An unusual network of α-MnO_(2) nanowires with structure-induced hydrophilicity and conductivity for improved electrocatalysis

具有结构诱导的亲水性和导电性的α-MnO_(2)纳米线网络用于电催化

Nanowires with anisotropic morphologies have been applied in various scientific and technological areas.It is also widely employed to fabricate nanowires into high-dimensional superstructures(arrays,networks etc.)to overcome the shortcomings of low-dimensional nanowires.However,typical strategies for constructing these superstructures are restricted to complicated and harsh synthetic conditions,not to mention unique 3D structures with advanced properties beyond common superstructures.Herein,we report an unusual network ofα-MnO_(2)nanowires with structure-induced hydrophilicity and conductivity.In the network,the nanowires are interconnected from all directions by nodes,and the 3D network structure is formed from the endless connection of nodes in a node-by-node way.The unique network structure brings about high hydrophilicity and conductivity,both of which are positive factors for an efficient electrocatalyst.Accordingly,the α-MnO_(2) network was tested for electrocatalytic water oxidation and showed significantly enhanced activity compared with isolatedα-MnO_(2)nanowires and 3Dα-MnO_(2)microspheres.This study not only provides a synthetic route toward an advanced network structure but also a new idea for the design of materials for electrochemistry with both efficient mass diffusion and charge transfer.

具有各向异性特征的低维纳米线已被应用于各类科学技术领域.纳米线也被广泛用于制备高维超级结构(纳米线阵列和纳米线网络等),以克服低维纳米线自由堆积导致化学反应过程中内部空间不足等缺点.但是,构造这些超级结构的典型策略仅限于复杂和苛刻的组装合成手段,因此.在温和条件下使用简单的方法直接合成基于纳米线的新型3D超结构仍然是重要且具有挑战性的工作.本文在没有使用任何表面活性剂的条件下通过简单水热法制备了一种独特a-MnO2纳米线网络,同时这一新颖的结构使制备的材料具有优异的结构诱导的亲水性和导电性.在此超级结构中,纳米线通过节点从各个方向互相连接形成网络,网络结构由节点之间的逐节点连接形成.与离散的α-MnO_(2)纳米线和3Dα-MnO_(2)微米球相比α-MnO_(2)网络超级结构的电催化水氧化活性显著增强.物质扩散和电荷转移能力是电催化剂性能的两大重要影响因素,因此,本文对比研究了这三种材料的亲水性和导电性对电催化水氧化的影响程度.在α-MnO_(2)网络超级结构中,丰富开放空间有利于物质扩散.在水溶液的非均相催化中,水的扩散和与催化位点的结合很重要.水滴静态接触角测量结果表明,α-MnO_(2)网络超级结构具有较高的亲水性.通常,长纳米线的暴露晶面较稳定,它们与溶剂分子间的相互作用较弱.然而,由于大量的空隙结构导致的虹吸效应,本文α-MnO_(2)纳米线网络结构表现出高亲水性.同时,本文采用四点探针法测试了三种催化剂的薄层电阻,与离散的a-MnO2纳米线中线与线之间的物理接触不同,网络结构中线与线是通过化学方式连接的.因此,网络结构内的电荷转移比随机堆积的纳米线和微米球要快得多.本文还通过电化学方法进一步证明了α-MnO_(2)网络超级结构中高效的物质扩散和电荷转移.网络结构中,基于活化电流和静态电流的Tafel值相近,该结果表明即使在没有消除传质限制情况下,这种独特纳米网络的丰富内部空间使得传质阻力几乎可以忽略,具有高传质效率.根据Laviron方程计算出的电子转移速率常数表明,网络结构的电子转移速率比其他两个对比催化剂快得多,说明α-MnO_(2)纳米线网络超级结构同时具有高效的物质扩散和电荷转移能力.综上,本文不仅为构筑高级网络结构提供了一条新的合成途径,而且为设计具有高效物质扩散和电荷转移的电化学材料提供了新思路.