Electrospun TiO 2 Fiber Composite Photoelectrodes for Water Splitting D. Regonini,* ,† A. C. Teloeken, ‡ A. K. Alves, ‡ F. A. Berutti, ‡ K. Gajda-Schrantz, † C. P. Bergmann, ‡ T. Graule, † and F. Clemens* ,† † Laboratory for High Performance Ceramics, EMPA-Swiss Federal Laboratories for Materials Science & Technology, U ̈ berlandstrasse 129, 8600 Dü bendorf, Switzerland ‡ Federal University of Rio Grande do Sul, Laboratory of Ceramic Materials, Av. Osvaldo Aranha, 99, Porto Alegre, RS, 90035-190, Brazil * S Supporting Information ABSTRACT: This work has focused on the development of electrospun TiO 2 fiber composite photoelectrodes for hydro- gen production by water splitting. For comparison, similar photoelectrodes were also developed using commercial TiO 2 (Aeroxide P25) nanoparticles (NPs). Dispersions of either fibers or P25 NPs were used to make homogenous TiO 2 films on fluorine-doped SnO 2 (FTO) glass substrates by a doctor blade (DB) technique. Scanning electron microscopy (SEM) analysis revealed a much lower packing density of the DB fibers, with respect to DB-P25 TiO 2 NPs; this was also directly reflected by the higher photocurrent measured for the NPs when irradiating the photoelectrodes at a light intensity of 1.5AM (1 sun, 1000 W/m 2 ). For a better comparison of fibers vs. NPs, composite photoelectrodes by dip-coating (onto FTO) TiO 2 sol-gel (SG) matrixes containing an equal amount (5 or 20 wt %) of either fibers or P25 NPs were also investigated. It emerged that the photoactivity of the fibers was significantly higher. For composites containing 5 wt % TiO 2 fibers, a photocurrent of 0.5 mA/cm 2 (at 0.23 V vs Ag/AgCl) was measured, whereas 5 wt % P25 NPs only provided 0.2 mA/cm 2 . When increasing to 20 wt % fibers or NPs, the photocurrent decreased, because of the formation of microcracks in the photoelectrodes, because of the shrinkage of the sol-gel. The high photoactivity of the fiber- based electrodes could be confirmed by incident photon to current efficiency (IPCE) measurements. Remarkably, the IPCE of composites containing 5 wt % fibers was between 35% and 40% in the region of 380-320 nm, and when accounting for transmission/reflection losses, the absorbed photon to current efficiency (APCE) was consistently over 60% between 380 nm and 320 nm. The superior photoactivity is attributed to the enhanced electron transport in the electrospun fibers, with respect to P25 NPs. According to this study, it is clear that the electronic connectivity ensured by the sol-gel also contributes positively to the enhanced photocurrent. KEYWORDS: electrospinning, fibers, TiO 2 , water splitting, composite photoelectrodes 1. INTRODUCTION The photoelectrochemical splitting of water into hydrogen and oxygen requires semiconductors with conduction and valence bands energy straddling the electrochemical potentials of the hydrogen evolution reaction (HER, H + /H 2 ) and the oxygen evolution reaction (OER, O 2 /H 2 O), and is capable of absorbing light with photon energies of >1.23 eV. Since the electron (e - ) and electron holes (h + ) transfer processes at the seminconductor/liquid interface are subjected to losses due to overpotentials (i.e. voltage drop, concentration gradients), the required band-gap necessary to drive water splitting is generally considered to be in the range of 1.6-2.4 eV. 1 Among the materials capable of addressing such thermodynamic require- ments, a primary role is played by TiO 2 , which has been extensively investigated 2-4 since the seminal work of Fujishima and Honda in 1972. 5 TiO 2 is widely regarded as an efficient, environmentally friendly, economically accessible, photostable, and biologically inert photocatalyst. 3,4 The main drawbacks of TiO 2 are (i) its rather too-large band-gap (3.0 eV for rutile and 3.2 eV for anatase), hence the possibility to harvest only a small portion (5%) of the solar energy spectrum; 3 and (ii) high recombination of photogenerated e - and h + . The extension of the absorption range of TiO 2 into the visible-light range is still an ongoing issue and is generally addressed either by doping 3,6,7 or by coupling the TiO 2 with a narrower band-gap semiconductor. 4,7 Received: August 16, 2013 Accepted: October 18, 2013 Published: October 18, 2013 Research Article www.acsami.org © 2013 American Chemical Society 11747 dx.doi.org/10.1021/am403437q | ACS Appl. Mater. Interfaces 2013, 5, 11747-11755