NiO nanoparticles anchored on phosphorus-doped α-fe₂o₃ nanoarrays: An efficient hole extraction p–n heterojunction photoanode for water oxidation

The photoelectrochemical (PEC) water-splitting efficiency of a hematite-based photoanode is still far from the theoretical value due to its poor surface reaction kinetics and high density of surface trapping states. To solve these drawbacks, a photoanode consisting of NiO nanoparticles anchored on a gradient phosphorus-doped α-Fe₂ O₃ nanorod (NR) array (NiO/P-α-Fe₂ O₃) was fabricated to achieve optimal light absorption and charge separation, as well as rapid surface reaction kinetics. Specifically, a photoanode with the NR array structure allowed a high mass-transport rate to be achieved, while phosphorus doping effectively decreased the number of surface trapping sites and improved the electrical conductivity of α-Fe₂O₃. Furthermore, the p–n junction that forms between NiO and P-α-Fe₂O₃ can further improve the PEC performance due to efficient hole extraction and the water oxidization catalytic activity of NiO. Consequently, the NiO/P-α-Fe₂ O₃ NR photoanode produced a high photocurrent density of 2.08 mAcm² at 1.23 V versus a reversible hydrogen electrode and a 110 mV cathodic shift of the onset potential. This rational design of structure offers a new perspective in exploring high-performance PEC photoano-des.