Eckhardt Janis K, Heiliger Christian, Elm Matthias T
Institute for Theoretical Physics, Justus Liebig University, Heinrich-Buff-Ring 16, Giessen D-35392, Germany.
Center for Materials Research (ZfM), Justus Liebig University, Heinrich-Buff-Ring 16, Giessen D-35392, Germany.
ACS Appl Mater Interfaces. 2023 Jul 26;15(29):35332-35341. doi: 10.1021/acsami.3c05561. Epub 2023 Jul 13.
The unique architecture of ordered mesoporous oxides makes them a promising class of materials for various electrochemical applications, such as gas sensing or energy storage and conversion. The high accessibility of the internal surface allows tailoring of their electrochemical properties, e.g., by adjusting the pore size or surface functionalization, resulting in superior device performance compared to nanoparticles or disordered mesoporous counterparts. However, optimization of the mesoporous architecture requires reliable electrochemical characterization of the system. Unfortunately, the interplay between nanocrystalline grains, grain boundaries, and the open pore framework hinders a simple estimation of material-specific transport quantities by using impedance spectroscopy. Here, we use a 3D electric network model to elucidate the impact of the pore structure on the electrical transport properties of mesoporous thin films. It is demonstrated that the impedance response is dominated only by the geometric current constriction effect arising from the regular pore network. Estimating the effective conductivity from the total resistance and the electrode geometry, thus, differs by more than 1 order of magnitude from the material-specific conductivity of the solid mesoporous framework. A detailed analysis of computed impedances for varying pore size allows for the correlation of the effective conductivity with the material-specific conductivity. We derive an empirical expression that accounts for the porous structure of the thin films and allows a reliable determination of the material-specific conductivity with an error of less than 8%.
有序介孔氧化物独特的结构使其成为一类在各种电化学应用中很有前景的材料，如气体传感或能量存储与转换。内表面的高可达性使得可以通过调整孔径或表面功能化等方式来定制其电化学性质，与纳米颗粒或无序介孔材料相比，能带来更优异的器件性能。然而，介孔结构的优化需要对该体系进行可靠的电化学表征。不幸的是，纳米晶粒、晶界和开放孔框架之间的相互作用阻碍了通过阻抗谱简单估算材料特定的输运量。在此，我们使用三维电网络模型来阐明孔结构对介孔薄膜电输运性质的影响。结果表明，阻抗响应仅由规则孔网络产生的几何电流收缩效应主导。因此，根据总电阻和电极几何形状估算的有效电导率与固体介孔框架的材料特定电导率相差超过1个数量级。对不同孔径下计算得到的阻抗进行详细分析，可以将有效电导率与材料特定电导率关联起来。我们推导了一个经验表达式，该表达式考虑了薄膜的多孔结构，能够可靠地确定材料特定电导率，误差小于8%。
