Electrochemical reactions in power sources and sinks: Personal reflections on progress and future prospects

Abstract

The basis of all electrochemical power sources such as fuel cells, batteries, and photoelectrochemical devices is the energy-producing electrochemical reactions, whose high rates, to the exclusion of all parasitic or deleterious reactions, is the paramount goal desired in all research and development work in electrochemical energy conversion and storage. A subjective evaluation of the status of some of these key electrochemical reactions is undertaken in relation to the materials problems involved; an outline of the recent progress is given together with the current focus and future possibilities. An elementary examination of the fundamental aspects of some of these reactions, e.g., the electrocatalysis of the hydrogen and the oxygen reaction is carried out in a manner which emphasizes their salient features both in the configuration of a power source, ( i.e., fuel cell) and that of the complementary power sink ( i.e., electrolyzer). It is observed that considerable progress has been made in the electrocatalysis of the hydrogen and oxygen evolution reactions with the discovery of the so-called BP electrocatalysts by Brown et al. recently. The earlier DSA catalysts for the chlorine evolution reaction are also clearly a milestone. Much progress has also been made in the commercialization of phosphoric acid fuel cells for utilities, in the exploratory materials work on photoelectrochemical cells, and in understanding the fundamental constraints and the materials problems of several storage batteries. Future progress is urgently needed in the nearly intractable problem of the stable and active non-noble metal electrocatalysts for the oxygen reduction reaction. The promise of much future activity and perhaps some breakthroughs are clearly indicated in the following areas: photoelectrochemical cells - both for photoelectrolyses, and, the electrochemical photovoltaics; commercialization of Li-SOCl 2 primary batteries and related systems; optimization and commercial availability of some of the currently researched batteries for vehicular and load-levelling applications; development of the entire area of conducting polymer electrodes and ionic polymeric electrolytes; chemically modified (derivitized) electrode surfaces; and the development of concepts treating living beings as electrochemical power sources.