(Invited) Engineering Hematite Interfaces By Dual Modification for Sunlight Driven Water Oxidation Reaction

Abstract

The present study describes the role of different modifiers on the overall hematite photocurrent response, which allowed a dual material insertion increasing the charge separation without compromise the surface catalysis. The pristine and Sn-hematite electrodes were obtained with two different morphologies (columnar, CN, and ellipsoid (EN) nanostructure) by low-cost aqueous chemical method. The following step was the addition at the Sn-hematite surface of a spinel cocatalyst that was also synthesized via chemical method. Sn-hematite-cocatalyst (Ni2FeOx) electrodes were submitted to additional thermal treatment under nitrogen atmosphere to activate the material surface. The pristine hematite electrode showed considerable enhancement on photocurrent density J, in comparison with previous work in our group for both method from a range of ~ 30 µA.cm-2 up to 0.2 mA.cm-2 and 1.0 mA.cm-2 to 2.0 mA.cm-2 at 1.23 VRHE, for CN and EN photoelectrodes respectively. Sn-addition onto hematite electrodes clearly increased flat band potential promoting a good charge separation and shifts the onset to a higher potential, attributed to the surface state created by this modification. Notoriously, Sn-hematite electrode loaded with FeNiOx exhibited the highest photocurrent density suggesting a partially passivation of surface states created during the electrode designing. The well-known co-catalyst acted majoritypassivating the surface states instead of improving surface for catalysis. The dual modification contributes to understand the role of different modifiers that is possible to satisfactorily improve charge separation maintaining the conductivity attributed to intermetallic ions. In summary, the synergy of Sn+4 and Ni2FeOX addition enables us to promote a shift on the onset towards a lower potential and enhancing the photocurrent density.The authors gratefully acknowledge support from FAPESP (Grant 2017/11986-5) and Shell and the strategic importance of the support given by ANP (Brazil’s National Oil, Natural Gas and Biofuels Agency) through the R&D levy regulation.