The Promotion of Base Metal Catalysts for the Electrochemical Oxygen Evolution Reaction

As the energy needs of society continue to grow, and pressure to produce fewer emissions continues to mount, clean alternatives will be utilized to meet these demands. Conventional renewable technologies (wind and solar, etc.) have great potential, but cannot be used as base-load power, at least not in the traditional sense. Rather, these technologies would require the further adoption of energy storage technologies, such as water splitting, to convert the energy produced into chemical bonds for later use to match demand. Water splitting currently suffers from large energetic barriers, on the oxygen side, that create a need for catalysts, and high costs associated with the best available catalysts, ruthenium and iridium. This work focuses on developing and understanding ways to promote the catalysis of the oxygen evolution reaction on earth-abundant base metal catalysts. We utilize a combination of electrochemical and in situ surface characterization techniques to correlate changes in the surface chemistry to changes in catalyst activity. Three systems are examined for their potential effect on the OER. The first two focus on the promotion of NiO materials, examining the effect of changing the alkali cation present in the hydroxide electrolyte, and adding iron to the NiO materials. For the cations, the electrochemical activity is found to increase by a factor of two, switching from a LiOH solution to a CsOH solution of the same concentration. The use of in situ Raman spectroscopy suggests that different phases of the oxidized Ni oxyhydroxides are promoted in the presence of the different cations, with γ-NiOOH promoted in CsOH while β-NiOOH is observed in LiOH. The addition of Fe results in large increases in OER activity up to a loading of 10 mol% Fe, where the further addition of Fe decreases activity. Raman spectra of the electrodes suggest at low Fe loadings, the Ni oxidation to γ- NiOOH is promoted, while further addition of Fe blocks access to active catalyst sites. Finally, we demonstrate the use of Fe-TAML molecular complex as an electrocatalyst for the OER. Fe-TAML is shown to be electrochemically active, and through immobilization, much higher catalyst utilization is achieved.