Pergamon Int. Z Hydrogen Energy, Vol. 19, No. 7, pp. 633-639, 1994 Copyright © 1994International Association tor Hydrogen Energy ElsevierScienceLtd Printed in Great Britain.All rights reserved 036(~3199/94 $7.00+ 0.00 1 kW PAFC STACK: A CASE HISTORY V. RECUPERO,V. ALDERUCCI,R. Ol LEONARDO, M. LAGAN.~, G. ZAPPALAand N. GIORDANO CNR Institute for Transformation and Storage of Energy, via S. Lucia sopra Contesse 39, 98126 S. Lucia Messina, Italy (Received for publication 12 July 1993) Abstract--The activity on PAFC technology at the CNR Institute for Transformation and Storage of Energy started in 1983. In recent years, the research has been carried out within the framework of national prograrnmes (ENEA-Progetto Volta). The aim was to design, build and test a 1 kW power unit, integrated with a methanol reforming unit of the same size. Development of this prototype has progressed successfully:the development of proprietary component materials (catalyst, electrodes and matrix) and engineering systems has been achieved. Scale-up of cells from laboratory size (a single cell of 72 cm2) to a 100 W stack (six cells of 200 cm2) and to 1 kW, (25 cells of 400 cm2, air cooled) has been successful. The present analysis is used to emphasize the different steps which have carried us to this goal. 1. INTRODUCTION The phosphoric acid fuel cell (PAFC) technology is generally identified as being the nearest to commercial- ization for electric utility power generation. Although a lot of studies exist about each single main problem (i.e. catalyst and electrode optimization, cell and stack design, long-term performance, etc.) very few studies summarize complete research which starts from the basic materials to attain the final product or prototype. In this work we present the activities of the CNR Institute for Transformation and Storage of Energy aimed at the development of an original prototype of a 1 kW PAFC stack, integrated with a methanol reformer unit of the same size. The key features towards this objective have been: • know-how related to the preparation of an extremely active Pt electrocatalyst supported on active and noncorrodible carbon; • a proprietary procedure for preparation of elec- trodes having high catalyst utilization; • optimization of the SiC matrix prepared by a rolling procedure; • a proprietary design of the basic stack module (original bipolar plates, continuous acid replenish- ment system, simplified stack hardware design); • testing in a single cell, at 100 W and 1 kW scale; • optimization of the engineering system. 2. BASIC COMPONENTS The first step of the research has been the development of the proprietary phosphoric acid fuel cell components (catalyst, electrodes and matrix); the methodology of preparation and the principal requisites obtained are illustrated later. Catalyst The catalyst is prepared by impregnation of a carbon support with an aqueous solution of chloroplatinic acid. Platinum reduction is obtained by solution of a reducing agent, sodium dithionite, the so-formed Pt colloidal dispersion having an average particle size in the range 20-50 ]~ is absorbed on the carbon and separated from aqueous solution by filtering, then dried to provide a dry powder form and finally activated under controlled con- ditions. The unique characteristics of our catalyst (high Pt stability, optimal crystallite size distribution, etc.) reside upon the support peculiarities: good porosimetric distri- bution, high graphitization index, high surface area and good electric conductivity. Electrodes The electrodes are prepared from carbon paper (Toray TGP090), wet-proofed with a FEP (polyethylene-propy- lene) solution, dried at 70°C and sintered at 375°C for 10 min. The catalyst ink is prepared by mixing and stirring at 50-60°C for 15 min, HzO, PTFE (polytetrafluoroethy- lene) solution (61~o wt/wt) and a prefixed quantity of 20~o Pt/C catalyst. Following this, isopropyl alcohol is added to the catalyst ink and the flocculate screen printed on the carbon paper. The electrodes are dried in two steps, at 120°C for 1 h and at 280°C for 30 min, and then sintered (340°C for the cathode and 350°C for the anode). The final contents of PTFE are 40~o for the 633