Light‐Driven Water Splitting Mediated by Photogenerated Bromine

Light‐driven water splitting was achieved using a dye‐sensitized mesoporous oxide film and the oxidation of bromide (Br − ) to bromine (Br 2 ) or tribromide (Br 3 − ). The chemical oxidant (Br 2 or Br 3 − ) is formed during illumination at the photoanode and used as a sacrificial oxidant to drive a water oxidation catalyst (WOC), here demonstrated using [Ru(bda)(pic) 2 ], ( 1 ; pic=picoline, bda=2,2′‐bipyridine‐6,6′‐dicarboxylate). The photochemical oxidation of bromide produces a chemical oxidant with a potential of 1.09 V vs. NHE for the Br 2 /Br − couple or 1.05 V vs. NHE for the Br 3 − /Br − couple, which is sufficient to drive water oxidation at 1 (Ru V/IV ≈1.0 V vs. NHE at pH 5.6). At pH 5.6, using a 0.2  m acetate buffer containing 40 m m LiBr and the [Ru(4,4′‐PO 3 H 2 ‐bpy)(bpy) 2 ] 2+ ( RuP 2+ , bpy=2,2′‐bipyridine) chromophore dye on a SnO 2 /TiO 2 core–shell electrode resulted in a photocurrent density of around 1.2 mA cm −2 under approximately 1 Sun illumination and a Faradaic efficiency upon addition of 1 of 77 % for oxygen evolution.