Meiling Xiao

Meso/Macroporous Nitrogen‐Doped Carbon Architectures with Iron Carbide Encapsulated in Graphitic Layers as an Efficient and Robust Catalyst for the Oxygen Reduction Reaction in Both Acidic and Alkaline Solutions

Meso-/macroporous nitrogen-doped carbon architectures with iron carbide encapsulated in graphitic layers are fabricated by a facile approach. This efficient and robust material exhibits superior catalytic performance toward the oxygen reduction reaction in both acidic and alkaline solutions and is the most promising alternative to a Pt catalyst for use in electrochemical energy devices.

Enhanced Catalytic Performance of Composition‐Tunable PtCu Nanowire Networks for Methanol Electrooxidation

Ultrathin PtCux (x=1, 2 and 3) nanowire networks (NWMs) with controllable compositions were successfully synthesized by using Triton X‐100 as the structure‐directing agent in aqueous solution. The as‐prepared PtCux nanocrystals were characterized by transmission electron microscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy, cyclic voltammetry, and chronoamperometry. The results show that electrocatalytic performance of the PtCux NWNs towards the methanol oxidation reaction is enhanced relative to that of commercial Pt/C catalysts. Moreover, if the initial atomic ratio of Pt/Cu is 1:2, the corresponding PtCu2 NWNs catalyst generates mass activity that is 3.77‐fold higher and specific activity that is 2.71‐fold higher than the corresponding properties of commercial Pt/C catalysts. The enhanced activity can be attributed to a unique structure and a modified electronic effect.

Rapid synthesis of a PtRu nano-sponge with different surface compositions and performance evaluation for methanol electrooxidation

A rapid strategy to synthesize a highly active PtRu alloy nano-sponge catalyst system for methanol electro-oxidation is presented. The greatly increased Pt utilization, anti-CO poisoning ability and electronic effect resulting from the porous nano-sponge structure could account for the performance improvement.

Growth mechanism and active site probing of Fe3C@N-doped carbon nanotubes/C catalysts: guidance for building highly efficient oxygen reduction electrocatalysts

Non-platinum (NP) electrocatalysts with high activity and durability for oxygen reduction reactions (ORR) are required for fuel cells and other renewable systems. To avoid trial-and-error methods and achieve the rational design and synthesis of efficient NP catalysts, in-depth knowledge of the formation/growth mechanism of nanocatalysts and the origin of active sites is highly desirable. Here, we report a new class of NP catalysts with a novel structure of Fe3C encapsulated in N-doped carbon nanotubes/C. We study the formation mechanism of the nanostructure to pave the way for controlled fabrication of high-performance NP catalysts. The encapsulation of iron into carbon occurs during the first step of CNT growth and the surface functional groups on carbon black are identified as being essential for forming CNTs. The catalyst shows ultrahigh catalytic performance in both acid and alkaline media. We also examine the structure–performance dependency. The catalytic performance is highly dependent on the nanostructure and the encapsulation of Fe3C. Fe affects the catalytic performance through electronic effects rather than by directly participating in the active sites. This result is confirmed by DFT calculations, which show an increase in the density of states and a reduction in the local work function, XPS studies, and electrochemical measurements. The likelihood of N participating in the active sites is low because the catalytic performance does not depend on pyridinic and graphitic N.

Significantly enhanced oxygen reduction reaction performance of N-doped carbon by heterogeneous sulfur incorporation: synergistic effect between the two dopants in metal-free catalysts

Developing highly active non-noble metal oxygen reduction reaction (ORR) catalysts is crucial for a variety of renewable energy applications including fuel cells and metal–air batteries. Heteroatom doped carbon materials, known as metal-free catalysts, show potential applications in the ORR, and may be promising replacement candidates for expensive, scarce platinum catalysts. Despite the inspiring progress made, the performance of the current metal-free carbon catalysts is still far from satisfactory for large-scale applications. Herein, we introduce an effective and robust ORR catalyst based on N, S co-doped carbon materials with abundant surface active sites. Electrochemical results indicate that the incorporation of sulfur into nitrogen-doped carbon (S-NCx) can dramatically improve the stability of the catalyst by improving the selectivity of O2 electro-reduction to H2O. Density functional theory calculations reveal that sulfur doping lowers the energy barrier of O2(ads) hydrogenation to form OOH(ads), thus leading to enhanced intrinsic activity. In particular, the correlation between ORR activity and nitrogen and sulfur species in these materials is studied in-depth, and it is found the ORR performance of S-NCx catalysts is significantly affected by pyridinic N and C–S–C contents.

