Gabriel McAndrews1,2,Andrew Yeang1,Yuchun Cai1,Christopher Barile3,Michael McGehee1
University of Colorado Boulder1,National Renewable Energy Laboratory2,University of Nevada, Reno3
Gabriel McAndrews1,2,Andrew Yeang1,Yuchun Cai1,Christopher Barile3,Michael McGehee1
University of Colorado Boulder1,National Renewable Energy Laboratory2,University of Nevada, Reno3
Reversible metal electrodeposition (RME) is a growing field with applications ranging from batteries (e.g. Li, Zn) to dynamic glazings for thermal emissivity (e.g. Ag) or windows (e.g. Cu, Bi, Ag, Zn). Dynamic windows based on RME can enhance building efficiency up to 20% due to reduced lighting, heating, and cooling loads while reducing glare.<sup>[1]</sup> While a reductive potential is applied, RME windows based on Cu and Bi can adjust light transmission from ~ 70 % to < 0.1 % (“privacy state”) when ~180 nm of metal is electrodeposited on the transparent conducting electrode.<sup>[2]</sup> Uniform, smooth, and compact films enable RME windows to reach low transmission states with color neutrality at large scale,<sup>[2]</sup> and the transparency of the window can be regained by switching the polarity of the potential.<sup>[3,4]</sup><br/><br/>We find that films plated to privacy state transmission with a Cu-Bi ratio of ~2:1 fracture and delaminate within 24 hours resulting in a visually unattractive window with lost active metal and a reduced dynamic range. While the Cu-Bi film is stress free upon deposition, after 4 hours of resting 38 MPa of tensile stress develops. Likewise, pure Cu films exhibit 142 MPa of tension after deposition. The tension in Cu-Bi and Cu films combined with the Cu(ClO<sub>4</sub>)<sub>2</sub> in the electrolyte results in severe, widespread sinusoidal cracks and delamination due to stress corrosion cracking (SCC). In contrast, electrodeposited Bi films have compressive stress, likely due to high self-diffusion and insertion of atoms into grain boundaries during plating. We emphasize the importance of stress characterization in electrodeposited films to identify susceptibility to mechanical failure driven by SCC. In turn, we demonstrate a Bi-based dynamic window with crack-free resting stability that exceeds 9 weeks.<br/><br/>[1] M. Krarti, <i>J. Build. Eng.</i> <b>2022</b>, <i>45</i>, 103462.<br/>[2] M. T. Strand, T. S. Hernandez, M. G. Danner, A. L. Yeang, N. Jarvey, C. J. Barile, M. D. McGehee, <i>Nat. Energy</i> <b>2021</b>, <i>6</i>, 546.<br/>[3] T. S. Hernandez, C. J. Barile, M. T. Strand, T. E. Dayrit, D. J. Slotcavage, M. D. McGehee, <i>ACS Energy Lett.</i> <b>2018</b>, <i>3</i>, 104.<br/>[4] T. S. Hernandez, M. Alshurafa, M. T. Strand, A. L. Yeang, M. G. Danner, C. J. Barile, M. D. McGehee, <i>Joule</i> <b>2020</b>, <i>4</i>, 1501.