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

We describe two different functionalities of one metallo-organic film assembled on the surface of a transparent metal-oxide electrode. 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 dihydrogen and oxygen. The product output is stable for at least 7 hours in an aqueous electrolyte at pH = 6.9, with a Faradaic efficiency (FE) of ~70%.