The microstructural dependence of ionic transport in bi-continuous nanoporous metal

• Main Authors: Wang, Congcheng, Tsang, Anson, Xiao, Diwen, Xu, Yuan, Yang, Shida, Liu, Ling-Zhi, Zheng, Qiang, Liu, Pan, Jin, Hai-Jun, Chen, Qing
• Format: Journal Article
• Language: English
• Published: 25-08-2021
• Subjects: Physics - Applied Physics; Physics - Chemical Physics
• DOI: 10.48550/arxiv.2108.11529

Ionic transports in nanopores hold the key to unlocking the full potential of
bi-continuous nanoporous (NP) metals as advanced electrodes in electrochemical
devices. The precise control of the uniform NP metal structures also provides
us a unique opportunity to understand how complex structures determine
transports at nanoscales. For NP Au from the dealloying of a Ag-Au alloy, we
can tune the pore size in the range of 13 nm to 2.4 microns and the porosity
between 38% and 69% via isothermal coarsening. For NP Ag from the
reduction-induced decomposition of AgCl, we can control additionally its
structural hierarchy and pore orientation. We measure the effective ionic
conductivities of 1 M NaClO4 through these NP metals as membranes, which range
from 7% to 44% of that of a free solution, corresponding to calculated pore
tortuosities between 2.7 and 1.3. The tortuosity of NP Au displays weak
dependences on both the pore size and the porosity, consistent with the
observed self-similarity in the coarsening, except for those of pores < 25 nm,
which we consider deviating from the well-coarsened pore geometry. For NP Ag,
the low tortuosity of the hierarchical structure can be explained with the
Maxwell-Garnett equation and that of the oriented structure underlines the
random orientation as the cause of slow transport in other NP metals. At last,
we achieve high current densities of CO2 reduction with these two
low-tortuosity NP Ags, demonstrating the significance of the
structure-transport relationships for designing functional NP metals.