Hartmut Wendt

Binary and ternary anode catalyst formulations including the elements W, Sn and Mo for PEMFCs operated on methanol or reformate gas

In an exploratory approach to find improved electrocatalyst formulations binary and ternary carbon supported catalysts with the elements Pt and Ru, W, Mo or Sn, respectively, amending the choice of Pt and Pt/Ru catalysts by addition of non-Pt metal cocatalysts were manufactured by impregnation and a colloid method and tested towards their activity for anodic oxidation of H 2 containing 150 ppm CO and of methanol. Membrane-electrode-assemblies with noble metal loadings of 0.4 mg cm -2 were manufactured and tested in fuel cell operation at 75°C with H 2 fuel contaminated by CO and at 95°C for operation on methanol. Cocatalytic activities were found for the elements W and Mo for oxidation of H 2 /CO and methanol while in the case of Sn a cocatalytic activity was only found for H 2 /CO-oxidation. Both for oxidation of methanol and H 2 /CO the system Pt/Ru/W was superior to the other systems tested. The colloid method was found to be highly suitable for synthesizing polymetallic PEM catalysts.

Porosity and catalyst utilization of thin layer cathodes in air operated PEM-fuel cells

Better performance of and higher electrocatalyst utilization in proton-exchange membrane fuel cells equipped with thin film electrodes is achieved by exploiting pore forming additives in the electrode recipe formulation. Preparing the membrane–electrode assembly by a hot spraying procedure already provides 35% porosity. Additional coarse porosity is obtained by adding pore formers to the electrocatalyst slurry which is used for the hot spraying process. This allows for a better access of oxygen from air to the depth of the cathode. For air operation at ambient pressure and low catalyst loading of 0.15mgPtcm-2 a current density of 200mAcm-2 at 0.7V cell voltage can be obtained with such electrodes.

Tecnologia de células a combustível

The fuel cell principle was discovered by Sir Grove 150 years ago. However material problems prohibited its commercialization for a long time. A change has been occurring during the last 30 years, so two types of fuel cell technologies can be distinguished: low and high temperature operation cells. Nowadays, only phosphoric acid cells are commercially offered as 200 kWel power plants. Membrane cells are more suitable for automobile electrotraction with a very low (or no) environmental impact. The fuel continues, however, to play a very particular role, since hydrogen is not easy to store and to transport. The more promising target is the utilization of liquid methanol. The Brazilian scenario concerning this kind of technology is discussed.

Nine years of research and development on advanced water electrolysis. A review of the research programme of the Commission of the European Communities

AbstractThe development of advanced water electrolysis was one of the main tasks of the R & D programme on hydrogen funded, within its main R & D programme on Energy, by the Commission of the European Communities. Most of the work has been concentrated on the development of alkaline water electrolysis, as this process appears particularly promising. (Water electrolysis based on ‘acidic’ solid polymer electrolytes, developed during the last 10 years, seems to be a potentially attractive alternative technology, at least for electrolysers of smaller scale (up to 100kW). Even at this size, however, there is not yet evidence of any overall economic advantage over advanced alkaline cells.)The results of 9 years of R & D in this field are critically examined, by reviewing the improvements achieved on the components of the electrolytic cell as well as the overall modification of the cell design. The anode, cathode and diaphragm have been the components investigated, but also the constituent materials, the nature of the electrolyte and its operating conditions have been dealt with. Three main lines of advanced electrolyser development were identified in the course of these investigations. The corresponding charcteristics are:(i)low temperature (70°C to 90°C), low current density (i=0.1–0.3 A cm−2);(ii)moderate temperature (<120°C), high current density (i up to 1 A cm−2), medium pressure (5–10 bars);(iii)medium temperature (120–160°C), high current density (i=1–2 A cm−2), moderately high pressure (30 bars). In cell design, very compact cell units have been devised, in which a ‘zero gap’ configuration (anode and cathode are placed directly on the diaphragm) is generally adopted, resulting in very low internal cell resistance (about 0.2 Ω cm2). Potential energy savings of 20 to 30% can be anticipated for the advanced electrolysis.In addition to this work on advanced alkaline water electrolysis, some limited research efforts on high temperature (>1100 K) water vapour electrolysis have been made and are reported. The latter work has been concentrated on the production of thin-layer doped zirconia solid electrolytes (d=50μm), potentially leading to high performance cells. The economic implications of high-temperature vapour electrolysis, however, cannot be judged at the present status of development.

The partition of amines between water and an organic solvent phase

Abstract The partition of a series of protonated amines (aniline, benzylamine, 2-phenylethylamine and related compounds) between water and nitrobenzene was investigated using electrochemical approaches (cyclic voltammetry and differential pulse stripping voltammetry) which made it possible to infer the transport and thermodynamic parameters of the partition process. Micromolar concentrations of the protonated amines in the aqueous phase can be determined by DPSV at the electrolyte hanging drop electrode. The function of an amine as the proton acceptor in the facilitated proton transfer across the water/organic solvent phase was discussed.

