Corrosion Resistance and Catalytic Activity toward the Oxygen Reduction Reaction of CoCrFe_xNi (0 ≤ x ≤ 0.7) Thin Films

Abstract

Corrosion resistance and catalytic activity toward the oxygen reduction reaction (ORR) in an alkaline environment are two key properties for water recombination applications. In this work, CoCrFe x Ni (0 ≤ x ≤ 0.7) thin films were deposited by magnetron sputtering on polished steel substrates. The native passive layer was 2–4 nm thick and coherent to the columnar grains determined by transmission electron microscopy. The effect of Fe on the corrosion properties in 0.1 M NaCl and 1 M KOH and the catalytic activity of the films toward ORR were investigated. Electrochemical impedance spectroscopy and potentiodynamic polarization measurements indicate that CoCrFe0.7Ni and CoCrFe0.3Ni have the highest corrosion resistance of the studied films in NaCl and KOH, respectively. The high corrosion resistance of the CoCrFe0.7Ni film in NaCl was attributed to the smaller overall grain size, which leads to a more homogeneous film with a stronger passive layer. For CoCrFe0.3Ni in KOH, it was attributed to a lower Fe dissolution into the electrolyte and the build-up of a thick and protective hydroxide layer. Scanning Kelvin probe force microscopy showed no potential differences globally in any of the films, but locally, a potential gradient between the top of the columns and grain boundaries was observed. Corrosion of the films was likely initiated at the top of the columns where the potential was lowest. It was concluded that Fe is essential for the electrochemical activation of the surfaces and the catalytic activity toward ORR in an alkaline medium. The highest catalytic activity was recorded for high Fe-content films (x ≥ 0.5) and was attributed to the formation of platelet-like oxide particles on the film surface upon anodization. The study showed that the combination of corrosion resistance and catalytic activity toward ORR is possible for CoCrFe x Ni, making this material system a suitable candidate for water recombination in an alkaline environment.

Electrolyte engineering for effective seawater splitting based on manganese iron chromium layered triple hydroxides as novel bifunctional electrocatalysts

“…The higher corrosion resistance ( R c ) and charge transfer resistance ( R ct ) with lower capacitance ( Y 0 ) values indicate better corrosion resistive properties of the electrode. 43,44 Interestingly, in inhibitor-containing electrolyte environments, MFC-2 shows much higher R ct and R c values along with lower capacitance ( Y ) values following the trends of HPO 4 2− > CO 3 2− > SO 4 2− compared to electrolytes without any inhibitors. Moreover, the inherent frequency dependence impedance ( Z ) behaviour of the system was investigated by drawing Bode impedance and Bode phase angle plots in an alkaline electrolyte with and without inhibitors (Fig.…”

New age chloride shielding strategies for corrosion resistant direct seawater splitting

“…51 Very recently, Linder and his coworkers developed CoCrFe x Ni alloy thin films with variable Fe-content (0 ≤ x ≤ 0.7), which was sputtered on the steel plate as the corrosion resistant material for the oxygen reduction reaction in the chloride-containing electrolyte. 36 The investigation indicated that with higher Fe-content, more defects were created, which led to the formation of a passive layer on to the electrode, providing the much needed corrosion resistance. Furthermore, the phase transformation from hexagonal close-packed (HCP) toward face-centered cubic (FCC) with increasing Fe-content also seemed to have a major role toward corrosion prohibition.…”

“…35 The larger charge transfer resistance and corrosion resistance together with lower constant phase element values indicate the efficient anticorrosion properties of the working electrode. 36 On the other hand, the qualitative corrosion kinetics of the working electrode for both cathodic and anodic reactions can be measured from the PD plots. In the PD experiments, the potential scan rate should be optimized first to adjust the stable phases amongst the working electrode and the reference electrode in the presence of a harsh electrolyte environment.…”

High-entropy layered hydroxide for efficient and sustainable seawater oxidation

“…A higher E corr and more negative I corr indicate better anti-corrosion ability of the electrocatalysts. 48,49 In this regard, HE-LH showed a higher E corr of 0.89 V and lower I corr of 2.7 Â 10 À8 A cm À2 than Q-LH (E corr = 0.873 V and I corr = 6.3 Â 10 À8 A cm À2 ) and T-LH (E corr = 0.862 V and I corr = 7.39 Â 10 À8 A cm À2 ), as also tabulated in Table S4 (ESI †), indicating better corrosion inhibition properties. The anti-corrosive nature of HE-LH is also reflected by its calculated highest polarization resistance (R p ) value along with lowest corrosion rate compared to the other LHs in highchloride-content electrolyte.…”