Thermoelectric generators (TEGs) transform a heat flow into electricity. Thermoelectric materials are being investigated for electricity production from waste heat (co-generation) and natural heat sources. For temperatures below 200 °C, the best commercially available inorganic semiconductors are bismuth telluride (Bi(2)Te(3))-based alloys, which possess a figure of merit ZT close to one. Most of the recently discovered thermoelectric materials with ZT>2 exhibit one common property, namely their low lattice thermal conductivities. Nevertheless, a high ZT value is not enough to create a viable technology platform for energy harvesting. To generate electricity from large volumes of warm fluids, heat exchangers must be functionalized with TEGs. This requires thermoelectric materials that are readily synthesized, air stable, environmentally friendly and solution processable to create patterns on large areas. Here we show that conducting polymers might be capable of meeting these demands. The accurate control of the oxidation level in poly(3,4-ethylenedioxythiophene) (PEDOT) combined with its low intrinsic thermal conductivity (λ=0.37 W m(-1) K(-1)) yields a ZT=0.25 at room temperature that approaches the values required for efficient devices.

A mixed ionic–electronic conductor based on nanofibrillated cellulose composited with poly(3,4‐ethylene‐dioxythio­phene):­poly(styrene‐sulfonate) along with high boiling point solvents is demonstrated in bulky electrochemical devices. The high electronic and ionic conductivities of the resulting nanopaper are exploited in devices which exhibit record values for the charge storage capacitance (1F) in supercapacitors and transconductance (1S) in electrochemical transistors.

This study presents a novel, green, and efficient way of preparing crosslinked aerogels from cellulose nanofibers (CNFs) and alginate using non‐covalent chemistry. This new process can ultimately facilitate the fast, continuous, and large‐scale production of porous, light‐weight materials as it does not require freeze‐drying, supercritical CO2 drying, or any environmentally harmful crosslinking chemistries. The reported preparation procedure relies solely on the successive freezing, solvent‐exchange, and ambient drying of composite CNF‐alginate gels. The presented findings suggest that a highly‐porous structure can be preserved throughout the process by simply controlling the ionic strength of the gel. Aerogels with tunable densities (23–38 kg m−3) and compressive moduli (97–275 kPa) can be prepared by using different CNF concentrations. These low‐density networks have a unique combination of formability (using molding or 3D‐printing) and wet‐stability (when ion exchanged to calcium ions). To demonstrate their use in advanced wet applications, the printed aerogels are functionalized with very high loadings of conducting poly(3,4‐ethylenedioxythiophene):tosylate (PEDOT:TOS) polymer by using a novel in situ polymerization approach. In‐depth material characterization reveals that these aerogels have the potential to be used in not only energy storage applications (specific capacitance of 78 F g−1), but also as mechanical‐strain and humidity sensors.

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A combination of nanofibrils and nanoparticles is used to fabricate polymer-based freestanding electrochromic materials which exhibit contrasts >20 in devices.

Paper is emerging as a promising flexible, high surface‐area substrate for various new applications such as printed electronics, energy storage, and paper‐based diagnostics. Many applications, however, require paper that reaches metallic conductivity levels, ideally at low cost. Here, an aqueous electroless copper‐plating method is presented, which forms a conducting thin film of fused copper nanoparticles on the surface of the cellulose fibers. This paper can be used as a current collector for anodes of lithium‐ion batteries. Owing to the porous structure and the large surface area of cellulose fibers, the copper‐plated paper‐based half‐cell of the lithium‐ion battery exhibits excellent rate performance and cycling stability, and even outperforms commercially available planar copper foil‐based anode at ultra‐high charge/discharge rates of 100 C and 200 C. This mechanically robust metallic‐paper composite has promising applications as the current collector for light‐weight, flexible, and foldable paper‐based 3D Li‐ion battery anodes.

Complementary circuits, processing digital signals, are a cornerstone of modern electronics. Such circuits require both p- and n-type transistors. Polyelectrolytes are used as gate insulators in organic thin film transistors (OTFTs) to establish an electric double layer capacitor upon gate bias that allows low operational voltages (<1 V). However, stable and low-voltage operating n-channel organic transistors have proven difficult to construct. Here, we report ultra-low voltage n-channel organic polymer-based transistors that are stable in ambient atmosphere. Our n-type OTFTs exhibit on/off ratios around 103 for an applied drain potential as low as 0.1 V. Since small ions are known to promote electrochemical reactions within the semiconductor’s channel bulk and typically slow down the transistor, we use a solid polycationic gate insulator that suppresses penetration of anions into the n-channel semiconductor. As a result, our n-channel OTFTs switch on in under 5 ms and off in less than 1 ms.

Because solar and wind power produce electricity intermittently, electricity needs to be stored in large batteries composed of materials of high abundancy. X. Crispin and co‐workers demonstrate, in article number 1500305, that paper functionalized with a conducting polymer constitutes a promising electrode for supercapacitors, and potentially batteries. Atomic force microscopy reveals cellulose nanofibers with a conducting polymer coating, as demonstrated in the paper battery of the cover image.