Haining Zhang

Approaching high temperature performance for proton exchange membrane fuel cells with 3D ordered silica/Cs2.5H0.5PW electrolytes

Development of new types of proton conducting materials with efficient transport of protons is one of the most important remaining challenges for elevated-temperature proton exchange membrane fuel cells. Herein, we report the design and synthesis of a new type of proton conducting material based on three dimensional ordered macroporous silica (3DOM silica) incorporated with inorganic Cs2.5H0.5PW electrolytes. The highly ordered structure of 3DOM silica provides well inter-connected pathways for efficient proton transport, especially at high operating temperatures. At a doping amount of 90 wt% of Cs2.5H0.5PW, the proton conductivity of the formed composite electrolyte reaches 0.248 S cm−1 at 170 °C and the activation energy is about 5.775 kJ mol−1. The novel electrolytes also showed good stability as well as excellent single cell performance at 170 °C. The results described here demonstrate that the 3DOM silica/Cs2.5H0.5PW electrode has great potential for high temperature proton exchange membrane fuel cell applications.

Impregnation of imidazole functionalized polyhedral oligomeric silsesquioxane in polymer electrolyte membrane for elevated temperature fuel cells

Imidazole functionalized polyhedral oligomeric silsesquioxane (ImPOSS) is synthesized and introduced into a polymer electrolyte membrane for elevated temperature applications. Aggregates of ImPOSS containing 30–40 blocks of POSS cages are observed. The synthesized ImPOSS are well distributed in the hybrid membrane without further aggregation during the membrane formation process. The resulting hybrid membrane exhibits strong Coulombic interaction between sulfonic acid groups on Nafion and imidazole moieties on ImPOSS, leading to increased glass transition temperature and improved thermal stability of the membranes. Under anhydrous conditions, Vogel–Tamman–Fulcher type temperature-dependent proton conductivity is observed, suggesting that structural reorganization of incorporated imidazole moieties dominates the long-range proton transfer in the hybrid membrane. The anhydrous proton conductivity of hybrid membranes containing 35 wt% of ImPOSS reaches 0.0256 S cm−1 at 140 °C. The output voltage of a single cell assembled from the hybrid membrane is observed to be 0.41 V at 600 mA cm−2 under 120 °C and 25% relative humidity using hydrogen and oxygen as reaction gases. The results show the potential applicability of ImPOSS-Nafion hybrid membranes for elevated polymer electrolyte membrane fuel cells.

Anhydrous Proton Conducting Materials Based on Sulfonated Dimethylphenethylchlorosilane Grafted Mesoporous Silica/Ionic Liquid Composite

Efficient membrane proton conductivity at elevated temperatures (>100 °C) and reduced humidification conditions is a critical issue hindering fuel cell commercialization. Herein, proton conducting materials consisting of high surface area acid catalyzed mesoporous silica functionalized with sulfonated dimethylphenethylchlorosilane was investigated under anhydrous conditions. The organic moiety covalently bonded to the silica substrate via active hydroxyl groups on the silica pore surface. The structure and dynamic phases of the attached organic molecule were characterized and qualitatively determined by XRD, TEM, FT-IR, and solid state NMR. The amount of grafted organic molecules was estimated to be 2.45 μmol m(-2) by carbon elemental analysis. The so-formed composite materials showed adequate thermal stability up to 300 °C as determined by TGA. Under anhydrous conditions, ionic conductivity of the composite material upon ionic liquid impregnation reaches a peak value of 1.14 × 10(-2) S cm(-1) at 160 °C associated with the activation energy of 9.24 kJ mol(-1) for proton transport.

Proton conduction of polyAMPS brushes on titanate nanotubes

Proton conducting materials having reasonable proton conductivity at low humidification conditions are critical for decrease in system complexity and improvement of power density for polymer electrolyte membrane fuel cells. This study shows that polyelectrolyte brushes on titanate nanotubes formed through surface-initiated free radical polymerization exhibit less humidity-dependent proton conduction because of the high grafting density of polymer electrolyte chains and well-distribution of ionic groups. The results described in this study provide an idea for design of new proton conductors with effective ion transport served at relatively low humidification levels.

Decorating titanate nanotubes with protonated 1,2,4-triazole moieties for anhydrous proton conduction.

Anhydrous proton conducting materials based on surface attachment of protonated 1,2,4-triazole moieties on titanate nanotubes are prepared through self-assembly technique. (1)H MAS NMR spectra have revealed that the triazole moieties located at the outer surface of nanotubes. The distance between two ionic groups at the surface is observed to be shorter than 1nm, which may facilitate the formation of continuous proton conducting domains, leading to easy proton transport through segmental motion and structural re-organization in the absence of water. The maximum proton conductivity of the synthesized materials reaches about 2.4×10(-3)Scm(-1) at 160°C under anhydrous conditions.

Degradation of Silicone Rubbers in Fenton’s Reagents

Gaskets are applied in PEMFCs (proton exchange membrane fuel cells) to keep reactant gases and liquid within their respective regions, which are of great significance for the both sealing and electrochemical performance of fuel cells during the long-term operation. In this study, the degradation of silicone rubbers, often selected as seals in PEMFCs, in Fenton’s reagents with different H2O2 concentrations was investigated. The changes in chemical properties, mechanical behavior and surface morphology of the samples were studied before and after exposure to the test environment over time. It is found that increasing H2O2 concentration will degrade the rubbers more severely. The experimental results elucidate the degradation mechanism of silicone rubbers in Fenton’s reagents and the influence of H2O2 in the degradation process.

Nitrogen-doped porous carbon derived from surface-attached polymer layers for oxygen reduction reaction under acidic conditions

We reported the synthesis of nitrogen-doped carbon using surface-attached polyelectrolyte layers as precursors. The synthesized material has a large surface area of 800 m2·g-1 with uniformed pore distribution. Benefitfed from the high pyridinic nitrogen content, the synthesized nitrogen-doped porous carbon material exhibits promising electrocatalytic activity toward oxygen reduction reactions in acidic medium and very high stability against continuous cyclic voltammetry scans. The experimental results demonstrate that surface-attached polyelectrolyte layers are promising carbon and nitrogen sources for the formation of heteroatom-doped porous carbon materials.