Reactive nanotemplates for synthesis of highly efficient electrocatalysts: beyond simple morphology transfer

Efficient electrocatalysts for energy conversion in general, and fuel cell operation and water electrolysis in particular, are pivotal for carbon-free hydrogen production. While the requirements of successful electrocatalysts include a high number density of catalytically active sites, high surface-to-volume ratio, inherently high catalytic activity, and robustness of the catalyst surface structure under harsh operating conditions, it is extremely difficult to synthesize nanocatalysts that could possess all these structural characteristics. Nanotemplate-mediated synthesis, namely, the coating or filling of a template with a desired material phase followed by the removal of the template, has captured the interest of researchers because of the ease of creating hollow-structured nanocatalysts with a high surface to volume ratio. Recent studies, however, have revealed that nanotemplates could be more than just passive supports because they greatly affect catalytic performance by creating an unusual synergy between the substrate and catalyst and by providing dopants to the actual catalyst phase owing to their reactive nature. In this review, we discuss the most notable recent advances in the nanotemplate-based synthesis of electrocatalysts as well as the unusual effects of nanotemplates on the performance of nanocatalysts. We also provide an outlook for this fledgling field so that future research efforts could be focused on the development of practically useful electrocatalysts that could shape the future of energy technologies.

Enhancement of Hydrogen Productions by Accelerating Electron-Transfers of Sulfur Defects in the CuS@CuGaS2 Heterojunction Photocatalysts

CuS and CuGaS2 heterojunction catalysts were used to improve hydrogen production performance by photo splitting of methanol aqueous solution in the visible region in this study. CuGaS2, which is a chalcogenide structure, can form structural defects to promote separation of electrons and holes and improve visible light absorbing ability. The optimum catalytic activity of CuGaS2 was investigated by varying the heterojunction ratio of CuGaS2 with CuS. Physicochemical properties of CuS, CuGaS2 and CuS@CuGaS2 nanoparticles were confirmed by X-ray diffraction, ultraviolet visible spectroscopy, high-resolution transmission electron microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy. Compared with pure CuS, the hydrogen production performance of CuGaS2 doped with Ga dopant was improved by methanol photolysis, and the photoactivity of the heterogeneous CuS@CuGaS2 catalyst was increased remarkably. Moreover, the 0.5CuS@1.5CuGaS2 catalyst produced 3250 μmol of hydrogen through photolysis of aqueous methanol solution under 10 h UV light irradiation. According to the intensity modulated photovoltage spectroscopy (IMVS) results, the high photoactivity of the CuS@CuGaS2 catalyst is attributed to the inhibition of recombination between electron-hole pairs, accelerating electron-transfer by acting as a trap site at the interface between CuGaS2 structural defects and the heterojunction.

Mesoporous Hollow Sb/ZnS@C Core-Shell Heterostructures as Anodes for High-Performance Sodium-Ion Batteries

Combining the advantage of metal, metal sulfide, and carbon, mesoporous hollow core-shell Sb/ZnS@C hybrid heterostructures composed of Sb/ZnS inner core and carbon outer shell are rationally designed based on a robust template of ZnS nanosphere, as anodes for high-performance sodium-ion batteries (SIBs). A partial cation exchange reaction based on the solubility difference between Sb₂ S₃ and ZnS can transform mesoporous ZnS to Sb₂ S₃ /ZnS heterostructure. To get a stable structure, a thin contiguous resorcinol-formaldehyde (RF) layer is introduced on the surface of Sb₂ S₃ /ZnS heterostructure. The effectively protective carbon layer from RF can be designed as the reducing agent to convert Sb₂ S₃ to metallic Sb to obtain core-shell Sb/ZnS@C hybrid heterostructures. Simultaneously, the carbon outer shell is beneficial to the charge transfer kinetics, and can maintain the structure stability during the repeated sodiation/desodiation process. Owing to its unique stable architecture and synergistic effects between the components, the core-shell porous Sb/ZnS@C hybrid heterostructure SIB anode shows a high reversible capacity, good rate capability, and excellent cycling stability by turning the optimized voltage range. This novel strategy to prepare carbon-layer-protected metal/metal sulfide core-shell heterostructure can be further extended to design other novel nanostructured systems for high-performance energy storage devices.

