The DSK System of Fuel Cell Electrodes

Abstract

Double skeleton catalyst (DSK) electrodes combine the high catalytic activity of Raney powder catalysts with the mechanical rigidity and electrical conductivity of bulk metals. They consist of a supporting macroskeleton pressed and sintered of metal grains of uniform size and Raney catalyst grains embedded in its pores. The authors have prepared more than 3000 different samples and investigated the following parameters: composition and particle size of both catalyst and macroskeleton, blending ratio of these two components, mixing process, pressing and sintering conditions, and a special potentiostatic process to leach the inactive component (Al or Zn) by . This “controlled activation” provides extremely high activity and uniform pore sizes, avoiding too narrow and too large pores. Such “homeoporous” electrodes offer some 10−2 pores with three phase boundaries, each contributing several microamperes to the total current density. Detailed recipes are given for the production of hydrogen DSK electrodes containing Raney Ni catalyst in a Ni macroskeleton and generating up to 750 ma/cm2 at 40 mv polarization at 85°C. Oxygen DSK electrodes contain a new brittle Ag Raney alloy in a supporting Ni macroskeleton. The open‐cell polarization φ‐U0 at 85°C is 100 mv only and the maximum current density about 500 ma/cm2. Such electrodes with fine pore coating layers are absolutely gas tight and show nearly 100% Faraday efficiency. Although the oxygen DSK electrodes contain but 0.05 g Ag/cm2 they reach the ideal process delivering 4 electrons per O2 molecule instead of the Berl process with 2 electrons. A battery with such electrodes fed with impure H2 and O2 in uninterrupted service one year showed no deterioration. Therefore the lifetime of DSK cells is estimated to be at least 103, perhaps some 104 amphr/cm2. Different types of DSK electrodes such as economy electrodes used for the dissolved fuel fuel cell, and valve electrodes for the electrochemical storage of energy are described. They also act as electrolytic compressors without moving parts and can control catalytic reactions automatically. DSK electrodes may be used for light storage batteries. Mo‐ and W‐DSK electrodes offer the possibility of the electrochemical oxidation of CO. DSK electrodes belong to the most promising systems disclosed hitherto and are capable of further improvement.