In the present work, a special competitive adsorbent, ethanol, is proposed for in situ release product inhibition of a hydrophobic product system from a hydrophobic carbon catalyst support. Product inhibition is serious in electrochemical hydrogen pump hydrogenation reactors (EHPRs) due to slow molecular diffusion of the products through the microporous flow channels (1–10 μm). The hydrogenation rate of maleic acid decreases rapidly with reaction time, only 37.4% retention after 10 h reaction. By introducing ethanol in the aqueous solution, both reaction rate and conversion after 10 h reach 1.46 folds of those without ethanol. Evidenced by competitive adsorption, the adsorption capacity of the product amber acid is decreased by 98% on carbon particles compared with that without ethanol. Ethanol takes most of the place of amber acid due to much better affinity with carbon support, which releases more amber acid molecules into the bulk solution and relieves product inhibition. Kinetics parameters are fitted with modified Langmuir–Hinshelwood kinetics by considering the influence of ethanol competitive adsorption on maleic acid hydrogenation performance.Keywords: Adsorption effect; Biomass hydrogenation; Catalyst layer; Electrochemical hydrogen pump hydrogenation reactor; Product inhibition;

•A novel approach is proposed to design AEMs with flexible ether-containing side chain.•Enhanced mobility of side chains and ion interactions promote micro-phase separation.•Conductivity (72 mS cm−1) and swelling (7.3%) are well balanced even at 60 °C.•Good alkaline stability (60 °C, 1 M KOH for 168 h) is obtained.A novel approach is proposed to design anion exchange membranes (AEMs) containing pendent imidazolium side chains with flexible ether-containing spacer by the Williamson etherification between chloromethylated polysulfone and as-synthesized hydroxyl-bearing imidazolium. The introduction of long flexible ether-containing spacer chains enhances the mobility of terminated imidazolium groups and ion interactions. It facilitates the formation of a good hydrophilic/hydrophobic micro-phase separation structure, which is confirmed by the scattering peak of SAXS. As a result, the membranes exhibit high conductivity and excellent anti-swelling ability. The membrane with IEC of 1.55 mmol g−1 shows considerable hydroxide conductivity (72 mS cm−1, 60 °C), low swelling ratio (7.3%, 60 °C), and great tensile strength in hydrated state (43.4 MPa, 20 °C). The existence of long spacer chain also improved the alkaline stability. After immersion in 60 °C, 1 M KOH solution for 168 h, hydroxide conductivity and tensile strength of the membrane remain constant. The ether-containing side chains fabricated in this work provides a universal promising method to balance hydroxide conductivity and dimensional and alkaline stability.

•Fabrication of through-plane conductive channels by aligned electrospun nanofibers.•–SO3− groups aggregate by electrostatic attraction and promote conductive channels.•Through-plane conductivity is nearly twice as much as that of the cast membrane.•Higher tensile strength and cell power density comparing Nafion115 (1.5 & 1.2 fold).A novel approach is proposed to fabricate sulfonated poly (phthalazinone ether sulfone ketone) (SPPESK) proton exchange membranes with ordered through-plane electrospinning nanofibers, which provide nano-scale through-plane proton conductive channels along the thickness direction of the membranes, aiming to satisfy the challenging requirement of high through-plane proton conductivity in fuel cell operations. Induced by electrostatic attraction of strong electric field, the negatively charged sulfonic acid groups tend to aggregate towards surface of the electrospun fibers, which is evidenced by TEM and SAXS and further induces aggregation of the sulfonic acid groups in the SPPESK inferfiber voids filler along the surface of the nanofibers. The aligned electrospun nanofibers carries long-range ionic clusters along the thickness direction of the membrane and results in much higher total through-plane conductivity in the thickness aligned electrospun membranes, nearly twice as much as that of the cast SPPESK membrane. With smooth treatment, the thickness aligned electrospun SPPESK membranes exhibit higher single cell power density and tensile strength as compared with Nafion 115 (around 1.2 and 1.5 folds, respectively). Such a design of thickness aligned nano-size proton conductive channels provide feasibility for high performance non-fluorinated PEMs in fuel cell applications.A novel approach is proposed to fabricate PEM with nano-scale proton conductive channels along the thickness-direction of membranes by electrospinning.Download high-res image (281KB)Download full-size image

