On the Electrolytic Stability of Iron-Nickel Oxides Florian D. Speck, Kevan E. Dettelbach, Rebecca S. Sherbo, Danielle A. Salvatore, Aoxue Huang, Curtis P. Berlinguette  Chem  Volume 2, Issue 4, Pages 590-597 (April 2017) DOI: 10.1016/j.chempr.2017.03.006 Copyright © 2017 Elsevier Inc. Terms and Conditions

Chem 2017 2, 590-597DOI: (10.1016/j.chempr.2017.03.006) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 1 Electrochemical Analysis of the FeNiOx Films (A) Cyclic voltammograms (CVs) recorded at a scan rate of 1 mV/s in 5.4 M KOH on conditioned electro- and photo-deposited films; the second cycle is shown. (B) Chronopotentiometric measurements in 5.4 M KOH at 200 mA/cm2 featured a slight rise in voltage for the FeNiOx films. (The lower potential of the NiOx film is due to a relatively higher film thickness.) Chronopotentiometric (CP) measurements were then conducted at 200 mA/cm2 for 24 hr for investigating the stability of the catalysts. The traces all showed reasonable temporal stability, but there was an increasing trend in voltage over the course of each experiment. This voltage increase was very small (<0.2 V), however, and not significant enough to signal significant structural changes of the film. A comparison of the CVs measured on the films immediately before and after (Figure S1) the CP measurement also revealed nominal changes in overpotentials (defined here as the potential required to reach 0.5 mA/cm2), which would be expected with changes in film composition (Table S1). Chem 2017 2, 590-597DOI: (10.1016/j.chempr.2017.03.006) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 2 Physical Analysis of the Film Composition and Morphology (A) Relative iron content of FeNiOx films before and after 24 hr of electrolysis as determined by XRF measurements. (The films each contained ∼25% iron after electrochemical conditioning and before 24 hr of electrolysis; not shown.) See also Figure S4. (B) XPS data recorded on FeNiOx NIRDD films before (blue) and after (red) 24 hr electrolysis demonstrate a change in iron content. See also Figure S3. (C) SEM top-view images of NIRDD films show the low surface coverage of FeNiOx. Inset: the same film before electrolysis highlights the conformal nature of the film. Scale bar, 1 μm. See also Figure S2. (D) SEM top-view images of NIRDD films show the high surface coverage of NiOx after 24 hr of sustained electrolysis at 200 mA/cm2. Inset: the same film before electrolysis highlights the conformal nature of the film. Scale bar, 1 μm. Chem 2017 2, 590-597DOI: (10.1016/j.chempr.2017.03.006) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 3 Electrochemical Evidence of Iron Deposition on the Ni-Cathode (A) Schematic of the experimental procedure to electrochemically show iron deposition. See also Figure S3. (B) CVs recorded at a scan rate of 1 mV/s on the Ni-cathode electrode before the experiment (dotted), after conditioning of the film (dashed), and after electrolysis (solid). The corresponding catalyst films on the anode were NIRDD NiOx (black), NIRDD FeNiOx (blue), and electrodeposited FeNiOx (red). The rate of iron depletion of the high-aspect-ratio electrodeposited film is assumed to be greater than that of the NIRDD films. Therefore, a large amount of the depleted iron is left behind in the electrochemical cell for conditioning, and less iron is deposited during electrolysis. Chem 2017 2, 590-597DOI: (10.1016/j.chempr.2017.03.006) Copyright © 2017 Elsevier Inc. Terms and Conditions

Figure 4 Investigations of Both the Anode and Cathode in Various KOH Electrolytes before and after Electrolysis (A) Iron content of anode catalyst films before (solid) and after (streaked) 24 hr of electrolysis obtained by XRF shows dependence of iron depletion on the OH− concentration. (B) CVs on the Ni-cathode exhibit iron-free behavior before electrolysis (dotted) and indicate deposited iron after 24 hr of electrolysis (solid) at 10 mA/cm2 for all three electrolyte concentrations. CVs were acquired from 1.0 to 1.7 V versus RHE at a scan rate of 1 mV/s in the indicated electrolyte. Chem 2017 2, 590-597DOI: (10.1016/j.chempr.2017.03.006) Copyright © 2017 Elsevier Inc. Terms and Conditions