Two-Dimensional Polyphenylene Networks with Tunable Micropores for Hydrogen Storage

Abstract

Micropores, especially ultramicropores with pore size smaller than 1 nm, play a crucial role in hydrogen storage. In this contribution, we report on bulk production of two-dimensional (2D) polyphenylene networks (PPNs) through a solution-based Wurtz reaction. A self-assembled mechanism is proposed for the formation of 2D PPNs based on molecular dynamics simulations. The morphology, structure, surface chemistry, and textural properties of the PPNs are greatly influenced by anneal treatment at 450–550 °C in terms of deep thermal dechlorination and cyclodechlorination. The annealed PPNs are featured with moderate specific surface area (SBET) and wealthy micropores, which can be finely tuned by varying the anneal temperature. For PPNs, there is no direct correlation between the H₂-uptake capacity and individual textural parameters such as SBET, Sₘᵢcᵣₒₚₒᵣₑ, Vₜₒₜₐₗ ₚₒᵣₑ, Vₘᵢcᵣₒₚₒᵣₑ, and Vₘₑₛₒₚₒᵣₑ. The H₂-uptake capacity is highly dependent on the distribution of ultramicropores and the pore volume of ultramicropores in the range of 0.5–0.8 nm (Vᵤₗₜᵣₐₘᵢcᵣₒₚₒᵣₑ ₀.₅–₀.₈ₙₘ). The PPNs annealed at 500–520 °C, possessing moderate SBET (459.3–564.9 m² g–¹), relatively high Vᵤₗₜᵣₐₘᵢcᵣₒₚₒᵣₑ ₀.₅–₀.₈ₙₘ, and ultramicropores concentrated at 0.69–0.71 nm, exhibit superior H₂-storage capacity (4.28–5.39 mmol g–¹) at 77 K and 1 atm.