Boosted Z-scheme photocatalytic overall water splitting with faceted Bi4TaO8Cl crystals as water oxidation photocatalyst

We have identified a facet-assisted mechanism for photocarrier separation in flux-treated Bi4TaO8Cl crystals that expose mainly {001} and {110} facets. These two crystal facets have different energy states that provide an internal electric field to split photocarriers towards different crystal facets. We have further leveraged the phenomenon by facet-selective deposition of CoOx cocatalyst at {001} crystal facets where holes are accumulated to expedite interfacial charge transfer reactions. The coupling of these two facet-engineering techniques brings exquisite control over the flow of photocarriers which cascade continuously from bulk to the surface for catalytic reactions. Under optimal conditions, the CoOx-deposited Bi4TaO8Cl achieves an unprecedentedly high apparent quantum efficiency of 27% at 420 ± 20 nm for water oxidation into O2. Stable overall water splitting into H2 and O2 (molar ratio 2:1) under visible light irradiation has also been realized in a Z-scheme system employing the CoOx-deposited Bi4TaO8Cl as the O2-evolution moiety.