Improving the OER Activity of Titania Via Doping and Adlayers

The oxygen evolution reaction (OER) was investigated theoretically on modified rutile(110) surfaces at density functional theory level in search for inexpensive but active catalyst materials required for water electrolysis. Ti substitution by Nb in rutile and furthermore adding adlayers of transition metal (TM) oxides, with TM $=$ Ir, Ru and Rh, substantially improves titania OER activity. The catalytic activity was assessed by the overpotential of the OER which was calculated from adsorption energies of the intermediates M-O, M-OH and M-OOH. Different reaction mechanisms were suggested depending on the presence or absence of M-OOH. Materials with iridium dioxide in the top layer have similar overpotentials, both as adlayer on (doped) ${\mathrm{TiO}}_2$ and as pure ${\mathrm{IrO}}_2$ . Thus, the percentage of this expensive and scarce element can be drastically reduced without deteriorating the activity. A monolayer of ${\mathrm{RuO}}_2$ on rutile ${\mathrm{TiO}}_2$ has an even lower overpotential compared to pure ${\mathrm{RuO}}_2$ . In addition, ${\mathrm{RhO}}_2$ and ${\mathrm{RhO}}_2$ : ${\mathrm{Nb}}_{1/3}{\mathrm{Ti}}_{2/3}{O}_2$ were identified as catalysts with higher OER activity than ${\mathrm{IrO}}_2$ .