Eutectic-derived synthesis of hierarchically nanoporous copper for electrochemical actuation and solar steam generation

The utilization of nanoporous copper (np-Cu) as a metallic actuator has gained attention in recent years due to its cost-effectiveness in comparison to other precious metals. Despite this, the enhancement of np-Cu’s actuation performance remains a challenge due to limitations in its strain amplitude and actuation rate. Additionally, np-Cu has been deemed as a promising material for solar absorption due to its localized surface plasmon resonance effect. However, practical applications such as solar steam generators (SSGs) utilizing np-Cu have yet to be documented. In this study, we present the development of hierarchically nanoporous copper (HNC) through the dealloying of a eutectic Al-Cu alloy. The hierarchical structure of the HNC features a combination of ordered flat channels and randomly distributed continuous nanopores, which work in synergy to improve actuation performance. The ordered flat channels, with a sub-micron scale, facilitate rapid mass transport of electrolyte ions, while the nano-sized continuous pores, due to their large specific surface area, enhance the induced strain. Our results indicate that the HNC exhibits improved actuation performance, with a two times increase in both strain amplitude and rate in comparison to other reported np-Cu. Additionally, the HNC, for the first time, showcases excellent solar steam generation capabilities, with an evaporation rate of 1.47 kg·m⁻²·h⁻¹ and a photothermal conversion efficiency of 92% under a light intensity of 1 kW·m⁻², which rivals that of nanoporous gold and silver film. The enhanced actuation performance and newly discovered solar steam generation properties of the HNC are attributed to its hierarchically porous structure.