All-in-One Derivatized Tandem p+n-Silicon–SnO2/TiO2 Water Splitting Photoelectrochemical Cell

Mesoporous metal oxide film electrodes consisting of derivatized 5.5 μm thick SnO2 films with an outer 4.3 nm shell of TiO2 added by atomic layer deposition (ALD) have been investigated to explore unbiased water splitting on p, n, and p+n type silicon substrates. Modified electrodes were derivatized by addition of the water oxidation catalyst, [Ru(bda)(4-O(CH2)3PO3H2)-pyr)2], 1, (pyr = pyridine; bda = 2,2′-bipyridine-6,6′-dicarboxylate), and chromophore, [Ru(4,4′-PO3H2-bpy) (bpy)2]2+, RuP2+, (bpy = 2,2′-bipyridine), which form 2:1 RuP2+/1 assemblies on the surface. At pH 5.7 in 0.1 M acetate buffer, these electrodes with a fluorine-doped tin oxide (FTO) back contact under ∼1 sun illumination (100 mW/cm2; white light source) perform efficient water oxidation with a photocurrent of 1.5 mA/cm2 with an 88% Faradaic efficiency (FE) for O2 production at an applied bias of 600 mV versus RHE (ACS Energy Lett., 2016, 1, 231−236). The SnO2/TiO2–chromophore–catalyst assembly was integrated with the Si electrodes by ...