Guoqiang Zhao

Readily Exfoliated TiSe2 Nanosheets for High-Performance Sodium Storage

Materials with sheet-like morphologies are highly desirable candidates for energy storage and conversion applications, due to the confined atomic thickness and high surface area, which would largely improve the electrochemical reaction kinetics. In this work, the sodium storage performance of TiSe2 nanosheets and corresponding sodiation/desodiation reaction mechanism are studied for the first time. TiSe2 nanosheets are readily exfoliated from bulk TiSe2 after quick ultrasonication or grinding. The TiSe2 nanosheets exhibit a reversible capacity of 147u2005mAhu2009g-1 at 0.1u2005Au2009g-1 , and show excellent rate capability with a capacity of 103u2005mAhu2009g-1 at an ultra-high current density of 10.0u2005Au2009g-1 . The combined in situ XRD and ex-situ HRTEM results suggest that sodium storage in TiSe2 is achieved through a multi-step intercalation/deintercalation mechanism. Besides, TiSe2 might be a promising 2D nanomaterial platform for other energy and electronic applications due to its easy exfoliation and unique physicochemical properties.

Epitaxial growth of Ni(OH)2 nanoclusters on MoS2 nanosheets for enhanced alkaline hydrogen evolution reaction

Constructing heterostructures is an effective strategy for designing efficient electrocatalysts. MoS2 is a star catalyst for hydrogen evolution reaction (HER) in acidic media; however, the alkaline HER activity is deficient due to the sluggish water dissociation process. Herein, Ni(OH)2/MoS2 heterostructures with Ni(OH)2 nanoclusters epitaxially decorated on the surface of MoS2 are synthesized towards the alkaline HER. As compared with MoS2, the epitaxial Ni(OH)2/MoS2 heterostructures show significantly enhanced HER activity in 1 M KOH, and the overpotential is decreased by nearly 150 mV to reach a current density of 10 mA cm-2. The substantial increase in turnover frequency (TOF) demonstrates that the intrinsic activity is greatly improved after the incorporation of Ni(OH)2 nanoclusters. The presence of Ni(OH)2 nanoclusters would provide additional water dissociation sites while MoS2 is ready for the adsorption and combination of the generated H*, and this so-called synergistic effect eventually induces significantly enhanced alkaline HER kinetics. Besides, the electron transfer from Ni(OH)2 to MoS2 increases the proton affinity of MoS2. The present results describe an interesting case of an atomic-scale electrochemically inert material promoted HER process, and would open a new avenue into designing efficient hetero-nanostructures towards electrocatalytic applications.

CoSe2/MoSe2 Heterostructures with Enriched Water Adsorption/Dissociation Sites towards Enhanced Alkaline Hydrogen Evolution Reaction

Transition-metal dichalcogenides (TMDs) are promising electrocatalysts toward the hydrogen evolution reaction (HER) in acid media, but they show significantly inferior activity in alkaline media due to the extremely sluggish water dissociation kinetics. Herein, CoSe2 /MoSe2 heterostructures with CoSe2 quantum dots anchored on MoSe2 nanosheets are synthesized towards enhanced alkaline HER catalytic activity. The incorporation of CoSe2 is intended to construct additional water adsorption sites on the basal planes of MoSe2 to promote water dissociation. The CoSe2 /MoSe2 heterostructures show substantially enhanced activity over MoSe2 and CoSe2 in 1u2009m KOH. The optimal overpotential required to reach a current density of 10u2005mAu2009cm-2 is merely 218u2005mV, which is more than 100u2005mV greater than that of MoSe2 , which is by far the best performance demonstrated for precious-metal-free catalysts. Detailed analyses based on electrochemical testing demonstrate that the water adsorption and subsequent dissociation process is accelerated by CoSe2 species with rich edge sites; meanwhile, MoSe2 species provide sufficient active sites for the adsorption and combination of adsorbed hydrogen (H. ). These results provide an effective strategy for developing earth-abundant catalysts with high activity for the alkaline HER, and are of great significance to promote the practical application of alkaline water electrolysis.

Iron-doped nickel molybdate with enhanced oxygen evolution kinetics

Electrochemical water splitting is one of the potential approaches for making renewable energy production and storage viable. The oxygen evolution reaction (OER), as a sluggish four-electron electrochemical reaction, has to overcome high overpotential to accomplish overall water splitting. Therefore, developing low-cost and highly active OER catalysts is the key for achieving efficient and economical water electrolysis. In this work, Fe-doped NiMoO4 was synthesized and evaluated as the OER catalyst in alkaline medium. Fe3+ doping helps to regulate the electronic structure of Ni centers in NiMoO4 , which consequently promotes the catalytic activity of NiMoO4 . The overpotential to reach a current density of 10u2005mAu2009cm-2 is 299u2005mV in 1u2009m KOH for the optimal Ni0.9 Fe0.1 MoO4 , which is 65u2005mV lower than that for NiMoO4 . Further, the catalyst also shows exceptional performance stability during a 2u2005h chronopotentiometry testing. Moreover, the real catalytically active center of Ni0.9 Fe0.1 MoO4 is also unraveled based on the exu2005situ characterizations. These results provide new alternatives for precious-metal-free catalysts for alkaline OER and also expand the Fe-doping-induced synergistic effect towards performance enhancement to new catalyst systems.