Simultaneously improving solar water oxidation kinetics and passivating surface states of hematite by loading an amorphous Ni doped cobalt phosphate layer

Abstract

High surface states density of hematite photoanodes results in their low water oxidation kinetics and high surface electrons-holes recombination. To overcome these inherent drawbacks, various methods have been adopted, especially loading oxygen evolution catalysts and depositing oxide passivation layers. We report here an efficient way to promote the photocurrent of Fe2O3 photoanodes via depositing a thin layer of Co0.84Ni0.16-Pi. With the Co0.84Ni0.16-Pi deposit on its surface, the photocurrent density of Fe2O3 increases by ca. 42% at 0.23 V vs. Ag/AgCl, and the onset potential shifts 200 mV cathodically. In contrast, Co-Pi@Fe2O3 photoanode shows only 20% enhancement in photocurrent density under otherwise identical condition. The dark current densities of the photoanodes give an evidence that both Co0.84Ni0.16-Pi and Co-Pi are good oxygen evolution catalysts. Moreover, different from sparsely distributed Co-Pi nanoparticles, a 2–3 nm amorphous Ni doped cobalt phosphate layer can be also an effective passivation layer for surface states of hematite, which has been demonstrated by the analyses of Mott-Schottky plots and electrochemical impedance spectroscopy. This work demonstrates the dual roles of an amorphous oxygen evolution co-catalyst on hematite photoanodes and provides a simple method for designing highly efficient photoanodes.