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Department of Inorganic Technology, ICT Prague

Technical Electrochemistry Group I, lab A023

CHARACTERIZATION OF A PEMELECTROLYZER

INTRODUCTION

Hydrogen, as a commodity chemical, is nowadays mainly produced from fossil fuels by steamreforming or partial oxidation. However, it is possible to produce hydrogen in a clean way usingelectricity and water. Industrially, there is an established method that uses potassiumhydroxide electrolyte, from which hydrogen and oxygen is evolved upon passing an electricalcurrent. A competing method using an acidic polymer electrolyte is emerging, called the PEMwater electrolysis, the acronym PEM standing for polymerelectrolyte membrane. Althoughnot implemented on an industrial scale, this method offers higher efficiency and higher processintensity, i.e., lower space demands. !he reason why this method is not used industrially lies in

its high investment costs and lifetime issues. "evertheless, on a laboratory scale, there is aplethora of available devices, one of which you will test in this wor#.

Fig. 1 Scheme of a PEM elec!ol"#e!.

THEORY OF OPERATION

PEM electrolysis is a complementary process to the PEM fuel cell. In a PEM electroly$er %much li#e in a PEM fuel cell % a cathode and an anode are separated by a polymerelectrolytemembrane, which acts as a separator and a proton conductor. &n the anode, water is oxidi$edto gaseous oxygen' the remaining proton is transported through the membrane to the cathodeside where it is reduced to hydrogen gas % the product of interest. Electrochemical reactions aregiven below(

Anode( )H)& * + &) -H -e Ered* /.)0 1 2/3

4athode( -H -e*+ )H) Ered* 5.55 1 2)3

&verall( )H)& *+ &) )H) 67r* -8-.) #9:mol 203

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CELL $OLTA%E

In thermodynamics, electromotive force 2E3 of a cell can be calculated from the cell reactionusing formula 2-3, where z is the number of electrons exchanged in the reaction and F is the;araday constant.

67 * $;E 2-3

In the waterelectrolysis case, the electromotive force is negative, which means that we have tosupply energy to the cell to ma#e the watersplitting happen. !he cell e

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HOME PREPARATION

Aside from reading the text above, answer these