On-Board Vehicle, Cost Effective Hydrogen Enhancement Technology for Transportation PEM Fuel Cells

摘要

Final Report of On-Board Vehicle, Cost Effective Hydrogen Enhancement Technology for Transportation PEM Fuel Cells. The objective of this effort was to technologically enable a compact, fast start-up integrated Water Gas Shift-Pd membrane reactor for integration into an On Board Fuel Processing System (FPS) for an automotive 50 kWe PEM Fuel Cell (PEM FC). Our approach was to: (1) use physics based reactor and system level models to optimize the design through trade studies of the various system design and operating parameters; and (2) synthesize, characterize and assess the performance of advanced high flux, high selectivity, Pd alloy membranes on porous stainless steel tubes for mechanical strength and robustness. In parallel and not part of this program we were simultaneously developing air tolerant, high volumetric activity, thermally stable Water Gas Shift catalysts for the WGS/membrane reactor. We identified through our models the optimum WGS/membrane reactor configuration, and best Pd membrane/FPS and PEM FC integration scheme. Such a PEM FC power plant was shown through the models to offer 6% higher efficiency than a system without the integrated membrane reactor. The estimated FPS response time was < 1 minute to 50% power on start-up, 5 sec transient response time, 1140 W/L power density and 1100 W/kg specific power with an estimated production cost of $35/kW. Such an FPS system would have a Catalytic Partial Oxidation System (CPO) rather than the slower starting Auto-Thermal Reformer (ATR). We found that at optimum WGS reactor configuration that H{sub 2} recovery efficiencies of 95% could be achieved at 6 atm WGS pressure. However optimum overall fuel to net electrical efficiency ({approx}31%) is highest at lower fuel processor efficiency (67%) with 85% H{sub 2} recovery because less parasitic power is needed. The H{sub 2} permeance of {approx}45 m{sup 3}/m{sup 2}-hr-atm{sup 0.5} at 350 C was assumed in these simulations. In the laboratory we achieved a H{sub 2} permeance of 50 m{sup 3}/(m{sup 2}-hr-atm{sup 0.5}) with a H{sub 2}/N{sub 2} selectivity of 110 at 350 C with pure Pd. We also demonstrated that we could produce Pd-Ag membranes. Such alloy membranes are necessary because they aren't prone to the Pd-hydride {alpha}-{beta} phase transition that is known to cause membrane failure in cyclic operation. When funding was terminated we were on track to demonstrated Pd-Ag alloy deposition on a nano-porous ({approx}80 nm) oxide layer supported on porous stainless steel tubing using a process designed for scale-up.