Stainless steel made to rust: a robust water-splitting catalyst with benchmark characteristics

Abstract

The oxygen evolution reaction (OER) is known as the efficiency-limiting step for the electrochemical cleavage of water mainly due to the large overpotentials commonly used materials on the anode side cause. Since Ni-Fe oxides reduce overpotentials occurring in the OER dramatically they are regarded as anode materials of choice for the electrocatalytically driven water-splitting reaction. We herewith show that a straightforward surface modification carried out with AISI 304, a general purpose austenitic stainless steel, very likely, based upon a dissolution mechanism, to result in the formation of an ultra-thin layer consisting of Ni, Fe oxide with a purity > 99%. The Ni enriched thin layer firmly attached to the steel substrate is responsible for the unusual highly efficient anodic conversion of water into oxygen as demonstrated by the low overpotential of 212 mV at 12 mA/cm 2 current density in 1 M KOH, 269.2 mV at 10 mA/cm 2 current density in 0.1 M KOH respectively. The Ni, Fe-oxide layer formed on the steel creates a stable outer sphere, and the surface oxidized steel samples proved to be inert against longer operating times (> 150 ks) in alkaline medium. In addition Faradaic efficiency measurements performed through chronopotentiometry revealed a charge to oxygen

X20CoCrWMo10-9//Co3O4: a metal–ceramic composite with unique efficiency values for water-splitting in the neutral regime

“…In our recent report we unmasked a dissolution process to be likely responsible for the enrichment of catalytic active species on the surface of AISI 304 steel during electroactivation 26 . A substantial mass loss of around 6 mg took place whilst the electro-activation of X20CoCrWMo10-9 steel as well and in addition the formation of a black-grey layer on the Pt-counter electrode could be obtained (Table S3).…”

“…Unfortunately we could not extract a meaningful FTIR spectrum from the oxide containing surface of Co-300 upon direct measurement of the specimen. This experience we had already put before when surface oxidized steel S235 or AISI 304 were studied 25,26,45 . As the evanescent wave penetrates only up to some microns into the sample a good contact between ATR diamond and the sample is crucial and obviously was not ensured.…”

“…We determined for the OER upon iron oxide-based layers in 0.1 M phosphate (pH 7) buffer solution η=462 mV at 1 mA/cm 2 current density 25 which is still far below the OER performance of up to date electrocatalysts shown in alkaline regime. 26 Iron based films 27,28 ,Ni-(oxy)hydroxide-borate 29 , cobalt phosphate compounds 30,31 , cobalt borate/graphene 32 …”

Bi‐Functional Iron‐Only Electrodes for Efficient Water Splitting with Enhanced Stability through In Situ Electrochemical Regeneration

“…For example, cobalt constitutes the largest cost in most Li-ion rechargeable batteries (LiCoO 2 ), which has contributed to significant research into its replacement with iron (LiFePO 4 ) and manganese (LiMnO 2 ) analogs. [ 33 ] Approaches to overcome the use of more expensive metals in catalysis include the use of ultra-low concentrations of the active catalyst embedded in a lower-cost matrix [ 34 ] or in this case the identifi cation of active species which contain only Earth-abundant elements. [ 30 ] Only three transition metals (titanium, manganese, and iron) are truly abundant in Earth's crust (the primary source of metal ores) and within this group, iron is by far the most plentiful.…”

Controlling hydrogen evolution on iron electrodes

“…There are many reasons favouring the use of NiFe cells as cost effective solutions to store grid-scale amounts of energy, such as: low cost of raw materials, environmentally friendliness, tolerance to electrical abuse, long life (in the order of thousands cycles of charge and discharge) and compatibility with PV's [11]. Moreover, it has been recognized that this technology would be suitable for relatively low specific energy applications (30e50 W h kg À1 ) [12].…”