Recent advances on solar water splitting using hematite nanorod film produced by purpose-built material methods
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toelectrochemical cells offer a more elegant, clean, and sustainable way to store solar energy as chemical energy through the splitting of water into its primitive form (H2 and O2). Among many metal oxides pointed as candidates for this application, the fundamental characteristics of hematite (a-Fe2O3), such as abundance, excellent chemical stability in an aqueous environment, and favorable optical band gap, emerged as a promising photoanode. Although attractive, the poor optoelectronic properties necessitate a large application of overpotential for split water assisted by solar irradiation, limiting the high performance of this material. Since the electrode was built using materials in nanoscale, significant advances were achieved. This review highlights new insights and recent progress in the use of a purpose-built material process to build hematite electrodes for improving photocatalytic activity. In addition, reduction on the required overpotential by effective controltreatment of morphology and surface of vertically aligned hematite nanorods will be addressed. An interesting set of results were also discussed revisiting a novel strategy recently presented in the literature and complementary advances was illustrated. These latest efforts aid in pointing out the challenges or obstacles to be overcome using this morphology and in defining new opportunities.
I. INTRODUCTION
Nowadays, the storage and conversion of energy into chemical fuels from sunlight by water oxidation has become one of the most exciting topics in the energy field. Water and sunlight playing in harmony can provide a clean, unlimited, sustainable, and renewable energy free from carbon produced by photoelectrochemical (PEC) water splitting using a photosensible material. Fujishima and Honda1 were pioneers in demonstrating the photocatalytic effect using a semiconductor material to directly convert sunlight irradiation into chemical energy (hydrogen and oxygen). Since this seminal work, the PEC cell has been considered a more elegant and practical way to produce environmentally friendly fuels.2–5 For this purpose, many semiconductor materials such as WO36–10or TiO211,12 were exploited as photoanodes in PEC cells exhibiting considerable activity; however, due to their low stability in aqueous ambient and/or large band gap conferred a low usable portion of the solar spectrum, limiting commercial utilization.4,13–15 In the last decade, experimental and theoretical studies have been dedicated to finding an ideal material to efficiently mimic nature by artificially producing the biologic photosynthesis.10,12,16–22 In this context, hematite arise as the cheapest and most promising semiconductor material due to its natural a)
Address all correspondence to this author. e-mail: fl[email protected], fl[email protected] DOI: 10.1557/jmr.2013.302 16
J. Mater. Res., Vol. 29, No. 1, Jan 14, 2014
http://journals.cambridge.org
Downloaded: 16 Jun 2014
abundance, low band gap (2.1 eV, allowing absorption of a large portion of solar irradiation), high stabilit
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