Abstract: Electrocatalysis, photocatalysis, and photoelectrocatalysis constitute three pivotal technologies for sustainable energy conversion. However, the interwoven concepts and applications among them have hindered a profound understanding of their shared principles and differentiated mechanisms. Delafossite-type oxides (ABO₂), characterized by their unique layered structure and highly tunable electronic properties, serve as an ideal model platform for a systematic comparison of these three catalytic pathways on a unified material basis. This review employs Delafossite as a lens to deconstruct the fundamental distinctions among electrocatalysis, photocatalysis, and photoelectrocatalysis in terms of energy input, charge generation/transport dynamics, and interfacial processes. The analysis reveals that, despite their disparate operational paradigms, the ultimate performance ceiling of each technology is uniformly governed by the material’s efficiency in managing the spatiotemporal behavior of charge carriers. Building upon this common principle, this review provides a critical assessment of the performance bottlenecks of Delafossite in each catalytic mode and proposes forward-looking, multi-level fusion strategies. These span from intelligent material design (e.g., adaptive heterojunctions, gradient functional devices) to innovative system integration (e.g., temporally sequenced reactors, on-chip photoelectrochemical coupling). Furthermore, this review outlines key challenges facing the field, including the need for cross-scale characterization, multi-physics theoretical simulation, and unified evaluation standards. It concludes with a perspective on a future vision of on-demand, customized energy-chemical conversion enabled by artificial intelligence-aided design, aiming to provide a clear theoretical framework and guidline for developing next-generation efficient and intelligent catalytic systems.