## 5 Conclusions  
In conclusion, this work showed the improved catalytic efficiency and OER selectivity of Mn-Mo-Ru catalysts over previously studied transition metal-doped Mn-Mo catalysts. In both NaCl solution and raw seawater, the Mn-Mo-Ru catalysts demonstrated strong performance toward OER with reduced CER. Extended testing in continuous raw seawater highlighted the need for further improvement of the Mn-Mo catalysts. This work highlighted that common catalysts, such as Ru, can be used as successful dopants in CER-suppressing catalysts. **Supplementary Materials:** The following are available online at [[https://www.mdpi.com/article/10.3390/app112411911/s1](https://www.mdpi.com/article/10.3390/app112411911/s1)]([https://www.mdpi.com/article/10.3390/app112411911/s1](https://www.mdpi.com/article/10.3390/app112411911/s1)), Figure S1: SEM micrographs at 500\(\times\) of (a) 0.2 M Mn-0.003 M Mo-0.003 M W, (b) 0.2 M Mn-0.003 M Mo-0.009 M Ru, and (c) 0.2 M Mn-0.003 M Mo-0.1 M Co. Figure S2: (a) XPS survey spectra from the Mn-Mo-0.006 M Ru electrode and associated spectra from the Ru 3p region for the (b) Mn-Mo-0.006 M Ru and (c) Mn-Mo electrodes and the Ru 3d region of the (d) Mn-Mo-0.009 M Ru and (e) Mn-Mo electrodes. Figure S3: (a) FE toward OER after 30 min in artificial seawater (ASW) and 0.1 M phosphate buffer + 0.5 M NaCl (PB) for different transition metal-doped Mn-Mo catalyst. (b) Charge passed toward OER in noted electrolyte, calculated by taking the FE * the total charge passed after 30 min. Figure S4: Charge passed toward OER in ASW and PB for different concentrations of Co- and Ru-doped Mn-Mo catalysts. Figure S5: Chronoamperometric analysis for (a) Mn-Mo-0.006 M Ru and (b) Mn-Mo-0.009 M Ru in raw seawater indicates that 0.009 M Ru-containing electrode has better stability. Figure S6: (a) FE toward OER and (b) charge passed toward OER at 60, 90, and 120 min in artificial seawater (ASW) for bare (Blue) and Nafion(r)-coated Mn-Mo-0.006 M Ru electrode. Figure S7: Comparison of Mn-Mo-0.006 M Ru electrode (pH 1) following chronopointometric testing in raw seawater flume both (a) before and (b) after testing showing (c) exposure of the IrO\({}_{2}\) base layer in the EDS map, and (d) the cathode following seawater testing showing deposition of a salt layer. **Author Contributions:** Conceptualization R.M.A., K.A.S., and G.A.G. ; methodology, P.A., N.D., R.M.A., K.A.S., and L.-J.K.; formal analysis, P.A., N.D., R.M.A., and K.A.S. ; investigation, P.A., N.D., N.M.A., J.A.S., L.-J.K., C.W., D.M.S., M.H.E., and J.V.C. ; resources, N.D. and D.M.S. ; data curation, P.A., N.D., M.H.E., and J.V.C. ; writing--original draft preparation, P.A., N.D., R.M.A., and K.A.S. ; writing--review and editing, P.A., R.M.A., and K.A.S. All authors have read and agreed to the published version of the manuscript. **Funding:** The research described in this paper/on this poster/in this report was conducted under the Laboratory Directed Research and Development Program at Pacific Northwest National Laboratory, a multiprogram national laboratory operated by Battelle for the U.S. Department of Energy and the Department of Energy Office of Energy Efficiency and Renewable Energy (DOE ERE) Water Power Technology's Seedling Program. **Data Availability Statement:** The data presented in this study are available on request from the corresponding author. The data are not publicly available due to ongoing proprietary research. **Acknowledgments:** [PERSON] acknowledges support from Oregon State University as a Callahan Faculty Scholar. P.A. acknowledges support from the Link Foundation Energy Fellowship. R.M.A acknowledges the staff at the PNNL Marine Sciences Laboratory and [PERSON] and [PERSON] for programmatic support. XPS measurements were performed using EMSL (grid.436923.9), a DOE Office of Science User Facility sponsored by the Office of Biological and Environmental Research. R.M.A and N.D. acknowledge the support of the Laboratory Directed Research and Development Program at Pacific Northwest National Laboratory.