From the Internal Combustion Engine to the Fuel Cell: Moving towards the Hydrogen Economy

摘要

Pollution emissions from mobile sources have been controlled for the last 25 years by monolithic catalysts in the exhaust system. The catalysts enhance the rate of conversion of unburncd CO, 11C and NO_x to harmless products. Throughout the world emission standards are becoming ever more stringent, thus demanding more from the catalyst and engineering design of the power source. Furthermore, fossil fuel combustion generates large quantities of greenhouse gases such as CO_2. The widespread use of fuel efficient lean bum vehicles is hindered by lack of an adequate technology for NO_x reduction. Although progress has been made with NO_x -storage systems, especially in Japan, the presence of sulfur and complicated regeneration requirements have hindered their application. Is it time to investigate alternative means of power generation that will not require after-treatment? The automobile companies throughout the world are answering yes. The fuel cell generates power by direct conversion of chemical energy, i.e., H_2 and O_2, to electrical energy avoiding the traditional combustion processes that generate pollutants. Furthermore, the system power efficiency is no longer limited by the Carnot cycle in which chemicals must be first combusted to produce mechanical energy. Greater efficiency translates to energy conservation and lower emissions of CO_2 depending on the source of hydrogen necessary to operate the fuel cell. For this reason there has been tremendous research in attempting to develop fuel cells as an alternative to conventional combustion systems used for power generation. The state-of-the-art of the modem automotive emission control catalysts is discussed. The major part of this paper lists some of the catalyst challenges for generating fuel cell grade hydrogen.