Pt–Pb hollow sphere networks: self-sacrifice-templating method and enhanced activity for formic acid electrooxidation

We demonstrate a self-sacrifice-templating method to synthesize Pt–Pb hollow-sphere networks, in which the hollow-spheres arise from the self-sacrifice of in situ formed Pb nanoclusters without the use of a pre-existing template and the networks originate from the diffusion-limited aggregation process. Of particular interest is that the as-prepared Pt–Pb catalyst shows a significantly enhanced activity for formic acid electrooxidation.

Promotion of Mesoporous Vanadium Carbide Incorporated on Resorcinol–Formaldehyde Resin Carbon Composites with High‐Surface‐Areas on Platinum Catalysts for Methanol Electrooxidation

Vanadium carbide incorporated on resorcinol–formaldehyde resin carbon (V8C7@RFC) was synthesized as a novel mesoporous catalyst‐support material by pyrolysis of the resorcinol–formaldehyde resin and NaVO3 mixture. The material’s BET surface area was 564 m2 g−1 and thus much higher than that of 389 m2 g−1 for the carbon powders yielded by resin carbonation. Physical characterization revealed that the supporting material possesses a mesoporous structure and Pt nanoparticles are homogeneously dispersed on the V8C7@RFC surface. Electrochemical measurements demonstrated that the V8C7‐modified Pt catalyst exhibits a negative shift of over 100 mV in the onset potential for COads electrooxidation and a dramatically enhanced activity in methanol oxidation reaction. The enhancement was mainly attributed to the electronic effect between Pt and V8C7 and the mesoporous structure providing ideal anchor sites for Pt dispersion.

Selectively doping pyridinic and pyrrolic nitrogen into a 3D porous carbon matrix through template-induced edge engineering: enhanced catalytic activity towards the oxygen reduction reaction

Developing cost-effective and highly efficient oxygen reduction electrocatalysts, such as non-precious metal and metal-free catalysts, is undoubtedly crucial for the commercialization of low-temperature fuel cells. Here, edge-rich nitrogen doped porous carbon catalysts for the oxygen reduction reaction (ORR) with a high proportion of pyridinic and pyrrolic N (up to 94%) were synthesized by an in situ released CO2 activation method, using glucose and melamine as precursors and nano-CaCO3 as the template. The catalysts exhibit a three-dimensional structure, hierarchical pores and large pore volumes. Benefiting from the increased active site density and structural advantage, the optimized catalyst shows excellent ORR activity with a half-wave potential of 0.853 V and long-term stability in alkaline media, which is among the best for metal-free catalysts reported to date.

Chemically activating MoS 2 via spontaneous atomic palladium interfacial doping towards efficient hydrogen evolution

Lacking strategies to simultaneously address the intrinsic activity, site density, electrical transport, and stability problems of chalcogels is restricting their application in catalytic hydrogen production. Herein, we resolve these challenges concurrently through chemically activating the molybdenum disulfide (MoS2) surface basal plane by doping with a low content of atomic palladium using a spontaneous interfacial redox technique. Palladium substitution occurs at the molybdenum site, simultaneously introducing sulfur vacancy and converting the 2H into the stabilized 1T structure. Theoretical calculations demonstrate the sulfur atoms next to the palladium sites exhibit low hydrogen adsorption energy at –0.02 eV. The final MoS2 doped with only 1wt% of palladium demonstrates exchange current density of 805 μA cm−2 and 78 mV overpotential at 10 mA cm−2, accompanied by a good stability. The combined advantages of our surface activating technique open the possibility of manipulating the catalytic performance of MoS2 to rival platinum.While water reduction may provide a carbon-neutral means to produce hydrogen gas, there is a scarcity of efficient, earth-abundant electrocatalysts. Here, the authors add palladium into MoS2 materials to activate and stabilize the conductive basal plane to improve the electrocatalytic activity.

Structural Advantage Induced by Sulfur to Boost the Catalytic Performance of FeNC Catalyst towards the Oxygen Reduction Reaction

Among various replacement candidates for precious‐metal catalysts towards the cathodic oxygen reduction reaction (ORR) of fuel cells, FeNC material has been perceived as the most promising one. Herein, we report an FeNC catalyst featured with highly uniform texture and high BET specific surface area. This catalyst was synthesized by a facile one‐step pyrolysis process accompanied by the sulfur‐induced in situ delamination effect, using glucose, trithiocyanuric acid and ferrous gluconate as precursors. The structural characteristics led to increased exposed active sites, which may be responsible for the dramatically improved activity of the final S‐doped FeNC catalyst with elevated half‐wave potentials in both acid (0.76 V vs. 0.68 V) and alkaline (0.87 V vs. 0.84 V) media compared to the sulfur‐free control sample.