Knowledge about the techniques for producing electricity using hydrogen is making headway all over the world. In Brazil, the latest result in this area happened at the Institute of Nuclear Energy and Research (Ipen), where a group of researchers has succeeded in assembling a prototype of a new kind of fuel cell in the country. They produced a conductor of electricity called an electrolyte – a fundamental part for equipment that transforms hydrogen and oxygen into electricity – using a ceramic material made up of zirconium oxide and yttrium oxide, two raw materials found in abundance in Brazilian mineral deposits. Zirconium oxide is extracted from a mineral called baddeleyite, and yttrium from monazite sand. The two purified materials are produced at Ipen itself.
Ceramics are one alternative to the kind of cell most disseminated nowadays, which is made up of electrolytes made of polymer and called PEM (which stands for Proton Exchange Membrane), also already developed at Ipen and produced in an experimentally by two Brazilian companies, Electrocell and UniTech (please see Pesquisa FAPESP Nos. 92 and 103). “The polymer electrodes have to be imported, while the one we use can by synthesized completely in Brazil”, says physicist Reginaldo Muccillo, the coordinator of the research at Ipen. He and his group are part of the Multidisciplinary Center for the Development of Ceramic Materials (CMDMC), one of FAPESP’s Research, Innovation and Diffusion Centers, which has the coordination of Professor Elson Longo, from the Federal University of São Carlos (UFSCar).
Called solid oxide fuel cells (or SOFCs, for short), they are differentiated from the PEM cells mainly in the way they operate. The PEMs work at temperatures of around 100°C, while the ceramic ones, which is Ipen’s case, work at from 800 to 1,000°C. This characteristic rules out the possibility of supplying energy for driving automobiles and other kinds of vehicle, a function that the automobile industry reserves for PEM cells. But the high temperatures provide the solid oxide cells with the capacity for cogenerating electricity and heat to drive industrial turbines and heating systems, and to heat, for example, industrial boilers and domestic boilers that take hot water to the shower and to the faucets. Besides this attribute, the electricity generated fulfills the normal functions of a fuel cell, such as making electronic apparatuses work and lighting up lamp bulbs.
The solid oxide cells can be constructed for high powers, in the order of megawatts, which includes adjusting the mismatch caused at peak times for the demand for electricity, preventing the brusque variation that occurs mainly at the end of the afternoon, when usage is greater. The automobile industry itself is studying the use of this kind of cell to take the place of batteries and to supply electricity for air-conditioning equipment. “Fuel cells work like a battery, but the difference is that the cells do not stop working as long as there is a supply of fuel”, Muccillo explains.
“We managed to get the cell to function on the twenty-second attempt. The researchers who were testing the equipment were euphoric”, Mucillo recalls. The work was carried out between November 2004 and March 2005, although the researcher has been working in the area of electroceramics for sensors and fuel cells since 1992. The research that resulted in the ceramic composition for the fuel cell began with a thematic project of FAPESP and with financing from the Research, Innovation and Diffusion Centers (Cepids), besides recent projects from the sectorial funds for energy (CTEnerg) and petroleum (CTPetro).
“The thematic project served for us to make headway in basic knowledge about the intergranular phenomena of ceramics, and Cepid brought us the perspective of innovation. In the end, we succeeded in producing a material equal or superior to those used in solid oxide cells abroad”, says Muccillo. They prepared all the components at Ipen itself, in presses and furnaces that work at a high temperature, and they analyzed the microstructure and the electrical behavior of the materials. They also produced two essential parts that are similar to the plates that act as positive and negative sides in primary (such as in radio)and storage batteries ( such as in cars). These plates, which are given the names of anode and cathode and are also produced with ceramics, form a sandwich with the electrolyte in the middle. In solid oxide cells, this construction is round, and not rectangular, as in the PEMs.
