Electrochromism or Water Splitting in Neutral Aqueous Solutions by a Metallo‐Organic Assembly

Herein, two different functionalities of one metallo-organic film assembled on the surface of a transparent metal-oxide electrode are described. Two redox-active elements, electrochromic iron–polypyridyl complexes and catalytically active palladium centers, operate by applying different potentials in aqueous solutions. The color of the material can be cycled 1500 times from dark purple to colorless by electrochemically addressing the Fe2+/3+ centers at 0.0–1.0 V (vs Ag/Ag+). The differences between the transmittance of these two states is high: ΔT = 52%. Catalytic water oxidation can occur by palladium oxide particles that form in situ by applying a higher potential (1.22–2.0 V vs Ag/Ag+), resulting in the formation of hydrogen and oxygen. The catalyst is active for at least 7 h in an aqueous electrolyte at pH = 6.9, with a Faradaic efficiency of ≈70%.