Anion exchange membrane fuel cells (AEMFCs) have been developed as promising energy conversion devices for stationary and mobile applications due to their potentially low cost. To realize high-performance AEMFCs, new polymeric membranes are needed that are highly conductive and chemically stable. Here we report a systematic study of anion exchange membranes (AEMs) with multiple cations per side chain site to demonstrate how this motif can boost both the conductivity and stability of poly­(2,6-dimethyl-1,4-phenylene oxide)-based AEMs. The highest conductivity, up to 99 mS/cm at room temperature, was observed for a triple-cation side chain AEM with 5 or 6 methylene groups between cations. This conductivity was considerably higher than AEM samples based on benzyl­trimethyl­ammonium or benzyl­dimethylhexyl­ammonium groups with only one cation per side chain site. In addition to high conductivity, the multication side chain AEMs showed good alkaline and dimensional stabilities. High retention of ion exchange capacity (IEC) (93% retention) and ionic conductivity (90% retention) were observed for the triple-cation side chain AEMs in degradation testing under 1 M NaOH at 80 °C for 500 h. Based on the high-performance triple-cation side chain AEM, a Pt-catalyzed fuel cell with a peak power density of 364 mW/cm2 was achieved at 60 °C under 100% related humidity.

Bipolar membranes maintain a steady pH in electrolytic cells through water autodissociation at the interface between their cation- and anion-exchange layers. We analyze the balance of electric field and catalysis in accelerating this reaction.

Currently, a serious problem obstructing the large-scale clinical applications of fluorescence technique is the shallow penetration depth. Two-photon fluorescence microscopic imaging with excitation in the longer-wavelength near-infrared (NIR) region (>1100 nm) and emission in the NIR-I region (650-950 nm) is a good choice to realize deep-tissue and high-resolution imaging. Here, we report ultradeep two-photon fluorescence bioimaging with 1300 nm NIR-II excitation and NIR-I emission (peak ∼810 nm) based on a NIR aggregation-induced emission luminogen (AIEgen). The crab-shaped AIEgen possesses a planar core structure and several twisting phenyl/naphthyl rotators, affording both high fluorescence quantum yield and efficient two-photon activity. The organic AIE dots show high stability, good biocompatibility, and a large two-photon absorption cross section of 1.22 × 10 GM. Under 1300 nm NIR-II excitation, in vivo two-photon fluorescence microscopic imaging helps to reconstruct the 3D vasculature with a high spatial resolution of sub-3.5 μm beyond the white matter (>840 μm) and even to the hippocampus (>960 μm) and visualize small vessels of ∼5 μm as deep as 1065 μm in mouse brain, which is among the largest penetration depths and best spatial resolution of in vivo two-photon imaging. Rational comparison with the AIE dots manifests that two-photon imaging outperforms the one-photon mode for high-resolution deep imaging. This work will inspire more sight and insight into the development of efficient NIR fluorophores for deep-tissue biomedical imaging.

Rationale: Cerebrovascular diseases, together with malignancies, still pose a huge threat to human health nowadays. With the advantages of its high spatial resolution and large penetration depth, fluorescence bioimaging in the second near-infrared spectral region (NIR-II, 900-1700 nm) and its related imaging-guided therapy based on biocompatible fluorescence dyes have become a promising theranostics method.Methods: The biocompatibility of IR-820 we used in NIR-II fluorescence bioimaging was verified by long-term observation. The model of the mouse with a cranial window, the mouse model of middle cerebral artery occlusion (MCAO) and a subcutaneous xenograft mouse model of bladder tumor were established. NIR-II fluorescence cerebrovascular functional imaging was carried out by IR-820 assisted NIR-II fluorescence microscopy. Bladder tumor was treated by NIR-II fluorescence imaging-guided photothermal therapy.Results: We have found that IR-820 has considerable NIR-II fluorescence intensity, and shows increased brightness in serum than in water. Herein, we achieved real time and in vivo cerebrovascular functional imaging of mice with high spatial resolution and large penetration depth, based on IR-820 assisted NIR-II fluorescence microscopy. In addition, IR-820 was successfully employed for NIR-II fluorescence imaging and photothermal therapy of tumor in vivo, and the subcutaneous tumors were inhibited obviously or eradicated completely.Conclusion: Due to the considerable fluorescence intensity in NIR-II spectral region and the good photothermal effect, biocompatible and excretable IR-820 holds great potentials for functional angiography and cancer theranostics in clinical practice.

A series of tough and chemically stable semi-interpenetrating network anion exchange membranes (SIPN AEMs) composed of a rigid and ion-conductive component, quaternized poly­(2,6-dimethyl phenylene oxide) (QAPPO), and a hydrophilic, cross-linked, flexible poly­(ethylene glycol)-co-poly­(allyl glycidyl ether) (xPEG–PAGE) component were synthesized. The SIPN AEMs containing both rigid and flexible polymer constituents exhibited outstanding mechanical strength and flexibility and were much tougher than conventional QAPPO membranes. The introduction of the hydrophilic network ensured SIPN AEMs with high hydration numbers, which contributed to the high ion conductivity of these materials. The physical properties of the SIPN AEMs could be varied by the mass fractions of the QAPPO and xPEG–PAGE components, and a trade-off was observed between the samples’ conductive and swelling properties. Among the compositions studied, SIPN-60-2 (MassQAPPO‑60/MassPEG–PAGE = 2:1) with an IEC of 1.43 mmol/g was found to have balanced ionic conductivity (67.7 mS/cm at 80 °C) and swelling ratio (26% at 80 °C). The alkaline stabilities of the SIPN AEMs were evaluated in 1 M NaOH at 80 °C for 30 days. Good mechanical (72% and 74% retention in tensile strength and elongation at break, respectively) and dimensional (11% increase in water uptake) stability was retained by the SIPN AEM due to the presence of the alkali-resistant xPEG–PAGE network. The quaternary ammonium groups in SIPN-60-2 were found to be relatively stable (24% and 26% decrease in IEC and OH– conductivity in 1 M NaOH at 80 °C for 30 days, respectively), and the low initial IEC and the high dimensional stability of the membrane protected the cation from severe degradation during the extended aging test.

