Another Step Forward for Fuel Cell Technology
While fuel cell technology is widely touted for myriad applications, cost remains the primary impediment to large-scale utilization in today's market. André Taylor, Assistant Professor of Chemical Engineering, is working to resolve this issue by reducing the cost associated with expensive noble metal based catalysts (i.e. platinum; Pt). In a recent publication in the Journal of Catalysis (vol. 259, pp. 5-16), Taylor et al. successfully demonstrated a novel technique of using supercritical fluids to controllably load metal nanoparticles onto the surface of 1-D carbon materials.
Current polymer electrolyte membrane (PEM) and direct methanol fuel cell technologies commonly utilize inexpensive carbon black as a catalyst support. While such material offers reasonable surface areas at a low cost, the Pt utilization is quite low. This is due to the fact that the Pt particles are isolated from participating in the electrochemical reaction because of the material geometry and pore size distribution. This ultimately drives up the cost by wasting the expensive Pt. To mitigate this effect, researchers have investigated the utility of 1-D carbon materials, such as carbon nanotubes and carbon fibers. Such 1-D carbon structures display promising material properties, including high electrical conductivity and chemical resistance, making them suitable for fuel cell applications. Their high length-to-diameter ratio and surface areas mean that particle isolation can be minimized, resulting in more efficient utilization of the catalyst. However, obtaining a homogenous metal deposition on the inert hydrophobic surface of these materials has proven difficult. Traditional metal loading methods, such as wet impregnation (typically used for carbon black) are not feasible and common alternative methods of introducing chemical functional (i.e. carboxyl) groups are not only time consuming, but have been found to compromise the integrity of the structure.
The latest development in metal loading has involved the use of supercritical fluids, which could minimize defects on the carbon structure. In this recently published research, Taylor compared the effects of synthesis conditions employing high-temperature and supercritical methanol on Pt particle size, loading, and fuel cell performance using single-walled carbon nanotubes and carbon fibers.
The result? A simple one-step synthesis approach to effectively decorate 1-D carbon supports with platinum. Taylor's method not only proved to exhibit high performance and Pt utilization for PEM fuel cell applications, but also did so without compromising the durability of the structure with surface modification using chemical functional groups. His group further demonstrated for the first time that high temperature methanol can be a viable synthesis medium for producing fuel cell catalysts. Taylor's research is a true breakthrough for fuel cell technology. While the cost of carbon nanotubes remains high, we may be trading one expense (i.e., platinum) for another. However, as Professor Taylor points out, as carbon nanotubes are proven in new devices and applications, the economies of scale should lower this present cost. Nonetheless, this new method of nanomaterial synthesis offers a dramatic improvement over existing techniques and has broad-scale applications that extend beyond fuel cells. Taylor leads the University's Transformative Materials and Devices Group.