Sikan Peng

A Gemini Quaternary Ammonium Poly (ether ether ketone) Anion‐Exchange Membrane for Alkaline Fuel Cell: Design, Synthesis, and Properties

To reconcile the tradeoff between conductivity and dimensional stability in AEMs, a novel Gemini quaternary ammonium poly (ether ether ketone) (GQ-PEEK) membrane was designed and successfully synthesized by a green three-step procedure that included polycondensation, bromination, and quaternization. Gemini quaternary ammonium cation groups attached to the anti-swelling PEEK backbone improved the ionic conductivity of the membranes while undergoing only moderate swelling. The grafting degree (GD) of the GQ-PEEK significantly affected the properties of the membranes, including their ion-exchange capacity, water uptake, swelling, and ionic conductivity. Our GQ-PEEK membranes exhibited less swelling (≤ 40 % at 25-70 °C, GD 67 %) and greater ionic conductivity (44.8 mS cm(-1) at 75 °C, GD 67 %) compared with single quaternary ammonium poly (ether ether ketone). Enhanced fuel cell performance was achieved when the GQ-PEEK membranes were incorporated into H2 /O2 single cells.

Ultra-low loading Pt decorated coral-like Pd nanochain networks with enhanced activity and stability towards formic acid electrooxidation

Novel Pd based coral-like nanochain networks decorated with ultra-low loading (0.66 at%) Pt (Pt-on-PdCNNs) were successfully synthesized through a facile wet chemical method. The Pt-on-PdCNNs exhibited significantly enhanced activity and stability towards formic acid electrooxidation, which was ascribed to their unique properties such as the highly interconnected networks, the more exposed Pd(111) planes and the reduced CO formation and adsorption on the Pt–Pd surface.

Enhancement of hydrogen production in a single chamber microbial electrolysis cell through anode arrangement optimization

Reducing the inner resistances is crucial for the enhancement of hydrogen generation in microbial electrolysis cells (MECs). This study demonstrates that the optimization of the anode arrangement is an effective strategy to reduce the system resistances. By changing the normal MEC configuration into a stacking mode, namely separately placing the contacted anodes from one side to both sides of cathode in parallel, the solution, biofilm and polarization resistances of MECs were greatly reduced, which was also confirmed with electrochemical impedance spectroscopy analysis. After the anode arrangement optimization, the current and hydrogen production rate (HPR) of MEC could be enhanced by 72% and 118%, reaching 621.3±20.6 A/m3 and 5.56 m3/m3 d respectively, under 0.8 V applied voltage. A maximum current density of 1355 A/m3 with a HPR of 10.88 m3/m3 d can be achieved with 1.5 V applied voltage.

A novel polysulfone–polyvinylpyrrolidone membrane with superior proton-to-vanadium ion selectivity for vanadium redox flow batteries

A novel kind of effective vanadium ion-suppressed polysulfone–polyvinylpyrrolidone (PSF–PVP) membrane with high ion selectivity, superior stability and low cost is designed and constructed for vanadium redox flow batteries (VRFBs). The VRFB with the PSF–PVP–50 membrane exhibits impressive coulombic efficiency (98%) as well as energy efficiency (89%), and outstanding stability during the 2000 h continuous charge–discharge cycling test.

Nonionic surfactant greatly enhances the reductive debromination of polybrominated diphenyl ethers by nanoscale zero-valent iron: Mechanism and kinetics

Nanoscale zero-valent iron (nZVI) has been considered as an effective agent for reductive debromination of polybrominated diphenyl ethers (PBDEs). But the high lipophilicity of PBDEs will hinder their debromination owing to the inefficient contact of PBDEs with nZVI. In this study, different ionic forms of surfactants were investigated aiming to promote PBDE debromination, and the beneficial effects of surfactant were found to be: nonionic polyethylene glycol octylphenol ether (Triton X-100, TX)>cationic cetylpyridinium chloride (CPC)>anionic sodium dodecyl benzenesulfonate (SDDBS). Except for with SDDBS, the promotion effect for PBDE debromination was positively related to the surfactant concentrations until a critical micelle concentration (CMC). The debromination process of octa-BDE and its intermediates could be described as a consecutive reaction. The corresponding rate constants (k) for the debromination of parent octa-BDE (including nona- to hepta-BDEs), the intermediates hexa-, penta-, and tetra-BDEs are 1.24 × 10(-1) h(-1), 8.97 × 10(-2) h(-1), 6.50 × 10(-2) h(-1) and 2.37 × 10(-3) h(-1), respectively.

