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Qiao J.,Donghua University | Xu L.,Donghua University | Liu Y.,Tohoku University | Xu P.,Donghua University | And 3 more authors.
Electrochimica Acta | Year: 2013

Development of high-performance cost-effective electrocatalyts that can replace Pt catalyst have been a central theme in polymer electrolyte membrane fuel cells (PEMFCs) including direct methanol fuel cells (DMFCs). Here we show that carbon-supported pyridine-cobalt nanoparticles (CoPy/C) can generate a high catalytic activity toward the oxygen reduction reaction (ORR). The catalysts are synthesized using cobalt sulfate heptahydrate (CoSO4· 7H2O) and pyridine (Py) as the Co and N precursors via a solid state reaction by heat-treatment in an inert atmosphere at 800 °C. In particular, the ORR kinetics on these catalyst materials are evaluated using rotating disk electrode (RDE) technique in electrolytes of various KOH concentrations, ranging from 0.05 to 12 M. The Koutecky-Levich equation analyses indicate that the transferred electron number, n, per oxygen molecule on CoPy/C electrode depend on the low negative ovevrpotentials in low KOH concentrations, whereas in high KOH concentrations the values of n for oxygen reduction depend on the high negative overpotentials, and varies between 3.5 and 4.0. These catalysts exhibit the superior methanol tolerance to commercial 40%Pt/C catalyst, and the negative effect of high KOH concentration is much less for CoPy/C than for Pt/C, suggesting the promising utilization of CoPy/C as electrocatalysts for alkaline polymer electrolyte membrane fuel cells. © 2013 Elsevier Ltd.

Zhang J.,Donghua University | Qiao J.,Donghua University | Jiang G.,Donghua University | Jiang G.,University of Waterloo | And 3 more authors.
Journal of Power Sources | Year: 2013

The novel, low-cost anion-exchange membranes (abbreviated as PVA/PDDA-OH-), made from poly(vinyl alcohol) and poly(diallyldimethylammonium chloride) blends, are successfully synthesized by a combined thermal and chemical cross-linking technique. The hydroxide (OH -) conductivity, water uptake, ion exchange capacity (IEC), thermal stability, oxidative stability and alkaline stability of PVA/PDDA-OH- membranes are measured to evaluate their applicability in alkaline fuel cells. The effects of cross-linking procedure, cross-linking time and membrane composition on OH- conductivity are studied using AC impedance technique. It is found that by cross-linking modifications, the membranes exhibit excellent thermal stability with onset degradation temperature high above 170 C, a relatively high oxidative stability at 60 C, and a strong alkaline stability in 8 M KOH at 80 C. High OH- conductivity of 0.025 S cm-1 is achieved at 25 C and reaches up to 0.037 S cm-1 at 80 C. For exploring the conducting mechanisms, the concentration and mobility of charge carries of the membranes are also measured. The H 2/O2 fuel cell tests with PVA/PDDA-OH- membranes yield the peak power density of 11.5 mW cm-2 and greatly increase to 35.1 mW cm-2 depending on PVA/PDDA mass ratio, on a low metal loading on both the anode and the cathode of 0.5 mg (Pt) cm-2 at ambient temperature. © 2013 Elsevier B.V. All rights reserved.

Ding L.,Donghua University | Qiao J.,Donghua University | Dai X.,Donghua University | Zhang J.,Donghua University | And 2 more authors.
International Journal of Hydrogen Energy | Year: 2012

