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Published October 2017 | Supplemental Material
Journal Article Open

Enhanced Photoelectrochemical Water Splitting of Hematite Multilayer Nanowires Photoanode with Tuning Surface State via Bottom-up Interfacial Engineering

Abstract

The optimization of multiple interfaces in hematite (α-Fe_2O_3) based composites for photoelectrochemical water splitting to facilitate charge transport in the bulk is of paramount importance to obtain enhanced solar-to-fuel efficiency. Herein, we report the fabrication of ITO/Fe_2O_3/Fe_2TiO_5/FeNiOOH multi-layer nanowires and a series of systematic experiments designed to elucidate the mechanism underlying the interfacial coupling effect of the quaternary hematite composite. The hierarchical ITO/Fe_2O_3/Fe_2TiO_5/FeNiOOH nanowires display photocurrents that are more than an order of magnitude greater than those of pristine Fe_2O_3 nanowires (from 0.205 mA cm^(−2) to 2.2 mA cm^(−2) at 1.23 V vs. RHE and 1 Sun), and higher than those of most of the recently reported state-of-the-art hematite composites. Structural, compositional and electrochemical investigations disclose that the surface states (SS) are finely regulated via the atomic addition of an Fe_2TiO_5 layer and FeNiOOH nanodots, while the upgrading of back contact conductivity and charge donor densities originate from the epitaxial relationship and enhanced Sn doping contributed from the ITO underlayer. We attribute the superior water oxidation performance to the interfacial coupling effect of the ITO underlayer (Sn doping and back contact conductivity promoter), the atomic level Fe_2TiO_5 coating (Ti doping, surface state density and energy level modulation) and the FeNiOOH nanodot electrocatalyst (regulating surface state energy level). Our work suggests an effective pathway for rational designing of highly active and cost-effective integrated photoanodes for photoelectrochemical water splitting.

Additional Information

© 2017 The Royal Society of Chemistry. The article was received on 26 May 2017, accepted on 18 Jul 2017 and first published on 18 Jul 2017. This work was supported by the Spanish Ministerio de Economia y Competitividad (MINECO, grant CTQ2015-71287-R) through coordinated Projects TNT-FUELS, e-TNT (MAT2014-59961-C2), WINCOST ENE2016-80788-C5, the BIST Ignite Project inWOC and the Generalitat de Catalunya (2014-SGR-797 and 2014-SGR-1638). Part of the present work was performed in the framework of Universitat Autònoma de Barcelona Materials Science PhD program. We acknowledge Dr Guillaume Sauthier from the ICN2 for the XPS measurements. ICN2 and ICIQ acknowledge support from the Severo Ochoa Program (MINECO, Grant SEV-2013-0295 and SEV-2013-0319). ICN2 and ICIQ are funded by the CERCA Programme/Generalitat de Catalunya. Author contribution: PengYi Tang, Jordi Arbiol and Joan Ramon Morante designed the experiments. PengYi Tang carried out the XRD, UV-Vis spectra, SEM, EDS, TEM, STEM-EELS maps, atomic supercell models, hydrothermal reaction, sintering process, photo-electrodeposition, and electrochemical experiments. HaiBing Xie, Alejandro Pérez Rodríguez and Edgardo Saucedo carried out the ITO sputtering experiments. Carles Ros, Martí Biset-Peiró and Teresa Andreu carried the ALD TiO2 deposition experiments. LiJuan Han and José Ramón Galán-Mascarós participated in part of the PEIS experiments and PEIS data analysis. Guillaume Sauthier carried out the XPS spectrum experiments. PengYi Tang, Jordi Arbiol, YongMin He, Wesley Kramer and Joan Ramon Morante co-wrote the manuscript and all authors edited the manuscript.

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