Anisotropic thermoelectric transport properties in polycrystalline SnSe_(2)

It is reported that SnSe_(2) consisting of the same elements as SnSe, is a new promising thermoelectric material with advantageous layered structure. In this work, the thermoelectric performance of polycrystalline SnSe_(2) is improved through introducing SnSe phase and electron doping(Cl doped in Se sites). The anisotropic transport properties of SnSe_(2) are investigated. A great reduction of the thermal conductivity is achieved in SnSe_(2) through introducing SnSe phase, which mainly results from the strong SnSe_(2)–SnSe inter-phase scattering. Then the carrier concentration is optimized via Cl doping, leading to a great enhancement of the electrical transport properties, thus an extraordinary power factor of ^5.12 μW·cm^(-1)·K^(-2) is achieved along the direction parallel to the spark plasma sintering(SPS) pressure direction( P). Through the comprehensive consideration on the anisotropic thermoelectric transport properties, an enhanced figure of merit ZT is attained and reaches to ^ 0.6 at 773 K in SnSe_(2)-2% SnSe after 5% Cl doping along the P direction, which is much higher than ^ 0.13 and ^ 0.09 obtained in SnSe_(2)-2% SnSe and pristine SnSe_(2) samples, respectively.

Chlorine doped graphitic carbon nitride nanorings as an efficient photoresponsive catalyst for water oxidation and organic decomposition

Rationally engineering the microstructure and electronic structure of catalysts to induce high activity for versatile applications remains a challenge. Herein, chlorine doped graphitic carbon nitride(Cl-doped g-C3N4) nanorings have been designed as a superior photocatalyst for pollutant degradation and oxygen evolution reaction(OER). Remarkably, Cl-doped g-C3N4 nanorings display enhanced OER performance with a small overpotential of approximately 290 m V at current density of 10 m A cm^-2 and Tafel slope of 83 m V dec-1, possessing comparable OER activity to precious metal oxides RuO2 and IrO2/C. The excellent catalytic performance of Cl-doped g-C3N4 nanorings originates from the strong oxidation capability,abundant active sites exposed and efficient charge transfer. More importantly, visible light irradiation gives rise to a prominent improvement of the OER performance, reducing the OER overpotential and Tafel slope by 140 m V and 28 m V dec^-1, respectively, demonstrating the striking photo-responsive OER activity of Cl-doped g-C3N4 nanorings. The great photo-induced improvement in OER activity would be related to the efficient charge transfer and the·OH radicals arising spontaneously on CN-Cl100 catalyst upon light irradiation. This work establishes Cl-doped g-C3N4 nanorings as a highly competitive metal-free candidate for photoelectrochemical energy conversion and environmental cleaning application.