Environmental problems are rooted in the modern science paradigm. The scientific analytical method necessitates a certain kind of idealization, thereby neglecting some aspects of a phenomenon in question. This inevitable negligence can be a critical factor for an environmental problem. In coping with environmental problems, it is therefore necessary to understand the nature of science as well as develop appropriate technical measures needed on a daily basis. To develop a comprehensive understanding of the problems of environmental degradation and resource depletion, thermophysical concepts such as energy, entropy and exergy will be useful. These concepts will advance the understanding of the problems from various viewpoints that the reductionist science paradigm fails to embrace.

From the points of view of environmental protection and the effective use of energy resources, the replacement of combustion engines by hybrid systems is now progressing rapidly in the field of automobile technology. Furthermore, in the long term, the realization of fuel cell vehicles is expected; therefore, the research and development of secondary batteries and fuel cells have been accelerated. Since these breakthroughs depend on the evolution of energy materials, cooperation and competitiveness, including those of material suppliers, coexist. On the other hand, the commercialization of fuel cells in the field of mobile systems will be demanded owing to the need for the increase in usage time. The cost reduction of fuel cells for mobile use is more realistic compared with that for automobile use, so fuel cells for mobile use are expected to be commercialized within two years.

Within the next generation of photovoltaic devices, dye-sensitized solar cells (DSCs) are one of the foci of today’sresearch interest. In this paper, we discuss DSCs from the viewpoint of physics. The equivalent-circuit model of DSCs is proposed by an analysis of internal resistance. The methods of improving short-circuit current density, open circuit voltage, and fill factor are demonstrated on the basis of the equivalent-circuit model of DSCs. The fair and accurate evaluation method of cell performance for DSCs is also explained. As a result, a maximum efficiency of 10.4% (aperture illumination area 1.004 cm², confirmed by a public test center) was achieved. The current state and future prospects of DSCs are also surveyed.

In recent years, the direct methanol fuel cell (DMFC), with its distinguished characteristics as a small, lightweight and off-plug power generating system for portable electronic devices, has, in particular, attracted the attention of many researchers. First, in this report, the author gives a general overview of the fundamental DMFC structure and principal power-generation mechanisms based on thermodynamic theory. Thereafter, the report focuses on explaining the electrode reaction mechanisms at electrocatalysts and methanol crossover caused by the use of polymer electrolyte membrane. Finally, a brief introduction on some examples of DMFC systems specialized for portable applications are presented.

With the increasing importance of reading electronic documents, expectations are high that a new electronic paper can be developed that is as convenient as conventional hard-copy paper and enables access to digital information. At present, a great deal of fundamental and applied research is being carried out on various methods of producing electronic paper, including microcapsule-type electrophoretic displays, toner displays based on the movement of fine particles, and polymer-dispersed liquid crystal and liquid crystal/organic photoconductor double-layered electronic papers.

The strong oxidation ability and superhydrophilicity of TiO₂ photocatalysts under light irradiation have been applied for environmental harmonious purification and the development of various self-cleaning materials. Furthermore, TiO₂ photocatalysts induce various artificial photosynthetic reactions such as the decomposition of water to produce H₂ and O₂ or the reduction of CO₂ with water into organic compounds such as CH₃OH and CH₄. In this review, recent advances in the science and technology of TiO₂ photocatalysts for environmental harmonious purification and the efficient conversion of solar energy into chemical energy will be introduced. Particular attention is focused on the recent progress in the development of visible-light-responsive TiO₂ photocatalysts.

Today, many kinds of and large amounts of synthetic plastics are produced mainly from limited fossil resources, namely, petroleum oil. These materials are indispensable for our lives and industries, but they can cause problems in the earth’s environment and will cause the exhaustion of fossil oil. Biodegradable polymers that are producible from renewable plant resources are expected to become alternative plastic materials to solve such problems. In this review, the production, properties and biodegradation of these biodegradable plastics are discussed.

Soil and groundwater pollution by toxic chemicals such as trichloroethylene, tetrachloroethylene, polychlorinated dibenzodioxins, oils and heavy metals is of international concern because of their global distribution, persistence, and toxicity. Various attempts are now being made to develop and evaluate groundwater and soil clean-up technologies. To clean up heavy metals and chlorinated compounds, physical and chemical remediation methods are commonly applied. However, these technologies are expensive. Therefore, the development of cheap and safe bioremediation technologies is of great concern. Bioremediation technologies use microorganisms to treat contaminants by enhancing natural biodegradation mechanisms through the addition of microorganisms, nutrients, electron donors and/or electron acceptors. The current and future status of bioremediation technologies for cleaning up volatile chlorinated compounds, dioxins, oils and mercury in groundwater and soil environments is discussed.