Redox-bipolar COFs. As mentioned above, the design of COFs with both high specific capacity and high voltage is one of the current challenges to achieve high energy densities. In this sense, the construction of COFs combining n-type and p-type building blocks can be an efficient approach to increase both parameters. This concept was first demonstrated by the synthesis of an imine-linked 2D COF (TP-TA) with Kagome topology based on the condensation reaction between tetraphenyl-p-phenylenediamine (TP) and terephthaldehyde (TA). In this case, the C=N linkages can be reduced acting as ntype moieties, while p-type TP building block can undergo 2 e - oxidation process and combine with two PF6 -from the electrolyte. This bipolar-type COF showed a specific capacity of 207 mAh g -1 (at 200 mA g -1 ), an average redox voltage of 3.6 V vs Li/Li + and good cycling stability (93% retention after 1500 cycles). Another representative example of this design strategy is a 2D COF (TPPDA-CuPor) composed of tetratopic p-type TP and bipolar-type porphyrin building blocks (Fig. ), which provides a high redox potential and a high number of redoxactive centres. Indeed, TPPDA-CuPor COF cathode exhibited an average voltage of 2.7 V vs Li/Li + and specific capacity of 142 mAh g -1 at 60 mA g -1 , resulting in a calculated energy density of 371 Wh kg -1 . In addition, the bipolar redox mechanism was further confirmed by DFT calculations and ex situ XPS. More recently, Feng and co-workers have reported a redoxbipolar COF based on n-type imides and p-type triazine moieties that was investigated as cathode for rechargeable aluminium batteries achieving a specific capacity of 132 mAh g -1 and excellent cycling stability (97% capacity retention after 4000 cycles). We also note that a similar approach has been carried out for the synthesis of an amorphous porous organic polymer based on the polyimide condensation of mellitic acid trianhydride (n-type) and diamino N-methyl phenothiazine (ptype). Such dual-redox porous organic polymer was used as electrode in symmetric all-organic batteries displaying a specific capacity of 57 mAh g -1 (2 C) and capacity retention of 57% at high rates (60 C). The design of bipolar-type COFs is still in its infancy and new combinations of building blocks as well as advanced in-situ/ex-situ mechanism studies are still needed to boost the performance of this promising type of COF electrodes.