Optimization of charge transport in a Co–Pi modified hematite thin film produced by scalable electron beam evaporation for photoelectrochemical water oxidation

Hematite (α-Fe2O3) is an attractive candidate for photoelectrochemical (PEC) hydrogen generation by oxidation of water due to its low cost, earth-abundance and appropriate bandgap. However, large scale production of hematite thin films with efficient PEC performance is a challenging problem in the field. In this article, based on an electron beam evaporation method, we provide a scalable route for preparation of a Co–Pi modified hematite thin film with efficient solar water oxidation properties. To our knowledge, no work has been done on photoelectrochemical characterization of Co–Pi modified hematite films prepared based on electron beam evaporation. We show that by optimization of deposition conditions including the film thickness and annealing temperature and performing the deposition in an oxygen medium, an efficient PEC performance is achieved from the produced pristine hematite photoanode. By various characterizations including XRD, EDX, SEM, transient photocurrent and I–V measurements, and impedance spectroscopy, it is shown that the efficient performance is attributed to the improved crystalline structure and suppression of recombination centres originated from the defects in bulk and surface of the hematite layer. Also with deposition of different thicknesses of Co–Pi electro-catalysts on the hematite layer, the optimum structure for fast water oxidation and charge transfer kinetics across the interface of the photoanode and electrolyte is obtained. The most efficient photoanode delivers up to 1.5 (mA cm−2) at the potential of 1.5 V versus the reversible hydrogen electrode (RHE), which is among the large value photocurrents attained from a hematite-based photoanode, but with the advantage of large scale production capability of the proposed method of this work.