Defect engineering of graphynes for energy storage and conversion

•Defect types of solid materials are classified.•The forms of various defects in graphynes are given.•The application of different defect types of graphynes are introduced.•The opportunities and challenges of defective graphynes are discussed. Graphynes have great application potential in energy storage and conversion. However, due to the limitation of specific surface area and active site, their energy storage capacity and catalytic efficiency are expected to be further improved. Defect engineering is a complex technique that can alter the geometry and chemical environment of a subject via introducing defects. Defects such as vacancy and heteroatom can expose a lot of coordination unsaturated sites, change the charge distribution around the carbon atom and improve graphynes cycle stability, thus markedly promoting the catalytic activity and significantly optimizing the battery energy storage of graphynes. In this paper, the research progress of defect engineering of graphynes in energy storage, electrocatalysis and photocatalysis is reviewed. Firstly, the classification of defects in solid materials and the forms of various defects in graphynes are given. Secondly, the application of different defect types, such as elemental doping, vacancy, single-atom catalyst and heterojunction on graphynes for energy storage, catalysis and solar cells are introduced. Finally, the opportunities and challenges for the future research on defective graphynes are discussed.