Haolin Tang

Metal–Organic‐Framework‐Derived Dual Metal‐ and Nitrogen‐Doped Carbon as Efficient and Robust Oxygen Reduction Reaction Catalysts for Microbial Fuel Cells

A new class of dual metal and N doped carbon catalysts with well‐defined porous structure derived from metal–organic frameworks (MOFs) has been developed as a high‐performance electrocatalyst for oxygen reduction reaction (ORR). Furthermore, the microbial fuel cell (MFC) device based on the as‐prepared Ni/Co and N codoped carbon as air cathode catalyst achieves a maximum power density of 4335.6 mW m−2 and excellent durability.

Advanced Separators for Lithium‐Ion and Lithium–Sulfur Batteries: A Review of Recent Progress

Li-ion and Li-S batteries find enormous applications in different fields, such as electric vehicles and portable electronics. A separator is an indispensable part of the battery design, which functions as a physical barrier for the electrode as well as an electrolyte reservoir for ionic transport. The properties of the separators directly influence the performance of the batteries. Traditional polyolefin separators showed low thermal stability, poor wettability toward the electrolyte, and inadequate barrier properties to polysulfides. To improve the performance and durability of Li-ion and Li-S batteries, development of advanced separators is required. In this review, we summarize recent progress on the fabrication and application of novel separators, including the functionalized polyolefin separator, polymeric separator, and ceramic separator, for Li-ion and Li-S batteries. The characteristics, advantages, and limitations of these separators are discussed. A brief outlook for the future directions of the research in the separators is also provided.

Fabrication and Performance of Polymer Electrolyte Fuel Cells by Self-Assembly of Pt Nanoparticles

Self-assembled Pt nanoparticle electrode and membrane-electrode-assembly (MEA) of polymer electrolyte fuel cells (PEFC) have been successfully prepared by using charged Pt nanoparticles. The charged Pt nanoparticles were prepared by alcoholic reduction in the presence of ionic poly(diallyldimethylammonium chloride) (PDDA) and diallyldimethylammonium chloride (DDA) stabilizers. A MEA with Pt loading of 2.8 ′ 0.1 μg cm - 2 was fabricated by the self-assembly of the charged Pt nanoparticles to the Nafion membrane surface probably via the sulfonic acid function sites, SO - 3 . The performance of the self-assembled MEA was 2.3 mW cm - 2 , corresponding to a Pt utilization of 821 W per 1 g Pt. The Pt-DDA and Pt-PDDA nanoparticle showed significant electrochemical catalytic activity for the O 2 reduction reactions. The results show that the self-assembled Pt nanoparticles were able to form a Pt monolayer and such a monolayered structure could potentially offer a powerful tool in the fundamental studies in the PEFC systems.

A novel inorganic proton exchange membrane based on self-assembled HPW-meso-silica for direct methanol fuel cells

Direct methanol fuel cells (DMFCs) based on high-temperature (100–300 °C) proton exchange membranes (HT-PEMs) offer significant advantages over the current low-temperature DMFCs based on perfluorosulfonic acid (e.g., Nafion™), such as reduction in CO poisoning via faster reaction kinetics, thus increasing the energy efficiency and reducing precious metal loading. This paper reports a novel inorganic proton exchange membrane based on 12-tungstophosphoric acid mesoporous silica (HPW-meso-silica) nanocomposites. The HPW-meso-silica was synthesized via a one-step self-assembly route assisted by a triblock copolymer, Pluronic P123, as the structure-directing surfactant. The threshold of the HPW content in the nanocomposites for the conductivity of mesoporous silica is 5 wt%. The best results were obtained at 25 wt% HPW-meso-silica, delivering a high proton conductivity of 0.091 S cm−1 at 100 °C under 100% relative humidity (RH) and 0.034 S cm−1 at 200 °C under 3% RH and a low activation energy of 14.0 kJ mol−1. The maximum power density of a cell with a 25 wt% HPW-meso-silica membrane is 19 mW cm−2 at 25 °C and increased to 235 mW cm−2 at 150 °C in methanol fuel.

Emerging methanol-tolerant AlN nanowire oxygen reduction electrocatalyst for alkaline direct methanol fuel cell

Replacing precious and nondurable Pt catalysts with cheap materials is a key issue for commercialization of fuel cells. In the case of oxygen reduction reaction (ORR) catalysts for direct methanol fuel cell (DMFC), the methanol tolerance is also an important concern. Here, we develop AlN nanowires with diameters of about 100–150 nm and the length up to 1 mm through crystal growth method. We find it is electrochemically stable in methanol-contained alkaline electrolyte. This novel material exhibits pronounced electrocatalytic activity with exchange current density of about 6.52 × 10−8 A/cm2. The single cell assembled with AlN nanowire cathodic electrode achieves a power density of 18.9 mW cm−2. After being maintained at 100 mA cm−2 for 48 h, the AlN nanowire-based single cell keeps 92.1% of the initial performance, which is in comparison with 54.5% for that assembled with Pt/C cathode. This discovery reveals a new type of metal nitride ORR catalyst that can be cheaply produced from crystal growth method.

