Lianqin Wang

Nanotechnology makes biomass electrolysis more energy efficient than water electrolysis

The energetic convenience of electrolytic water splitting is limited by thermodynamics. Consequently, significant levels of hydrogen production can only be obtained with an electrical energy consumption exceeding 45 kWh kg(-1)H2. Electrochemical reforming allows the overcoming of such thermodynamic limitations by replacing oxygen evolution with the oxidation of biomass-derived alcohols. Here we show that the use of an original anode material consisting of palladium nanoparticles deposited on to a three-dimensional architecture of titania nanotubes allows electrical energy savings up to 26.5 kWh kg(-1)H2 as compared with proton electrolyte membrane water electrolysis. A net energy analysis shows that for bio-ethanol with energy return of the invested energy larger than 5.1 (for example, cellulose), the electrochemical reforming energy balance is advantageous over proton electrolyte membrane water electrolysis.

Electrooxidation of Ethylene Glycol and Glycerol on Pd-(Ni-Zn)/C Anodes in Direct Alcohol Fuel Cells

The electrooxidation of ethylene glycol (EG) and glycerol (G) has been studied: in alkaline media, in passive as well as active direct ethylene glycol fuel cells (DEGFCs), and in direct glycerol fuel cells (DGFCs) containing Pd-(Ni-Zn)/C as an anode electrocatalyst, that is, Pd nanoparticles supported on a Ni-Zn phase. For comparison, an anode electrocatalyst containing Pd nanoparticles (Pd/C) has been also investigated. The oxidation of EG and G has primarily been investigated in half cells. The results obtained have highlighted the excellent electrocatalytic activity of Pd-(Ni-Zn)/C in terms of peak current density, which is as high as 3300 A g(Pd)(-1) for EG and 2150 A g(Pd)(-1) for G. Membrane-electrode assemblies (MEA) have been fabricated using Pd-(Ni-Zn)/C anodes, proprietary Fe-Co/C cathodes, and Tokuyama A-201 anion-exchange membranes. The MEA performance has been evaluated in either passive or active cells fed with aqueous solutions of 5 wt % EG and 5 wt % G. In view of the peak-power densities obtained in the temperature range from 20 to 80 °C, at Pd loadings as low as 1 mg cm(-2) at the anode, these results show that Pd-(Ni-Zn)/C can be classified amongst the best performing electrocatalysts ever reported for EG and G oxidation.

Direct Alcohol Fuel Cells: Toward the Power Densities of Hydrogen‐Fed Proton Exchange Membrane Fuel Cells

A 2 μm thick layer of TiO2 nanotube arrays was prepared on the surface of the Ti fibers of a nonwoven web electrode. After it was doped with Pd nanoparticles (1.5 mgPd  cm(-2) ), this anode was employed in a direct alcohol fuel cell. Peak power densities of 210, 170, and 160 mW cm(-2) at 80 °C were produced if the cell was fed with 10 wt % aqueous solutions of ethanol, ethylene glycol, and glycerol, respectively, in 2 M aqueous KOH. The Pd loading of the anode was increased to 6 mg cm(-2) by combining four single electrodes to produce a maximum peak power density with ethanol at 80 °C of 335 mW cm(-2) . Such high power densities result from a combination of the open 3 D structure of the anode electrode and the high electrochemically active surface area of the Pd catalyst, which promote very fast kinetics for alcohol electro-oxidation. The peak power and current densities obtained with ethanol at 80 °C approach the output of H2 -fed proton exchange membrane fuel cells.

Energy Efficiency of Alkaline Direct Ethanol Fuel Cells Employing Nanostructured Palladium Electrocatalysts

Carbon supported nanostructured palladium or palladium alloys are considered the best performing anode electrocatalysts currently employed in alkaline electrolyte membrane direct ethanol fuel cells (AEM‐DEFCs). High initial peak power densities are generally obtained as Pd preferentially favors the selective oxidation of ethanol forming acetate thus avoiding strongly poisoning intermediates such as CO. However, few studies exist that investigate DEFC performance in terms of both energy efficiency and discharge energy density, as well as power density depending on the concentration of fuel. In this paper we have determined such parameters for room temperature air breathing AEM‐DEFCs equipped with Pd based anodes, anion exchange membranes and FeCo/C cathode electrocatalysts. Combined with the optimization of the fuel composition a maximum energy efficiency of ≈7 % was obtained for this AEM‐DEFC. Such a performance suggests that devices of this type are suitable for supplying low power applications such as small portable electronic devices.

Dechlorination of Monochlorobenzene Using Organic Mediators

In the presence of an organic mediator such as dibenzofuran, the reduction of chlorobenzene occurs indirectly and at substantially less negative potentials compared to its direct reduction at a glassy carbon cathode in acetonitrile. By using the indirect, mediator approach to reduction of chlorobenzene, constant current electrolysis at carbon plate cathodes can give complete dechlorination with high current efficiency. Both divided and undivided cells were used, each having their own advantages. Besides dibenzofuran, naphthalene and biphenyl were successfully tested as organic mediators for chlorobenzene reduction. During the entire electrolysis, the mediator concentration remained practically constant so that substantially less mediator was required in comparison to the substrate, i.e., chlorobenzene. Higher concentrations of mediator can be beneficial, e.g., a dibenzofuran:chlorobenzene ratio of 2:5:5 as compared to 1:5, if the electrolysis is to be conducted at higher current density. For electrolysis of large amounts of chlorobenzene, an approach where the substrate is added periodically to a solution of the (reduced) mediator is recommended. A comparison of the results from direct vs. indirect dechlorination of chlorobenzene clearly demonstrates the substantial superiority of the latter approach.