Objective and Method Currently, there remains a lack of criteria for technical certification, designation, and classification of carbon dioxide (CO₂) storage technologies due to their cross-disciplinary nature and ambiguous scopes. To address this issue, this study proposes technical certification criteria and designation principles, as well as analyzes four types of common CO₂ storage technologies: geologic storage, underground space storage, ocean water storage, and utilization and storage. Accordingly, a classification philosophy and scheme for these technologies is determined.

Results and Conclusions In terms for technical certification criteria, a CO₂ storage technology has to meet four criteria: (1) it must enable effective, long-term to permanent separation of CO₂ from the atmosphere; (2) it must be anthropogenic activity aimed at reducing atmospheric CO₂ beyond statutory requirements; (3) it should do no significant harm to the environment. Regarding the designation in Chinese and English (including English abbreviations) for CO₂ storage technologies, the following principles should be followed: (1) well-known technology names should be used without modification, while technologies similar to those widely recognized should be designated following the designation principles of the latter. For emerging technologies, the most frequently used Chinese and English names, as identified using academic search engines, shall be used. For English terms, "sequestration" and "storage" differ slightly in the field of carbon removal. Specifically, "sequestration" emphasizes scientific mechanisms, while "storage" highlights a broader scale or is more engineering-oriented. A generally hierarchical classification philosophy is proposed in this study. First, based on their differences in storage environments, CO₂ storage technologies can be divided into terrestrial and marine categories. Second, several types can be determined based on CO₂ storage space and mechanism. Third, further classification is performed by storage depth and scale. Fourth, the minimum types can be determined by further classification by storage proportion and time. Using this classification philosophy, a classification scheme for CO₂ storage technologies is determined, consisting of two levels and seven indicators. The first level comprises storage environment, storage space, and storage mechanism, which are three qualitative indicators. The second level is composed of sub-class, model, grade, and pattern, corresponding to four quantitative indicators, i.e., storage depth, storage scale, storage proportion, and storage time, respectively.