| The current challenges facing proton exchange membrane fuel cell are mainly from the high cost and low durability of important components, such as the polyelectrolytes, the noble metal electrocatalysts, and the graphite bipolar plates. The downsides can be greatly improved by switching from an acidic medium to a basic one, using alkaline electrolyte membranes. In the basic environment, the catalyst activity of Pt toward oxygen reduction reaction (ORR) is much higher, leading to reduced Pt loading and extended choices for non-noble Pt catalysts. In addition, the alcohol crossover problem can be significantly reduced due to OH- ion transporting oppose to methanol. The alkaline membrane, as a key componet of alkaline fuel cell, has dual functions of separation of the fuel from the oxidizer, and OH" conduction. PVA is a kind of biodegradable polymer materials with good film forming property and low cost. This work aims to develope novel PVA-based alkaline blend membranes with simple preparation, moderate price and excellent electrochemical properties through the blending way, and finally to obtain high power performance.This work focuses on the preparation and characterization of poly(vinyl alcohol) (PVA/KOH), poly(vinyl alcohol)/poly(vinyl pyrrolidone) (PVA/PVP/KOH), poly(vinyl alcohol)/poly(ethylene glycol) dimethyl ether (PVA/PEGDE/KOH) alkaline blend membranes, and the poly(vinyl alcohol)/Poly(acrylamide-co-diallyldimethylammonium chloride) (PVA/PAADDA) and poly(vinyl alcohol)/Poly(acrylamide-co-diallyldimethylammonium chloride)/poly(ethylene glycol) dimethyl ether (PVA/PAADDA /PEG) alkaline anion exchange membranes, and then makes the following progresses:(1) The PVA/KOH alkaline membranes exhibit good thermal stability around 200℃. The ionic conductivity of PVA/KOH alkaline membranes ranges from 1.23×10-4to 4.73×10-4 S/cm at room temperature. The membranes are found very stable even in 10M KOH solution up to 80℃without losing any integrity and ionic conductivity. In addition, the PVA/KOH membranes present excellent methanol resistance. The methanol uptake of the membrane is 10 times lower than that of Nafion 115 membrane after conditioned at 100℃. The PVA/KOH membrane applied in alkaline direct methanol fuel cell (DMFC) showes a power density of 10.21 mW/cm2 at 90℃with the OCV ranged from 0.87 to 0.91 V.(2) PVA and PVP, and/or PEGDE has good compatibleness, while the addition of PVP and PEGDE can also greatly improve the ionic conductivity of the alkaline blend membranes. The ionic conductivity of PVA/PVP and PVA/PEGDE alkaline membranes can reach 2×10-3 S/cm and 1.43×10-3 S/cm, respectively. The PVP and/or PEGDE modified PVA based membranes show good thermal stability, alkaline tolerance and durablity. The ionic conductivty of the obtained PVA/PVP and PVA/PEGDE membranes show no obvious decrease after the membrane being treated in 10M KOH solution at elevated temperature of 80℃.(3) The ionic conductivity of PVA/PAADDA alkaline anion exchange membranes range from 0.69 to 1.14×10-3 S/cm at room temperature with the ion exchange capacity among 0.91 to 1.61 mmol/g. The ionic conductivity of the membranes shows almost no change after treated in 6M KOH at elevated temperatures (25-80℃) for 24 h. In addition, PVA/PAADDA membranes exhibit excellent methanol permeability. The methanol permeability of the membrane ranges from 1.82 to 2.98×10-7 cm2/s at room temperature, which is 6 to 10 times lower than that of Nafion115 membrane.The improved compatibleness and thermal stability of the PVA/PAADDA/PEG membranes can be observed compared to PVA/PAADDA membranes with addition of PEG Moverover, the PVA/PAADDA/PEG membranes can tolerant the basic treatment up to the concentration of 10M. The PVA/PAADDA/PEG membrane applied in alkaline direct methanol fuel cell (DMFC) showes a power density of 15.36 mW/cm2 at 70℃with the OCV around 0.85 V. The peak current density is 38.4 mA/cm2 when the cell voltage is 0.4 V.
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