Synthesis and catalytical properties of hierarchical nanoporous copper from θ and η phases in CuAl alloys

Abstract

Greenhouse gases, such as carbon dioxide, have a great impact on global warming and climate change. CO2 trapping and reduction have been one of the solutions to slow down the temperature rise. Copper has proven to be an effective electrocatalyst to transform CO2 into useful organic compounds, such as CH4, C2H4, and HCOOH. Here, nanoporous copper (NPC), that are synthesized from various precursor phases of Cu–Al alloys, like pure Al solid solution α, CuAl2 θ and CuAl η phases, with different relative densities and ligament sizes are being used as electrocatalyst for CO2 reduction reaction (CO2RR). The ligament sizes of the NPCs can be adjusted with the use of dealloying solution, either in HCl or NaOH, and dealloying temperatures. In this study, the ligament sizes were available from the range of 51–116 nm. A hierarchical structure containing a lamellar eutectic structure with an interlayer spacing of 6 μm in the parent phases is observed from NPC synthesized from Cu18Al82. The results show that the current density of CO2RR using NPC as electrocatalyst is 2–5 times higher than that of using copper foil. The ligament size effect is more obvious than the relative density effect since the peak current density was obtained from the NPC with ligament size of 76 nm. The product distribution suggested that NPC with hierarchical structure has higher Faraday efficiency of ethylene than conventional NPC or Cu foil at high overpotential.