Structural-enhanced bacterial cellulose based alkaline exchange membranes for highly selective CO2 electrochemical reduction and excellent conductive performance in flexible zinc-air batteries

Through the combinations of layer-by-layer method and double cross-linking process, OH– conducting membrane based on bacterial cellulose (BC) had been synthesized with the modification by Poly (diallyldimethyl-ammonium chloride) (PDDA) and Poly (vinyl alcohol) (PVA) of different molecular weights. Under the help of PVA, an enhanced internal three-dimensional network could be easily constructed to overcome the disadvantage of excessively loosely binding in the BC membrane. Charge carrier PDDA were confirmed by FTIR and SEM to be firmly embedded into the network while studies on XRD and DSC indicated that amorphous content which was beneficial to ionic transfer and ions hopping held the large proportion in the membrane. Stability measurements such as thermogravimetric analysis, mechanical properties, alkaline and oxygen resistance were carried out, showing that the prepared membranes possessed excellent durable performance under various extreme conditions. Moreover, OH– conductivity and water uptake were intensively investigated by changing crosslinking conditions, KOH concentrations and PVA molecular weights. Achieving the maximum σOH− of 72.95 mS cm−1 at room temperature, the LPVA-PDDA-BC-OH– membrane showed the lowest calculated activation energy value of 10.211 KJ mol−1, indicating that both Grotthus and vehicle mechanisms played an important role on ionic transportation. When as-prepared LPVA-PDDA-BC-OH– membrane was applied for CO2 electrochemical reduction (CO2ER) in 0.5 M KHCO3, current density could reach up to 47.44 mA cm−2 at −1.06 VRHE. Meanwhile, Faradaic efficiency for formate (FEHCOO−) could achieve the maximum value of 67.89 % that dampened only 7.09 % after 20 h electrolysis. Furthermore, when as-prepared LPVA-PDDA-BC-OH– membrane was assembled into the flexible zinc-air batteries (F-ZAB), excellent power density of 130.3 mW cm−2 could be obtained at room temperature.