  Water splitting allows the storage of solar energy into chemical bonds
(H2+O2) and will help to implement the urgently needed replacement of limited
available fossil fuels. Particularly in neutral environment electrochemically
initiated water splitting suffers from low efficiency due to high
overpotentials caused by the anode. Electro-activation of X20CoCrWMo10-9, a
Co-based tool steel resulted in a new composite material
(X20CoCrWMo10-9//Co3O4) that catalyzes the anode half-cell reaction of water
electrolysis with a so far unequalled effectiveness. The current density
achieved with this new anode in pH 7 corrected 0.1 M phosphate buffer is over a
wide range of overpotentials around 10 times higher compared to recently
developed, up-to-date electrocatalysts and represents the benchmark performance
advanced catalysts show in regimes that support water splitting significantly
better than pH 7 medium. X20CoCrWMo10-9//Co3O4 exhibited electrocatalytic
properties not only at pH 7, but also at pH 13, which is much superior to the
ones of IrO2-RuO2, single-phase Co3O4- or Fe/Ni- based catalysts. Both XPS and
FT-IR experiments unmasked Co3O4 as the dominating compound on the surface of
the X20CoCrWMo10-9//Co3O4 composite. Upon a comprehensive dual beam FIB-SEM
(focused ion beam-scanning electron microscopy) study we could show that the
new composite does not exhibit a classical substrate-layer structure due to the
intrinsic formation of the Co-enriched outer zone. This structural
particularity is basically responsible for the outstanding electrocatalytic OER
performance.
