Jiantao Han

High-Performance Direct Methanol Fuel Cells with Precious-Metal-Free Cathode.

Direct methanol fuel cells (DMFCs) hold great promise for applications ranging from portable power for electronics to transportation. However, apart from the high costs, current Pt‐based cathodes in DMFCs suffer significantly from performance loss due to severe methanol crossover from anode to cathode. The migrated methanol in cathodes tends to contaminate Pt active sites through yielding a mixed potential region resulting from oxygen reduction reaction and methanol oxidation reaction. Therefore, highly methanol‐tolerant cathodes must be developed before DMFC technologies become viable. The newly developed reduced graphene oxide (rGO)‐based Fe‐N‐C cathode exhibits high methanol tolerance and exceeds the performance of current Pt cathodes, as evidenced by both rotating disk electrode and DMFC tests. While the morphology of 2D rGO is largely preserved, the resulting Fe‐N‐rGO catalyst provides a more unique porous structure. DMFC tests with various methanol concentrations are systematically studied using the best performing Fe‐N‐rGO catalyst. At feed concentrations greater than 2.0 m, the obtained DMFC performance from the Fe‐N‐rGO cathode is found to start exceeding that of a Pt/C cathode. This work will open a new avenue to use nonprecious metal cathode for advanced DMFC technologies with increased performance and at significantly reduced cost.

Graphene-Roll-Wrapped Prussian Blue Nanospheres as a High-Performance Binder-Free Cathode for Sodium-Ion Batteries

Sodium iron hexacyanoferrate (Fe-HCF) has been proposed as a promising cathode material for sodium-ion batteries (SIBs) because of its desirable advantages, including high theoretical capacity (∼170 mAh g-1), eco-friendliness, and low cost of worldwide rich sodium and iron resources. Nonetheless, its application faces a number of obstacles due to poor electronic conductivity and structural instability. In this work, Fe-HCF nanospheres (NSs) were first synthesized and fabricated by an in situ graphene rolls (GRs) wrapping method, forming a 1D tubular hierarchical structure of Fe-HCF NSs@GRs. GRs not only provide fast electronic conduction path for Fe-HCF NSs but also effectively prevent organic electrolyte from reaching active materials and inhibit the occurrence of side reactions. The Fe-HCF NSs@GRs composite has been used as a binder-free cathode with a capacity of ∼110 mAh g-1 at a current density of 150 mA g-1 (∼1C), the capacity retention of ∼90% after 500 cycles. Moreover, the Fe-HCF NSs@GRs cathode displays a super high rate capability with ∼95 mAh g-1 at 1500 mA g-1 (∼10C). The results suggest that the 1D tubular structure of 2D GRs-wrapped Fe-HCF NSs is promising as a high-performance cathode for SIBs.

Low-Cost and High-Performance Hard Carbon Anode Materials for Sodium-Ion Batteries

As an anode material for sodium-ion batteries (SIBs), hard carbon (HC) presents high specific capacity and favorable cycling performance. However, high cost and low initial Coulombic efficiency (ICE) of HC seriously limit its future commercialization for SIBs. A typical biowaste, mangosteen shell was selected as a precursor to prepare low-cost and high-performance HC via a facile one-step carbonization method, and the influence of different heat treatments on the morphologies, microstructures, and electrochemical performances was investigated systematically. The microstructure evolution studied using X-ray diffraction, Raman, Brunauer–Emmett–Teller, and high-resolution transmission electron microscopy, along with electrochemical measurements, reveals the optimal carbonization condition of the mangosteen shell: HC carbonized at 1500 °C for 2 h delivers the highest reversible capacity of ∼330 mA h g–1 at a current density of 20 mA g–1, a capacity retention of ∼98% after 100 cycles, and an ICE of ∼83%. Additionally, the sodium-ion storage behavior of HC is deeply analyzed using galvanostatic intermittent titration and cyclic voltammetry technologies.

