17. Juni 2015 : Stainless steel made to rust: a robust water-splitting catalyst with benchmark characteristics†

Helmut Schäfer,*a Shamaila Sadaf, a Lorenz Walder, a Karsten Kuepper, b Stephan Dinklage, c Joachim Wollschläger, c Lilli Schneider,b Martin Steinhart, a Jörg Hardege d and Diemo Daum Energy Environ. Sci., accepted 9th June 2015, doi: 10.1039/c5ee01601k

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 499%. 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 cm² current density in 1 M KOH, 269.2 mV at 10 mA cm² 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 (4150 ks) in alkaline medium. In addition Faradaic efficiency measurements performed through chronopotentiometry revealed a charge to oxygen conversion close to 100%, thus underpinning the conclusion that no ‘‘inner oxidation’’ based on further oxidation of the metal matrix below the oxide layer occurs. These key figures achieved with an almost unrivalled-inexpensive and unrivalled-accessible material, are among the best ever presented activity characteristics for the anodic water-splitting reaction at pH 13.

a Institute of Chemistry of New Materials and Center of Physics and Chemistry of New Materials, Universität Osnabrück

b Fachbereich Physik, Universität Osnabrück,
c Fakultät Agrarwissenschaften und Landschaftsarchitektur, Hochschule Osnabrück,
d School of Biological, Biomedical and Environmental Sciences, University of Hull.