Suli Wang

Influence of electrode structure on the performance of a direct methanol fuel cell

Direct methanol fuel cells (DMFCs) consisting of multi-layer electrodes provide higher performance than those with the traditional electrode. The new electrode structure includes a hydrophilic thin film and a traditional catalyst layer. A decal transfer method was used to apply the thin film to the Nafion(R) membrane. Results show that the performance of a cell with the hydrophilic thin film is obviously enhanced. A cell with the optimal thin film electrode structure operating at I M CH3OH, 2 atm oxygen and 90degreesC yields a current density of 100 mA/cm(2) at 0.53 V cell voltage. The peak power density is 120 mW/cm(2). The performance stability of a cell in a short-term life operation was also increased when the hydrophilic thin film was employed

Novel synthesis of highly active Pt/C cathode electrocatalyst for direct methanol fuel cell

A 40 wt% Pt/C cathode electrocatalyst with controlled Pt particle size of approximately 2.9 nm showing better performance than commercial catalyst for direct methanol fuel cell was prepared by a polyol process with water but without using stabilizing agent.

Preparation of highly active Pt/C cathode electrocatalysts for DMFCs by an improved aqueous impregnation method

An improved aqueous impregnation method was used to prepare 40 wt% Pt/C electrocatalysts. TEM analysis of the samples showed that the Pt particles impregnated for a short time have a very narrow size distribution in the range of 1–4 nm with an average size of 2.6 nm. UV-vis spectroscopy measurements verified that the redox reaction between PtCl62− and formaldehyde took place with a slow rate at ambient temperature via a two-step reaction path, where PtCl42− serves as an intermediate. The use of the short-time-impregnated 40 wt% Pt/C as cathode electrocatalysts in direct methanol fuel cells yields better performance than that of commercial 40 wt% Pt/C electrocatalyst. Experimental evidence provides clues for the fundamental understanding of elementary steps of the redox reactions, which helps in guiding the design and preparation of highly dispersed Pt catalyst for fuel cells.

Coupling Effect Between Cobalt Oxides And Carbon For Oxygen Reduction Reaction

Same selectivity hides different pathways: The same apparent 4-electron process for the oxygen-reduction-reaction hides different pathways over carbon-supported cobalt oxide catalysts depending on the potential. At low overpotentials, the ORR intermediate HO(2) (-) preferably disproportionates to oxygen, whereas at high overpotentials the disproportionation and reduction reaction occur in parallel.

Vertically oriented polypyrrole nanowire arrays on Pd-plated Nafion® membrane and its application in direct methanol fuel cells

Highly ordered polypyrrole nanowire arrays are constructed via electrochemically polymerizing pyrrole directly on Pd-modified Nafion® membrane. A significant enhancement in the performance and durability of direct methanol fuel cells (DMFCs) is observed when such an ordered structure is used as an ordered electrode.

Highly stable poly(ethylene glycol)-grafted alkaline anion exchange membranes

A mechanically and chemically stable poly(ethylene glycol) (PEG)-grafted poly(styrene-ethylene-co-butylene-styrene) (SEBS)-based alkaline anion exchange membrane (AAEM) was designed, prepared and characterized. When subjected to tensile strain, the elongation at breaking of these SEBS-based AAEMs was up to 500%, a value 80 times greater than that of an AAEM using polystyrene as the main chain. Remarkably, the ion exchange capacity (IEC), conductivity, dimensions and mechanical properties of this AAEM could remain almost unchanged in 2.5 M KOH at 60 °C for about 3000 h, indicating the excellent alkaline stability of the PEG-grafted SEBS-based AAEMs. As confirmed by TEM, the grafting of PEG could enlarge the size of the ion-conducting channels, significantly enhancing the conductivity of these AAEMs (80 °C, from 29.2 mS cm−1 to 51.9 mS cm−1). Furthermore, the peak power density of an H2/O2 single fuel cell using this SEBS-based AAEM was up to 146 mW cm−2 at 50 °C. Based on these outstanding properties, this membrane has potential application not only for fuel cells, but also for other electrochemical energy conversion and storage devices, such as redox flow and alkaline ion batteries.

