Hematite dodecahedron crystals with high-index facets grown and grafted on one dimensional structures for efficient photoelectrochemical H2 generation

Fe2O3 polyhedrons are one of the most promising morphologies for photoelectrochemical water splitting. In spite of recent reports on the successful synthesis of various Fe2O3 polyhedrons, the fabrication of defined photoelectrodes by anchoring the polyhedron in a suitable configuration remains a great challenge. Herein, we introduce a synthetic strategy to prepare Fe2O3 dodecahedrons with high-index {112} facets directly anchored on a one dimensional Fe2O3 nanoflake ({110} facets) electrode. Key is that the Fe2O3 nanoflakes act as seeds for the initiation of the growth of dodecahedral nanocrystals from an iron nitrate solution. The initial single crystals consist of Fe3O4 with exposed {110} basal surfaces that then in a thermal step can be converted to hematite with {112} facets. The resulting single crystal (bi-crystal) hematite photoanode demonstrates a high efficiency for solar water splitting with an excellent photoresponse due to the synergistic effects of direct grafting of the light harvesting and reactive polyhedron and the 1D transport geometry. Under optimized conditions the hematite polyhedrons on nanoflake-structure show photocurrent densities of 2.4 mA cm−2 at 1.23 VRHE and 3.5 mA cm−2 at 1.5 VRHE under AM 1.5 G simulated sunlight.