Reduction-Induced Decomposition: Spontaneous Formation of Monolithic Nanoporous Metals of Tunable Structural Hierarchy and Porosity

The beauty of dealloying, i.e., the selective dissolution of an alloy, lies in the spontaneous formation of bicontinuous nanoporous metal, whose robustness, conductivity, and high specific area are otherwise difficult to achieve in a monolithic form. However, a uniform structure of nanoporous metal requires a homogeneous alloy precursor, whose laborious fabrication has been limiting the application of dealloying and dealloyed materials. Here, we replace the alloy precursor with a compound, and design another type of selective dissolution, reduction-induced decomposition (RID). Using the RID of AgCl as an example, we chemically reduced bulk AgCl samples to create bicontinuous nanoporous Ag that resembles dealloyed structures. The monolithic material possesses a uniform ligament width of 72 nm and a specific area of 7.57 m2/g. The ligament width can be tuned in a range from 30 nm to 1 μm through coarsening, and the porosity from 57% to 87% by replacing silver cations in the compound with sodium cations. The RID of this multication compound can lead to a hierarchical structure, which evolves because of two simultaneous percolation dissolutions. The hierarchical nanoporous Ag delivered a stable performance as a high-capacity Ag/AgxO electrode owing to its micron-sized pores for fast mass transfer. RID not only provides an inexpensive alternative to dealloying, it also expands the design space of nanoporous materials for meeting diverse needs in electrochemical applications.