Junwei Wu

Recent Development of SOFC Metallic Interconnect

Interest in solid oxide fuel cells (SOFC) stems from their higher efficiencies and lower levels of emitted pollutants, compared to traditional power production methods. Interconnects are a critical part in SOFC stacks, which connect cells in series electrically, and also separate air or oxygen at the cathode side from fuel at the anode side. Therefore, the requirements of interconnects are the most demanding, i.e. , to maintain high electrical conductivity, good stability in both reducing and oxidizing atmospheres, and close coefficient of thermal expansion (CTE) match and good compatibility with other SOFC ceramic components. The paper reviewed the interconnect materials, and coatings for metallic interconnect materials.

Na-X zeolite templated and sulfur-impregnated porous carbon as the cathode for a high-performance Li–S battery

Significant efforts have recently been devoted to developing commercially viable high-capacity and low-cost lithium sulfur (Li–S) batteries. In this paper, we report Na-X zeolite templated porous carbon (ZPC) filled with sulfur as a cathode material for Li–S batteries. To immobilize liquid Li sulfide, the surface of NCP was modified by amphiphilic N-polyvinylpyrrolidone (PVP), making ZPC amphiphilic (denoted as A-ZPC). ZPC, A-ZPC and their corresponding composites with sulfur (ZPC–S and A-ZPC–S) were analyzed by various physical characterizations, charge–discharge profiling and electrochemical impedance spectroscopy (EIS). The results showed excellent performance of the A-ZPC–S composite cathode with 46 wt% sulfur loading, a specific capacity can be retained at 691 mA h g−1 even after 300 cycles under a rate of 1C, fading only 0.142% per cycle.

Fabrication of La2NiO4 nanoparticles as an efficient bifunctional cathode catalyst for rechargeable lithium–oxygen batteries

Efficient catalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are crucial enabling materials for rechargeable Li–O2 batteries. In the present work, La2NiO4 (LNO) synthesized by a hydrothermal process and modified Pechini method were studied as catalysts for rechargeable Li–O2 batteries. The catalyst prepared by the hydrothermal method shows a smaller particle size and a macroporous structure with 10× higher surface area than that synthesized by the Pechini counterpart, leading to a better electrocatalytic activity. The improved OER catalytic activity of the hydrothermal-LNO nanoparticles was confirmed by a 150 mV lower recharge potential than the Pechini-LNO particles and catalyst-free pure Super P (SP) electrode. In addition, the hydrothermal-LNO catalyzed battery cell delivered a first discharge capacity of 14 310.9 mA h g−1 at 0.16 mA cm−2, compared to 8132.4 mA h g−1 of the Pechini-LNO and 7478.8 mA h g−1 of the pure SP electrode, demonstrating higher catalytic ORR activity of the hydrothermal-LNO particles. Overall, the LNO nanoparticles are a promising cathode catalyst for non-aqueous electrolyte based Li–O2 batteries.

A novel sulfur-impregnated porous carbon matrix as a cathode material for a lithium–sulfur battery

A novel sulfur-impregnated porous carbon matrix (PCM-Z-S) has been prepared as a cathode material for a lithium–sulfur battery. The porous carbon matrix (PCM-Z), which was obtained using de-waxed cotton and ZnCl2 as an activator, has a surface area of 1056 m2 g−1 and a pore volume of 1.75 cm3 g−1. The PCM-Z was mixed with sublimed sulfur and then heated in nitrogen gas to form a carbon–sulfur 58 wt% composite (PCM-Z-S) which has excellent electrochemical proprieties. The PCM-Z-S delivers a capacity of 850 mA h g−1 at 1C and retains 630 mA h g−1 after nearly 200 cycles which are values much higher than that of a carbon matrix prepared without ZnCl2. These results show the sulfur-impregnated porous carbon matrix (PCM-Z-S) has great potential as a cathode material in a lithium–sulfur battery.

