Instead of obtaining hydrogen to circulate through the cells, researchers want to make direct use of the natural gas in the devices, thereby saving one of the stages of the process and bringing costs down.
A group of researchers of the Research Center for Gas Innovation (RCGI) wants to develop a fuel cell that operates directly with natural gas. This device was originally created to work with hydrogen, the so-called “fuel of the future” (H2). However, hydrogen is not a source of energy that is readily available in nature. It needs to be separated from certain molecules, including natural gas itself or ethanol, for example, or also obtained using other processes, such as the electrolysis of water.
“The main problem with the economy of hydrogen is its availability. The cheapest way of obtaining hydrogen, these days, is from natural gas. Over 90% of all the hydrogen produced in the world these days comes from natural gas”, says physicist Fabio Coral Fonseca, a researcher at the Institute for Nuclear and Energy Research (IPEN) and the coordinator of the Advancing Fuel Cells for Operation on Natural Gas project of the RCGI. Mr. Fonseca and his team, apart from working on the improvement of two types of fuel cells so that they can operate on less “pure” (and cheaper) hydrogen, also have the goal of conceiving a device which operates directly on natural gas.
“The technological secrets lie in the fuel cell, which is a highly efficient energy converter. It manages to convert hydrogen into electricity by electrical and chemical means, without the need to pass through carbon cycles. In theory, its efficiency of conversion is 83% (while that of a combustion engine is typically between 20% and 30%). The electrochemical principle is quite simple and has been known for centuries: the reaction between hydrogen and oxygen, producing water and electricity. However, like any new technology, the fuel cell has to be improved”. Basically, according to Mr. Fonseca, there is a need to create devices which are cheaper and last longer.
Fuel Cells – The physicist and his team are working with two different types of fuel cells: the polymeric type (or the low-temperature kind) and the ceramic type (or high-temperature type). The polymeric cells are made of two electrodes – which are in fact metallic nanoparticles (normally platinum-based), anchored in carbon. Separating these electrodes, a transparent polymer often operates as an electrolyte, with the ability to transport hydrogen ions (H+) and to make the electrons circulate throughout the external circuit, thereby generating electricity. The polymeric cells operate at a maximum temperature of 80º C.
In the case of ceramic cells, the electrolyte is zirconium dioxide (ZrO2) stabilized with yttrium sesquioxide (Y2O3). The set is like that of the polymeric cell: electrodes (anode and cathode) deposited in separate layers by the electrolyte. The ceramic cell can operate at temperatures of up to one thousand degrees Celsius. “Working at a high temperature, the reactions occur quicker, and there is no need to use precious metals such as platinum to form the electrode. On the other hand, there are also undesirable reactions; for this reason there are also durability problems”. The ceramic cells, different from the polymeric variety, tolerate the presence of carbon monoxide (CO), but can form carbon deposits on the anode, meaning that there is a decline in the usable life of the device.
To generate current and power, the fuel cells – both polymeric and ceramic – have to be piled up within a compartment where there is circulation of hydrogen on one side and of oxygen on the other. Enhancing the cells, the IPEN group wants to obtain devices that operate directly with natural gas. “We are currently studying and testing new materials and new strategies, so that we may use natural gas directly onto this cell, without the formation of carbon deposits.”
In his opinion, in Brazil there is no technology to operate a fuel cell based on natural gas. “We have never operated a cell with natural gas, and the RCGI will be very important for us in this regard. It is a very courageous move on our part to try to create electrocatalysts to make oxidation direct from methane, but for this purpose, we would need materials that no-one in the world has.”
In the case of ceramic cells, the team operates small fuel cells, as a way to test materials and concepts. The devices that would be used “in real life” are more than ten times the size of the cell prepared by Mr. Fonseca and his team for studies. “I believe that five years from now we will have managed to make this small cell operate directly on natural gas, with the most suitable materials for this end. Now, moving from a small cell to a large one is a major technological leap and requires a much larger volume of investment”.