NiO Nanoparticles Anchored on Phosphorus‐Doped α‐Fe 2 O 3 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‐Fe 2 O 3 nanorod (NR) array (NiO/P‐α‐Fe 2 O 3 ) 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‐Fe 2 O 3 . Furthermore, the p–n junction that forms between NiO and P‐α‐Fe 2 O 3 can further improve the PEC performance due to efficient hole extraction and the water oxidization catalytic activity of NiO. Consequently, the NiO/P‐α‐Fe 2 O 3 NR photoanode produced a high photocurrent density of 2.08 mA cm −2 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 photoanodes.