•Thermoplastic interpenetrating polymer network AEM based on PBI has been developed.•Physically crosslinking makes better compatibility and chain flexibility than sIPN.•Good balance achieves between conductivity and swelling (96.7 mS cm−1, 4.4%, 80 °C).A new series of thermoplastic interpenetrating polymer network (TIPN) anion exchange membranes (AEMs) based on poly [2,2′- (p-oxydiphenylene) −5, 5′-bibenzimidazole] (OPBI) and poly(1, 2-dimethy-3-allylimidazolium) (PDAIm) (PBI/DAIm TIPN) has been developed. With 1, 2-dimethy-3-allylimidazolium (DAIm) polymerization in presence of OPBI polymer chains, two kinds of uncrosslinked polymer chains, i.e. PDAIm and OPBI interpenetrate with each other to form a physically crosslinking network. Small steric hindrance effect of the DAIm monomer and non-covalent crosslinking interpenetrating polymer chains contribute to better compatibility and chains flexibility in the TIPN compared with the blend and semi-interpenetrating networks, which are evidenced by SEM and SAXS, promote the aggregation of hydrophilic groups and induce connective ionic conductive channels. PBI/DAIm TIPN membranes achieve well-balanced performance between high hydroxide conductivity and dimensional stability because of the dynamically forced compatibility feature of TIPN. Especially, the PBI/DAIm TIPN-65/0.5 membrane exhibits high hydroxide conductivity (96.7 mS cm−1) and low swelling ratio (4.4%) at 80 °C. With low overall alkali uptake (2.89%) and IEC (0.63 mmol g−1) of functional groups, it exhibits excellent chemical stability in 1 M KOH at 60 °C for 96 h (94.0% retention) and high tensile strength (48.2 MPa) in hydrated state. These observations suggest TIPN structure provides a promising solution to the electrochemical-mechanical balance of AEMs.

•Orientated GO/Nafion ultra-thin layer (440 nm) coated composite membrane is prepared.•Balance of vanadium crossover and H+ conduction by GO orientation in ultra-thin layer.•GO/Nafion exhibits lower capacity decay rate (0.23%) than Nafion 212 over 200 cycles.Graphene oxide (GO)/Nafion composite membranes, with orientated GO nanosheets in parallel to the surface of the ultra-thin coating layer (400–440 nm), are prepared by spin coating method and evidenced by electron microscopy analysis. Orientation of GO maximizes the vanadium ions barrier effect of GO. The GO/Nafion membrane (M-2) achieves lower vanadium ion permeability (8.2 × 10−8 cm2 min−1, only 2.64% of the pristine Nafion membrane), and higher coulombic efficiency and energy efficiency (92.9–98.8% and 81.5–88.4%, respectively) comparing with the pristine Nafion membrane (73.3–90.5% and 68.9–79.1%, respectively) at current densities of 20–100 mA cm−2. With the design of orientated GO nanosheets and ultra-thin GO/Nafion coating layer, good balance between vanadium crossover suppression and protons conduction retention is achieved. M-2 exhibits excellent battery performances over 200 charge-discharge cycles. The capacity decay rate is about 0.23% per cycle, much lower than those assembled with Nafion 212 (0.40% per cycle) and the recast Nafion membrane (0.44% per cycle). Spin coating with water suspensor leads to uniform dispersion of GO and good binding between GO/Nafion coating layer and substrate Nafion membrane. Therefore, the composite membrane could be reinforced by GO and keep integration even with 200 cycles operation.

A novel alkaline group, hexamethylenetetramine (HMTA) with four tertiary amine groups and β-hydrogen-absent structure, has been employed as mono-quaternization reagent to prepare HMTA mono-quaternized polysulfone anion exchange membranes (PSF-QuOH AEMs). Analyzed by molecular dynamics simulations, mono-quaternized HMTA shows a superior aggregating ability by strong electrostatic interaction with hydroxide to suppress water swelling even at high IECs. In particular, the PSF-QuOH membrane with a high IEC of 2.23 mmol g−1 exhibits a low swelling ratio of 21% even at 60 °C. The resulting high concentration of cationic groups and the interactions between multiple hydrogen atoms in HMTA and hydroxide/water are helpful to induce the formation of the continuous and efficient hydrogen-bond networks, promoting ionic transport. High hydroxide conductivity of 35 mS cm−1 is achieved at 20 °C. Excellent swelling resistance also benefits the mechanical and chemical stabilities of the PSF-QuOH membranes. A considerable mechanical strength of 17.7 MPa is observed in the fully hydrated membrane. The hydroxide conductivity is stable at around 86% of the initial value after 1 M KOH immersion at 60 °C for 168 h.

