AVS 62nd International Symposium & Exhibition
    Energy Frontiers Focus Topic Tuesday Sessions
       Session EN+AS+EM+SE+SS-TuM

Invited Paper EN+AS+EM+SE+SS-TuM10
Interface Design for Efficient and Stable Photoelectrochemical Water Splitting

Tuesday, October 20, 2015, 11:00 am, Room 211B

Session: Photocatalysis
Presenter: Joel Ager, Lawrence Berkeley National Laboratory
Correspondent: Click to Email
Solar photoelectrochemical (PEC) water splitting is potential future carbon-neutral energy source which could dramatically change the landscape of global energy generation and storage. The half reactions for water splitting are as follows:

2H+ + 2 e- <-> H2 (1)

H2O <-> 2e- +2H+ + 1/2O2. (2)

The free energy change for the overall reaction, H2O <-> H2 + 1/2O2 corresponds to 1.23 eV per electron transferred; however, typically >1.5 V is required to overcome kinetic limitations, particularly for the O2 evolution reaction. The most commonly used approach for integrated solar water splitting employs photocathodes (H2 or hydrocarbon producing) and photoanodes (O2 producing) linked in a tandem geometry [1].

The interface challenges required to demonstrate a practical system which is both efficient and stable under operation are substantial and severe. In addition to constructing interfaces, either solid-solid or solid liquid, which achieve the desired photovoltaic charge separation, the surfaces of these photoelectrodes can be a failure point under sustained operation due to corrosion. We have found that the use of nanoscale conformal oxide layers can greatly reduce corrosion rates. Moreover, it is possible to achieve both high performance and lifetime by the use of protection layers which are also tuned for selective carrier contact.

Examples of such a strategy will be shown for photocathodes [2-5] and for photoanodes [5]. Recent work on p-type transparent oxides (p-TCOs) used as selective hole contacts for photoanodes will be emphasized. For example, it will be shown that using NiCo2O4 as the p-TCO and n-type Si as a prototypical light absorber, a rectifying heterojunction capable of light driven water oxidation can be created. By placing the charge separating junction in the Si using a np+ structure and by incorporating a highly active Ni-Fe oxygen evolution catalyst, efficient light-driven water oxidation can be achieved. The generality of the p-TCO protection approach is demonstrated by multi-hour, stable, water oxidation with n-InP/p-NiCo2O4 heterojunction photoanodes.

Acknowledgements. This material is based upon work performed by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under Award Number DE-SC0004993.

References.

1. J. W. Ager et al., Energy Environ. Sci. (2015). DOI:10.1039/C5EE00457H

2. M. H. Lee et al., Ang. Chemie Int. Edition51 10760 (2012).

2. Y. Lin et al., Nano Letters13 5615 11 (2013)

3. Y. Lin et al., J. Phys. Chem. C 119, 2308 (2015).

4. J. Yang et al., J. Amer. Chem. Soc.136 6191 (2014).