Recently emerged ionic thermoelectric conversion with the Soret effect is advantageous in providing large thermopower on the order of ≈1-10 mV K −1 , but the origin of the large thermopower and the methodology of attaining superior thermoelectric performances are yet to be disclosed. Here, key parameters and their optimization for outstanding thermoelectric responses with polystyrene sulfonic acid (PSS-H) are unveiled. It is found that the thermo-diffusion of water boosts proton transport, playing a key role in obtaining large ionic thermopower by promoting unidirectional migration of protons from a hotter to colder side. When graphene oxide (GO) embedded in PSS-H is aligned along the transport direction of protons and water, their diffusion along the in-plane direction of GO is promoted, enlarging both ionic thermopower and ionic electrical conductivity. PSS-H containing 3 wt% GO possesses extremely large ionic power factors up to 1.8 mW m −1 K −2 and ionic figure-of-merits up to 0.85 at 23 °C. This study provides not only preeminent thermoelectric performances based on ion transport but also identifies the influence of the key parameters on thermoelectric properties, suggesting controllability of thermo-diffusion of ions depending on inclusions in base materials, which will draw numerous subsequent research with their alterations.
In-operando study coupled with voltage/current
profiles are presented
in order to unveil lithium insertion processes into 3D porous carbon
nanotube (CNT) structures whose surfaces were altered to have lithiophobic,
lithiophilic, and hybridized lithiophobic/philic characteristics using
graphitic surfaces with/without carboxyl/hydroxyl groups. We found
the lithiophobic graphitic surfaces hindered lithium insertion into
the scaffold despite the high conductivity of CNT. The lithiophilic
surface caused another problem of lithium deposition on the outer
surface of the electrode, clogging pores and engendering dendrites.
Conversely, in the hybridized CNT, lithiophilic trenches partially
created on the pristine CNT allowed for uniform lithium deposition
into the pores by simultaneously improved lithium attraction and charge
transfer, reaching a high areal capacity of 16 mAh cm–2 even with a current density of 8 mA cm–2 without
noticeable dendrite formation and volume expansion. Our hybridization
approach provides valuable insight to realize a high-energy-density
anode by uniformly impregnating lithium into porous media.
We fabricated nanowires of a conjugated oligomer and applied them to organic field-effect transistors (OFETs). The supramolecular assemblies of a thienoisoindigo-based small molecular organic semiconductor (TIIG-Bz) were prepared by co-precipitation with 2-bromobenzaldehyde (2-BBA) via a combination of halogen bonding (XB) between the bromide in 2-BBA and electron-donor groups in TIIG-Bz, and chalcogen bonding (CB) between the aldehyde in 2-BBA and sulfur in TIIG-Bz. It was found that 2-BBA could be incorporated into the conjugated planes of TIIG-Bz via XB and CB pairs, thereby increasing the π − π stacking area between the conjugated planes. As a result, the driving force for one-dimensional growth of the supramolecular assemblies via π − π stacking was significantly enhanced. TIIG-Bz/2-BBA nanowires were used to fabricate OFETs, showing significantly enhanced charge transfer mobility compared to OFETs based on pure TIIG-Bz thin films and nanowires, which demonstrates the benefit of nanowire fabrication using 2-BBA.
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