A bilateral electrochemical hydrogen pump reactor is proposed for the first time. In one electrochemical hydrogen pump (EHP) configuration, in situ adsorbed hydrogen atoms for phenol hydrogenation at the cathode are donated by the dehydrogenation of 2-propanol instead of a conventional H2 or H2O anode feedstock. For the anodic 2-propanol dehydrogenation EHP reactor, by increasing Pt–Ru/C catalyst loading and applying a pulse current operation, the applied potential can be controlled below 0.2 V, which is much lower than the thermodynamic dissociation potential of water (1.23 V). For the cathodic cyclohexanone hydrogenation EHP reactor, the hydrogenation rate reaches 73.9 mmol h−1 g−1Pd, nearly three times of that in aqueous-phase selective hydrogenation reactors. Pd/C and Pt/C catalysts have high catalytic selectivity to cyclohexanone (95.5%) and cyclohexanol (95.4%), respectively. In the bilateral EHP reactor, 2-propanol dehydrogenation and phenol hydrogenation are completed simultaneously, exhibiting a comparable hydrogenation rate, selectivity and conversion to that in the individual EHP reactors. The feasibility of the bilateral EHP reactor provides a novel idea to efficiently integrate multiple reactors into one configuration, which greatly simplifies hydrogen production, storage and transportation, as well as reactor equipment.

A novel method of improving interfacial compatibility in electrospun anion exchange membranes (AEMs) is developed by using imidazolium-functionalized polysulfone (IMPSF) as both electrospun fiber mats and interfiber voids filler. Scanning electron microscopy (SEM) illustrates the defect-free and fiber-retained morphology of the IMPSF electrospun AEMs. Transmission electron microscopy (TEM) shows better aggregation of ion clusters in the IMPSF electrospun AEMs. As a result, the electrospun AEMs prepared in the present work exhibit much higher hydroxide conductivity increment than most reported electrospun AEMs (around 1.7 folds in 20 °C water and 100 folds at 60 °C, relative humidity (RH) 40% as compared with the corresponding cast AEMs). Excellent interfacial compatibility and microphase separation morphology also promote swelling resistance and mechanical and alkaline stabilities of the IMPSF electrospun composite AEMs. Compared with the cast AEMs, tensile strength increment is up to 22%, alkaline stability increases more than one fold after immersing in 1 M KOH at 60 °C for 24 h. Results in the present work are helpful to componential design of the electrospun AEMs.

A novel alkaline group, hexamethylenetetramine (HMTA) with four tertiary amine groups and β-hydrogen-absent structure, has been employed as mono-quaternization reagent to prepare HMTA mono-quaternized polysulfone anion exchange membranes (PSF-QuOH AEMs). Analyzed by molecular dynamics simulations, mono-quaternized HMTA shows a superior aggregating ability by strong electrostatic interaction with hydroxide to suppress water swelling even at high IECs. In particular, the PSF-QuOH membrane with a high IEC of 2.23 mmol g−1 exhibits a low swelling ratio of 21% even at 60 °C. The resulting high concentration of cationic groups and the interactions between multiple hydrogen atoms in HMTA and hydroxide/water are helpful to induce the formation of the continuous and efficient hydrogen-bond networks, promoting ionic transport. High hydroxide conductivity of 35 mS cm−1 is achieved at 20 °C. Excellent swelling resistance also benefits the mechanical and chemical stabilities of the PSF-QuOH membranes. A considerable mechanical strength of 17.7 MPa is observed in the fully hydrated membrane. The hydroxide conductivity is stable at around 86% of the initial value after 1 M KOH immersion at 60 °C for 168 h.