Environmentally Friendly Recycling of Fuel-Cell Membrane Electrode Assemblies by Using Ionic Liquids.

The platinum nanoparticles used as the catalyst in proton exchange membrane fuel cells (PEMFCs) represent approximately 46 % of the total price of the cells for a large-scale production, and this is one of the barriers to their commercialization. Therefore, the recycling of the platinum catalyst could be the best alternative to limit the production costs of PEMFCs. The usual recovery routes for spent catalysts containing platinum are pyro-hydrometallurgical processes in which a calcination step is followed by aqua regia treatment, and these processes generate fumes and NOx emissions, respectively. The electrochemical recovery route proposed here is more environmentally friendly, performed under "soft" temperature conditions, and does not result in any gas emissions. It consists of the coupling of the electrochemical leaching of platinum in chloride-based ionic liquids (ILs), followed by its electrodeposition. The leaching of platinum was studied in pure ILs and in ionic-liquid melts at different temperatures and with different chloride contents. Through the modulation of the composition of the ionic-liquid melts, it is possible to leach and electrodeposit the platinum from fuel-cell electrodes in a single-cell process under an inert or ambient atmosphere.

Dismantling and chemical characterization of spent Peltier thermoelectric devices for antimony, bismuth and tellurium recovery.

Major uses of thermoelectricity concern refrigeration purposes, using Peltier devices, mainly composed of antimony, bismuth and tellurium. Antimony was identified as a critical raw material by EU and resources of bismuth and tellurium are not inexhaustible, so it is necessary to imagine the recycling of thermoelectric devices. That for, a complete characterization is needed, which is the aim of this work. Peltier devices were manually dismantled in three parts: the thermoelectric legs, the alumina plates on which remain the electrical contacts and the silicone paste used to connect the plates. The characterization was performed using five Peltier devices. It includes mass balances of the components, X-ray diffraction analysis of the thermoelectric legs and elemental analysis of each part of the device. It appears that alumina represents 45% of a Peltier device in weight. The electrical contacts are mainly composed of copper and tin, and the thermoelectric legs of bismuth, tellurium and antimony. Thermoelectric legs appear to be Se-doped Bi2Te3 and (Bi0,5Sb1,5)Te3 for n type and p type semiconductors, respectively. This work shows that Peltier devices can be considered as a copper ore and that thermoelectric legs contain high amounts of bismuth, tellurium and antimony compared to their traditional resources.

Economic bismuth-film microsensor for anodic stripping analysis of trace heavy metals using differential pulse voltammetry.

Stripping analysis has been widely recognised as a powerful tool in trace metal analysis. Its remarkable sensitivity is attributed to the combination of a preconcentration step coupled with pulse measurements that generate an extremely high signal-to-background ratio. Mercury-based electrodes have traditionally been used to achieve high reproducibility and sensitivity in the stripping technique. Because of the toxicity of mercury, however, new alternative electrode materials are highly desired, particularly for on-site monitoring. Use of thin films of bismuth deposited on platinum or glassy-carbon substrates has recently been proposed as a possible alternative to mercury--bismuth is "environmentally friendly", of low toxicity, and is in widespread pharmaceutical use. In this paper the preparation of economic bismuth-film microelectrodes by electrodeposition on a copper substrate and their application to heavy metal analysis are described. Bismuth-film electrodes were prepared by potentiostatic electrodeposition. Optimum conditions for chemical and electrochemical deposition to obtain an adherent, reproducible, and robust deposit were determined. The suitability of such microelectrodes for analysis of heavy metals was evaluated by anodic stripping voltammetry of cadmium. The analytical performance of bismuth-film electrodes for anodic stripping voltammetry of heavy metals was evaluated for non-deaerated solutions containing Cd2+, Pb2+, and Zn2+ ions. Well-defined peaks with low background current were obtained by use of differential pulse voltammetry. Linear calibration plots were obtained for Cd2+ in acidified tap water at concentrations ranging from 2 x 10(-8) to 1 x 10(-7) mol L(-1) and from 1 x 10(-7) to 1 x 10(-6) mol L(-1) with relative standard deviations of 5% (n = 15) at the 1 x 10(-7) mol L(-1) level. The method was then successfully used to monitor the Cd2+ content of plant extracts and validated by polarographic and ICP-MS measurements. These results open the possibility of using bismuth-coated copper electrodes as an alternative to mercury-based electrodes for analysis of heavy metals. The main problem remaining, which prevents on-site monitoring of heavy metals, is the need to use slightly acidic media, because formation of bismuth hydroxide on the film surface above pH 4.3 leads to non-reproducible measurements. Further experiments will be performed to discover whether electrode conditioning can be used to enable reproducible measurement in on-site monitoring of cadmium in natural waters. Moreover, further study should be conducted to evaluate the potential of BiFE for analysis of several pollutants of interest that are usually determined electrochemically by using mercury-based electrodes.