Zhishan Li

Electronic properties of edge-functionalized zigzag graphene nanoribbons on SiO2 substrate

Based on first-principles calculations, electronic properties of edge-functionalized zigzag graphene nanoribbons (ZGNRs) on SiO(2) substrate are presented. Metallic or semiconducting properties of ZGNRs are revealed due to various interactions between edge-hydrogenated ZGNRs and different SiO(2)(0001) surfaces. Bivalent functional groups decorating ZGNRs serve as the bridge between active edges of ZGNRs and SiO(2). These functional groups stabilize ZGNRs on the substrate, as well as modify the edge states of ZGNRs and further affect their electronic properties. Bandgaps are opened owing to edge state destruction and distorted lattice in ZGNRs.

Rational Design of Cobalt–Iron Selenides for Highly Efficient Electrochemical Water Oxidation

Exploring active, stable, earth-abundant, low-cost, and high-efficiency electrocatalysts is highly desired for large-scale industrial applications toward the low-carbon economy. In this study, we apply a versatile selenizing technology to synthesize Se-enriched Co1-xFexSe2 catalysts on nickel foams for oxygen evolution reactions (OERs) and disclose the relationship between the electronic structures of Co1-xFexSe2 (via regulating the atom ratio of Co/Fe) and their OER performance. Owing to the fact that the electron configuration of the Co1-xFexSe2 compounds can be tuned by the incorporated Fe species (electron transfer and lattice distortion), the catalytic activity can be adjusted according to the Co/Fe ratios in the catalyst. Moreover, the morphology of Co1-xFexSe2 is also verified to strongly depend on the Co/Fe ratios, and the thinner Co0.4Fe0.6Se2 nanosheets are obtained upon selenization treatment, in which it allows more active sites to be exposed to the electrolyte, in turn promoting the OER performance. The Co0.4Fe0.6Se2 nanosheets not only exhibit superior OER performance with a low overpotential of 217 mV at 10 mA cm-2 and a small Tafel slope of 41 mV dec-1 but also possess ultrahigh durability with a dinky degeneration of 4.4% even after 72 h fierce water oxidation test in alkaline solution, which outperforms the commercial RuO2 catalyst. As expected, the Co0.4Fe0.6Se2 nanosheets have shown great prospects for practical applications toward water oxidation.

A Universal Method to Engineer Metal Oxide–Metal–Carbon Interface for Highly Efficient Oxygen Reduction

Oxygen is the most abundant element in the Earths crust. The oxygen reduction reaction (ORR) is also the most important reaction in life processes and energy converting/storage systems. Developing techniques toward high-efficiency ORR remains highly desired and a challenge. Here, we report a N-doped carbon (NC) encapsulated CeO2/Co interfacial hollow structure (CeO2-Co-NC) via a generalized strategy for largely increased oxygen species adsorption and improved ORR activities. First, the metallic Co nanoparticles not only provide high conductivity but also serve as electron donors to largely create oxygen vacancies in CeO2. Second, the outer carbon layer can effectively protect cobalt from oxidation and dissociation in alkaline media and as well imparts its higher ORR activity. In the meanwhile, the electronic interactions between CeO2 and Co in the CeO2/Co interface are unveiled theoretically by density functional theory calculations to justify the increased oxygen absorption for ORR activity improvement. The reported CeO2-Co-NC hollow nanospheres not only exhibit decent ORR performance with a high onset potential (922 mV vs RHE), half-wave potential (797 mV vs RHE), and small Tafel slope (60 mV dec-1) comparable to those of the state-of-the-art Pt/C catalysts but also possess long-term stability with a negative shift of only 7 mV of the half-wave potential after 2000 cycles and strong tolerance against methanol. This work represents a solid step toward high-efficient oxygen reduction.

Fabrication of nanopore and nanoparticle arrays with high aspect ratio AAO masks

How to use high aspect ratio anodic aluminum oxide (AAO) membranes as an etching and evaporation mask is one of the unsolved problems in the application of nanostructured arrays. Here we describe the versatile utilizations of the highly ordered AAO membranes with a high aspect ratio of more than 20 used as universal masks for the formation of various nanostructure arrays on various substrates. The result shows that the fabricated nanopore and nanoparticle arrays of substrates inherit the regularity of the AAO membranes completely. The flat AAO substrates and uneven AAO frontages were attached to the Si substrates respectively as an etching mask, which demonstrates that the two kinds of replication, positive and negative, represent the replication of the mirroring of Si substrates relative to the flat AAO substrates and uneven AAO frontages. Our work is a breakthrough for the broad research field of surface nano-masking.