RESUMEN
We present a novel approach to achieve n-type doping in graphene and create graphene p-n junctions through a photoinduced electron doping method using photobase generators (PBGs). The unique properties of PBGs allow us to spatially and temporally control the doping process via light activation. The selective irradiation of specific regions on the graphene film enables switching their doping from p- to n-type, as confirmed by changes in the electromotive force and Seebeck and Hall coefficients. We demonstrate a stable (over 2 months) high electron mobility exceeding 1000 cm2 V-1s-1 using Hall effect measurements. The precise control of doping and the creation of p-n junctions in graphene offer exciting possibilities for various electronic, optoelectronic, and thermoelectric applications. Furthermore, we fabricate transparent graphene thermocouples with a high electromotive force of approximately ca. 80 µV/K, which validates the reliability and effectiveness of our approach for temperature sensing applications. This work paves the way for high-performance graphene-based electronic devices via controlled doping and patterning techniques. These findings provide valuable insights for the practical implementation of graphene in various fields.
RESUMEN
An isotropic thermo-electrochemical cell is introduced with a high Seebeck coefficient (S e) of 3.3 mV K-1 that uses a ferricyanide/ferrocyanide/guanidinium-based agar-gelated electrolyte. A power density of about 20 µW cm-2 is achieved at a temperature difference of about 10 K, regardless of whether the heat source is on the top or bottom section of the cell. This behavior is very different from that of cells with liquid electrolytes, which exhibit high anisotropy, and for which high S e values are achieved only by heating the bottom electrode. The guanidinium-containing gelatinized cell does not exhibit steady-state operation, but its performance recovers when disconnected from the external load, suggesting that the observed power drop under load conditions is not due to device degeneration. The large S e value and isotropic properties can mean that the novel system represents a major advancement from the standpoint of harvesting of low-temperature heat, such as body heat and solar thermal heat.
RESUMEN
The preparation of air and thermally stable n-type carbon nanotubes is desirable for their further implementation in electronic and energy devices that rely on both p- and n-type material. Here, a series of guanidine and amidine bases with bicyclic-ring structures are used as n-doping reagents. Aided by their rigid alkyl functionality and stable conjugate acid structure, these organic superbases can easily reduce carbon nanotubes. n-Type nanotubes doped with guanidine bases show excellent thermal stability in air, lasting for more than 6 months at 100 °C. As an example of energy device, a thermoelectric p/n junction module is constructed with a power output of ca. 4.7 µW from a temperature difference of 40 °C.
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This paper shows how protonated 3,4-ethylene dioxythiophene moieties can be used as an end group to make organic conductors. An organic semiconductor 2,5-bis(5-(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-3-dodecylthiophen-2-yl)thieno[3,2-b]thiophene is designed and synthesized. This molecule could be doped by protonic acid in both solution and solid-state, resulting in a broad absorption in the near-infrared range corresponding to polaron and bipolaron absorption. Electrical conductivity of ca. 0.1 S cm-1 was obtained at 100 °C (to avoid the water uptake by the acid). The adducts with protons bound at the end-thiophene α-position were confirmed by 1H Nuclear Magnetic Resonance spectra.
RESUMEN
Ferricyanide/ferrocyanide/guanidinium-based thermoelectrochemical cells have been investigated under different loading conditions in this work. Compared with ferricyanide/ferrocyanide-based devices, the device with guanidinium-added electrolytes shows higher power and energy densities. We observed that the enhanced performance is not due to the ionic Seebeck effect of guanidinium but because of the configuration entropy change resulting from the selective binding of Gdm+ to Fe(CN)64-. However, the device with guanidinium-added electrolyte does not show steady-state operation. The two possible reasons include (1) the difficult diffusion of Fe(CN)63- into the crystal layer of (Gdm+)n[Fe(CN)64-] at the hot electrode and (2) the difficult precipitation of (Gdm+)n[Fe(CN)64-] formed at the cold side upon the binding of the reduced Fe(CN)64- with Gdm+. Nevertheless, the performance recovers once the device is disconnected from the external loading. Due to the high thermopower after adding guanidinium, we successfully fabricate self-powered sensors by connecting four flexible cells in series. The sensors can transfer humidity, temperature, and air pressure data wirelessly using body heat. Therefore, ferricyanide/ferrocyanide/guanidinium is a promising electrolyte material for applications of low-grade energy harvesting.
