Converting chemical energy into electrical energy can be done in different ways, but for chemical energy stored in various fuels (alcohols, hydrogen, hydrocarbons) electrochemical (fuel) cells are the most direct, and have the potential to be very efficient.
The electrochemistry side of fuel cells is rather straightforward. Hydrogen, possibly with some carbon, on one side combines with oxygen on the other to produce water and possibly carbon dioxide. The half reactions are separated so that the energy difference between reagents and products can be harvested as electrical energy.
The industry is currently challenged by the need to design systems and materials that allow efficient electron transfer (catalysts) while being very long lived (e.g. avoiding CO poisoning). This materials development for fuel cells requires a great deal of electrochemical testing, from measuring device impedances to rotated ring disk electrode catalyst studies.
DC testing of fuel cells/materials includes RRDE work, cyclic voltammetry and polarization curves. RRDE is a common collector/generator setup used for catalyst testing. It requires a bipotentiostat and rotator. Cyclic voltammetry is a powerful physical/analytical electrochemical technique which is good for measuring and comparing the thermodynamics, kinetics, and mechanisms of various reactions. Polarization curves are frequently run on complete devices and are a standard test for fuel cell evaluation.
AC testing of fuel cells—i.e. electrochemical impedance spectroscopy (EIS)—has become more common as the technique has become more widely available. EIS generally gives much more information about the system than does a polarization curve, but it also requires a bit more expertise on the part of the researcher to implement and analyze successfully.
EIS can identify problems that limit a fuel cell’s efficiency, it can help optimize a cell, and it can determine anodic and cathodic process mechanisms. It is particularly good for measuring the equivalent series resistance (ESR) of fuel cells—ESR can be a major source of power loss in a low impedance device. Because of the modeling capability of EIS, you can also extract information on kinetics and mass transport in the fuel cell, both of which are crucial factors to fuel cell performance. EIS is useful in both research and QC applications. EIS of fuel cells runs into some of the same low impedance device and setup limitations that also show up in batteries and supercapacitors.