Enabling Overall Water Splitting By Iron Oxide and Silicon

Photoelectrochemical water splitting promises a large-scale solar energy storage solution.  Its development has been impeded by poor performance of photoanodes, particularly in the capabilities of photovoltage generation.  Using the prototypical photoanode material of hematite as a study tool, we show that structural disorders on or near the surfaces are an important reason for the low photovoltages.  A facile re-growth strategy was developed to readily alter the surfaces for reduced disorders.  A record-low turn-on voltage of 0.45 V (vs. reversible hydrogen electrode) was measured.  The result permitted us to construct devices made of three most abundant elements on the Earth crust (O, Si, and Fe) to split water with only sunlight as the energy input at an overall efficiency of 0.91%.