Solid-state chemistry languished as an esoteric discipline till interest exploded on the so-called high-Tc superconductor materials; oxides were discovered to have unique properties in this regard. Paralleling this was the gradual realization that solid-state chemistry principles underpinned many technologically-important areas such as batteries, supercapacitors, and even solar cells. The culmination of this trend was in the application of solid-state chemistry to the preparation and characterization of electrode materials in photoelectrochemical (PEC) cells.

This perspective talk will examine how solid-state chemistry principles have contributed both to the design and synthesis of photoelectrode materials for PEC applications related to water splitting, CO₂ reduction, and environmental remediation. The design of new-generation oxide semiconductors with the correct optoelectronic and bulk/interfacial chemistry characteristics needed to efficiently drive the above reactions will be addressed. The list of material pre-requisites for efficient solar fuels generation or photocatalytic degradation is daunting and it is hardly surprising that a “magic bullet” material has not emerged even after 4 decades of R&D effort. However, these same challenges have attracted researchers drawn from diverse communities including solid-state/device physics, photophysics/photochemistry, colloid chemistry, ultra-fast spectroscopy, classical inorganic chemistry, environmental chemistry and organometallics.

To keep the discussion coherent, only a very limited subset of topics will be addressed in this talk. The progression from binary to ternary, and even quaternary oxides will be examined from the perspective of “band-gap engineering” (a much-maligned word!) and tuning of the interfacial semiconductor surface/fluid energetics. Examples will be drawn from recent research in the speaker’s laboratory and with collaborators.^1-4

Acknowledgements

The author thanks his collaborators, particularly, Prof. Csaba Janaky (University of Szeged, Hungary) and the National Science Foundation (CHE- 1303803) for partial funding support.

References

1. K. Rajeshwar, C. Janaky, W-Y. Lin, D. A. Roberts and W. A. Wampler, “Photocatalytically Prepared Metal Nanocluster-Oxide Semiconductor-Carbon Nanocomposite Electrodes for Driving Multielectron Transfer,” J. Phys. Chem. Lett. 4. 3468-3478 (2013) (Perspective).

2. K. Rajeshwar, C. Janaky and A. Thomas, “Photocatalytic Activity of Inorganic Semiconductor Surfaces: Myths, Hype, and Reality,” J. Phys. Chem. Lett. 6, 139-147 (2015) (Viewpoint).

3. C. Janaky and K. Rajeshwar, “The Role of (Photo)Electrochemistry in the Rational Design of Hybrid Conducting Polymer/Semiconductor Assemblies: From Fundamental Concepts to Practical Applications,” Prog. Poly. Sci. 43, 96-135 (2015).

4. K. Rajeshwar, C. Janaky and E. Kescenovity, “Electrodeposition of Inorganic Oxide/Nanocarbon Composites: Opportunities and Challenges,” ChemElectroChem 3, 181-192 (2016).