For the electrochemical tests that determine the power of the new cell, Muccillo invited researchers from the Materials Department of the Technology for Development Institute (Lactec), from Paraná, a group that is also in a partner in projects of the CTEnerg and CTPetro. They measured the power of the cell and concluded that it has 20 milliwatts. This value is that of a single cell, and it can be increased many times with modifications to the project, which are now under way. To arrive at the need for 5 kilowatts from a middle class house, various other equal devices will have to be made and joined together, in such a way that they reach this power level. “The next stages are going to serve towards improving the assembly of the cells and to master the technology for its manufacture”, Muccillo says.
Evolution of the materials
This kind of equipment had already been designed and assembled in the United States 30 years ago. “The problem is that it was very expensive and did not get so far as to be marketed.” Recently, with the evolution of the materials, the German company Siemens started to think again about solid oxide fuel cells, along with research centers in the world. One example of the growth of interest in research and development of this equipment was demonstrated at the 9th International Symposium on SOFC, held between May 15 and 20 in Quebec, in Canada. About 400 people took part in a hundred talks and in the presentation of hundreds of works by researchers from companies, universities and research centers, under the sponsorship of the Electrochemical Society, of the United States, and of the SOFC Society of Japan. Muccillo and his group from Ipen’s Materials Science and Technology Center (CCTM) were present, presenting projects carried out at the institute, besides another work in partnership with researchers from the University of Rome, in Italy, who developed a chemical technique for synthesizing ceramic materials for a SOFC cathode. “They develop the components and send them for us to test here. But we are not using this material in Ipen’s cell yet.”
Path of the oxygen
One of the advantages of the new ceramic electrolyte developed by the researchers from Ipen is its capacity for supporting high temperatures for a long time, without losing its properties. It is a material that needs to have a direct interaction with the oxygen (O2) applied onto it, because it is on the surface of this ceramic that the molecule of the gas is broken up. “The zirconium oxide lets the ion (O2-) pass through, but prevents the totality of the gas from passing.” The electrons, with a negative charge, existing in the cathode, generate electricity together with the electrons of the hydrogen injected and broken on the anode side. The protons (H+), with a positive charge, that are left over in the anode, receive the ions of the oxygen that goes through the electrolyte, to form water (H2O). Water is produced because the ions from the oxygen, when they pass through the ceramic conductor, in the inside of the cell, find the hydrogen on the other side. The path that leads to these reactions happens inversely in the PEM cells. In the case of the polymeric membrane, it is the hydrogen protons that pass through the membrane to the other side in the encounter with oxygen and consequent formation of water.
The solid oxide cell, in the same way as other kinds, can also take the hydrogen from other fuels like methanol and natural gas, in a process called reform. Usually, hydrogen is obtained by water hydrolysis, a process that is still expensive. “Reform is one of our worries. We want to use a reformer of ethanol (the alcohol that in Brazil is extracted from sugarcane). The high temperature facilitates the use of this process, which can be activated by the very heat generated in the cell.”
The researchers from Ipen have not patented the solid oxide cell. “These materials that we use to synthesize the ceramic are available in the market. What we are interested in is to acquire competence in developing this kind of cell.” The synthesis of the ceramics has now yielded three doctoral theses, five master’s dissertations and over 20 works published in scientific magazines in the last few years. “Our objective now is to make this cell competitive and more powerful, to improve development in the laboratory. If Brazilian industry wants to develop our cell, it’s not going to have to pay royalties abroad not to import electrolytes.”
1. Study of intergranular phenomena in ceramic oxides (nº 99/10798-0); Modality Thematic Project; Coordinator Reginaldo Muccillo – Ipen; Investment R$ 328,610.97 and US$ 217,952.29 (FAPESP)
2. Ceramics for Sofc fuel cells; Modality Research, Innovation and Diffusion Centers (Cepid); Coordinator Elson Longo – Multidisciplinary Center for the Development of Ceramic Materials; Investment R$ 1,200,000.00 a year for the whole Cepid