Cathodes for chlorate electrolysis with nanocrystalline Ti±Ru±Fe±O catalyst A. GEBERT 1;2 , M. LACROIX 1 , O. SAVADOGO 1 * and R. SCHULZ 3 1 Laboratoire d'eÂlectrochimie et de mateÂriaux eÂnergeÂtiques, E Â cole Polytechnique de MontreÂal, C.P. 6079, succ. Centre- ville, MontreÂal, Qc, Canada H3C 3A7 2 IFW Dresden, Helmholtzstrasse 20, Dresden D-01069, Germany 3 Technologies eÂmergentes de production et de stockage, Institut de recherche d'Hydro-QueÂbec, Varennes, Qc, Canada J3X 1S1 (*author for correspondence) Received 10 August 1999; accepted in revised form 22 February 2000 Key words: chlorate electrolysis, high activity, hydrogen cathodes, nanocrystalline Ti±Ru±Fe±O catalyst Abstract Cathodes for chlorate electrolysis were prepared by mixing nanocrystalline Ti±Ru±Fe±O catalyst powder with small amounts of Te¯on and subsequent hot pressing on a carbon±Te¯on sublayer. Initially, the electrode materials were characterized by SEM, EDX, XRD and BET measurements. The behaviour of electrodes with catalyst loadings from 300 mg cm 2 reduced to 10 mg cm 2 was investigated in chlorate electrolyte with pH 6.5 and in part, for comparison, in 1 M sodium hydroxide solution at 70  C. Several methods have been used: cyclic voltammetry for the determination of double layer capacitance, Tafel plot analysis, cathodic potentiodynamic polarization and potentiostatic tests at i 250 mA cm 2 . The as-milled catalyst powder electrodes showed a high activity for the HER in chlorate electrolyte particularly expressed in low overpotentials of about 580 mV at 250 mA cm 2 for catalyst loadings down to 20 mg cm 2 and high double layer capacitances in the freshly prepared state. These electrodes show increased activity at low polarization. The long-term stability during electrolysis was also analysed. 1. Introduction In chlorate electrolysis about one half of the total production cost is due to the high electrical energy consumption. Many eorts have been directed towards a reduction of the overall cell voltage, particularly by lowering anodic and cathodic overpotentials. The intro- duction of the dimensionally stable anode (DSA) has allowed a decrease in overvoltage to a small value of 50 mV at 250 mA cm 2 . Then, most of the energy losses occur at the cathode. Mild steel cathodes are mostly used presently but they exhibit high overpotentials (850 to 1100 mV) at 250 mA cm 2 . On the other hand, under open circuit conditions (o.c.p.), that is, during standstill periods, steel-based cathodes are not stable in chlorate electrolyte. This results in a relatively short cathode lifetime. It has been shown that titanium cathodes are stable at o.c.p. but suer from hydrogen embrittlement during electrolysis [1, 2]. To date, no stable cathodes are available for industrial chlorate electrolysis. There is, thus, an urgent requirement in the development of new cathode materials with lower potentials for HER and more stability in chlorate electrolyte. The cathodic performance of ruthenium oxide (RuO 2 ) coated elec- trodes prepared by thermal decomposition of RuCl 3 on Ti substrates [3, 4] and on Ni substrates [5] and by electro- codeposition of RuO 2 powder with Ni [4] has been investigated in 1 M sodium hydroxide solution and partly in chlorate electrolyte. Their electrocatalytic activity for HER after preactivation was found to be signi®cantly improved compared to that of steel. However, RuO 2 is thermodynamically unstable, that is, shows disposition for partial reduction to lower oxidation states [4]. Furthermore, RuO 2 coated electrodes were eroded by strong gas evolution [3]. Thus, long-term stability of those electrodes cannot be expected in industrial atmospheres. Recently, nanocrystalline Ti±Ru±Fe±O alloys [2, 6] (and Ti±Ru±Fe±Cr±O alloys [7]) have been developed as new cathode materials for chlorate electrolysis. It was shown that they can easily be prepared by high energy ball milling of pure Ti and RuO 2 powder under formation of a ®ne mixture of two new phases [2]: a hcp Ru-like phase and cubic RuTi(Fe)O were obtained. Iron is usually incorporated by wear debris of the milling tools and is additionally alloyed into the material. It has been shown that iron does not signif- icantly aect the excellent catalytic parameters of the HER for electrodes based on those nanocrystalline alloys [2]. Depending on the Ti/RuO 2 ratio, overpoten- tials at 250 mA cm 2 of only 550 to 600 mV were Journal of Applied Electrochemistry 30: 1061±1067, 2000. 1061 Ó 2000 Kluwer Academic Publishers. Printed in the Netherlands.