The active, carbon-supported copper phthalocyanine (CuPc/C) nano-catalyst, as a novel cathode catalyst for oxygen reduction reaction, is synthesized via a combined solvent-impregnation along with the high temperature treatment. The catalytic activities of both pyrolyzed and unpyrolyzed catalysts are screened by linear sweep voltammetry (LSV) employing a rotating disk electrode (RDE) technique to quantitatively obtain the oxygen reduction reaction (ORR) kinetic constants and the reaction mechanisms. The results show that heat-treatment can significantly improve the ORR activity of the catalyst, and the optimal heat-treated temperature is around 800 °C, under which, an onset potential of 0.10 V and a half-wave potential of -0.05 V are achieved in alkaline electrolyte. Besides the ORR kinetic rate is increased, the ORR electron transfer number is also increased from 2.5 to 3.6 with increasing heat-treatment temperature from 600 to 800 °C. Also, the effect of catalyst loading in the catalyst layer on the corresponding ORR activity is also studied, and finds that increasing the catalyst loading, the catalyzed ORR kinetic current density can be significantly increased. For a fully understanding of this heat-treatment temperature effect, XRD, TEM, SEM-EDX, TG and XPS are used to identify the catalyst structure and composition. TG results demonstrated that the presence of Cu prevents phthalocyanine from thermal decomposition, thus contribute to higher nitrogen content which can form more Cu-Nx activity sites for the ORR. XPS analysis indicates that both pyridinic-N and graphitic-N may be responsible for the enhanced ORR activity. © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Xu L.,Donghua University | Ding L.,Donghua University | Dai X.-F.,Donghua University | Zhang J.,Donghua University | And 3 more authors.
Gaodeng Xuexiao Huaxue Xuebao/Chemical Journal of Chinese Universities | Year: 2013

Nanostructure CoPy catalyst(15Co%25%Py/C, mass fraction) for the oxygen reduction reaction(ORR)was prepared by cobalt sulfate hepathydrate(CoSO4·7H2O) and pyridine(Py) as the Co and N precursors supported on Vulcan XC-72R, and followed by heat treatment in an inert atmosphere at 800°C. Electrochemical performances were evaluated using rotating disk electrode(RDE) technique in terms of its ORR activity in electrolytes containing various concentrations of KOH. The results show that the concentration of KOH has significant impact on the ORR performance of the CoPy/C catalyst. In 0.05 mol/L KOH, CoPy/C(in O2) can produce the obvious ORR current, giving the onset potential at 0.10 V(vs. SHE). The diffusion-limiting current density was 4.39 mA/cm2 at -0.381 V. RDE results reveal that CoPy/C catalyst in 0.05 and 0.1 mol/L KOH solution catalyze the ORR via four-electron pathway. XPS analysis indicates that both pyridinic-N and graphitic-N are responsible for the enhanced ORR activity.

Dai X.,Donghua University | Shi P.,Donghua University | Ding L.,Donghua University | Tian B.,Pearl Hydrogen Technology Co. | And 2 more authors.
ECS Transactions | Year: 2012

This work reports PDDA and QHECE-functionalized graphene nanosheets (N-GNSs) as metal-free catalyst for the oxygen reduction reaction in alkaline media. Although GNSs, PDDA or QHECE alone has little catalytic activity, their hybrid exhibits an unexpected high ORR activity. The structure, morphology, composition, and surface properties of the N-GNSs catalysts were characterized by transmission electron microscopy (TEM), and linear sweep voltammetry (LSV) as well as rotating disk electrode (RDE) techniques. An enhancement in the ORR electrocatalytic activity on N-GNSs was observed with increasing the mass ratio of N:GNSs, where QHECE:GNSs = 1:4 exhibits the highest activity for the ORR with onset potential and the half-wave potential of 0.06V and -0.1V, respectively. © The Electrochemical Society.

Ding L.,Donghua University | Qiao J.,Donghua University | Dai X.,Donghua University | Zhang J.,Donghua University | And 2 more authors.
ECS Transactions | Year: 2012

Effects of Fe addition on the electrocatalytic activity for oxygen reduction reaction (ORR) are studied over carbon-supported CoPc, which were prepared using a milling method combined with a heat-treatment procedure. The catalysts were characterized using CV, LSV and RDE in acid electrolyte. The results reveal that CoPc/C modified with 5%Fe after 600°C shows the best activity when Fe loading ranged from 0.5% to 8% nominal, and was higher than that of pure CoPc/C catalyst at the same measuring conditions. The ORR mechanism on the CoPc5%Fe/C-600 catalyst is mainly between 2e - and 3e - reduction pathway which is better than a 2e - reduction pathway on pure CoPc/C catalyst. The degree of oxygen reduction is improved on CoPc/C catalyst after modification with Fe. ©The Electrochemical Society.

Pearl Hydrogen Technology Co. | Date: 2012-03-06

Fuel cells.

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