thermoelectric materials.