S. Hu, M. Yao, K. Sun, C.-Y. Chi, M. Lichterman, C. Zhou, P. Daniel Dapkus, N.S. Lewis
Keywords: water splitting, solar hydrogen, nanowire, protective coating
Summary:Defect tolerance in electrochemical corrosion protection is an important concept to achieving the thousand-hour stability and >15% solar-to-fuel efficiency target set by US Department of Energy. Recently, a general protective-coating strategy for stabilizing the otherwise unstable semiconductor–electrolyte interfaces for water oxidation and hydrogen production in pH 14 electrolytes base have been demonstrated for an entire class of technologically important semiconductor light absorbers. Furthermore, wire-shape light absorbers with conformal protective coatings showed unprecedented > 2200 hours of stability for continuous water oxidation. On the other hand, no corrosion protection strategy is inherently robust unless the protected light absorbers is either immune to corrosion (like TiO2) or self-passivating (like Si) thus preventing further corrosion and dissolution. Here I will introduce a defect-tolerate design, where discrete nanowire geometry not only enables manufacture of flexible photosynthetic membranes, but also confine defects within the affected region by virtue of the self-passivating mechanism via the discrete nanowire geometry. The protected photoelectrodes effected quantitative water oxidation under simulated AM 1.5 illumination with an open-circuit potential of -0.78 V vs the formal potential for oxygen evolution and a light-limited photocurrent density of 9.1 mA cm-2 under 1-Sun. Finally, I will outline the challenges and opportunities of nanomaterials towards scalably manufacturable artificial photosynthetic devices that directly convert solar energy into chemical fuels.