Janus type Water-Splitting Catalysts have attracted highest attention as a tool of choice for solar to fuel conversion. AISI Ni 42 steel was upon harsh anodization converted in a bifunctional electrocatalyst. Oxygen evolution reaction-(OER) and hydrogen evolution reaction (HER) are highly efficiently and steadfast catalyzed at pH 7, 13, 14, 14.6 (OER) respectively at pH 0, 1, 13, 14, 14.6 (HER). The current density taken from long-term OER measurements in pH 7 buffer solution upon the electro activated steel at 491 mV overpotential (η) was around 4 times higher (4 mA/cm 2 ) in comparison with recently developed OER electrocatalysts. The very strong voltagecurrent behavior of the catalyst shown in OER polarization experiments at both pH 7 and at pH 13 were even superior to those known for IrO 2 -RuO 2 . No degradation of the catalyst was detected even when conditions close to standard industrial operations were applied to the catalyst. A stable Ni-, Fe-oxide based passivating layer sufficiently protected the bare metal for further oxidation. Quantitative charge to oxygen-(OER) and charge to hydrogen (HER) conversion was confirmed. High resolution XPS spectra showed that most likely γ−NiO(OH) and FeO(OH) are the catalytic active OER and NiO is the catalytic active HER species.

In spite of the drastic oil price collapse in the second half of 2014 resulting in a price below 30 $/barrel in January 2016 1 , the exploration of promising renewable energy sources for the Abstract: Water splitting allows the storage of solar energy into chemical bonds (H 2 +O 2 ) 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 (η) caused by the anode. Electro-activation of X20CoCrWMo10-9, a Co-based tool steel resulted in a new composite material (X20CoCrWMo10-9//Co 3 O 4 ) 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 η 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//Co 3 O 4 exhibited electrocatalyticproperties not only at pH 7, but also at pH 13, which is much superior to the ones of IrO 2 -RuO 2 , single-phase Co 3 O 4 -or Fe/Ni-based catalysts. Both XPS and FT-IR experiments unmasked Co 3 O 4 as the dominating compound on the surface of the X20CoCrWMo10-9//Co 3 O 4 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.2 future is one of the significant challenges for scientists and engineers concerned with energy issues research. Splitting of water into hydrogen and oxygen by exploiting solar energy transforms water to an inexhaustible and environmental friendly fuel source 2,3,4,5,6,7,8,9 .Electrocatalytically initiated hydrogen-and oxygen formation from water is considered an important realization of this solar to fuel conversion route 10,11,12 but is typically hampered by the high overpotentials oxygen evolution on the anode side goes with 13,14 . This is particularly true when the electrochemical cleavage of more or less untreated water is intended-; hence, when the splitting procedure is carried out at neutral pH value. 17,18,19,20,21,22,23,24 . Scheme 1 gives some idea of the position of current heterogeneous catalysts in terms of their efficiency regarding OER in neutral regime. The significant improvement of the voltage-current behavior can be taken from both-, the non-steady state ( Figure 1a) as well as the steady state polarization (Figure 1b) experiments. Results OER properties in neutral mediumThe CV of sample Co-300 shows along the entire curve substantially stronger current to voltage ratio than the CV of sample Co and reached, at the upper...

The use of proton exchange membrane (PEM) electrolyzers is the method of choice for the conversion of solar energy when frequently occurring changes of the current load are an issue. However, this technique requires electrolytes with low pH. All oxygen evolving electrodes working durably and actively in acids contain IrOx. Due to their scarcity and high acquisition costs, noble elements like Pt, Ru and Ir need to be replaced by earth abundant elements. We have evaluated a cobalt containing steel for use as an oxygen-forming electrode in H2SO4. We found that the dissolving of ingredients out of the steel electrode at oxi-dative potential in sulfuric acid, which is a well-known, serious issue, can be substantially reduced when the steel is electro-oxidized in LiOH prior to electrocatalysis. Under optimized synthesis conditions a cobalt-containing tool steel was rendered into a durable oxygen evolution reaction (OER) electrocatalyst (weight loss: 39 µg mm −2 after 50 000 s of chronopotentiometry at pH 1) that exhibits overpotentials down to 574 mV at 10 mA cm −2 current density at pH 1. Focused ion beam SEM (FIB-SEM) was success-fully used to create a structure-stability relationship.

2High overpotentials, particularly an issue of common anode materials, hamper the process of water electrolysis for clean energy generation. Thanks to immense research efforts up to date oxygen evolution electrocatalysts based on earth-abundant elements work efficiently and stably in neutral and alkaline regimes. However, non-noble metal-based anode materials that can withstand low pH regimes are considered to be an indispensable prerequisite for the water splitting to succeed in the future.All oxygen evolving electrodes working durably and actively in acids contain Ir at least as an additive. Due to its scarcity and high acquisition costs noble elements like Pt, Ru and Ir need to be replaced by earth abundant elements. We have evaluated a Ni containing stainless steel for use as an oxygen-forming electrode in diluted H 2 SO 4 . Unmodified Ni42 steel showed a significant weight loss after long term OER polarization experiments. Moreover, a substantial loss of the OER performance of the untreated steel specimen seen in linear sweep voltammetry measurements turned out to be a serious issue. However, upon anodization in LiOH, Ni42 alloy was rendered in OER electrocatalysts that exhibit under optimized synthesis conditions stable overpotentials down to 445 mV for 10 mA cm -2 current density at pH 0. Even more important: The resulting material has proven to be robust upon long-term usage (weight loss: 20 µg/mm 2 after 50 ks of chronopotentiometry at pH 1) towards OER in H 2 SO 4 . Our results suggest that electrochemical oxidation of Ni42 steel in LiOH (sample Ni42Li205) results in the formation of a metal oxide containing outer zone that supports solution route-based oxygen evolution in acidic regime accompanied by a good stability of the catalyst.3

The electrodeposition of noble metals using corresponding dissolved metal salts represents an interesting process for the improvement of the electrocatalytic hydrogen evolution reaction (HER) properties of less active substrate materials. The fact that only a small fraction of the dissolved noble metals reaches the substrate represents a serious obstacle to this common procedure. We therefore chose a different path. It was found that the HER activity of Ni42 alloy drastically increased (η=140 mV at j=10 mA cm−2; pH 1) when a platinum counter electrode was used during polarization experiments in acid. This improvement was caused by a platinum transfer from the platinum anode to the steel cathode, a process which occurred simultaneously to the hydrogen evolution. The negligible accumulation of Pt (26 μg) in the electrolyte turns this straight‐forward transfer procedure into a highly cost‐effective, environmentally friendly, and waste reducing approach for the generation of cheap, stable and effective HER electrodes.