II.1 Project Results: Hydrogen 48 GCEP Technical Report - 2004 II.1.3 Micro and Nano Scale Electrochemistry: Application to Fuel Cells Investigators Fritz B. Prinz, Professor, Mechanical Engineering, Materials Science and Engineering; Ryan O’Hayre, Minhwan Lee, Graduate Researchers Introduction Fuel cells offer the tantalizing promise of cleaner electricity with less impact on the environment than traditional energy conversion technologies. This is because fuel cells are direct electrochemical energy conversion devices. In other words, they convert chemical energy, in the form of a fuel and oxidant, directly into electrical energy. Contrast this to combustion engines, which first convert chemical energy into heat, heat into mechanical energy, and finally mechanical energy into electricity. Widespread fuel cell viability will not occur without further technological breakthroughs. The emerging domain of nanoscience and technology may provide solutions. As identified in a U.S. Government report[1] on basic research needs for the hydrogen economy, nanoscience introduces powerful and virtually untapped new dimensions to fuel cell research. Why should nanoscience be so beneficial to fuel cells? The answer comes from a deeper understanding of the fundamental principles involved in the electrochemical generation of electricity. Fuel cells produce electricity by converting a primary energy source (a fuel) into a flow of electrons. This conversion necessarily involves some sort of energy transfer step, where the energy from the source is passed along to the electrons constituting the electric current. This transfer has some finite rate and must occur at an interface or reaction surface. Thus, the amount of electricity produced scales with the amount of reaction surface area or interfacial area available for the energy transfer. Larger surface areas translate into improved performance. Unsurprisingly, then, the desire for large surface areas has led to a focus on nano-materials. A cube of material measuring 1 nm per side has 10 6 times greater surface to volume ratio compared to a cube of material measuring 1 mm per side. In addition, to increasing the ‘outside’ surface area of a particle by decreasing its dimensions one can also increase ‘internal’ surface area by introducing atomic defects such as dislocations to enhance species diffusivity and chemical reactivity. Despite recent technological successes wrought by the clever incorporation of nano- structured materials in fuel cells, we are still far away from possessing a solid scientific understanding of what is really going on at the nano-scale. Many critical questions remain. For example: • What are the characteristic dimensions over which energy transfer or charge transfer reactions can effectively occur? • Is there such a thing as too small? If the periodicity of a nano-structured interface is smaller than the characteristic energy transfer dimension, the answer may be yes.