Due to its abundance and chemical stability, hematite (α-Fe 2 O 3) is a promising n-type semiconductor photoelectrode. This is particularly true in the frame of the rapidly developing area of photoelectrochemical (PEC) sensing, where the short excited-state lifetime and the small carrier diffusion length of hematite can be beneficially employed. On the other hand, H 2 O 2 is an essential molecule for biological, environmental and industrial applications. In this article, we report a simple method to prepare photoelectroactive hematite layers on fluorine-doped SnO 2 (FTO) and we use these surfaces for H 2 O 2 PEC sensing. The so-created sensors allow to reliably detect H 2 O 2 down to a sub-µM concentration with a large linear range and a good reusability. H 2 O 2 is a crucial molecule. First, it is a marker for oxidative stress and a major factor of pathophysiological complications in serious diseases. [1,2] H 2 O 2 is also present in the natural environment [3] and commonly employed as a reagent in paper, textile or food industry. Hence, fast and accurate monitoring of H 2 O 2 is of great interest to medicine, environmental and industrial processing. Analytical protocols based on chromatography, [4] titration, [5] spectrophotometry, [6] fluorescence, [7] chemiluminescence, [8] and electrochemistry [9,10] have been used to detect this molecule and the development of H 2 O 2 sensors attracts considerable attention. [9,11] Photoelectrochemical (PEC) sensing is based on the photoinduced charge transfer at a semiconductor/liquid interface. It is a rather new and rapidly-developing research area which sensing combines aspects of electrochemical and optical sensing. [12,13] PEC sensing decouples excitation (light) and detection (electrochemical) signals, which is expected to significantly increase the signal-to-noise ratio with respect to electrochemical sensing. [13] Besides, it is also promising because it enables 2D reaction confinement on the transducer surface (i.e. on the photoelectrode) [14,15] which can be useful for electrode reuse [16,17] or for the design of multiplexed arrays. [18,19] So far, PEC sensing has been mainly employed for the detection of biological macromolecules, [20] in immuno-[21] or apta-[22] assays and has also been explored for the detection of small organic molecules such as antioxidants [23] or glucose. [24,25] While H 2 O 2 is a widely-employed hole scavenger in the field of energy-related photoelectrochemical research (typically used to probe the upper performance of water-splitting photoanodes), [26,27] the PEC sensing of H 2 O 2 has been only reported on TiO 2 , [28-30] WO 3 , [31] ZnO, [32,33] BiVO 4 , [34,35] and Si [36]-based photoanodes and on Cu 2 O, [37] CuO, [38] CdS, [39] and CuInS 2 [40]-based photocathodes. Hematite (α-Fe 2 O 3) is a promising photoanode material due to its great abundance, low-cost, chemical stability and its high theoretical photoconversion efficiency. [41,42] Nevertheless, it also has a short excited-state lifetime and a small hole diffusion length. This is a severe drawback for energy-related applications [41,42] but can be a great advantage for the design of PEC sensor arrays activated by micrometer-sized spots of light. [15,17] Hematite photoanodes have been previously employed for the PEC sensing of biological macromolecules, [43,44] neurotransmitters, [17] endocrine disruptors, [45,46] glucose, [25,44] inorganic pollutants, [47] and metal cations. [48] In this paper, we report the preparation of hematite photoanodes by a convenient spin-coating/annealing method and the use of these surfaces for H 2 O 2 PEC sensing. Figure 1. a) Scheme showing the method used to deposit hematite on FTO. b) Colored SEM image showing a cross-section of the hematite deposited on FTO. c) SEM image showing a top view of the hematite coating on FTO. d) XRD pattern of the deposited layer (black line), the red lines indicate the peaks position and relative intensity for hematite (ICSD #15840). e) High-resolution TEM image of the prepared hematite layer, the distance between the (210) planes is indicated. f) [12 1] zone axis SAED patterns recorded on hematite. Our hematite precursor is poly(vinylferrocene) (pvf), a Fe-containing polymer, dissolved in tetrahydrofuran (THF), which was spin-coated onto FTO slides and subsequently annealed, as shown in Figure 1a. A similar approach was previously employed by our group, however, with a low annealing temperature (300 °C) in order to deposit amorphous catalytic FeO x layers. [49] In the present work, we wanted to assess the feasibility of growing semiconductor films, we thus employed a higher annealing