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Issue 37, 2013
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A semiconductor/mixed ion and electron conductor heterojunction for elevated-temperature water splitting

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Abstract

Photoelectrochemical cells (PECs) have been studied extensively for dissociating water into hydrogen and oxygen. Key bottlenecks for achieving high solar-to-hydrogen efficiency in PECs include increasing solar spectrum utilization, surmounting overpotential losses, and aligning the absorber/electrochemical redox levels. We propose a new class of solid-state PECs based on mixed ionic and electronic conducting (MIEC) oxides that operates at temperatures significantly above ambient and utilizes both the light and thermal energy available from concentrated sunlight to dissociate water vapor. Unlike thermochemical and hybrid photo-thermochemical water-splitting routes, the elevated-temperature PEC is a single-step approach operating isothermally. At the heart of the solid-state PEC is a semiconductor light absorber coated with a thin MIEC layer for improved catalytic activity, electrochemical stability, and ionic conduction. The MIEC, placed between the gas phase and the semiconductor light absorber, provides a facile path for minority carriers to reach the water vapor as well as a path for the ionic carriers to reach the solid electrolyte. Elevated temperature operation allows reasonable band misalignments at the interfaces to be overcome, reduces the required overpotential, and facilitates rapid product diffusion away from the surface. In this work, we simulate the behavior of an oxygen-ion-conducting photocathode in 1-D. Using the detailed-balance approach, in conjunction with recombination and electrochemical reaction rates, the practical efficiency is calculated as a function of temperature, solar flux, and select material properties. For a non-degenerate light absorber with a 2.0 eV band-gap and an uphill band offset of 0.3 eV, an efficiency of 17% and 11% is predicted at 723 and 873 K, respectively.

Graphical abstract: A semiconductor/mixed ion and electron conductor heterojunction for elevated-temperature water splitting

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Publication details

The article was received on 18 Jun 2013, accepted on 11 Jul 2013 and first published on 11 Jul 2013


Article type: Paper
DOI: 10.1039/C3CP52536H
Citation: Phys. Chem. Chem. Phys., 2013,15, 15459-15469
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    A semiconductor/mixed ion and electron conductor heterojunction for elevated-temperature water splitting

    X. Ye, J. Melas-Kyriazi, Z. A. Feng, N. A. Melosh and W. C. Chueh, Phys. Chem. Chem. Phys., 2013, 15, 15459
    DOI: 10.1039/C3CP52536H

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