Liang-Liang Feng

Carbon-Armored Co9S8 Nanoparticles as All-pH Efficient and Durable H2-Evolving Electrocatalysts

Splitting water to produce hydrogen requires the development of non-noble-metal catalysts that are able to make this reaction feasible and energy efficient. Herein, we show that cobalt pentlandite (Co9S8) nanoparticles can serve as an electrochemically active, noble-metal-free material toward hydrogen evolution reaction, and they work stably in neutral solution (pH 7) but not in acidic (pH 0) and basic (pH 14) media. We, therefore, further present a carbon-armoring strategy to increase the durability and activity of Co9S8 over a wider pH range. In particular, carbon-armored Co9S8 nanoparticles (Co9S8@C) are prepared by direct thermal treatment of a mixture of cobalt nitrate and trithiocyanuric acid at 700 °C in N2 atmosphere. Trithiocyanuric acid functions as both sulfur and carbon sources in the reaction system. The resulting Co9S8@C material operates well with high activity over a broad pH range, from pH 0 to 14, and gives nearly 100% Faradaic yield during hydrogen evolution reaction under acidic (pH 0), neutral (pH 7), and basic (pH 14) media. To the best of our knowledge, this is the first time that a transition-metal chalcogenide material is shown to have all-pH efficient and durable electrocatalytic activity. Identifying Co9S8 as the catalytically active phase and developing carbon-armoring as the improvement strategy are anticipated to give a fresh impetus to rational design of high-performance noble-metal-free water splitting catalysts.

Metallic Co9S8 nanosheets grown on carbon cloth as efficient binder-free electrocatalysts for the hydrogen evolution reaction in neutral media

The development of efficient non-noble metal hydrogen-evolving electrocatalysts is of paramount importance for sustainable hydrogen production from water. Herein, we report the direct growth of metallic Co9S8 nanosheets on carbon cloth (CC) through a facile one-pot solvothermal method. We also show that the introduction of a tiny amount of Zn2+ ions (Zn : Co mol ratio of 0.5–1 : 100) in the synthesis system can reduce the thickness, improve the crystallinity, and optimize the surface structure of Co9S8 nanosheets, without Zn-doping. Furthermore, we show that the resulting Co9S8/CC materials can serve as efficient, binder-free, non-noble metal electrocatalysts for the hydrogen evolution reaction (HER) under neutral conditions (pH 7). In particular, the Co9S8/CC material (synthesized in the presence of Zn2+ ions) affords a current density of 10 mA cm−2 at a low overpotential of 175 mV, has great catalytic stability as long as 100 h, and gives about 100% faradaic yield towards the HER in neutral media. The materials excellent catalytic performance toward the HER is attributed primarily to the synergistic effects of Co9S8s intrinsic catalytic ability, the ultrathin nanosheet array architecture and the self-supporting feature.

Growth of molybdenum carbide micro-islands on carbon cloth toward binder-free cathodes for efficient hydrogen evolution reaction

Design and synthesis of efficient noble metal-free hydrogen evolution catalysts is of paramount importance for the practical application of water-splitting devices. Herein, we report a novel synthetic method to grow dispersed molybdenum carbide (Mo2C) micro-islands on flexible carbon cloth (CC). This method involves the controlled synthesis of a supramolecular hybrid between cetyltrimethyl ammonium cations and molybdate anions on CC, followed by simple thermal treatment of this supramolecular hybrid in Ar to form Mo2C on CC in situ. In this synthesis, the presence of cetyltrimethyl ammonium bromide is proven to be important because it effectively immobilizes molybdate ions on CC on the one hand and functions as a carbon source for the formation of Mo2C on the other. Moreover, the as-prepared Mo2C/CC composite material can serve as efficient binder-free cathodes toward the hydrogen evolution reaction (HER). The Mo2C/CC affords a current density of 10 mA cm−2 at a low overpotential of 140 mV and works stably in acidic media with a Faraday yield of ∼100%. The isolated island architecture of Mo2C ensures rich active sites to be exposed and allows the easy interaction of reactants (e.g., protons) with the active sites. Also, the strong adhesion between Mo2C and carbon cloth facilitates electron transport/transfer in the composite material and is helpful for the achievement of excellent catalytic stability.

Facile synthesis of single-crystalline hollow α-Fe2O3 nanospheres with gas sensing properties

High-quality single-crystalline hollow α-Fe2O3 nanospheres were prepared, using the ZnS–CHA (CHA = cyclohexylamine) nanohybrid as an additive through a solvothermal reaction, which avoids tedious steps and a high temperature calcination process. The formation process of these hollow nanospheres can be divided into two stages: (i) formation of solid Fe2O3 nanospheres and (ii) preferential inside-out dissolution of the solid nanoparticles to form hollow nanospheres. Due to the unique single-crystalline hollow structure, the as-obtained α-Fe2O3 nanomaterial exhibits enhanced gas sensing properties.