Synthesis and electrochemical properties of lithium zinc titanate as an anode material for lithium ion batteries via microwave method

Lithium zinc titanate (Li2ZnTi3O8) anode material has been synthesized via a microwave method for the first time. The physical and electrochemical performances of the as-prepared sample are characterized by X-ray diffraction patterns (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), galvanostatic charge–discharge tests, cyclic voltammetry (CV) tests, and electrochemical impedance spectroscopy (EIS). It is found that the pristine Li2ZnTi3O8 obtained via the microwave method at 780 W for 10 min exhibits a typical cubic spinel structure with P4332 space group. The electrochemical measurements indicate that the Li2ZnTi3O8 anode material displayed a highly reversible capacity and excellent cycling stability. The initial charge capacities of Li2ZnTi3O8 nanoparticles were 216.8 mA h g−1, 197.4 mA h g−1, 192.6 mA h g−1, 174.5 mA h g−1 at 50 mA g−1, 100 mA g−1, 300 mA g−1 and 500 mA g−1, respectively. After 50 cycles, charge capacities of 263.5 mA h g−1, 234.8 mA h g−1, 223.2 mA h g−1 and 208.4 mA h g−1 can be retained, with no significant capacity fading. This indicates that the microwave method has a great potential application in synthesizing Li2ZnTi3O8 anode materials for lithium ion batteries.

Fabrication of (Co,Mn)3O4/rGO Composite for Lithium Ion Battery Anode by a One-Step Hydrothermal Process with H2O2 as Additive.

Binary transition metal oxides have been regarded as one of the most promising candidates for high-performance electrodes in energy storage devices, since they can offer high electrochemical activity and high capacity. Rational designing nanosized metal oxide/carbon composite architectures has been proven to be an effective way to improve the electrochemical performance. In this work, the (Co,Mn)3O4 spinel was synthesized and anchored on reduced graphene oxide (rGO) nanosheets using a facile and single hydrothermal step with H2O2 as additive, no further additional calcination required. Analysis showed that this method gives a mixed spinel, i.e. (Co,Mn)3O4, having 2+ and 3+ Co and Mn ions in both the octahedral and tetrahedral sites of the spinel structure, with a nanocubic morphology roughly 20 nm in size. The nanocubes are bound onto the rGO nanosheet uniformly in a single hydrothermal process, then the as-prepared (Co,Mn)3O4/rGO composite was characterized as the anode materials for Li-ion battery (LIB). It can deliver 1130.6 mAh g-1 at current density of 100 mA g-1 with 98% of coulombic efficiency after 140 cycles. At 1000 mA g-1, the capacity can still maintain 750 mAh g-1, demonstrating excellent rate capabilities. Therefore, the one-step process is a facile and promising method to fabricate metal oxide/rGO composite materials for energy storage applications.

CHAPTER 5:Interconnect Materials for SOFC Stacks

Interconnects are one of the most challenging materials issues for solid oxide fuel cell (SOFC) stacks. They are exposed to both oxidizing conditions at the cathode and reducing conditions at the anode, at elevated temperatures, and must maintain good conductivity and good mechanical stability. Both ceramic and metallic interconnects have been used extensively for different working temperatures. Ceramic perovskite (ABO3) interconnects, which typically are used in the higher temperature ranges (900–1000 °C), dopant elements and concentrations at both A and B sites can be altered to control properties of electronic conductivity, thermal expansion coefficient (TEC), and stability. Metallic interconnects can be used at lower temperatures (typically 400–800 °C), are potentially much lower in cost, and are more mechanically stable in the typical temperature range of use. Because of the cost advantage, we will focus the metallic interconnect materials and on issues such as materials selection from various alloys, challenges for metallic materials, and how to handle them, more specifically, various coatings to suppress scale growth and Cr poisoning effect. (Mn,Co)3O4 spinel coatings are the most promising coatings to meet the application requirements. Furthermore, for both ceramic and metallic interconnect materials, designs and applications from industrial teams are reviewed.