Anion exchange membranes (AEMs) are a promising class of materials that enable non-noble metals to be used as catalysts in fuel cells. Compared to their acidic counterparts, typically Nafion and other perfluorosulfonate-based membranes, the low OH– conductivity in AEMs remains a concern as these materials are developed for practical applications. Cross-linked macromolecular structures are a popular way to optimize the trade-off between the ionic conductivity and the water swelling of AEMs with high ion exchange capacities (IECs). However, common cross-linked AEMs (e.g., x(QH)­QPPO) that have high degrees of cross-linking with low molecular weight between cross-links are usually mechanically brittle. Moreover, the cross-links in AEMs can hinder the transport of OH–, leading to unsatisfactory conductivities. Here we report a series of elastic and highly conductive poly­(2,6-dimethyl­phenylene oxide) (PPO)-based AEMs (x(QH)3QPPO) containing flexible, long-chain, multication cross-links. The strength and flexibility of the x(QH)3QPPO samples are significantly improved as compared to the conventional x(QH)­QPPO membranes and multication un-cross-linked materials reported previously. The high conductivities in these new materials (x(QH)3QPPO-40, IEC = 3.59 mmol/g, σOH– = 110.2 mS/cm at 80 °C) are attributed to the distinct microphase separation observed in the x(QH)3QPPO membranes by SAXS and TEM analyses. Furthermore, the x(QH)3QPPO samples exhibit good dimensional (swelling ratio of x(QH)3QPPO-40 is 25.0% at 80 °C) and chemical (22% and 25% decrease in IEC and OH– conductivity in 1 M NaOH at 80 °C for 30 days, respectively) stabilities, making this cross-linking motif suitable for potential membrane applications in fuel cells and other electrochemical devices.

A series of chemically stable and ionically conductive side-chain anion exchange membranes (AEMs) based on poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) backbones and alkyltrimethylammonium cations are reported in this work. Two alkyltrimethylammonium groups with n-propyl (C 3 ) and n-pentyl (C 5 ) alkyl chains were tethered onto PPO backbones through secondary amine moieties, resulting in two side-chain AEMs, that is, NC 3 Q-PPO and NC 5 Q-PPO and NC 5 Q-PPO. In comparison to benzylic QA groups (e.g., benzyltrimethylammonium cations in quarternized PPO (QPPO) and benzylalkyldimethylammonium cations in comb-shaped PPOs (i.e., QC 3 -PPO and QC 6 -PPO)), the alkyltrimethylammonium cations of the side-chain PPOs, which do not possess highly reactive benzylic protons adjacent to both the aromatic ring and the cation, showed superior alkaline stability. After 30 days of aging in 1 mol/L NaOH solution at 80 °C, the retention of the conductivities of NC 3 Q-PPO (IEC = 2.17 mmol/g), NC 5 Q-PPO-40 (IEC = 2.03 mmol/g), and NC 5 Q-PPO-60 (IEC = 2.57 mmol/g) were 73.1%, 89.9%, and 81.2% compared with 39.8%, 41.2%, and 56.5% for the QPPO-40 (IEC = 2.27 mmol/g), QC 3 -PPO-40 (IEC = 2.22 mmol/g), and QC 6 -PPO-40 (IEC = 2.13 mmol/g) samples, respectively. In addition to good stability, the side-chain NC 5 Q-PPO-40 and NC 5 Q-PPO-60 with longer spacers between the aromatic polymer backbone and the cation exhibited high conductivities of 73.9 and 96.1 mS/cm at 80 °C in liquid water, while the swelling ratios were limited to 15% and 28%. The flexible linear spacer in NC 5 Q-PPO membranes induced distinct hydrophilic/hydrophobic microphase separation, which enhanced the physical properties of the membranes. Thus, we believe that the NC 5 Q-PPO-type AEMs derive their superior performance from both their unique chemical structures with n-pentyl cationic tethers and the microphase-separated morphologies of the materials driven by the side chain architecture.

Although the peak power density of anion exchange membrane fuel cells (AEMFCs) has been raised from ≈0.1 to ≈1.4 W cm −2 over the last decade, a majority of AEMFCs reported in the literature have not been demonstrated to achieve consistently high performance and steady-state operation. Poly(olefin)-based AEMs with fluorine substitution on the aromatic comonomer show considerably higher dimensional stability compared to samples that do not contain fluorine. More importantly, fluorinated poly(olefin)-based AEMs exhibit high hydroxide conductivity without excessive hydration due to a new proposed mechanism where the fluorinated dipolar monomer facilitates increased hydroxide dissociation and transport. Using this new generation of AEMs, a stable, high-performance AEMFC is operated for 120 h. When the fuel cell configuration is subjected to a constant current density of 600 mA cm −2 under H 2 /O 2 flow, the cell voltage declines only 11% (from 0.75 to 0.67 V) for the first 20 h during break-in and the cell voltage loss is low (0.2 mV h −1 ) over the subsequent 100 h of cell testing. The ease of synthesis, potential for low-cost commercialization, and remarkable ex situ properties and in situ performance of fluoropoly(olefin)-based AEM renders this material a benchmark membrane for practical AEMFC applications.