RESUMEN
The development of stretchable elastomer composites with considerable mechanical strength and electrical conductivity is desired for future applications in communication tools, healthcare, and robotics. Herein, we have developed a novel stretchable elastomer composite by employing a slide-ring (SR) material as a matrix for restoration and graphene oxide (GO) as a precursor for a conductive filler. Highly dispersed GO in an organic solvent, prepared via a new method developed by the authors, allowed the uniform dispersion of GO into the matrix by simply mixing the solvent and SR. The resultant SR/GO composite exhibited considerably high mechanical toughness and cyclic durability. These properties were approximately maintained after pulse laser irradiation to add electrical conductivity on the composite by photoreducing of the dispersed GO, and its electrical conductivity was higher than that of the SR/graphene, carbon nanotubes, or graphite composites. The potential of the SR/GO composite as a stretchable base substrate for wearable devices was demonstrated by producing a prototype humidity sensor, a human motion monitoring sensor, and an electrical heater based on the composite with conductive circuits drawn using pulse laser patterning.
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Thermoelectric power generation from waste heat is an important component of future sustainable development. Ion-conducting materials are promising candidates because of their high Seebeck coefficients. This study demonstrates that ionic hydrogels based on imidazolium chloride salts exhibit outstanding Seebeck coefficients of up to 10 mV K-1. Along with their relatively high ionic conductivities (1.6 mS cm-1) and extremely low thermal conductivities (â¼0.2 W m-1 K-1), these hydrogels have good potential for use in heat recovery systems. The voltage behavior in response to temperature difference (stable or transient) differs significantly depending on the metal electrode material. We evaluated the electrode-dependent temperature sensitivity of the double layer capacitance of these hydrogels, which revealed that the thermally induced polarization of ions at the interface is one of the main contributors to the thermovoltage. Our results demonstrate the potential capability for ion and metal interactions to be used as an effective baseline for exploring ionic thermoelectric materials and devices. The developed thermoelectric supercapacitor exhibits reversible charging-discharging behavior under repeated disconnecting-connecting of an external load with a constant temperature difference, which offers a novel strategy for heat-to-electricity energy conversion from steady-temperature heat sources.
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In this study, poly(3,4-ethylenedioxythiophene), a benchmark-conducting polymer, was doped by protons. The doping and de-doping processes, using protonic acid and a base, were fully reversible. We predicted possible doping sites along the polymer chain using density functional theory (DFT) calculations. This study sheds potential light and understanding on the molecular design of highly conductive organic materials.
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The electrical transport and thermoelectric property of boron carbide nanowires synthesized by a carbothermal method are reported. It is demonstrated that the nanowires achieve a higher Seebeck coefficient and power factor than those of the bulk samples. The conduction mechanism of the nanowires at low temperatures below 300 K is different from that of the sintered-polycrystalline and single-crystal bulk samples. In a temperature range of 200-450 K, there is a crossover between electrical conduction by variable-range hopping and phonon-assisted hopping. The inhomogeneous carbon concentration and planar defects, such as twins and stacking faults, in the nanowires are thought to modify the bonding nature and electronic structure of the boron carbide crystal substantially, causing differences in the electrical conductivity and Seebeck coefficient. The effect of boundary scattering of phonon at nanostructured surface on the thermal conductivity reduction is discussed.
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Exploring the various applications of conjugated polymers requires systematic studies of their physical properties as a function of the doping density, which, consequently, calls for precise control of their doping density. In this study, we report a novel solid-state photoinduced charge-transfer reaction that dedopes highly conductive polyelectrolyte complexes such as poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate). Varying the UV-irradiation time of this material allows the carrier density inside the film to be precisely controlled over more than 3 orders of magnitude. We extract the carrier density, carrier mobility, and Seebeck coefficient at different doping levels to obtain a clear image of carrier-transport mechanisms. This approach not only leads to a better understanding of the physical properties of the conducting polymer but also is useful for developing applications requiring patterned, large-area conducting polymers.
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The thermoelectric properties of poly(3,4-ethylenedioxythiophene) (PEDOT)-based materials have attracted attention recently because of their remarkable electrical conductivity, power factor, and figure of merit. In this review, we summarize recent efforts toward improving the thermoelectric properties of PEDOT-based materials. We also discuss thermoelectric measurement techniques and several unsolved problems with the PEDOT system such as the effect of water absorption from the air and the anisotropic thermoelectric properties. In the last part, we describe our work on improving the power output of thermoelectric modules by using PEDOT, and we outline the potential applications of polymer thermoelectric generators.
RESUMEN
We reported general methods for studying the thermoelectric properties of a polymer film in both the in-plane and through-plane directions. The bench-mark PEDOT/PSS films have highly anisotropic carrier transport properties and thermal conductivity. The anisotropic carrier transport properties can be explained by the lamellar structure of the PEDOT/PSS films where the PEDOT nanocrystals could be isolated by the insulating PSS in the through-plane direction. The anisotropic thermal conductivity was mainly attributed to the lattice contribution from PSS because the polymer chain is oriented along the substrate.
