Hui-Juan Zhang

The comparison of macroporous ceramics fabricated through the protein direct foaming and sponge replica methods

The macroporous ceramic samples fabricated using the sponge replica and protein direct foaming methods were compared in terms of porosity, density, compressive strength and microstructure. The egg white protein was applied in both fabrication methods as the binder or foaming agent. The samples fabricated using the protein direct foaming method were stronger and more uniform pore structures in the similar porosity. This result was supported through the Weibull modulus analysis and the scanning electron microscope microstructure observation.

Co-supported catalysts on nitrogen and sulfur co-doped vertically-aligned carbon nanotubes for oxygen reduction reaction

Co supported on nitrogen and sulfur co-doped vertically-aligned carbon nanotubes (Co/NS-CNT) has been fabricated as an efficient electrocatalyst for oxygen reduction reaction (ORR) by a two-step process involving sputtering of cobalt and subsequent annealing in a nitrogen and sulfur-containing atmosphere. The surface morphology, crystal structure and chemical composition of the samples have been investigated. Both cyclic voltammetry (CV) and rotating-disk electrode (RDE) measurements reveal that the annealing temperature has a significant impact on the ORR activity of the catalyst in both alkaline and acid electrolytes. And the best ORR performance is achieved for the catalyst annealed at 600 °C (Co/NS-CNT-600) in 0.1 M KOH solution, which exhibits an onset potential of 0.962 V and an ORR peak potential of 0.803 V. Rotating ring-disk electrode (RRDE) testing in KOH shows an electron transfer number of around 3.7, indicating a four-electron pathway-dominated ORR process. The Co/NS-CNT-600 catalyst also exhibits the best ORR catalytic activity in 0.5 M H2SO4 medium. The excellent ORR activity of the Co/NS-CNT catalyst is attributed to the synergistic effects from N and S co-doping and the increased active sites from metallic cobalt or CoS2.

Selective removal of metallic single-walled carbon nanotubes by microwave-assisted treatment of SWCNTs with nitronium ions

A facile and rapid technique for the selective removal of metallic single-walled carbon nanotubes (M-SWCNTs) was developed by microwave-assisted treatment of SWCNTs with nitronium ions. Upon exposure to microwaves, M-SWCNTs homogeneously dispersed in organic solution were prone to react with an electron acceptor reagent, i.e., positively charged nitronium ions as compared to their counterpart, namely, semiconducting (S)-SWCNTs. The well-functionalized M-SWCNTs were separated and removed from residual S-SWCNTs by ultracentrifugation and filtration. The resulting material contained highly enriched S-SWCNTs, the proportion of which increased from approximately 62 mol% in as-received SWCNTs to nearly 90 mol%. The effectiveness in removing M-SWCNTs was confirmed by the resonant Raman spectra and UV-vis-NIR absorption spectra. The microwave-enhanced separation mechanism was discussed as well.

Oxygen reduction reaction with efficient, metal-free nitrogen, fluoride-codoped carbon electrocatalysts derived from melamine hydrogen fluoride salt

In this study, we successfully demonstrate an efficient, metal-free nitrogen, fluoride-codoped carbon (NFC) oxygen reduction reaction (ORR) electrocatalyst, which is produced by directly pyrolyzing melamine hydrogen fluoride salt (using as a single N and F precursor for the first time) mixed with carbon black BP2000 in a N2 atmosphere. The ORR electrocatalytic performances are evaluated by rotating ring disk electrode experiments in 0.1 M KOH. The NFC electrocatalyst prepared at the optimized temperature of 1000 °C (NFC1000) demonstrates a high ORR electrocatalytic activity with a peak potential of 0.82 V (vs. RHE), half-wave potential of 0.82 V (vs. RHE), predominant direct 4-electron reaction pathway, and good durability and methanol tolerance. Transmission electron microscopy equipped with mapping, X-ray diffraction and X-ray photoelectron spectroscopy results indicate that NFC1000 possesses an amorphous carbon structure with a homogenous codoped distribution of N and F at 2.25 at% and 1.52 at%, respectively. N2 adsorption-desorption analysis reveals that the as-prepared NFC1000 has a high surface area of 1169 m2 g-1. This study provides a feasible approach to synthesize low-cost and highly efficient metal-free heteroatom-doped carbon-based electrocatalysts.