Ionics 10 (2004) 99 Performance of Solid State Protonic Battery with Different Cathodes R.U. Tiwari*, K. Singh and S.S. Bhoga Department of Physics, Nagpur University, Nagpur-440010, India *Department of Applied Physics, R.K.N.E.C, Gittikhadan, Katol Road, Nagpur-440013 (India) e-mail: tiwariru@rknec.edu, msrll @hotmail.com Abstract. To establish the fact that the performance of a solid state battery is predominantly governed by the cathode, primary electrochemical cells were fabricated using FeH(SO4)e-xH20 solid electrolyte having proton transport number close to unity (prepared by chemical route) taken in conjunction with five different cathodes MnO2, PbO2, V6013, 12 and TMAI iodine complex. Amongst these, better discharge characteristics along with thermodynamic and chemical stability of the cell were offered by TMAI iodine complex based cathode. Beside these, it provided short-circuit current, capacity and energy density of the order of 5 mA 4.5 mAh and 2.67 Wh/kg respectively due to the presence of highly active iodine, which is not free in TMAI compared to the cathode made of simply 12 . 1. Introduction Unmanageable pollution problem due to recent explosion in the portable electronics market is provoking the need for more environmental friendly components, away from toxic heavy metals such as lead, mercury and cadmium. Con- currently, research efforts in the cathode area for state-of-the- art batteries are tending to revert to the use of environmental friendly materials. The anode is the electrode, which gives electrons to the external circuit and is oxidized during the electrochemical reaction. On the other hand, the cathode is the electrode, which accepts the electrons from the external circuit and is reduced during the electrochemical reaction. The most advantageous combination of anode and cathode materials is normally selected in such a way that it is lightest, gives a high cell voltage and capacity. Such combinations, however, are not always practical. As a matter of fact the cathode, an electropositive half of the cell, also known as the oxidizing electrode, accepts electrons from the external circuit and ions from the electrolyte during the electrochemical cell discharge. The properties important in assessing the viability of a cathode material in electrochemical cell are an efficient oxidizing agent, chemically compatible with electrolyte materials, easy of handling, good electronic conductivity, intercalation, toxicity, high voltage, energy density, reversible cyc- ling. Solid state proton conductors are very attractive material for high energy density primary and secondary batteries, because of low weight of hydrogen and high Gibb's energy of formation of hydrogen compounds [1]. Compared to lithium and silver, though protonic solid state batteries are environment friendly lesser attempted in want of thermo- dynamic, chemical and electrochemical (high decomposition potential) stability of protonic solid electrolytes. In fact, the cathode material considerably governs the performance of batteries. Thus, in the present paper we report a systematic study of the performance of battery fabricated using FeH(SOa)2-xH2 O, a protonic solid electrolyte in conjunction with different cathodes namely MnO2, PbO2, V6013, I2 and tetramethyl ammonium iodide (TMAI) iodine complex. 2. Experimental Proceduure Solid electrolyte FeH(SO4)2-xH20 was prepared following chemical route by mixing ferrous sulphate with sulfuric acid in proper stoichiometric ratio under proper atmospheric condition. Then the reactant product was dried for twenty- four hours in vacuum. The details of technique to obtain total ionic transference number was similar to that described