title: p-Type Transparent Conducting Oxide/n-Type Semiconductor Heterojunctions for Efficient and Stable Solar Water Oxidation.
abstract: Achieving stable operation of photoanodes used as components of solar water splitting devices is critical to realizing the promise of this renewable energy technology. It is shown that p-type transparent conducting oxides (p-TCOs) can function both as a selective hole contact and corrosion protection layer for photoanodes used in light-driven water oxidation. Using NiCo2O4 as the p-TCO and n-type Si as a prototypical light absorber, a rectifying heterojunction capable of light driven water oxidation was created. By placing the charge separating junction in the Si using a np(+) structure and by incorporating a highly active heterogeneous Ni-Fe oxygen evolution catalyst, efficient light-driven water oxidation can be achieved. In this structure, oxygen evolution under AM1.5G illumination occurs at 0.95 V vs RHE, and the current density at the reversible potential for water oxidation (1.23 V vs RHE) is >25 mA cm(-2). Stable operation was confirmed by observing a constant current density over 72 h and by sensitive measurements of corrosion products in the electrolyte. In situ Raman spectroscopy was employed to investigate structural transformation of NiCo2O4 during electrochemical oxidation. The interface between the light absorber and p-TCO is crucial to produce selective hole conduction to the surface under illumination. For example, annealing to produce more crystalline NiCo2O4 produces only small changes in its hole conductivity, while a thicker SiOx layer is formed at the n-Si/p-NiCo2O4 interface, greatly reducing the PEC performance. The generality of the p-TCO protection approach is demonstrated by multihour, stable, water oxidation with n-InP/p-NiCo2O4 heterojunction photoanodes.
authors.affiliation: †Joint Center for Artificial Photosynthesis, ‡Materials Sciences Division, ¶Chemical Sciences Division, and §Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.|∥Department of Chemical and Biomolecular Engineering and ⊥Department of Materials Science and Engineering, University of California at Berkeley, Berkeley, California 94720, United States.
authors.forename: Le
authors.initials: L
authors.lastname: Chen
authors.affiliation: †Joint Center for Artificial Photosynthesis, ‡Materials Sciences Division, ¶Chemical Sciences Division, and §Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.|∥Department of Chemical and Biomolecular Engineering and ⊥Department of Materials Science and Engineering, University of California at Berkeley, Berkeley, California 94720, United States.
authors.forename: Jinhui
authors.initials: J
authors.lastname: Yang
authors.affiliation: †Joint Center for Artificial Photosynthesis, ‡Materials Sciences Division, ¶Chemical Sciences Division, and §Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.|∥Department of Chemical and Biomolecular Engineering and ⊥Department of Materials Science and Engineering, University of California at Berkeley, Berkeley, California 94720, United States.
authors.forename: Shannon
authors.initials: S
authors.lastname: Klaus
authors.affiliation: †Joint Center for Artificial Photosynthesis, ‡Materials Sciences Division, ¶Chemical Sciences Division, and §Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.|∥Department of Chemical and Biomolecular Engineering and ⊥Department of Materials Science and Engineering, University of California at Berkeley, Berkeley, California 94720, United States.
authors.forename: Lyman J
authors.initials: LJ
authors.lastname: Lee
authors.affiliation: †Joint Center for Artificial Photosynthesis, ‡Materials Sciences Division, ¶Chemical Sciences Division, and §Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.|∥Department of Chemical and Biomolecular Engineering and ⊥Department of Materials Science and Engineering, University of California at Berkeley, Berkeley, California 94720, United States.
authors.forename: Rachel
authors.initials: R
authors.lastname: Woods-Robinson
authors.affiliation: †Joint Center for Artificial Photosynthesis, ‡Materials Sciences Division, ¶Chemical Sciences Division, and §Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.|∥Department of Chemical and Biomolecular Engineering and ⊥Department of Materials Science and Engineering, University of California at Berkeley, Berkeley, California 94720, United States.
authors.forename: Jie
authors.initials: J
authors.lastname: Ma
authors.affiliation: †Joint Center for Artificial Photosynthesis, ‡Materials Sciences Division, ¶Chemical Sciences Division, and §Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.|∥Department of Chemical and Biomolecular Engineering and ⊥Department of Materials Science and Engineering, University of California at Berkeley, Berkeley, California 94720, United States.
authors.forename: Yanwei
authors.initials: Y
authors.lastname: Lum
authors.affiliation: †Joint Center for Artificial Photosynthesis, ‡Materials Sciences Division, ¶Chemical Sciences Division, and §Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.|∥Department of Chemical and Biomolecular Engineering and ⊥Department of Materials Science and Engineering, University of California at Berkeley, Berkeley, California 94720, United States.
authors.forename: Jason K
authors.initials: JK
authors.lastname: Cooper
authors.affiliation: †Joint Center for Artificial Photosynthesis, ‡Materials Sciences Division, ¶Chemical Sciences Division, and §Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.|∥Department of Chemical and Biomolecular Engineering and ⊥Department of Materials Science and Engineering, University of California at Berkeley, Berkeley, California 94720, United States.
authors.forename: Francesca M
authors.initials: FM
authors.lastname: Toma
authors.affiliation: †Joint Center for Artificial Photosynthesis, ‡Materials Sciences Division, ¶Chemical Sciences Division, and §Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.|∥Department of Chemical and Biomolecular Engineering and ⊥Department of Materials Science and Engineering, University of California at Berkeley, Berkeley, California 94720, United States.
authors.forename: Lin-Wang
authors.initials: LW
authors.lastname: Wang
authors.affiliation: †Joint Center for Artificial Photosynthesis, ‡Materials Sciences Division, ¶Chemical Sciences Division, and §Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.|∥Department of Chemical and Biomolecular Engineering and ⊥Department of Materials Science and Engineering, University of California at Berkeley, Berkeley, California 94720, United States.
authors.forename: Ian D
authors.initials: ID
authors.lastname: Sharp
authors.affiliation: †Joint Center for Artificial Photosynthesis, ‡Materials Sciences Division, ¶Chemical Sciences Division, and §Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.|∥Department of Chemical and Biomolecular Engineering and ⊥Department of Materials Science and Engineering, University of California at Berkeley, Berkeley, California 94720, United States.
authors.forename: Alexis T
authors.initials: AT
authors.lastname: Bell
authors.affiliation: †Joint Center for Artificial Photosynthesis, ‡Materials Sciences Division, ¶Chemical Sciences Division, and §Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.|∥Department of Chemical and Biomolecular Engineering and ⊥Department of Materials Science and Engineering, University of California at Berkeley, Berkeley, California 94720, United States.
authors.forename: Joel W
authors.initials: JW
authors.lastname: Ager