Xiaochang Qiao

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.

In situ growth of cobalt sulfide hollow nanospheres embedded in nitrogen and sulfur co-doped graphene nanoholes as a highly active electrocatalyst for oxygen reduction and evolution

Developing high-performance bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) using nonprecious metal-based catalysts is a major challenge for achieving the commercial success of regenerative fuel cells and rechargeable metal–air batteries. In the present study, we designed a new type of bifunctional catalyst by embedding cobalt sulfide hollow nanospheres in nitrogen and sulfur co-doped graphene nanoholes (Co1−xS/N–S–G) via a simple, one-pot pyrolysis method. The catalyst had a high specific surface area (390.6 m2 g−1) with a hierarchical meso–macroporous structure. In an alkaline medium, the catalyst exhibited high ORR catalytic activity, with a half-wave potential 30 mV more positive and a diffusion-limiting current density 15% higher than a commercial Pt/C catalyst, and the catalyst is also highly active for OER with a small overpotential of 371 mV for 10 mA cm−2 current density. Its overall oxygen electrode activity parameter (ΔE) is 0.760 V, which is smaller than that of Pt/C and most of the non-precious metal catalysts in previous studies. Furthermore, it demonstrated better durability towards both the ORR and OER. Detailed investigation clarified that the materials excellent electrocatalytic performance is attributable to: (1) a synergistic effect, induced by the presence of multiple types of active sites, including cobalt sulfide hollow nanospheres, nitrogen and sulfur dopants, and possible Co–N–C sites; (2) cobalt sulfide hollow nanospheres penetrating through the plane of graphene sheets form strong interaction between them; (3) more edge defects associated with the existence of nanoholes on the graphene basal plane; and (4) the high surface area and efficient mass transfer arising from the hierarchical porous structure.

A hollow spherical doped carbon catalyst derived from zeolitic imidazolate framework nanocrystals impregnated/covered with iron phthalocyanines

A hollow spherical doped carbon catalyst with a large surface area and hierarchical porous structure is prepared by pyrolyzing zeolitic imidazolate framework nanocrystals (Z8Ncs) impregnated/covered with iron phthalocyanines (FePcs). It is found that the doping of FePcs into the Z8Nc precursor plays a crucial role in the structural evolution of the resulting hollow-core porous carbon as well as its high catalytic performance. Doped carbon catalysts derived from either Z8Ncs or FePcs exhibit poor activity towards oxygen reduction, whereas the catalyst derived from Z8Ncs impregnated/covered with FePcs exhibits extremely high performance in both acidic and alkaline media. In 0.1 M HClO4, its onset potential reaches up to 0.910 V, and its half-potential (0.790 V) is only 60 mV lower than that of the 20 wt% Pt/C catalyst (0.850 V). In 0.1 M KOH, its ORR activity even surpasses that of Pt/C. We suggest that the high performance of the catalyst is attributable to the following factors: (i) the high active site density caused by doping FePcs into/onto the highly porous, N-rich Z8Ncs, (ii) the high surface area and adequate active site exposure caused by its hollow spherical morphology, and (iii) the hierarchical porous structure which further facilitates the diffusion and adsorption of oxygen molecules.

An ultra high performance multi-element doped mesoporous carbon catalyst derived from poly(4-vinylpyridine)

A high performance doped carbon catalyst with ordered mesoporous structures and a high surface area (1217 m2 g−1) was prepared through a nanocasting-pyrolysis procedure by using poly(4-vinylpyridine) and iron chloride as the precursors and SBA-15 as the template. The catalyst exhibited excellent oxygen reduction reaction (ORR) performance, and was far more active than a commercial Pt/C catalyst in alkaline media, with its half-wave potential (−0.083 V, vs. Ag/AgCl) 64 mV more positive and current density at −0.1 V (vs. Ag/AgCl, −3.651 mA cm−2) almost three times higher than those of a commercial Pt/C catalyst (−0.147 V, vs. Ag/AgCl, and −0.967 mA cm−2), respectively. To our knowledge, it is one of the best carbon-based ORR catalysts to date in an alkaline medium. In addition to the outstanding ORR performance, our catalyst also illustrated excellent stability, methanol tolerance, and high catalytic efficiency. It is found that the total N contents and the compositions of each N species in the catalysts strongly depend on the pyrolysis temperatures. Furthermore, we found that the SBA-15 templates not only give catalysts well-defined mesoporous structures, but also seem to help increase the total N content whilst the proportion of each N species in the catalysts is not changed obviously.