Manufacturing Free-Standing, Porous Metallic Layers with Dynamic Hydrogen Bubble Templating

The 3D structure (i.e., microstructure) of porous electrodes governs the performance of emerging electrochemical technologies such as fuel cells, electrolysis, and batteries. Sustaining electrochemical reactions and convective-diffusive mass transport at high efficiency is complex and motivates the search for sophisticated microstructures with multimodal pore size distributions and pore size gradients. Here a new synthesis route for porous, metallic layers is presented that combines the characteristics of carbon structures (i.e., pore size, porosity) with the properties of metals (i.e., recyclability, conductivity). Building on the method of dynamic hydrogen bubble templating, a novel approach is engineered to manufacture thin, free-standing layers using an electrochemical flow cell through the introduction of an intermediate layer and optimization of the synthesis parameters. Mechanically stable layers are created with thicknesses ranging from approximate to 50 to approximate to 200 mu m comprising porous, dendritic structures, arranged to form a vascular network of larger pores with a gradient in radii from approximate to 5 mu m at the bottom and up to approximate to 36 mu m at the top of the material. Using X-ray tomographic data, the morphology is analyzed, and the diffusive transport through the material as a function of liquid filling is simulated and compared to state-of-the-art carbon fiber-based electrodes, showing significantly higher mass transfer properties. Using a sacrificial layer, free-standing copper foams are manufactured via dynamic hydrogen bubble templating. The isolated material with interconnected porosity enables promising opportunities in electrochemical technologies. The resulting foam features a porosity exceeding 90% and a bimodal pore size distribution. The large subgroup of pores is hierarchically organized with a size gradient across the thickness from 5 to 36 mu m. image