(511d) Dopant Profile and Activity in a-Fe2O3 for Solar Water Splitting

Hematite is an attractive material for photoelectrochemical water splitting owing to its ~2 eV bandgap, stability in alkaline electrolytes and abundance.  The interface between the semiconductor metal oxide and electrolyte is the location of primary interest for the overall water splitting process, yet methods for determining dopant concentration at this interface often give contradictory results.  Here, techniques including energy dispersive X-ray spectroscopy (EDS), electron energy loss spectroscopy (EELS), electrochemical impedance spectroscopy, electronic conductivity and secondary ion mass spectroscopy are compared to determine dopant density.  Discrepancies suggest that dopant activation, rather than simply increasing the dopant concentration, is key for achieving higher water splitting efficiencies.  Specifically, secondary ion mass spectroscopy, which measures total Sn present, gives values of Sn concentration which are higher than that obtained from conductivity measurements, which measures electrically active Sn.  Results are discussed in the broader context of photoelectrochemical hydrogen production and recommendations for improving the efficiency of water splitting with hematite are proposed.