be achieved by engineering the surface properties of MnO2. This approach is general, and could be
used to stabilize all kinds of catalysts, including metals, against corrosion in electrochemical devices.
Further development of this work could lead to stable, active and abundant materials to catalyze
oxygen evolution in PEM electrolysers and photoelectrolysers for water splitting.
5. Experimental Section
Computational details
The calculations in this work are done with the GPAW code and the revised Perdew-Burke-Ernzerhof
exchange and correlation approximation.61,88,89 Optimal positions for the termination atoms were
found by relaxing structures with a Broyden-Fletcher-Goldfarb-Shanno algorithm until a maximum
force of 0.05 eV/Å was obtained. All systems were optimized with (4,4,6) Monkhorst-Pack type kpoints
sampling and the effect of grid spacing converged at 0.15 Å. Between slabs 10 Å of vacuum was
introduced in the z direction while in x and y the slab could be repeated. Periodic boundary conditions
have been implemented throughout. Four kinds of rutile MnO2 systems were investigated. A bulk
MnO2 slab (2x2x1 repeated unit cells), a flat (110) MnO2 surface (4 layers in z-direction, 4 surface
metal atoms), a stepped (120) MnO2 surface (tilted (110) surface) and a (120) MnO2 surface with
introduced kinks. MnO2 lattice constants were optimized in this setup to be a=4.499 Å and c=2.909 Å.
For the surface structures, the bottom layer was fixed in order to have a bulk structure unaffected by
surface changes. Notably, the termination energies are not calculated as Gibbs free energies with
entropy contributions, since the comparison is between solid states only and no chemical reactions
are modeled. Furthermore, on a rutile (110) surface, two different metal sites will be present, one
being the coordinately unsaturated site (CUS) and the other the Bridge site, see Figure 1a.14 We
modelled steps and kinks as CUS and Bridge and found that the overall trend remained the same so
the results shown here are for the Bridge terminated structures. All the calculated values are listed in
Table S1.