Bingbing Tian

High-performance NaFePO4 formed by aqueous ion-exchange and its mechanism for advanced sodium ion batteries

Room-temperature sodium ion batteries (SIBs) have attracted tremendous attention recently as cheaper alternatives to lithium ion batteries (LIBs) for potential application in large-scale electrical energy storage stations. Among the various classes of iron phosphate cathodes used in SIBs, olivine NaFePO4 is one of the most attractive host materials for advanced sodium ion batteries owing to its electrochemical profile and high theoretical capacity. As an alternative to the organic-based electrochemical ion-exchange process which is disadvantaged by sluggish dynamics and co-intercalation of Li+, we investigated an aqueous-based, electrochemical-driven ion-exchange process to transform olivine LiFePO4 into highly pure olivine NaFePO4, which shows superior electrochemical performance. Using a combination of ab initio calculations and experiments, we demonstrate that the mechanism is attributed to the much faster Na+/Li+ ion-exchange kinetics of NaFePO4 at the aqueous electrolyte/cathode interface compared to the organic electrolytes. Operando Fe K-edge XANES and XRD were also carried out to study the staged evolution of phases during the sodiation/desodiation of NaFePO4 nanograins.

Chemical Vapor Deposition of High‐Quality Large‐Sized MoS2 Crystals on Silicon Dioxide Substrates

Large‐sized MoS2 crystals can be grown on SiO2/Si substrates via a two‐stage chemical vapor deposition method. The maximum size of MoS2 crystals can be up to about 305 μm. The growth method can be used to grow other transition metal dichalcogenide crystals and lateral heterojunctions. The electron mobility of the MoS2 crystals can reach ≈30 cm2 V−1 s−1, which is comparable to those of exfoliated flakes.

In Situ Observation and Electrochemical Study of Encapsulated Sulfur Nanoparticles by MoS2 Flakes

Sulfur is an attractive cathode material for next-generation lithium batteries due to its high theoretical capacity and low cost. However, dissolution of its lithiated product (lithium polysulfides) into the electrolyte limits the practical application of lithium sulfur batteries. Here we demonstrate that sulfur particles can be hermetically encapsulated by leveraging on the unique properties of two-dimensional materials such as molybdenum disulfide (MoS2). The high flexibility and strong van der Waals force in MoS2 nanoflakes allows effective encapsulation of the sulfur particles and prevent its sublimation during in situ TEM studies. We observe that the lithium diffusivities in the encapsulated sulfur particles are in the order of 10-17 m2 s-1. Composite electrodes made from the MoS2-encapsulated sulfur spheres show outstanding electrochemical performance, with an initial capacity of 1660 mAh g-1 and long cycle life of more than 1000 cycles.

Interface confined hydrogen evolution reaction in zero valent metal nanoparticles-intercalated molybdenum disulfide

Interface confined reactions, which can modulate the bonding of reactants with catalytic centres and influence the rate of the mass transport from bulk solution, have emerged as a viable strategy for achieving highly stable and selective catalysis. Here we demonstrate that 1T′-enriched lithiated molybdenum disulfide is a highly powerful reducing agent, which can be exploited for the in-situ reduction of metal ions within the inner planes of lithiated molybdenum disulfide to form a zero valent metal-intercalated molybdenum disulfide. The confinement of platinum nanoparticles within the molybdenum disulfide layered structure leads to enhanced hydrogen evolution reaction activity and stability compared to catalysts dispersed on carbon support. In particular, the inner platinum surface is accessible to charged species like proton and metal ions, while blocking poisoning by larger sized pollutants or neutral molecules. This points a way forward for using bulk intercalated compounds for energy related applications.

Recent advances in Fe (or Co)/N/C electrocatalysts for the oxygen reduction reaction in polymer electrolyte membrane fuel cells

Exploring cheap and stable electrocatalysts to replace Pt for the oxygen reduction reaction (ORR) is now the key issue for the large-scale application of fuel cells, especially polymer electrolyte membrane fuel cells. The recent emergence of Fe (or Co)/N/C catalysts has created tremendous opportunities for the development of non-precious metal catalysts for ORR in acidic media and thus presents great potential in the application of fuel cells. In this review, we summarize the recent advances in the Fe (or Co)/N/C catalysts for ORR in acidic media that have demonstrated comparable activity to the commercial Pt catalyst. The synthesis, structural characterization and underlying mechanism of Fe (or Co)/N/C catalysts are discussed. In addition, we highlight the interesting microstructures of the active site, new synthesis approaches, and the catalytic performances tuned by nonmetal heteroatom dopants. Finally, perspectives on the challenges and future opportunities are also discussed.

