| Summary: |
In 2005, the chemist Nobel Prize George Olah co-authored the book "Beyond oil and gas: the methanol economy" ; this author claims that, due to the challenges of transport and storage of hydrogen, methanol is a much better energy vector of the future. In this line, Palo et al. reported a sudden growth in the number of scientific publications concerning methanol steam reforming (SR) since 2000, while the research publications concerning ethanol reforming jumped in the year 2004. Nowadays, new catalysts for methanol SR working at lower temperatures and with higher activities are being proposed. Additionally, integration of SR with membrane reactors has been pointed out as favoring the methanol conversion and as a mean for purifying the hydrogen stream. Palladium based membranes are traditionally used, but they are fragile and expansive.
The present project concerns integrating methanol SR with hydrogen fuel cells in a single compact unit, taking advantage of a newly developed palladium membrane by one of the proponents. This new membrane uses only 10 % of palladium of the conventional membranes and it is more stable and more permeable. The new membrane is formed inside a nanoporous ceramic support, around 2µm beneath its surface, and is less than 3 µm thick. Traditionally, 50- µm foil palladium/silver membranes are employed when dealing with methanol SR .
In the foreseen system, hydrogen produced by methanol SR permeates selectively the palladium membrane. On the other side, H2 meets platinum nanoparticulated catalyst supported on the palladium membrane; in contact with the catalyst is the electrolyte - anode triple phase. Protons originated at the catalyst surface are collected through the electrolyte, e.g. phosphoric acid. Electrons are conducted to the outside through the palladium membrane. The ceramic membrane should be coated with a membrane electrolyte.
For high temperature hydrogen PEM (polymer electrolyte membrane) fuel cells it is norm  |
Summary
In 2005, the chemist Nobel Prize George Olah co-authored the book "Beyond oil and gas: the methanol economy" ; this author claims that, due to the challenges of transport and storage of hydrogen, methanol is a much better energy vector of the future. In this line, Palo et al. reported a sudden growth in the number of scientific publications concerning methanol steam reforming (SR) since 2000, while the research publications concerning ethanol reforming jumped in the year 2004. Nowadays, new catalysts for methanol SR working at lower temperatures and with higher activities are being proposed. Additionally, integration of SR with membrane reactors has been pointed out as favoring the methanol conversion and as a mean for purifying the hydrogen stream. Palladium based membranes are traditionally used, but they are fragile and expansive.
The present project concerns integrating methanol SR with hydrogen fuel cells in a single compact unit, taking advantage of a newly developed palladium membrane by one of the proponents. This new membrane uses only 10 % of palladium of the conventional membranes and it is more stable and more permeable. The new membrane is formed inside a nanoporous ceramic support, around 2µm beneath its surface, and is less than 3 µm thick. Traditionally, 50- µm foil palladium/silver membranes are employed when dealing with methanol SR .
In the foreseen system, hydrogen produced by methanol SR permeates selectively the palladium membrane. On the other side, H2 meets platinum nanoparticulated catalyst supported on the palladium membrane; in contact with the catalyst is the electrolyte - anode triple phase. Protons originated at the catalyst surface are collected through the electrolyte, e.g. phosphoric acid. Electrons are conducted to the outside through the palladium membrane. The ceramic membrane should be coated with a membrane electrolyte.
For high temperature hydrogen PEM (polymer electrolyte membrane) fuel cells it is normally used an electrolyte made of a very chemical and thermal stable polymer, PBI - polybenzimidazole, doped with phosphoric acid, which has been reported to be stable up to 230 °C. Such a phosphoric acid doped-PBI prevents the electrolyte to bleed from the ceramic membrane top layer and should support the cathode catalyst layer. At the cathode side, a conventional gas diffusion layer will be applied. This will drive electrons from the catalyst surface and distributes oxygen evenly over the membrane.
The present project goes beyond the state of the art mainly in the following aspects:
a) Use of a stable, low-Pd content and highly hydrogen permeable Pd-supported membrane.
b) Integration of a SR system with a fuel cell in a compact system. It is expected a higher energetic efficiency as a result of the synergy between the SR reaction (endothermic) and the fuel cell operation (exothermic).
c) Use of a very recently reported methanol SR catalyst, the La2CuO4. This nanostructured catalyst has a high activity even at temperatures as low as 150 °C and stays poorly studied.
Moreover, the proposed system can work at temperature as high as 500 °C, as long as the membrane electrolyte is stable. The literature reports proton conductive ceramic membranes operating between 200 and 400 °C. At these temperature ranges, other SR reactions are possible, namely using fuels with higher energy densities. For example, the ethanol SR occurs at temperatures as low as 350 °C.
The last and most striking innovative aspect of the present project is for the possibility to integrate the SR with a fuel cell in the same unit and operating with different fuels, namely with methanol and ethanol. |