Vacancy Occupation-Driven Polymorphic Transformation in Cobalt Ditelluride for Boosted Oxygen Evolution Reaction.

Transition-metal dichalcogenides (TMDs) hold great potential as an advanced electrocatalyst for oxygen evolution reaction (OER), but to date the activity of transition metal telluride catalysts are demonstrated to be poor for this reaction. In this study, we report the activation of CoTe2 for OER by doping secondary anions into Te vacancies to trigger a structural transition from the hexagonal to the orthorhombic phase. The achieved orthorhombic CoTe2 with partial vacancies occupied by P-doping exhibits an exceptional OER catalytic activity with an overpotential of only 241 mV at 10 mA cm-2 and a robust stability more than 24 h. The combined experimental and theoretical studies suggest that the defective phase transformation is controllable and allows the synergism of vacancy, doping as well as the reconstructed crystallographic structure, ensuring more exposure of catalytic active sites, rapid charge transfer, and energetically favorable intermediates. This vacancy occupation-driven strategy of structural transformation can also be manipulated by S- and Se-doping, which may offer useful guidance for developing tellurides-based electrocatalyst for OER.

In-situ embedding cobalt-doped copper sulfide within ultrathin carbon nanosheets for superior lithium storage performance.

Construction of well-defined hybrid composites consisting of transition metal sulfides and two-dimensional (2D) carbon nanosheets as high-performance anodes for lithium-ion batteries (LIBs) is of great significance but remains challenging. Herein, we have developed a novel strategy to in-situ fabricate a nanohybrid composites consisting of cobalt-doped copper sulfides nanoparticles embedded in 2D carbon nanosheets (2D Co-Cu2S@C) through a one-pot sulfurization of 2D nanosheet-like Co-doped copper-based metal-organic frameworks (MOFs) precursors. When applied as LIBs anodes, the as-prepared 2D Co-Cu2S@C composites could deliver a specific capacity of 780 mAh g-1 at 0.5 A g-1 after 300 cycles and a high-rate capability with 209 mAh g-1 at 5 A g-1, superior to most reported copper sulfide-based anodes. The exceptional performance could be attributed to the synergism of ultrathin structure (~4 nm), appropriate cobalt doping and strong carbon coupling, resulting in the shortened paths for Li+ transportation, enlarged exposing surface for Li+ adsorption, enhanced electric conductivity for charge transfer as well as robust mechanical property against volume expansion.