Understanding short-side-chain perfluorinated sulfonic acid and its application for high temperature polymer electrolyte membrane fuel cells

The great demand for high-temperature operation of polymer electrolyte membrane fuel cells (PEMFCs) has been well answered by short-side-chain perfluorinated sulfonic acid (SSC-PFSA) membranes through a good balance between transport properties and stability. It has been evidenced that fuel cells assembled with SSC-PFSA possess higher and more stable performance at elevated temperature up to 130 °C compared to that of fuel cells based on conventional long-side-chain (LSC) PFSA (Nafion®) membranes. Moreover, the shorter side-pendent chains and the absence of the ether group and of the tertiary carbon also endow SSC-PFSAs with better durability, making them more suitable for working at harsh conditions in fuel cell systems. This critical review is dedicated to summarizing the properties of SSC-PFSA and providing insight into an understanding of their micro-morphologies, mass diffusion, enhanced proton transportation and their mutual correlation. Diversified measurement techniques applied to investigate the evolution of micro-morphologies, unique diffusion and transportation properties of SSC-PFSAs are reviewed. Despite the higher crystalline and higher water absorption of SSC-PFSAs than those of LSC-PFSAs, the notably less developed and less interconnected ionic clusters in SSC-PFSAs lead to lower mass permeability, and hence the high water uptake is not as well translated into transportation performance as expected. The factors and reasons for the enhanced electrochemical performance of SSC-PFSAs such as higher proton conductivity at elevated temperatures and low humidity conditions are also discussed and understood. Highlights of recent advances in SSC-PFSA-based membranes for fuel cell applications at wider temperature ranges are summarized as general references for researchers to further prompt the development of SSC-PFSAs. The SSC-PFSAs based membranes give a bright future for the next generation of high-temperature PEMFCs.

Highly ordered and periodic mesoporous Nafion membranes via colloidal silica mediated self-assembly for fuel cells

Highly ordered and periodic mesoporous Nafion membranes with controlled structural symmetries including 2D hexagonal, 3D face-centered, 3D cubic-bicontinuous and 3D body-centered have been successfully synthesized by a novel colloidal silica mediated self-assembly method with high proton conductivity particularly under conditions of low humidity.

Ethylcellulose-coated polyolefin separators for lithium-ion batteries with improved safety performance.

With the widely use in portable electronic devices and electric vehicles, the safety of lithium-ion battery has raised serious concerns, in which the thermal stability of separator plays an essential role in preventing thermal runaway reactions. The novelty of this work is to coat commercialized polyethylene (PE) separator and trilayer polypropylene/polyethylene/polypropylene (PP/PE/PP) separator with ethylcellulose (EC), a thermally stable and renewable biomass. The formation of the EC layer with high porosity is through a simple dipping and extracting process. The effects of the EC layer on thermal shrinkage, electrolyte wettability and cell performance are investigated. After coating, the thermal shrinkage of PE separator at shutdown and meltdown point is reduced from 20% to 9% and 42% to 23% respectively, while the drop of OCV under increasing temperature is also postponed from 130°C to 160°C. The electrolyte wettability of pristine trilayer PP/PE/PP separator is greatly improved, leading to increased capacity retention from 28% to 99% of the cell.

Nafion membranes with ordered mesoporous structure and high water retention properties for fuel cell applications

Ordered mesoporous structures were successfully introduced into Nafion membranesvia a soft micelle templating method, using a non-ionic block copolymer surfactant, PEO127–PPO48–PEO127 (Pluronic F108). Atomic force microscopy (AFM) and small angle X-ray scattering (SAXS) analysis show the typical features of the formation of ordered mesopores in the as-prepared Nafion membranes. TGA and FTIR results show that the mesoporous Nafion (meso-Nafion) has a much higher water retention capability as compared to conventional Nafion membranes. The proton conductivities of meso-Nafion are much higher than those of Nafion 115 membranes especially at reduced relative humidity (RH) and elevated temperatures. The results show that the conductivity and water retention ability are sensitive to the surfactant loading. At 80 °C and 40%RH, the conductivity of the best meso-Nafion membrane is 0.07 S cm−1, 5 times better than 0.013 S cm−1 obtained on Nafion 115. At 60%RH and 80 °C, the cell with meso-Nafion reached a stable power output of 0.63 W cm−2, more than 2 times higher than the cell with pristine Nafion 115 under identical experimental conditions. When the RH reduced to 20%, the power output of meso-Nafion membranes is 5.6 times higher than that of Nafion 115. The cells with meso-Nafion membranes also demonstrate much better power output at elevated temperature of 120 °C and reduced humidity.

Self assembled 12-tungstophosphoric acid–silica mesoporous nanocomposites as proton exchange membranes for direct alcohol fuel cells

A highly ordered inorganic electrolyte based on 12-tungstophosphoric acid (H(3)PW(12)O(40), abbreviated as HPW or PWA)-silica mesoporous nanocomposite was synthesized through a facile one-step self-assembly between the positively charged silica precursor and negatively charged PW(12)O(40)(3-) species. The self-assembled HPW-silica nanocomposites were characterized by small-angle XRD, TEM, nitrogen adsorption-desorption isotherms, ion exchange capacity, proton conductivity and solid-state (31)P NMR. The results show that highly ordered and uniform nanoarrays with long-range order are formed when the HPW content in the nanocomposites is equal to or lower than 25 wt%. The mesoporous structures/textures were clearly presented, with nanochannels of 3.2-3.5 nm in diameter. The (31)P NMR results indicates that there are (≡SiOH(2)(+))(H(2)PW(12)O(40)(-)) species in the HPW-silica nanocomposites. A HPW-silica (25/75 w/o) nanocomposite gave an activation energy of 13.0 kJ mol(-1) and proton conductivity of 0.076 S cm(-1) at 100 °C and 100 RH%, and an activation energy of 26.1 kJ mol(-1) and proton conductivity of 0.05 S cm(-1) at 200 °C with no external humidification. A fuel cell based on a 165 μm thick HPW-silica nanocomposite membrane achieved a maximum power output of 128.5 and 112.0 mW cm(-2) for methanol and ethanol fuels, respectively, at 200 °C. The high proton conductivity and good performance demonstrate the excellent water retention capability and great potential of the highly ordered HPW-silica mesoporous nanocomposites as high-temperature proton exchange membranes for direct alcohol fuel cells (DAFCs).