Photocatalytic and photoelectrochemical processes are two key systems in harvesting sunlight for energy and environmental applications. As both systems are employing photoactive semiconductors as the major active component, strategies have been formulated to improve the properties of the semiconductors for better performances. However, requirements to yield excellent performances are different in these two distinctive systems. Although there are universal strategies applicable to improve the performance of photoactive semiconductors, similarities and differences exist when the semiconductors are to be used differently. Here, considerations on selected typical factors governing the performances in photocatalytic and photoelectrochemical systems, even though the same type of semiconductor is used, are provided. Understanding of the underlying mechanisms in relation to their photoactivities is of fundamental importance for rational design of high‐performing photoactive materials, which may serve as a general guideline for the fabrication of good photocatalysts or photoelectrodes toward sustainable solar fuel generation.

Cuprous Oxide (Cu O) is a photocatalyst with severe photocorrosion issues. Theoretically, it can undergo both self-oxidation (to form copper oxide (CuO)) and self-reduction (to form metallic copper (Cu)) upon illumination with the aid of photoexcited charges. There is, however, limited experimental understanding of the "dominant" photocorrosion pathway. Both photocorrosion modes can be regulated by tailoring the conditions of the photocatalytic reactions. Photooxidation of Cu O (in the form of a suspension system), accompanied by corroded morphology, is kinetically favourable and is the prevailing deactivation pathway. With knowledge of the dominant deactivation mode of Cu O, suppression of self-photooxidation together with enhancement in its overall photocatalytic performance can be achieved after a careful selection of sacrificial hole (h ) scavenger. In this way, stable hydrogen (H ) production can be attained without the need for deposition of secondary components.

Improving the stability of cuprous oxide (Cu 2 O) is imperative to its practical applications in artificial photosynthesis. In this work, Cu 2 O nanowires are encapsulated by metal-organic frameworks (MOFs) of Cu 3 (BTC) 2 (BTC = 1,3,5-benzene tricarboxylate) using a surfactant-free method. Such MOFs not only suppress the water vapor-induced corrosion of Cu 2 O but also facilitate charge separation and CO 2 uptake, thus resulting in a nanocomposite representing 1.9 times improved activity and stability for selective photocatalytic CO 2 reduction into CH 4 under mild reaction conditions. Furthermore, direct transfer of photogenerated electrons from the conduction band of Cu 2 O to the LUMO level of nonexcited Cu 3 (BTC) 2 has been evidenced by time-resolved photoluminescence. This work proposes an effective strategy for CO 2 conversion by a synergy of charge separation and CO 2 adsorption, leading to the enhanced photocatalytic reaction when MOFs are integrated with metal oxide photocatalyst.