Enhancing Sodium-Ion Storage Behaviors in TiNb2O7 by Mechanical Ball Milling

Sodium-ion batteries (SIBs) have shown extensive prospects as alternative rechargeable batteries in large-scale energy storage systems, because of the abundance and low cost of sodium. The development of high-performance cathode and anode materials is a big challenge for SIBs. As is well known, TiNb2O7 (TNO) exhibits a high capacity of ∼250 mAh g-1 with excellent capacity retention as a Li-insertion anode for lithium-ion batteries, but it has rarely been discussed as an anode for SIBs. Here, we demonstrate ball-milled TiNb2O7 (BM-TNO) as an SIB anode, which provides an average voltage of ∼0.6 V and a reversible capacity of ∼180 mAh g-1 at a current density of 15 mA g-1, and presents excellent cyclability with 95% capacity retention after 500 cycles at 500 mA g-1. A possible Na storage mechanism in BM-TNO is also proposed.

Amorphous Co–Fe–P nanospheres for efficient water oxidation

Transition metal phosphides are often studied as hydrogen evolution reaction cathode catalysts, but scarcely as oxygen evolution reaction (OER) anode catalysts for water oxidation. Herein, we report a new amorphous Co0.63Fe0.21P0.16 OER catalyst, which was prepared through a one-step solvothermal process. This catalyst exhibits extraordinary OER catalytic activity in alkaline media and is superior to the state of the art IrO2 in 1.0 M KOH, capable of yielding a current density of 10 mA cm−2 at an overpotential of only 217 mV. This newly achieved high activity outperforms most reported transition metal phosphide catalysts. During the OER, the surface layers of the Co0.63Fe0.21P0.16 nanospheres (200–500 nm) are oxidized, which show the typical Tafel slope of oxides around 40 mV dec−1. The in situ formation of surface Co oxides in the catalysts during the OER along with an optimal doping of Fe are found to be crucial for their remarkable activity. In particular, the metal-rich amorphous phosphide cores, i.e., substrates, probably contribute to OER performance of the catalysts due to their high electrical conductivity. This new type of surface oxidized amorphous transition metal phosphide would provide a new pathway for the design of high-performance OER electrocatalysts.

High valence Mo-doped Na3V2(PO4)3/C as a high rate and stable cycle-life cathode for sodium battery

NASICON-structure Na3V2(PO4)3 (NVP) is a potential cathode material for sodium ion battery, which is still confronted with low rate performance because of its poor conductivity. To address this problem, high-valance Mo6+ ion was introduced into NVP. The crystal structure, electrochemical performances, sodium ion diffusion kinetics and ion transfer mechanism of high valence Mo-doped Na3−5xV2−xMox(PO4)3/C (0 < x < 0.04) were investigated. X-ray diffraction, electron microscopy and XPS data confirmed high purity NASICON phosphate phases. The Na ion diffusion process was identified through CV measurement, which clearly shows rapid sodium ion transportation in the Mo-doped NASICON materials. Moreover, DFT calculations proved that Na ion diffusion is promoted by Mo doping. Benefiting from the superior Na ion kinetics, Na2.9V1.98Mo0.02(PO4)3 exhibited a performance of 90 mA h g−1 at 10C and preserved 83.5% of the original capacity after 500 cycles. Our studies demonstrate that high-valence Mo doped Na3V2(PO4)3/C is a promising cathode material for sodium ion batteries with super-high rate capability and stable cycle life.

Al doping effects on LiCrTiO4 as an anode for lithium-ion batteries

Al-Doped LiCrTiO4 anode materials are successfully synthesized by a conventional solid-state reaction. Their structural and electrochemical properties are systematically investigated. With increasing the Al doping level (x), the lattice parameters of LiAlxCr1−xTiO4 get smaller. Meanwhile, asymmetric polarization was significantly reduced during the charge/discharge process, in contrast to an enhanced compatibility of electrode materials with organic electrolyte. The Al-doped LiAl0.2Cr0.8TiO4 anode can still keep a discharge capacity of 123 mA h g−1 at 1C for 100 cycles and 109 mA h g−1 at 2C. More importantly, the Al-doped LiAl0.2Cr0.8TiO4 anode exhibits remarkable electrochemical properties at a high-temperature of 60 °C with a very stable capacity of about 145 mA h g−1 at 1C, and is promising as a high-performance anode.

