Iron is unstable as an oxygen evolution electrode in alkaline media. Thus, relatively expensive nickel-based electrodes are used in industrial alkaline water electrolysis. We show that an iron substrate can be rendered stable and electrocatalytically active for the oxygen evolution reaction by nano-scale surface modification with nickel. The electrocatalytic activity of such a surface-modified iron electrode is comparable to the recently-reported nickel-based catalysts. The electrocatalytic activity is due to a 50-nanometer layer of a high-surface area α-nickel hydroxide on the iron electrode. The nickel modification renders the iron electrode electricallyconductive, prevents dielectric breakdown, and thus endows anodic stability. The electrocatalytic activity is unchanged even after 1000 hours of continuous operation. The temperature of preparation is critical, as excessive dehydration of the hydroxide layer results in nickel ferrite formation and a drastic reduction in electrocatalytic activity. We report significant insight into the surface chemical composition and structure of the catalyst layer by X-ray Absorption Spectroscopy, Photoelectron Spectroscopy, and Transmission Electron Microscopy. Electrochemical kinetics analysis suggests that surface hydroxo-intermediates react with the hydroxide ions from the solution to evolve oxygen. Thus, the surface-modified iron substrates present an opportunity for improving the performance and reducing the cost of alkaline water electrolysis systems.

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Electrolysis of aqueous solutions of alkali is a promising approach for the production of pure hydrogen. For this approach to be economical on a large scale, the overpotentials for the electrode reactions and the high-cost of nickel-based electrode substrates must be reduced. We report here on the performance of an “all-iron” electrolyzer cell that uses inexpensive steel-based electrodes. This alkaline water electrolyzer uses a steel mesh coated with a thin catalytic coating of alpha-nickel hydroxide for the oxygen evolution electrode, and another steel mesh sputter-coated with nickel and molybdenum for the hydrogen electrode. An alkaline electrolyzer with these steel-based electrodes, a commercial Zirfon® separator, and a solution of 30% potassium hydroxide exhibited an electrolysis cell voltage of 1.83 V and 1.71 V at 100 mA cm−2 when operating at 23 °C and 70 °C, respectively. We show that the performance of the steel-based electrodes is comparable to commercial electrodes based on nickel substrates. When the cell was operated continuously for 100 h at 1 A cm−2 at 23 °C, there was no measurable loss in performance, providing a preliminary confirmation of the robustness of these iron-based electrodes and electrocatalysts. We conclude that cost-effective iron-based electrolyzers could be a promising route to low-cost hydrogen production.

Iron-based alkaline rechargeable batteries are promising candidates for large-scale energy storage applications owing to their low cost, robustness and environmental-friendliness. However, the widespread deployment of iron-based batteries has been limited by the low charging efficiency and poor discharge rate capability of the iron electrode. Our previous efforts on iron electrodes based on carbonyl iron powder and iron (II) sulfide have shown promise in overcoming these limitations. With the goal of understanding the role of sulfide additives, in this study, we have compared the performance of iron electrodes with iron (II) sulfide, iron (II) disulfide, copper (I) sulfide and zinc sulfide. The electrode containing zinc sulfide outperformed all other electrodes with a remarkable faradaic efficiency of 95% at C/2 rate and a specific discharge capacity close to 0.24 Ah g−1 at 1 C rate. The electrode did not lose any capacity for 750 cycles of repeated deep discharge at C/2 charge and discharge rates. Further, these electrodes could be cycled at 55 degrees Celsius with no noticeable change in performance. We attributed the excellent performance of zinc sulfide containing electrode to the low solubility of zinc sulfide in the electrolyte and the stability of zinc sulfide towards electro-reduction under the operating conditions of the iron electrode. These insights indicate that zinc sulfide is a promising additive for designing highly efficient and robust iron electrodes for alkaline nickel-iron and iron-air batteries.