Electrocatalytic and thermal activation of anodic oxygen- and cathodic hydrogen-evolution in alkaline water electrolysis

Abstract In micro-electrolysis cells (4 cm 2 electrode area) which possess a sandwich-configuration as used in advanced water electrolysis[1] different anodic and cathodic electrocatalysts, which did not contain noble metals were investigated over the current density range from 10 −4 to 1.0 A cm −2 and a temperature range from 30 to 130°C (electrolyte: 50 wt% caustic potash). Mechanically activated nickel electrodes, RuO 2 doped anodes and Pt-black covered cathodes served as comparison standards for H 2 and O 2 evolution. IR -drop connections were not applied. Nonetheless the measuring-method used allowed to keep IR -induced mistakes in voltage-reading in single-electrode voltages below 40 mV even at the highest current densities of 1.0 A cm −2 . Plots of voltage vs log current densities for anodic oxygen evolution possess slopes between 40 and 70 mV (100°C) dec −1 of current density which in some cases—especially at low temperatures—increased up to a value of 2 RT/F at higher current densities. By increasing the temperature these steeper parts of the anodic current—voltage curves very often disappear. The current-voltage curves of anodic oxygen evolution for different temperatures unexpectedly run nearly parallel to each other ie with a slope which is nearly independent of temperature and thus cannot be described according to the Butler—Volmer equation with a constant value of the formal charge-transfer coefficient β i . The effective activation energies obtained from dln i o /d(1/ T ) range from 70 to 100 kJ mole −1 . O 2 overpotentials at current densities around 1 A cm −2 are most efficiently decreased by (i) application of mixed oxides containing cobalt in at least two different valency states (Co II /Co III or Co III /Co IV ) and (ii) by use of higher working temperatures; roughened surfaces, however, are only of limited value in this respect. Voltage vs log current curves for cathodic hydrogen evolution show a pattern which is in agreement with the Butler—Volmer equation. The effective charge-transfer coefficient is close to 0.5 and increases slightly above this value for Raney-metal activated cathodes. The effective activation energies lie between the limits of 40 and 55 kJ mol −1 . Hydrogen evolution overpotentials are most efficiently decreased by (i) preparation of cathode surfaces with high roughness factors, (ii) using Ni, Co or Fe as cathode material and (iii) by increasing the working temperatures.

Fundamentals of electrosorption on activated carbon for wastewater treatment of industrial effluents

The potential of electroadsorption/desorption on activated carbon for waste water treatment of industrial effluents is studied. Adsorption isotherms of hydrophobic differently charged model substances on activated carbon were measured in order to obtain specific information about the influence of the charge (+1,−1 and 0) on the adsorbability of comparable, aromatic species and the influence of the bed potential on the adsorption equilibria. In all these cases the adsorption equilibria show a dependence on applied potential in electrolyte of approximately 1m ionic strength. With electrosorption from aqueous solution, a fivefold enhancement of the concentration in one potential controlled adsorption/desorption cycle is achievable. The use of the solvent methanol instead of water for desorption allows for a concentration enhancement by a factor of hundred in the desorptive step. The adsorption capacity of the activated carbon changes only slightly with cycle number. Two cell designs for the performance of potential controlled adsorption/desorption cycles on the large scale are discussed.

The 100 MW euro-Quebec hydro-hydrogen pilot project

Abstract The concept of a hydrogen-based, clean, renewable energy system, conceived by the Joint Research Centre-Ispra of the Commission of the European Communities, is currently investigated by European industries and the JRC-Ispra. The scope of the investigation is to establish the main characteristics of system and components and to give a first indication of costs. The 100 pilot project is to demonstrate the provision of clean and renewable primary energy in the form of Canadian hydropower converted via electrolysis into hydrogen and shipped to Europe, where it is stored and used in different ways: electricity/heat cogeneration, vehicle and aviation propulsion and hydrogen enrichment of natural gas for use in industry and households. Three transport/storage modes are investigated: methylcyclohexane as energy carrier shipped in normal oil product carriers, ammonia shipped in special tankers and liquid hydrogen shipped in special LH2 ships and aeroplanes. First evaluations indicate costs of the electrolytic hydrogen, produced with hydropower at 2 Can, cents kWh−1, stored in a European port of 69 Dpfg Nm−3 for the methylcyclohexane mode, 57 Dpfg Nm−3 for the ammonia mode, 30 Dpfg Nm−3 for the LH2 mode by ship transportation and 77/68 Dpfg Nm−3 by air transportation. These averaged equivalent costs of 20 Dpfg kWh−1 (th) of clean, renewable and stored energy suggest competitivity within the not too distant future.

Composite electrocatalysts for anodic methanol and methanol-reformate oxidation

Binary anode electrocatalyst formulations were prepared by adsorption of phthalocyanine and tetraphenylporphyrin complexes of different transition metals on a commercial carbon supported platinum catalyst. Only after pyrolyzing the complexes at 700 °C under nitrogen were catalysts of some activity obtained. A binary Pt/Ni electrocatalyst prepared by this procedure exhibits considerable anodic catalytic activity in the acidic environment of the Nafion® electrolyte for reformate and direct methanol oxidation for more than 400 h without deterioration. Ternary electrocatalyst formulations Pt/Ru/W = 1/1/y were produced according to the Bönnemann method. The Pt/Ru/W catalyst of 1/1/1.5 (mol/mol/mol) composition is optimal. Compared to the Pt/Ru catalyst, it enhances the performance of reformate (H2 + 150 ppm CO) fuel cells by 50% and of direct methanol fuel cells (steam/methanol vapour = 50:1 mol/mol) by 80%. Attached to a GC electrode by a thin Nafion® film, the catalysts were also tested for methanol oxidation in aqueous methanol solutions in half cells by slow potential stepping. This procedure is useful for fast initial screening.

Electrocatalysis and electrocatalysts for low temperature fuel cells: fundamentals, state of the art, research and development

This article deals with electrocatalysis and electrocatalysts for low temperature fuel cells and also with established means and methods in electrocatalyst research, development and characterization. The intention is to inform about the fundamentals, state of the art, research and development of noble metal electrocatalysts for fuel cells operating at low temperatures.