Manuela Bevilacqua

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.

A Biologically Inspired Organometallic Fuel Cell (OMFC) That Converts Renewable Alcohols into Energy and Chemicals

The simultaneous conversion of alcohols and sugars into energy and chemicals is a target of primary importance in sustainable chemistry. The realization of such a process provides renewable energy with no CO2 emission and, at the same time, leads to the production of industrially relevant feedstocks, such as aldehydes, ketones, and carboxylic acids, from biomasses. Two established types of fuel cells operating in alkaline media can convert the free energy of alcohols (RCH2OH) into electrical energy and the corresponding carboxylate product: the direct alcohol fuel cell (DAFC), and the enzymatic biofuel cell (EBFC). 8] In a DAFC, an alcohol such as ethanol (CH3CH2OH) is selectively converted into acetate (CH3COO ) and the electrolyte is an anionexchange membrane. On the anode, ethanol is oxidized, releasing four electrons [Eq. (1)] that are utilized to reduce one oxygen molecule to four hydroxide ions on the cathode [Eq. (2)]. Efficient devices of this type have been recently developed for a variety of renewable alcohols and polyalcohols, such as ethylene glycol, glycerol, 1,2-propandiol, and C6 and C5 sugars. [3–6] (For drawings of a DAFC, a EBFC, and typical power density curves, see the Supporting Information, Figure S1 a–d).

Self-Sustainable Production of Hydrogen, Chemicals, and Energy from Renewable Alcohols by Electrocatalysis

The selective and simultaneous production of hydrogen and chemicals from renewable alcohols, such as ethanol, glycerol, and ethylene glycol, can be accomplished by means of electrolyzers in which the anode electrocatalyst is appropriately designed to promote the partial and selective oxidation of the alcohol. In the electrolyzers described herein, the production of 1 kg of hydrogen from aqueous ethanol occurs with one-third the amount of energy required by a traditional H(2)/O(2) electrolyzer, by virtue of the much lower oxidation potential of ethanol to acetate vs. water to oxygen in alkaline media (E(0)=0.10 V vs. 1.23 V). The self-sustainability of H(2) production is ensured by the simultaneous production of 25 kg of potassium acetate for every kg of H(2), if the promoting co-electrolyte is KOH.

Electrochemical milling and faceting: Size reduction and catalytic activation of palladium nanoparticles

Improved performance through milling: A method for enhancing the catalytic activity of supported metal nanoparticles is reported. This method enhances the activity for the ethanol electro-oxidation of a supported palladium catalyst. The much higher catalytic performance is ascribed to the increased electrochemically active surface area as well as the generation of high-index facets at the milled nanoparticle surface.

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.

Improvement in the efficiency of an OrganoMetallic Fuel Cell by tuning the molecular architecture of the anode electrocatalyst and the nature of the carbon support

The electrooxidation of ethanol to acetate is achieved with Rh(I) diolefin amine complexes of the general formula [Rh(Y)(trop2NH)(L)] (L = PPh3, P(4-n-BuPh)3; Y = triflate, acetate; Bu = butyl) in direct alcohol fuel cells that have the peculiarity of containing a molecular anode electrocatalyst and, hence, are denoted as OrganoMetallic Fuel Cells (OMFCs). Changing the carbon black support from Vulcan XC-72 (Cv) to Ketjenblack EC 600JD (Ck) and/or the axial phosphane to produce non crystalline complexes has been found to remarkably change the electrochemical properties of the organorhodium catalysts, especially in terms of specific activity and durability. An in-depth study has shown that either Ck or P(4-n-butylPh)3 favour the formation of an amorphous Rh-acetato phase on the electrode, leading to a much more efficient and recyclable catalyst as compared to a crystalline Rh-acetate complex which is formed on Cv with PPh3 as the ligand. The ameliorating effect of the amorphous phase has been ascribed to its higher number of surface complex molecules as compared to the crystalline phase. A specific activity as high as 10 000 A gRh−1 has been found in a half cell, which is the highest value ever reported for ethanol electrooxidation.

Energy and Chemicals from the Selective Electrooxidation of Renewable Diols by Organometallic Fuel Cells

Organometallic fuel cells catalyze the selective electrooxidation of renewable diols, simultaneously providing high power densities and chemicals of industrial importance. It is shown that the unique organometallic complex [Rh(OTf)(trop2NH)(PPh3)] employed as molecular active site in an anode of an OMFC selectively oxidizes a number of renewable diols, such as ethylene glycol , 1,2-propanediol (1,2-P), 1,3-propanediol (1,3-P), and 1,4-butanediol (1,4-B) to their corresponding mono-carboxylates. The electrochemical performance of this molecular catalyst is discussed, with the aim to achieve cogeneration of electricity and valuable chemicals in a highly selective electrooxidation from diol precursors.

Nanostructured Fe–Ag electrocatalysts for the oxygen reduction reaction in alkaline media

The impregnation of Ketjen Black (C) with iron(II) and silver(II) phthalocyanines (MPc) individually or as a 1 : 1 stoichiometric mixture, followed by heat treatment at 600 °C under inert atmosphere, gave a series of novel nanostructured electrocatalysts AgPc/C(600), FePc/C(600) and FeAgPc/C(600) (ca. 3 wt% metal loadings) for the oxygen reduction reaction (ORR) in alkaline media. The catalysts were structurally characterized by XRPD, XPS, HR-TEM/STEM and chemisorption measurements. During the synthetic heat treatment of AgPc/C(600) at temperatures above 250 °C, the AgPc decomposed to form small finely dispersed carbon supported Ag nanoparticles (mean diameter 8.5 nm). This process was delayed for FeAgPc/C(600) to above 300 °C and the resulting Ag nanoparticles were much smaller (mean diameter 2.3 nm). As expected, at 600 °C the FePc/C(600) forms highly dispersed arrays of single Fe ions coordinated by four nitrogen atoms (Fe–N4 units). Electrodes coated with AgPc/C(600), FePc/C(600) and FeAgPc/C(600) were investigated for ORR in alkaline media by linear sweep voltammetry and the RRDE system was used to probe the production of HO2−. The electrochemical activity of all materials was analyzed by Tafel and Koutecky–Levich plots and the stability of each catalyst was followed using chronopotentiometry. Both Fe-containing electrocatalysts, FeAgPc/C(600) and FePc/C(600), were highly active for the ORR promoting exclusively the four electron pathway also during chronopotentiometry, while AgPc/C(600) was found to produce up to 35 mol% HO2−. Compared to FePc/C(600), the binary FeAgPc/C(600) catalyst displayed remarkably higher activity and stability. This experimental evidence could be explained in terms of a synergistic Ag–Fe interaction which results from the unique nanostructure that forms during heat treatment which consists of very finely dispersed Ag nanoparticles and Fe–N4 moieties.