Ziwu Liu

Sulfur and nitrogen co-doped carbon nanotubes for enhancing electrochemical oxygen reduction activity in acidic and alkaline media

Carbon materials have received an increasing amount of attention due to their low cost, long-term stability, and high electrocatalytic activity in catalyzing the cathodic oxygen reduction reaction (ORR). However, most of the carbon catalysts have exhibited their excellent activity only in alkaline media, which greatly hinders their practical application in polymer electrolyte membrane fuel cells (PEMFCs). In order to break the restriction of alkaline conditions, sulfur and nitrogen doped carbon nanotubes (SN-CNTs) were designed and successfully prepared via annealing of a mixture composed of nitrogen doped carbon nanotubes (N-CNTs) and sulfur. The result showed the as-prepared SN-CNTs have an enhanced ORR activity in both acidic and alkaline media compared with N doped CNTs (N-CNTs). This report also provides a new approach to explore low-cost electrocatalysts for practical fuel cell applications.

Novel silicon-doped, silicon and nitrogen-codoped carbon nanomaterials with high activity for the oxygen reduction reaction in alkaline medium

Novel silicon-doped, silicon and nitrogen-codoped carbon nanomaterials were prepared by chemical vapor deposition and evaluated by electrochemical tests. The Si-doped CNSs and Si, N-codoped CNTs exhibited high electrocatalytic activity and long-term stability for the oxygen reduction reaction in alkaline medium due to changes in the charge density and the energetic characteristics of the carbon framework, as evidenced by density functional theory calculations. This may be of great importance for the design of low-cost and efficient metal-free cathode electrocatalysts in future alkaline fuel cells.

N, S and P-ternary doped carbon nano-pore/tube composites derived from natural chemicals in waste sweet osmanthus fruit with superior activity for oxygen reduction in acidic and alkaline media

To promote the practical application of novel heteroatom-doped carbon electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells, in this work, low-cost nitrogen (N), sulfur (S) and phosphorus (P)-ternary doped carbon nano-pore/tube composites (NSP-CNPTCs) were synthesized by natural, cheap and environment-friendly N, S and P-containing chemicals extracted from waste sweet osmanthus fruit and a certain amount of dicyandiamide with ferric sulfate as a catalyst. Electrochemical tests demonstrated that the as-prepared NSP-CNPTCs exhibited superior ORR activity in both acidic and alkaline media, showing a new approach for utilizing natural heteroatom-containing chemicals in all heteroatom-rich biomasses to synthesize value-added heteroatom-doped carbon electrocatalysts in future fuel cells.

Facile and scalable synthesis of coal tar-derived, nitrogen and sulfur-codoped carbon nanotubes with superior activity for O2 reduction by employing an evocating agent

Since heteroatom-doped carbon nanomaterials were proved to be one of the most promising alternatives to noble metal platinum-based cathode electrocatalysts in fuel cells over the past years, considerable efforts have been devoted to promoting their practical application. Although much progress has been made, the large-scale practical application of these heteroatom-doped carbon nanomaterials is presently inaccessible due to the lack of a facile synthesis method and low-cost heteroatom precursors with broad sources. Herein, we used the cost-effective, nitrogen (N) and sulfur (S)-containing coal tar which has an abundant supply of N and S precursors to synthesize value-added N and S-codoped carbon electrocatalysts for the oxygen reduction reaction (ORR) by employing the evocating agent of dicyandiamide (DICY). The results demonstrated that DICY could effectively help coal tar to form N and S-codoped carbon nanotubes (NS-CNTs) on the surface of CoCl2 nanoparticles. The as-synthesized NS-CNTs exhibited highly comparable ORR activities to commercial Pt–C catalysts in both acidic and alkaline media. This report not only provides a novel, facile and scalable approach for the preparation of low-cost CNT electrocatalysts with superior ORR activities but also offers a new and clean-utilizing path for the harmful N and S elements in coal tar and helps to reduce environmental pollution.

Germanium-doped and germanium/nitrogen-codoped carbon nanotubes with highly enhanced activity for oxygen reduction in alkaline medium

To develop effective cathode electrocatalysts for the oxygen reduction reaction (ORR) in fuel cells, germanium (Ge)-doped and Ge/N-co-doped carbon nanotubes (CNTs) were synthesized by chemical vapor deposition in this work. Electrochemical tests demonstrated that the as-prepared Ge-doped and GeN-codoped CNTs exhibited obviously enhanced ORR activity in alkaline medium, showing that the doping of Ge into the carbon matrix could also improve the ORR activities of the CNTs and N-CNTs as in the cases of other reported heteroatoms and would be of great importance for designing more effective ORR electrocatalysts in future alkaline fuel cells.