Photoelectrocatalytic and Photocatalytic Reduction Using Diamond

Diamond has excellent physical and chemical stability and exhibits unique electrochemical properties. This chapter focuses on the behavior of diamonds as a photoelectrochemical electrode and photocatalyst under light irradiation. Since diamond has a large band gap, long wavelength light such as visible light cannot excite electrons from valence band to the conduction band. However, when irradiated with short wavelength ultraviolet light, a photocurrent based on electron excitation can be observed. Thus, diamond can act as a photoelectrochemical electrode. And also, the generated excited electrons can also give an opportunity as a photocatalyst under no bias. Since the conduction band of diamond is large negative, especially in the case of hydrogen-terminated diamond, it shows a negative electron affinity under light irradiation, and it generates dissolved electrons in a solution, which should reduce inactive molecules to make useful substances. In this chapter, we introduce reduction reactions utilizing negative electron affinity and also describe the effect of modification of the diamond surface on the reduction reaction, and finally, hybridization with nanomaterials that enhances the light absorption efficiency of diamond.