Polyquinoneimines for lithium storage: more than the sum of its parts

A straightforward synthetic strategy for the construction of electrode materials is demonstrated by the polymerization of two kinds of electrochemically active organic monomers without sacrificing specific capacity. Polyquinoneimines (PQIs), synthesised by the polycondensation reaction of 2,6-diaminoanthraquinone and the anhydrides, were used as a cathode in lithium ion batteries (LIBs). Electrochemical analysis such as CV and galvanostatic cycling reveals that PQIs exhibit the combined electrochemical properties of the two monomers. The mechanism of lithiation/delithiation of the PQIs has been investigated by means of electrochemical and spectroscopic (FTIR) analytical techniques. The as-prepared PQI-1 exhibits a higher specific capacity of 210 mA h g−1 and a better cycling performance (136 mA h g−1 after 200 cycles) compared with their polymeric precursors.

Reticular V2O5·0.6H2O Xerogel as Cathode for Rechargeable Potassium Ion Batteries

Potassium ion batteries (KIBs), because of their low price, may exhibit advantages over lithium ion batteries as potential candidates for large-scale energy storage systems. However, owing to the large ionic radii of K-ions, it is challenging to find a suitable intercalation host for KIBs and thus the rechargeable KIB electrode materials are still largely unexplored. In this work, a reticular V2O5·0.6H2O xerogel was synthesized via a hydrothermal process as a cathode material for rechargeable KIBs. Compared with the orthorhombic crystalline V2O5, the hydrated vanadium pentoxide (V2O5·0.6H2O) exhibits the ability of accommodating larger alkali metal ions of K+ because of the enlarged layer space by hosting structural H2O molecules in the interlayer. By intercalation of H2O into the V2O5 layers, its potassium electrochemical activity is significantly improved. It exhibits an initial discharge capacity of ∼224.4 mA h g-1 and a discharge capacity of ∼103.5 mA h g-1 even after 500 discharge/charge cycles at a current density of 50 mA g-1, which is much higher than that of the V2O5 electrode without structural water. Meanwhile, X-ray diffraction and X-ray photoelectron spectroscopy combined with energy dispersive spectroscopy techniques are carried out to investigate the potassiation/depotassiation process of the V2O5·0.6H2O electrodes, which confirmed the potassium intercalation storage mechanisms of this hydrated material. The results demonstrate that the interlayer-spacing-enlarged V2O5·0.6H2O is a promising cathode candidate for KIBs.

B, N Codoped and Defect‐Rich Nanocarbon Material as a Metal‐Free Bifunctional Electrocatalyst for Oxygen Reduction and Evolution Reactions

Abstract The development of highly active, inexpensive, and stable bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts to replace noble metal Pt and RuO2 catalysts remains a considerable challenge for highly demanded reversible fuel cells and metal–air batteries. Here, a simple approach for the facile construction of a defective nanocarbon material is reported with B and N dopants (B,N‐carbon) as a superior bifunctional metal‐free catalyst for both ORR and OER. The catalyst is prepared by pyrolyzing the composites of ethyl cellulose and high‐boiling point 4‐(1‐naphthyl)benzeneboronic acid in NH3 atmosphere with an inexpensive Zn‐based template. The obtained porous B,N‐carbon with rich carbon defects exhibits excellent ORR and OER performances, including high activity and stability. In alkaline medium, B,N‐carbon material shows high ORR activity with an onset potential (E onset) reaching 0.98 V versus reversible hydrogen electrode (RHE), very close to that of Pt/C, a high electron transfer number and excellent stability. This catalyst also presents the admirable ORR activity in acidic medium with a high E onset of 0.81 V versus RHE and a four‐electron process. The OER activity of B,N‐carbon is superior to that of the precious metal RuO2 and Pt/C catalysts. A Zn–air battery using B,N‐carbon as the air cathode exhibits a low voltage gap between charge and discharge and long‐term stability. The excellent electrocatalytic performance of this porous nanocarbon material is attributed to the combined positive effects of the abundant carbon defects and the heteroatom codopants.