Insight into the hydrogen evolution reaction of nickel dichalcogenide nanosheets: activities related to non-metal ligands

Transition metal dichalcogenides, MX₂ (M = Fe, Co, Ni, X = S, Se, Te), have been proven to be promising substitutes for noble metals in hydrogen evolution reactions (HERs). However, forthright comparisons of metal sulfides, metal selenides, and metal tellurides are rarely conducted, let alone the mechanism of the important role of their non-metal ligands. In this paper, we report the pilot study of a controllable method for the preparation of a series of NiX₂ (X = S, Se, Te) nanosheets via a facile anion-exchange reaction. Consequently, the HER activities and stabilities of NiS₂, NiSe₂, and NiTe₂ nanosheets were tested in both acid and alkaline solutions. The required overpotentials to reach 10 mA cm^-2 in 0.5 M H₂SO₄ for NiS₂, NiSe₂, and NiTe₂ were 213, 156, and 276 mV, respectively. The best performance of NiSe₂ was also confirmed in 1 M KOH. Besides NiS₂ and NiTe₂ nanosheets, the HER properties of NiSe₂ nanosheets are superior to most of the available nickel catalysts. Interestingly, the results from electrochemical measurements were found to be fully consistent with the data based on density function theory calculation. Among various factors that might influence the HER activities of nickel dichalcogenides, the free energies of hydrogen adsorption and conductivities have played important roles.

A heteroelectrode structure for solar water splitting: integrated cobalt ditelluride across a TiO2-passivated silicon microwire array

CoTe₂@TiO₂-Si-MWs provide active sites for proton reduction and combine surface hydrogen atoms into molecular hydrogen.

Template engaged synthesis of hollow ceria-based composites

Hollow ceria-based composites, which consist of noble metal nanoparticles or metal oxides as a secondary component, are being studied extensively for potential applications in heterogeneous catalysis. This is due to their unique features, which exhibit the advantages of a hollow structure (e.g. high surface area and low weight), and also integrate the properties of ceria and noble metals/metal oxides. More importantly, the synergistic effect between constituents in hollow ceria-based composites has been demonstrated in various catalytic reactions. In this feature article, we summarize the state-of-the-art in the synthesis of hollow ceria-based composites, including traditional hard-templates and more recently, sacrificial-template engaged strategies, highlighting the key role of selected templates in the formation of hollow composites. In addition, the catalytic applications of hollow ceria-based composites are briefly surveyed. Finally, challenges and perspectives on future advances of hollow ceria-based composites are outlined.

Carbon coated manganese monoxide octahedron negative-electrode for lithium-ion batteries with enhanced performance

Carbon coated MnO octahedra with narrow size distribution and good dispersity have been fabricated and applied as lithium ion battery anode materials.

Nanoporous hollow transition metal chalcogenide nanosheets synthesized via the anion-exchange reaction of metal hydroxides with chalcogenide ions

Nanoporous hollow transition metal chalcogenides are of special interest for a variety of promising applications. Although some advanced synthetic methods have been reported, the development of a facile and general strategy to fabricate porous hollow nanostructures of transition metal chalcogenides, especially with enhanced electrocatalytic performance, still remains highly challenged. Herein, we report a facile chemical transformation strategy to prepare nanoporous hollow Co3S4 nanosheets via the anion exchange reaction of Co(OH)2 with sulfide ions. The chemical transformation mechanism involves the as-formed layer of nanoporous cobalt sulfide on Co(OH)2 driven by the anion-exchange-reaction and lattice mismatch induced quick strain release, a following diffusion-effect-dominated core-shell hollow intermediate with hollow interiors, and subsequent Ostwald ripening growth of hollow nanosheets at elevated temperatures. This anion-exchange strategy of transition metal hydroxides with chalcogenide ions is also suitable for fabricating nanoporous hollow nanosheets of other metal chalcogenides (e.g., CoSe2, CoTe2, CdS, and NiS). The as-prepared nanoporous hollow Co3S4 nanosheets are found to be highly active and stable for electrocatalytic oxygen evolution reaction.