Highly alkaline stable N1-alkyl substituted 2-methylimidazolium functionalized alkaline anion exchange membranes

Steric hindrance and hyperconjugative effects, introduced at the N1 position of 2-methylimidazolium, greatly enhance the alkaline stability of the 2-methylimidazolium functional group. 2-Methylimidazolium small molecule compounds with N1-substituents (butyl, hexyl or octyl) are stable in 1 M KOH at 80 °C for more than 3000 h. Accordingly, the membranes based on N1-butyl, hexyl or octyl-substituted 2-methylimidzolium exhibited much more alkaline stability than membranes based on other substituted 2-methylimidazolium compounds, reflected by the almost unchanged IEC, conductivity and dimensions of the membranes after being exposed to 1 M KOH at 60 °C for hundreds of hours. This work reports the preparation of highly alkaline stable 2-methylimidazolium-based membranes by modifying the N1 position of 2-methylimidazolium.

Rational design of a highly efficient Pt/graphene–Nafion® composite fuel cell electrode architecture

High platinum requirements hinder the commercialization and wide adoption of polymer electrolyte membrane fuel cells (PEMFCs). Therefore, it is desirable to develop advanced electrode architectures that utilize Pt more effectively than the current designs. Herein, a novel electrode architecture based on Pt/graphene–Nafion® composite macroporous scaffold, prepared via facile freeze-drying approach, demonstrating ultra-high Pt utilization is presented. Within the electrode architecture, pores act as gas/liquid transport channels, whereas Nafion® ionomers act as proton carriers, and graphene sheets allow the conductance of electrons. By leveraging these tailored pathways for both mass and charges, a PEMFC prepared with this electrode architecture demonstrated superior performance, with a peak power density of 0.93 W cm−2 and cathode mass specific power density of 6.2 W mgPt−1. These values are 6-fold greater than those produced using a lamellar structure with the same mass loading of Pt/graphene–Nafion® and also 1.2-fold greater than the commercial Pt/C coated electrodes with the same Pt loading.

Bio-inspired Construction of Advanced Fuel Cell Cathode with Pt Anchored in Ordered Hybrid Polymer Matrix

The significant use of platinum for catalyzing the cathodic oxygen reduction reactions (ORRs) has hampered the widespread use of polymer electrolyte membrane fuel cells (PEMFCs). The construction of well-defined electrode architecture in nanoscale with enhanced utilization and catalytic performance of Pt might be a promising approach to address such barrier. Inspired by the highly efficient catalytic processes in enzymes with active centers embedded in charge transport pathways, here we demonstrate for the first time a design that allocates platinum nanoparticles (Pt NPs) at the boundaries with dual-functions of conducting both electrons by aid of polypyrrole and protons via Nafion® ionomer within hierarchical nanoarrays. By mimicking enzymes functionally, an impressive ORR activity and stability is achieved. Using this brand new electrode architecture as the cathode and the anode of a PEMFC, a high mass specific power density of 5.23 W mg−1Pt is achieved, with remarkable durability. These improvements are ascribed to not only the electron decoration and the anchoring effects from the Nafion® ionomer decorated PPy substrate to the supported Pt NPs, but also the fast charge and mass transport facilitated by the electron and proton pathways within the electrode architecture.

Electrochemically synthesized freestanding 3D nanoporous silver electrode with high electrocatalytic activity

Three-dimensional nanoporous metals of highly porous structure and interconnected ligaments are attractive for electrochemical reactions. Herein, freestanding 3D nanoporous silver (np-Ag) is prepared by a facile electrochemical approach, i.e., first electro-oxidizing silver to silver halides followed by electro-reduction of the silver halides by controlling the potential applied to the electrode. The np-Ag displays 130 and 11.5 times enhancement in catalytic activity for the oxygen reduction reaction and the formaldehyde electro-oxidation reaction, respectively, relative to the flat polycrystalline silver, and even outperforms the commercial nano-Pt catalyst. Detailed experimental and theoretical studies discover that both the facilitated mass transportation in the 3D interconnected porous structures and the favored kinetics contribute to the superior electro-catalytic activity of np-Ag.