# The Role of Surface Texture on the Photocatalytic H\({}_{2}\) Production on TiO\({}_{2}\)
## 1 Introduction
### History and Developments  
Usually the first example of water photosplitting is attributed to [PERSON] and [PERSON] and their 1972 paper published on Nature [16]. In their contribution rutile TiO\({}_{2}\) is used as a photoanode for the evolution of oxygen, while hydrogen evolution occurred at the platinum cathode. Their approach is therefore photoelectrochemical, because both irradiation and an external bias were required. There are only five references in their paper: the first is a 1910 paper [17], in which it was stated that water photolysis requires 190 nm or shorter wavelength light, while the other four are previous reports by  
Figure 1: Energy diagram for water splitting and for the reforming of selected organic compounds. Figure 2: (a) Energy diagram showing the conduction and valence band potentials of TiO\({}_{2}\) anatase, C1 and water-related redox couples at pH 7 and 298 K [10; 11; 12; 13] Monoelectronic couples are in red, bielectronic in black, the four-electron couple O\({}_{2}\)/H\({}_{2}\)O is in blue. (b) Simplified pictorial scheme of the methanol reforming on a irradiated Pt/TiO\({}_{2}\) particle. (c) Photoinduced charge separation and charge distribution in Pt/TiO\({}_{2}\) nanocomposites. E\({}_{\text{F, dark}}\) and E\({}_{\text{F, light}}\) represent the pseudo-Fermi levels in the dark and under irradiation, respectively. Adapted with permission from [14]. Copyright 1979 American Chemical Society. the same authors to a more specialized and narrow audience [18; 19; 20; 21]. The small bibliography and the large rate of self-citation were due to the seminal nature of their report, but also to the smaller number of people, with different habits towards scientific publication, working in the field compared to nowadays. These two factors are still determining the reception of that work by the scientific community. Due to its seminal character the article received the first citation only two years later, but then interest rose up in the end of the decade and does not appear to slow down (Figure 3a) [22]. Considered as a whole, the literature concerning photoreforming on TiO\({}_{2}\) is increasing almost exponentially (Figure 3b) as water photosplitting publications are. Nevertheless, the sole increase of publication rate as a function of time in not significant, because of the unprecedented increase in the volume of the scientific literature occurred in the last decades. Indeed, even smallpox related publications show an increasing trend, even though the last recorded case dates back to 1977 [23]. More significantly, the increasing trend of water photosplitting publications is more similar to that recorded for lithium ion batteries, whereas hydrogen storage is showing a less steep increase since 8-10 years. With the buildup of interest, the number of reports, experiments, and observations increased, empowering the understanding of the processes and the mechanisms involved. Compared to the beginning of the 1970s, nowadays we have a much vaster literature dealing with hydrogen production, heterogeneous photocatalysis and artificial photosynthesis. But even more than 50 years ago the first evidence that species such as CN\({}^{-}\), I\({}^{-}\)[20] Br\({}^{-}\), Cl\({}^{-}\), Ce\({}^{3+}\), Mn\({}^{2+}\)[24; 25] and certain organics [26] could be oxidized by irradiated semiconductor slurties such as ZnO, TiO\({}_{2}\) and CdS thanks to charge carrier transfer [27] were already recorded. Moreover, [PERSON] and coworkers sketched and demonstrated different strategies to evolve hydrogen in the presence (and also in the absence [28]) of TiO\({}_{2}\), even with visible light only [29; 30]. The electron transfer from TiO\({}_{2}\) conduction band to N\({}_{2}\) was also reported [31]. In 1979, [PERSON] published a comprehensive review [32] rationalizing the three possible approaches for the exploitation of electromagnetic energy with photoelectrochemical cells (PEC) based on semiconductors, namely photovoltaic, photosynthetic and photocatalytic.