Engineering Hierarchically Nano-Structured Cu Foams : Dynamic Hydrogen Bubble Templated Binder-Free Freestanding Electrodes for Energy Applications

The intelligent design of hierarchical metallic structures with optimized performance for targeted applications, such as energy devices, sensors, and catalysis, remains a significant challenge. In this study, electrochemically generated hydrogen bubbles are employed as dynamic negative templates for copper electrodeposition. This so-called dynamic hydrogen bubble templating approach (DHBT) yields highly porous hierarchical copper foams adorned with surface nano-structures. A comprehensive investigation of DHBT synthesis parameters is provided, organized into four categories: (1) deposition current density and time; (2) current modes, namely direct, pulsed, reversed, and alternating regimes; (3) physical conditions, including stirring and temperature; and (4) bath composition. The results demonstrate that morphological descriptors, such as pore size and density, foam thickness, electrochemically active surface area (ECSA), and nanoscale surface features, can be systematically and reproducibly tuned by varying these DHBT parameters. As a proof of concept, a simple three-step protocol for the fabrication of copper foam gas diffusion electrodes (GDEs) is presented. The resulting GDEs show promising CO2 reduction performance, achieving C2+ products Faradaic efficiencies of approximately 50% at -1.1 V versus reversible hydrogen electrode (RHE) and partial current densities of up to 104 mA cm−2 at -2.5 V versus RHE, with good operational stability tested for 12 h.