Abstract
This work provides new insights in the field of applied photoelectro chemistry based on the use of nanoporous carbons as additives to tungsten oxide for the photooxidation of water under potential bias. Using a nanoporous carbon of low surface functionalization as additive to WO3 we have shown the dependence of the photochemical oxidation of water with the wavelength of the irradiation source. Photoelectrochemical responses obtained under monochromatic illumination show a significant increase in the incident photon-to-current conversion efficiency (IPCE) values for electrodes featuring up to 20 wt% carbon additive. Photoelectrochemical transient responses also show a sharp potential dependence, suggesting that the performance of the electrodes is strongly influenced by the carrier mobility and recombination losses. Despite the modest IPCE values of the W/NC electrodes (due to high bulk recombination and poor electron transport properties of the electrodes), our data shows that the incorporation of an optimal amount of nanoporous carbon additive to WO3 can enhance the carrier mobility of the semiconductor, without promoting additional recombination pathways or shadowing of the photoactive oxide.
Highlights
Advances on the use of sunlight as a sustainable low-cost source of energy in various fields have rather been limited to the use of inorganic semiconductors -TiO2 and metal oxides and sulfides as CdS, Fe2O3, or ZnO among most representatives, that should be stable, nontoxic, inexpensive, and have suitable electronic band positions for an efficient visible light absorption [1e5].WO3 is a n-type semiconductor usually presenting a 3D arrangement of slightly distorted corner-shared [WO6] octahedra compared to the ideal cubic perovskite, responsible of its electrooptical, electrochromic, ferroelectric and catalytic properties [6e10]
Despite the modest incident photon-to-current conversion efficiency values obtained, our results demonstrate the higher photoconversion values of the photoanodes after the incorporation of the nanoporous carbon, due to the enhanced electron collection provided by the carbon additive
We have recently reported the visible light driven photoelectrochemical water photooxidation splitting on metal-free nanoporous carbons with varied surface functionalization [30,52,53]
Summary
WO3 is a n-type semiconductor usually presenting a 3D arrangement of slightly distorted corner-shared [WO6] octahedra compared to the ideal cubic perovskite (type ReO3), responsible of its electrooptical, electrochromic, ferroelectric and catalytic properties [6e10]. It is considered an interesting visible-light stable photoactive material due to its relatively large abundance, non toxicity, physical and chemical resilience in harsh environments, and most importantly its strong absorption features in the solar spectrum (i.e., band gap between 2.4 and 2.8 eV). 0.3 V vs Ag/AgCl) for the reduction of water without a bias voltage This provokes the surface accumulation of electrons, increasing the recombination rate and reducing the photoelectrochemical performance of the photoanode [9e13]
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