基于离子传导增强的多孔催化剂及其直接硼氢化钠燃料电池的研究

Study on a porous catalyst based on ion conduction enhancement and its direct borohydride fuel cell

多孔碳材料具有比传统碳载体更大的比表面积,具备担载更多电催化活性位点的能力。但多孔催化剂的孔内传质阻力较大,特别是孔内离子难以有效传导,导致电极反应的活性位利用率低下,电极过电位增大。直接硼氢化钠燃料电池(DBFC)是一种电动势高,无需贵金属作为催化剂的高能量密度碱性燃料电池,但较大的阴极极化导致电池能量密度难以提高。强化阴极催化剂的离子传导能力是降低阴极极化的有效手段之一。将阳离子交换树脂(Nafion)真空灌注于多孔催化剂孔道内可强化阳离子传导,以此提高催化位点利用率。得到的产物通过球磨粉碎得到外表面无树脂覆盖的催化剂粒子,以此避免树脂对粒子外表面覆盖对电子导电性的影响,从而降低电极极化提高催化性能。研究表明,以葡萄糖为碳源、吡咯为氮源、硝酸钴为过渡金属源制备的阴极催化剂,通过电子、离子传导强化处理,催化性能显著提高。使用了强化处理的催化剂的DBFC,室温下最大功率密度达到了280 mW×cm^(-2),其性能超过了铂的质量分数为28.6%的碳载铂催化剂。

Porous carbon materials have higher specific surface area than traditional carbon support materials,thus they are capable of loading more active-sites for electrochemical reaction.However,porous carbons present high mass transfer resistance.In particular,ions hardly transfer in pores that lead to poor utilization of active-sites for electrode reactions,and thereby exhibiting large polarization potential.Direct borohydride fuel cell(DBFC)is an alkaline fuel with high electromotive force and energy density,which do not need to use noble metals.However,its cathode shows large polarization that leads to low power density.Enhancement of ion transfer is one way to decrease cathode polarization.Herein,we attempted to synthesize a functionalized porous-carbon via vacuum Nafion-resin filling to improve the utilization of active-sites.The as-synthesized porous-carbon was ball-milled to create Nafion-free surfaces for enhancement of electric conduction among the catalyst particles.A high performance electrocatalyst was developed with such electric and ionic enhancements using glucose as the carbon source,pyrrole as the nitrogen source and cobalt nitrate as the transition metal source.The resultant DBFC had power density as high as 280 mW×cm-2 under ambient conditions.The activity of the developed electrocatalyst was better than that of commercial carbon-supported Pt with Pt content of 28.6%for oxygen reduction reaction.