Effects of bicarbonate and cathode potential on hydrogen production in a biocathode electrolysis cell

A biocathode with microbial catalyst in place of a noble metal was successfully developed for hydrogen evolution in a microbial electrolysis cell (MEC). The strategy for fast biocathode cultivation was demonstrated. An exoelectrogenic reaction was initially extended with an H2-full atmosphere to enrich H2-utilizing bacteria in a MEC bioanode. This bioanode was then inversely polarized with an applied voltage in a half-cell to enrich the hydrogen-evolving biocathode. The electrocatalytic hydrogen evolution reaction (HER) kinetics of the biocathode MEC could be enhanced by increasing the bicarbonate buffer concentration from 0.05 mol·L−1 to 0.5 mol·L−1 and/or by decreasing the cathode potential from − 0.9 V to − 1.3 V vs. a saturated calomel electrode (SCE). Within the tested potential region in this study, the HER rate of the biocathode MEC was primarily influenced by the microbial catalytic capability. In addition, increasing bicarbonate concentration enhances the electric migration rate of proton carriers. As a consequence, more mass H+ can be released to accelerate the biocathode-catalyzed HER rate. A hydrogen production rate of 8.44 m3·m−3·d−1 with a current density of 951.6 A·m−3 was obtained using the biocathode MEC under a cathode potential of − 1.3 V vs. SCE and 0.4 mol·L−1 bicarbonate. This study provided information on the optimization of hydrogen production in biocathode MEC and expanded the practical applications thereof.

A phosphotungstic acid self-anchored hybrid proton exchange membrane for direct methanol fuel cells

A phosphotungstic acid (HPW) self-anchored hybrid proton exchange membrane (PES/PVP-HPW) is prepared and evaluated in direct methanol fuel cells (DMFCs). The proton conductivity of the hybrid membrane is 0.045 S cm−1 at 25 °C, and reaches 0.078 S cm−1 at 80 °C. The hybrid membrane shows a methanol permeability of 1.65 × 10−6 cm2 s−1. The stability test for the hybrid membrane in 2 M methanol at 50 °C for about 100 h reveals that HPW is well immobilized in the hybrid membrane. The DMFC based on the PES/PVP-HPW hybrid membrane with a thickness of 55 μm exhibits comparable performance of 132 mW cm−2 to that of Nafion212 at 80 °C. The effects of the hybrid membrane thickness and methanol concentration on DMFCs performance are evaluated. The optimal methanol concentration and thickness of the membrane is about 1–2 M and 55 μm, respectively. Furthermore, a 130 h stability test for DMFC with PES/PVP-HPW demonstrates that the hybrid membrane is quite stable, which indicates that PES/PVP-HPW is an attractive low-cost alternative proton exchange membrane to Nafion® for portable power sources.

Nernst-ping-pong model for evaluating the effects of the substrate concentration and anode potential on the kinetic characteristics of bioanode

Understanding the electron-transfer mechanism and kinetic characteristics of bioanodes is greatly significant to enhance the electron-generating efficiencies in bioelectrochemical systems (BESs). A Nernst-ping-pong model is proposed here to investigate the kinetics and biochemical processes of bioanodes in a microbial electrolysis cell. This model can accurately describe the effects of the substrate (including substrate inhibition) and the anode potential on the current of bioanodes. Results show that the half-wave potential positively shifts as the substrate concentration increases, indicating that the rate-determining steps of anodic processes change from substrate oxidation to intracellular electron transport reaction. The anode potential has negligible effects on the enzymatic catalysis of anodic microbes in the range of -0.25 V to +0.1 V vs. a saturated calomel electrode. It turns out that to reduce the anodic energy loss caused by overpotential, higher substrate concentrations are preferred, if the substrate do not significantly and adversely affect the output current.

In situ construction of interconnected ion transfer channels in anion-exchange membranes for fuel cell application

To resolve the trade-off between conductivity and stability in anion-exchange membranes (AEMs), we proposed a strategy to modulate the membrane morphology from isolated ionic clusters to interconnected channels by precise adjustment of the amphiphilic architectures. From the perspective of AEM molecular designing, by synchronously increasing the amphiphilic segments, well-connected conductive nano-channels, comprising overlapped larger hydrophilic domains (35–40 nm), were constructed and validated by percolation theory. The whole synthesis process was green, avoiding the toxic chloromethyl methyl ether route. The unique molecular, spatial and micro-structures enabled the membranes to exhibit excellent performance. The connective hydrophilic channels significantly enhanced the conductivity, while the increasing hydrophobicity reduced the water uptake and swelling, improving the dimensional and chemical stability of the membranes. This strategy successfully solves the trade-off issue between conductivity and stability in AEMs.

Can bicarbonate replace phosphate to improve the sustainability of bioelectrochemical systems for H2 production

Phosphate is generally used as an effective electrolyte buffer in bioelectrochemical systems, but it is not sustainable. Bicarbonate, if it can replace phosphate as an alternative buffer, may improve the overall economic feasibility of microbial electrolysis cells (MEC) for its application in wastewater treatment and H2 production. In this study, the performance of single-chamber MECs with combo buffers with different PO43− to HCO3− (P/C) ratios was investigated. The results demonstrate that large (about 80%) but not complete replacement of PO43− with HCO3− is feasible, indicating phosphate is necessary to maintain the electric current and the stability of MECs. The current density of MEC with P/C at 20/80 (in mol%) was comparable to that with a full phosphate buffer, and can be kept stable for as long as 1800 h, under 0.5 to 0.9 V applied voltages. Analysis by using molecular approaches, including denaturing gradient gel electrophoresis and DNA sequencing, shows that P/C ratios affect the microbial community structure of the bioanode biofilm, especially on the population of Geobacter, which is a predominant and key exoelectrogenic bacteria to produce an electric current in MEC. The results of this study will broaden the knowledge of the buffer effect and promote the potential applicability of MECs for H2 production.