Manufacturing free-standing porous layers with dynamic hydrogen bubble templating

The three-dimensional 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. Drawing inspiration from porous metallic foams, here we engineer a novel method to manufacture free-standing, thin, porous foams via dynamic hydrogen bubble templating in an electrochemical flow cell, through the introduction of an intermediate layer and optimization of synthesis parameters (i.e. voltage, concentration and charge). We create mechanically stable foams with thicknesses ranging from ~50 µm to ~200 µm comprising porous, dendritic structures, arranged to form a vascular network of larger pores with a gradient in radii from ~5 µm at the bottom and up to ~36 µm at the top of the material. Using segmented X-ray tomographic data, we simulate the diffusive transport through the material as function of liquid filling and compare it to carbon fiber-based material. For all ranges of saturation, the metallic foams outperforms the fibrous structure, showcasing the potential of bimodal pore size architectures to improve two phase transport by optimizing the distribution of phases.