Teknik Elektrokimia 15/16 Semester genap Instructor: Rama Oktavian Office Hr.: T , Th ; 13-15, F ; 13-15

Teknik elektrokimia Fuel cell

Teknik elektrokimia Fuel cell

Teknik elektrokimia Fuel cell Carbon Dioxide Emissions Why is CO 2 a problem? All of the fossil fuels that we are burning lead directly to carbon dioxide. Most of this carbon dioxide is being poured directly into the atmosphere, where it adds to the existing CO 2 levels. The CO 2 concentrations in the earth’s atmosphere have already risen by over 25% in the past century. CO 2 is a greenhouse gas. Increasing its concentration in the earth’s atmosphere leads to a warming of the earth. The effect is already being observed, in higher air temperatures, receding glaciers, increase in wildfires, rising sea levels…

Teknik elektrokimia Fuel cell

Teknik elektrokimia Fuel cell

Teknik elektrokimia Fuel cell Transportable energy In addition to solutions like solar cells, or wind turbines, we need a way to store energy, and to move it around with us. We need portability for many applications (e.g. driving a car) We also need energy on demand (so we can have it even in the dark). That’s why fuels are so desirable—they are a transportable, storable form of energy. One way to store energy is in the form of hydrogen. Remember that hydrogen is considered the cleanest of the “clean” fuels because when it reacts with oxygen, the only product formed is water.

Teknik elektrokimia Fuel cell Getting electrical energy from chemical energy We could just put hydrogen and oxygen together in a reactor, effectively burning the hydrogen, to get energy out. A more efficient way of doing this is to use a fuel cell. A fuel cell directly converts chemical energy (that from reacting H 2 with O 2 ) into electrical energy. It does this by only letting the oxygen contact the hydrogen in a very controlled fashion. Let’s delve further into fuel cells

Teknik elektrokimia Fuel cell general principle  Fuel cells convert chemical energy to electric energy and heat  Combination of internal combustion engine and battery  More efficient than combustion, due to higher energy grade

Teknik elektrokimia Fuel cell

Teknik elektrokimia Fuel cell

Teknik elektrokimia Fuel cell

Teknik elektrokimia Fuel cell

Teknik elektrokimia Fuel cell

Teknik elektrokimia Fuel cell Types of fuel cells: Proton exchange membrane (PEMFC) Direct Methanol fuel cell (DMFC) Alkaline fuel cell (AFC) Phosphoric acid fuel cell (PAFC) (*) Molten-carbonate fuel cell (MCFC) (*) Solid-oxide fuel cell (SOFC) (*) (*) Suitable for microgrids.

Teknik elektrokimia Fuel cell

Teknik elektrokimia Phosporic acid Fuel cell First commercial fuel cell type Liquid H 3 PO 4 electrolyte in SiC matrix Operated at o C; expelled water used as steam for space and water heating Used for stationary applications with a combined heat and power efficiency of about 80%; electrical power efficiency alone is ~40% PAFC’s dominate the on-site stationary fuel cell market; 200 kW and 300 kW plants

Teknik elektrokimia Phosporic acid Fuel cell

Teknik elektrokimia Solid oxide Fuel cell O2O2 Anode Porous nickel/YSZ cermet Cathode Porous mixed- conducting oxide Solid ceramic electrolyte YSZ H 2 +O 2-  H 2 O + 2e - H2H2 ½ O 2 + 2e -  O 2- O 2- e-e- Advantages Solid electrolyte Doesn’t need humidification Fuel flexibility (H 2 and simple hydrocarbon) Non-precious metal catalyst (at high T, perovskites are used as catalyst ) Relatively high power density

Teknik elektrokimia Solid oxide Fuel cell

Teknik elektrokimia Molten carbonate Fuel cell

Teknik elektrokimia Polymer electrolyte membrane (PEM) Fuel cell

Teknik elektrokimia Fuel cell general principle Example: PEMFC The hydrogen atom’s electron and proton are separated at the anode. Only the protons can go through the membrane (thus, the name proton exchange membrane fuel cell).

Teknik elektrokimia Fuel cell general principle

Teknik elektrokimia Where does H 2 come from?  H 2 from natural gas  Shift to electrolysis  Fossil fuels 85% of current world energy, IEA  Must invest in renewable energy sources Hydrogen needs to be produced, and sometimes it also needs to be transported and/or stored. Hydrogen is not a renewable source of energy. Hence, FC are alternative sources of energy.

Teknik elektrokimia Hydrogen production

Teknik elektrokimia Hydrogen production

Teknik elektrokimia Hydrogen storage

Teknik elektrokimia Problems with fuel cell  The fuel cell uses oxygen and hydrogen to produce electricity.  The oxygen required for a fuel cell comes from the air.  In fact, in the PEM fuel cell, ordinary air is pumped into the cathode.  The hydrogen is not so readily available, however.  Hydrogen has some limitations that make it impractical for use in most applications.

Teknik elektrokimia Problems with fuel cell  For instance, you don't have a hydrogen pipeline coming to your house, and you can't pull up to a hydrogen pump at your local gas station.  Hydrogen is difficult to store and distribute, so it would be much more convenient if fuel cells could use fuels that are more readily available.  This problem is addressed by a device called a reformer.reformer  A reformer turns hydrocarbon or alcohol fuels into hydrogen, which is then fed to the fuel cell.