Xiaoyuan Zeng

Conversion of polystyrene foam to a high-performance doped carbon catalyst with ultrahigh surface area and hierarchical porous structures for oxygen reduction

A high-performance doped carbon catalyst with ultrahigh surface area (1123 m2 g−1) and hierarchical porous structures was prepared through an economical, non-template pyrolyzing approach using cross-linked polystyrene, melamine and iron chloride as precursors. The catalyst exhibits excellent oxygen reduction reaction (ORR) performance, outstanding methanol tolerance, remarkable stability, and high catalytic efficiency (nearly 100% selectivity for the four-electron ORR process). Remarkably, its ORR activity can even surpass that of the commercial Pt/C catalyst in alkaline media, with a half-wave potential 20 mV more positive. To the best of our knowledge, it is also one of the most active ORR catalysts in alkaline media to date. By investigating the effects of N dopants and Fe residue on the catalysts ORR performance, we find that residual Fe is as important as doped nitrogen in enhancing the ORR performance. The catalysts high ORR performance, outstanding stability and excellent methanol tolerance, combined with its hierarchical porous morphology, make it promising for the application in novel, environmentally friendly electrochemical energy systems. This research also provides a potential way to turn waste into wealth.

Ruthenium nanoparticles mounted on multielement co-doped graphene: an ultra-high-efficiency cathode catalyst for Li–O2 batteries

Developing a high-performance Li–O2 battery demands an air electrode with a high-efficiency bifunctional catalyst. Here we designed a new type of bifunctional cathode catalyst by mounting ruthenium nanoparticles on reduced graphene oxide co-doped with nitrogen, iron, and cobalt. The catalyst exhibited significantly higher ORR and OER activities than a commercial Pt/C catalyst in both aqueous and non-aqueous electrolytes. With this novel catalyst as the cathode, the battery exhibited an ultra-high reversible capacity of 23 905 mA h g−1 at a current density of 200 mA g−1. Furthermore, the battery also exhibited an excellent cycling stability—after 300 cycles of limited capacity, the discharge plateau potential decreased only slightly, and the energy efficiency was still above 60%. The battery also demonstrated good rate performance; with discharge current densities of up to 1000 and 2000 mA g−1, the capacities still reached 14 560 and 6420 mA h g−1, respectively. We suggest that the excellent performance of our catalyst can be ascribed to the excellent ORR performance of the multielement co-doped graphene and the excellent OER performance of the mounted Ru nanoparticles. In addition, the nanosheet structure with high surface area of the multielement co-doped graphene may result in the formation of uniform Li2O2 nanocrystals, which make the formation (discharge) and decomposition (charge) processes much more reversible.

Pd nanoparticles decorating flower-like Co3O4 nanowire clusters to form an efficient, carbon/binder-free cathode for Li–O2 batteries

A novel high-performance air cathode was prepared by synthesizing Co3O4 nanowire clusters on a nickel foam (NF) substrate and then decorating these clusters with Pd nanoparticles using a pulse electrodeposition method. This carbon-free and binder-free cathode had a well-defined, flower-like morphology, presenting clusters composed of nanowires with a diameter of ∼60 nm and a length of ∼5 μm on which were located Pd particles as small as 10 nm. The new cathode exhibited excellent low polarization and superior cycling performance. We found that its enhanced electrochemical properties could be attributed to the homogeneous distribution of Pd nanoparticles on the Co3O4 nanowires, which ensured uniform growth of Li2O2 on the Pd/Co3O4/NF electrodes. This, in turn, significantly improved the cathodes OER/ORR activity and aided the formation of discharge products with uniform morphologies, as well as the decomposition of these discharge products during recharging.