Photoelectrochemistry, semiconductor electrochemistry, and/or photocatalysis are of active research fields and thousands of papers are published in these fields annually. Many research groups are attracted in these subjects because of their potential importance in achieving carbon neutral society based on solar energy, a renewable energy. Although semiconductor electrochemistry had been studied systematically since 1950's and many reviews and books were published by early 1970's,^1-7 research on photoelectrochemistry became very active in the late 1970's after the 1st oil crisis triggered by the paper by Fujishima and Honda,⁸ in which they suggested that solar energy may be directly converted to a chemical energy, hydrogen, by using semiconductor/aqueous electrolyte solution/metal cells.⁸ Research activities were high in 1980's and the ECS has organized symposia on photoelectrochemistry/semiconductor electrochemistry in the annual meetings many times with the publications of proceeding volumes.^9-14 Many important developments were made in the 1970's and 1980's. Major target of the photoelectrochemistry/photocatalysis research changed from solar energy conversion to environmental issues^{12, 13} and activities gradually declined due to the lack of funding, particularly in the US.

There must be reasons why photoelectrochemistry lost supports as solar energy conversion process in 1990's and it is a good time to look back what had been achieved, what were the problems, and are these problems solved by now.

In this talk, I will try to sum up the results achieved by 1990's and compare them with current activities.

References
1. M. Green, in Modem Aspects of Electrochemistry, No. 2. Ed. by J. O'M. Bockris, Butterworths, London, 343-407 (1959).
2. J. F. Dewald. in Semiconductors. ACS Monograph, No. 140, Ed. by N. B. Hannay, Reinhold, New York, 727-752 (1959).
3. H. Gerischer. in Adv. Electrochem. Electrochem. Eng., Vol. 1, Ed. by P. Delahay, lnterscience, New York, 139-232 (1961).
4. P. J. Holmes. Ed., The Electrochemistry of Semiconductors, Academic. London, 1962.
5. V. A. Myamlin and Yu. V. Pleskov, Electrochemistry of Semiconductors. Plenum, New York. 1967.
6. H. Gerischer, in Physical Chemistry: An Advanced Treatise, Vol. IXA. Ed. by H. Eyring. Academic. New York. 1970, Chap. 5.
7. S. R. Morrison, Prog. Surf. Sci., 1(1971) 105.
8. A. Fujishima and K. Honda, Nature, 238 (1972) 37.
9. PV 77-3, "Semiconductor Liquid-Junction Solar Cells", Ed. by A. Heller.
10. PV 82-3, "Photoelectrochemistry: Fundamental Processes and Measurement Techniques. Ed. by W. L. Wallace, A. J. Nojik, and S. K. Deb.
11. PV 88-14, "Photoelectrochemistry and Electrosynthesis on Semiconducting Materials", Ed. by D.S. Ginley, A. Nojik, N. Armstrong, K. Honda, A. Fujishima, T. Sakata, and T. Kawai.
12. PV 93-18, Environmental Aspects of Electrochemistry and Photoelectrochemistry'', Ed. by M. Tomkiewicz, H. Yoneyama, R. Haynes, and Y. Hori.
13. PV 94-19, "Water Purification by Photocatalytic, Photoelectrochemical, and Electrochemical Processes", Ed. by T. L. Rose, E. Rudd, 0. Murphy, and B. E. Conway.
14. PV 97-20, "Photoelectrochemistry", Ed. by K. Rajeshwar, L. M. Peter, A. Fujishima, D. Meissner, and M. Tomkiewicz.