(167b) Synthesis of Nanoporous Metals through Thermal Decomposition of Transition Metal Dichalcogenides

Nanoporous metals with bicontinuous porosity are characterized by a high surface-to-volume ratio that makes them ideal for use in a range of applications including catalysis¹. The traditional methodology for the synthesis of nanoporous metals has relied on the chemical/electrochemical removal of a sacrificial metal from an alloy, a method known as dealloying. The driving force for dealloying is a difference in the equilibrium potentials and dissolution tendencies amongst the constituent metals. This limits the process to the formation of nanoporosity for only a few noble metals² e.g. Pt, Pd, Au etc. Additionally, it is required that both components of the parent alloy form a homogeneous solid solution, which puts further restrictions on the applicable systems. More recently liquid metal dealloying³ and vapor phase dealloying⁴ have been identified as alternative processes to chemical/electrochemical dealloying, relying on a difference in solubility/reactivity with an external fluid (liquid metal or gas, respectively) to drive the formation of nanoporosity. However, both these processes are restricted to a few alloy systems and the elevated temperatures required limit the attainable pore sizes to greater than 100 nm. Here, we present gas phase thermal decomposition of transition metal dichalcogenides (TMDs) as an alternative to dealloying that generates nanopores for a broader class of metals including refractory metals like W, Mo, Re etc. The chalcogen is removed from the surface by both reductive reaction with hydrogen and evaporation at elevated temperatures, which leads to the rearrangement of the remaining metal atoms and evolution of an interconnected bicontinuous nanoporous network. The length scales of the pores can be tuned by decomposition time, temperature and for some, by changing the identity of the sacrificial chalcogen element. Based on varying dynamics of pore formation and residual chalcogen contents for different TMDs, we have also proposed a mechanism that describes the atomic processes that govern nanoporosity evolution through thermal decomposition. The availability of a vast library of TMDs having inherent atomistic homogeneity makes it a universal technique that can be utilized to make a broad range of nanoporous metals.

References.

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