Sub-monolayers of iridium electrodeposited on Ti2AlC substrate as catalysts for hydrogen evolution reaction in sulfuric acid solution

Abstract

The hydrogen evolution reaction (HER) was investigated at sub-monolayers of iridium electrodeposited on Ti2AlC substrate. The lowest amount of electrodeposited iridium was 3 close-packed (111) monolayers (3 ML), while the highest one was 22 ML (3, 5, 10, 15 and 22 ML). The lowest and the highest amounts of iridium were electrodeposited by linear sweep voltammetry (LSV), while the other three samples were electrodeposited by controlled potential coulometry, from the solution containing 1 mM, or 3 mM K3IrCl6 + 0.5 M Na2SO4 (pH 6.2) at 70 °C. The HER was investigated by polarization and electrochemical impedance spectroscopy (EIS) measurements. Polarization curves for iridium sub-monolayers equal, or higher than 6 ML showed low Tafel slope of -14 to -16 mV dec-1 up to about -0.1 A cm-2, while at higher current densities the Tafel slopes increased, varying between -40 and -72 mV dec-1. The highest value of exchange current density (jo) was obtained for 6 ML of electrodeposited iridium, being -27.89 A g-1. The overpotential at j = -0.3 A cm-2 could be determined for samples containing 15 ML and 22 ML of iridium, being 82 mV.

Izdvajanje vodonika ispitivano je u rastvoru sumporne kiseline na elektrohemijski istaloženim slojevima (od 3 monosloja do 22 monosloja) iridijuma na podlozi od Ti2AlC. Najmanja i najveća količina iridijuma (3 i 22 monosloja) elektrohemijski su istaložene metodom linearne voltametrije, dok su preostala tri uzorka (6, 10 i 15 monoslojeva) elektrohemijski istaložena pri konstantnom potencijalu do potrebne količine naelektrisanja iz rastvora 1 mM, ili 3 mM K3IrCl6 + 0.5 M Na2SO4 (pH 6.2) na temperaturi rastvora od 70 °C. Reakcija izdvajanja vodonika ispitivana je na svim elektrodama snimanjem polarizacionih krivih. Za uzorak sa 22 monosloja Ir primenjena je i metoda impedanse. Polarizacione krive za uzorke sa 6, 10, 15 i 22 monosloja Ir bile su okarakterisane malom vrednošću Tafel-ovog nagiba od -14 to -16 mV dek-1 u oblasti gustina struja do -0.1 A cm-2, dok se Tafel-ov nagib povećavao pri većim gustinama struja varirajući od -40 do -72 mV dek-1. Najveća vrednost specifične gustine struje izmene (jo) dobijena je kod uzorka sa 6 monoslojeva Ir i iznosila je - 27.89 A g-1. Za uzorke sa 15 i 22 monosloja Ir vrednost prenapetosti pri gustini struje j = -0.3 A cm-2 (uslovi industrijske proizvodnje vodonika) iznosila je 82 mV.