**5. Conclusion**

The electrocatalytic ability of catalysts is usually determined by below two points: one is the intrinsic electrocatalytic activity, and another is the nanostructure. The nanostructure of TMCs can briefly be classified into 0D, 1D, 2D, and hierarchical nanostructures; those have different properties and could obviously affect the electrocatalytic ability. Herein, the partial reports about DSSCs with the electrocatalysts having 1D, 2D, or hierarchical nanostructures are selected for introduction and discussion. 1D nanostructure possesses several advantages, including the 1D electron transfer pathways, promoting electrolyte penetration, avoiding stack problem, and high reaction area. However, not all the electrocatalysts with 1D nanostructure show better performance than the Pt in DSSC application. Some of them lied down

on substrate; so, the advantage on vertical electron transport rout is not given. Furthermore, as the stacking problem comes out, it will lose surface are for reaction. 2D nanostructures possess the active site on edges or defects, and their 2D structure could provide the benefits below, such as directional electron and diffusion channels; these properties boost their DSSC performances obviously. However, the stacking problem and poor activity on basal plane of 2D materials also retarding their practical performance in DSSCs. Hierarchical nanostructure incorporates the profits of subunits, so it displays high reaction area, benefit electron transport rout, avoiding aggregation, enhanced electrolyte diffusion, *etc*. Several reports already demonstrated that the TMCs with hierarchical nanostructures show excellent electrocatalytic ability in DSSCs; they even exhibit better electrocatalytic performance than that of Pt.
