Materials for Sustainability
Multiple geophysical and social pressures are forcing a shift from fossil fuels to renewable and sustainable energy sources.
To effect this change, we must create the materials that will support emergent energy technologies. Solar energy is a top priority of the department, and we are devoting extensive resources to developing photovoltaic cells that are both more efficient and less costly than current technology. We also have extensive research around next-generation battery technology.
Widespread application of photovoltaic power to provide a significant fraction of the world’s energy needs will require a dramatic lowering of photovoltaic cell material cost and the use of inexpensive, abundant materials and low-cost fabrication strategies. One candidate material that has the potential to meet these requirements is Cu2ZnSnS4 (CZTS). CZTS has a favorable band gap for solar cell applications, is made entirely of abundant materials and has a high absorption coefficient to minimize the quantity of material used in devices.
The frontiers of energy storage research are expanding, thanks to the burgeoning science of nanotechnology. Stanford engineer Yi Cui and his team have manufactured new energy storage devices out of paper and cloth, with a range of potential applications. Their research also has shown that using silicon nanowires to replace carbon anodes in lithium ion batteries can significantly improve their performance.
For the transition to a hydrogen-based economy to become feasible and economically practical, many materials challenges must be addressed. Not the least of these is the engineering of a hydrogen storage material with high storage density (both gravimetric and volumetric), appropriate equilibrium pressure, favorable reaction kinetics, relative safety and low cost. Metal hydrides represent one attractive way to store large amounts of hydrogen due to the very high potential volumetric capacity, which can even exceed that of liquid hydrogen. So far, however, no single material has met all the requirements for a practical, reversible on-board storage material.
We combine the flexibility and control of physical vapor deposition to fabricate thin film samples with precise chemical compositions and microstructures in order to probe metal hydride reactions in a very controlled way. Using a variety of thin film and powder characterization techniques (from X-ray diffraction to quartz crystal microbalance measurements and gas adsorption in a Sievert's type apparatus) we monitor the thermodynamic, kinetic and structural properties of these materials to gain a more fundamental understanding about the processes limiting their practical implementations. By applying the knowledge learned from these highly controlled systems, we can engineer materials to better meet the challenges of a hydrogen-based economy.
Our research focuses on metal hydride materials and carbon nanotube-based materials for hydrogen storage. We collaborate with other institutions, working at Stanford as well as NASA Ames Research Center and the Stanford Synchrotron Radiation Lightsource.