The electrolysis of water has been at the forefront of catalysis research for over a decade and has gained tremendous attention since the introduction of metal-air cells and photoelectrochemical (PEC) water splitting devices that bridge the gap between carbon-based fuels and alternative energy resources.¹ However, these substantial advancements are still very expensive and inefficient to implement due in part to the non-spontaneous nature of the oxygen evolution reaction (OER). The OER is energy intensive; therefore, developing ways of reducing the overpotential and increasing the current throughput with catalytic materials is required.^1,2

The OER is a very complex mechanism that consists of various adsorption interactions at the electrode-electrolyte interface.² Therefore, efficient catalytic electrodes have a high active surface area for adsorbing intermediates, are stable in the electrolytic medium for long periods of time, and are good at electron transfer processes.² Mixed metal oxides are supported to be highly catalytic, stable, and can be formed using a variety of different experimental techniques.¹ Many of the mixed metal oxides being pursued are abundant and easily accessible.  Mixed metal oxides are also often found as by-products of corrosion in structural applications and high temperature processes.

These facts have led to our research in developing highly stable and electrochemically catalytic mixed metal oxides using different experimental techniques.  Nickel alloy-based oxides are of interest due to their promising electrocatalytic capabilities^3,4 when compared to the base metals alone. The ability to produce mixed metal oxides through facile techniques in mild conditions is highly desired.

Experimental

Catalytic electrodes were prepared using a variety of methods. These electrodes were then compared based on their electrochemical activity for catalyzing the OER. Preliminary experiments show promising and interesting results supporting a shift in overpotential and an increase in current density for the OER when the prepared mixed metal oxides are used as the working electrode in a traditional three-electrode configuration. 

Surface characterization using XPS, XRD, SEM, and Raman spectroscopy was employed to relate electrochemical response to the surface composition of the different electrodes to aid in determining the overall mechanism of catalytic activity.  It is also suggested that the breakdown of the outer surface oxide layer along with re-deposition throughout the electrochemical cycle might affect the overall electrochemical capabilities of these mixed metal oxide electrodes.

Results

Preliminary investigations suggest that electrode preparation technique and surface oxide film depth play a significant part in the catalytic activity of the mixed metal oxides. These results have led to further understanding of the OER mechanism and to better methods for preparing mixed metal oxide electrodes.

Figure I. Linear sweep voltammogram of base metal vs. prepared mixed metal oxide electrocatalyst

Acknowledgements: This work was partially funded by Department of Energy under contract DE-NE0008236.

References

1. C. Yuan., H. B. Wu, et al. Angew. Chem. Int. Ed.,53(6)1488-1504, (2014).
2. I. Katsounaros, S. Cherevko, A. R. Zeradjanin and K. J. J. Mayrhofer, Angew. Chem. Int. Ed., 53, 102-121, (2014).
3. H.-Y. Wang, Y.-Y. Hsu, R. Chen, T.-S. Chan, H. M. Chen and B. Liu, Adv. Energy. Mater.,  5,(2015).
4. H. Zhang, H. Y. Li, H. Y. Wang, K. J. He, S. Y. Wang, Y. G. Tang and J. J. Chen, J. Power Sources, 280, 640-648, (2015).