Highly Efficient Photoelectrochemical Water Splitting: Surface Modification of Cobalt‐Phosphate‐Loaded Co3O4/Fe2O3 p–n Heterojunction Nanorod Arrays.

Hematite (α‐Fe2O3) as a photoanode material for photoelectrochemical (PEC) water splitting suffers from the two problems of poor charge separation and slow water oxidation kinetics. The construction of p–n junction nanostructures by coupling of highly stable Co3O4 in aqueous alkaline environment to Fe2O3 nanorod arrays with delicate energy band positions may be a challenging strategy for efficient PEC water oxidation. It is demonstrated that the designed p‐Co3O4/n‐Fe2O3 junction exhibits superior photocurrent density, fast water oxidation kinetics, and remarkable charge injection and bulk separation efficiency (ηinj and ηsep), attributing to the high catalytic behavior of Co3O4 for the oxygen evolution reaction as well as the induced interfacial electric field that facilitates separation and transportation of charge carriers. In addition, a cocatalyst of cobalt phosphate (Co‐Pi) is introduced, which brings the PEC performance to a high level. The resultant Co‐Pi/Co3O4/Ti:Fe2O3 photoanode shows a photocurrent density of 2.7 mA cm−2 at 1.23 VRHE (V vs reversible hydrogen electrode), 125% higher than that of the Ti:Fe2O3 photoanode. The optimized ηinj and ηsep of 91.6 and 23.0% at 1.23 VRHE are achieved on Co‐Pi/Co3O4/Ti:Fe2O3, respectively, corresponding to the 70 and 43% improvements compared with those of Ti:Fe2O3. Furthermore, Co‐Pi/Co3O4/Ti:Fe2O3 shows a low onset potential of 0.64 VRHE and long‐time PEC stability. A well‐designed Co‐Pi/Co3O4/Ti:Fe2O3 photoanode displays efficient charge separation and transportation efficiency due to the induced interfacial electric field in the Co3O4/Ti:Fe2O3 p–n junction, as well as the fast water oxidation kinetics deriving from the high catalytic behavior of Co3O4 and Co‐Pi. [ABSTRACT FROM AUTHOR]