Editors' Choice-Review-Polymer Electrolyte Fuel Cell Science and Technology: Highlighting a General Mechanistic Pattern and a General Rate Expression for Electrocatalytic Processes

This article has been written for students and teachers of the science and technology of low-temperature fuel cells, as well as for scientists and engineers actively involved in research and development in this area. It offers first an analysis of fuel cell electrocatalytic processes, identifying a common pattern in the mechanisms of these processes which serves as basis for a universal expression describing the non-linear V vs log J dependences observed under kinetic control. This analysis serves, in turn, as an introduction to reviews of several polymer electrolyte fuel cell technologies covering both science and engineering aspects and including process mechanisms and rate equations for the fuel cell electrode processes. These reviews highlight the requirement of explicit consideration of various types of overpotential-driven site activation steps in the analysis of experimentally observed V vs log J dependences. In addition to the mature technology of proton-conducting membrane fuel cells, the H-2/air and NH3/air polymer electrolyte fuel cells using a hydroxide-ion conducting membrane as the electrolyte, are also discussed. Finally, a brief summary of remaining research and development needs and priorities is offered for each type of polymer electrolyte fuel cell discussed. This paper is a Critical Review in Electrochemical and Solid State Science and Technology (CRES ( 3 ) T).