A P2-Type Layered Superionic Conductor Ga-Doped Na2Zn2TeO6 for All-Solid-State Sodium-Ion Batteries

Here, a P2-type layered Na2 Zn2 TeO6 (NZTO) is reported with a high Na+ ion conductivity ≈0.6×10-3 u2005Su2009cm-1 at room temperature (RT), which is comparable to the currently best Na1+n Zr2 Sin P3-n O12 NASICON structure. As small amounts of Ga3+ substitutes for Zn2+ , more Na+ vacancies are introduced in the interlayer gaps, which greatly reduces strong Na+ -Na+ coulomb interactions. Ga-substituted NZTO exhibits a superionic conductivity of ≈1.1×10-3 u2005Su2009cm-1 at RT, and excellent phase and electrochemical stability. All solid-state batteries have been successfully assembled with a capacity of ≈70u2009mAhu2009g-1 over 10u2005cycles with a rate of 0.2u2005C at 80u2009°C. 23 Na nuclear magnetic resonance (NMR) studies on powder samples show intra-grain (bulk) diffusion coefficients DNMR on the order of 12.35×10-12 u2005m2 u2009s-1 at 65u2009°C that corresponds to a conductivity σNMR of 8.16×10-3 u2005Su2009cm-1 , assuming the Nernst-Einstein equation, which thus suggests a new perspective of fast Na+ ion conductor for advanced sodium ion batteries.

NiFe (Oxy) Hydroxides Derived from NiFe Disulfides as an Efficient Oxygen Evolution Catalyst for Rechargeable Zn-Air Batteries: The Effect of Surface S Residues

A facile H2 O2 oxidation treatment to tune the properties of metal disulfides for oxygen evolution reaction (OER) activity enhancement is introduced. With this method, the degree of oxidation can be readily controlled and the effect of surface S residues in the resulted metal (oxy)hydroxides for the OER is revealed for the first time. The developed NiFe (oxy)hydroxide catalyst with residual S demonstrates an extraordinarily low OER overpotential of 190 mV at the current density of 10 mA cm-2 after coupling with carbon nanotubes, and outstanding performance in Zn-air battery tests. Theoretical calculation suggests that the surface S residues can significantly reduce the adsorption free energy difference between O* and OH* intermediates on the Fe sites, which should account for the high OER activity of NiFe (oxy)hydroxide catalysts. This work provides significant insight regarding the effect of surface heteroatom residues in OER electrocatalysis and offers a new strategy to design high-performance and cost-efficient OER catalysts.

A new layered titanate Na2Li2Ti5O12 as a high-performance intercalation anode for sodium-ion batteries

Currently, it is a great challenge to find suitable electrode materials for sodium-ion batteries (SIBs) with large capacity, long cycle life, and high rate capability. Herein, we report a new layered titanate, Na2Li2Ti5O12 (NLT), derived from K2Li2Ti5O12 (KLT) via an ion-exchange method as a SIB anode material. KLT is prepared by a low-temperature solid-state reaction and then transformed into NLT by replacing potassium with sodium in a NaCl solution at room temperature. NLT provides a sodium-ion intercalation voltage at ∼0.5 V versus Na/Na+ and a reversible capacity of 175 mA h g−1 at a current density of 100 mA g−1. It also shows a high sodium-ion diffusion coefficient of 3.0 × 10−10 cm2 s−1, ensuring a high rate capability. For NLT, extremely high discharging rate capability is achieved with a capacity of more than 80 mA h g−1 at a 60 second full discharge and even with 70 mA h g−1 at a 34 second charge. Kinetics analysis based on cyclic voltammogram reveals a typical sodium-ion intercalation behavior in NLT. Furthermore, the first-principle calculation shows a lower migration energy barrier for sodium ions in NLT than that in other layered titanates. These results suggest that NLT is a very promising anode material for high-performance SIBs, especially for fast-charging stable SIBs.