Assessing the influence of processing parameters and external loading on the nanoporous structure and morphology of nanoporous gold toward catalytic applications

Nanoporous gold structure gains several unique physical and chemical properties from its nanoscale foam structure composed of ligaments and connected pores. The high specific surface area and interconnected pores make its structure ideal for gas catalysis. Catalytic activity arises in part from the high number density of surface steps and kinks at points of high curvature in the nanoporous structure. However, the structure also makes the material macroscopically brittle and unreliable for many applications due to poor mechanical stability. The ligament diameter, which regulates both desirable chemical properties and mechanical instability, can be tuned to over three orders of magnitude, but few morphology features can be adjusted independently of this. Here, we fabricate nanoporous gold with an average ligament diameter of around 10 nm while varying synthesis parameters and quantify the resulting morphology in order to evaluate the effect of processing on the resulting nanoscale foam structure. In situ tensile experiments are performed to observe how both individual ligaments and the foam structure's features change during deformation in real-time. We found two new morphology features that are independently controllable through synthesis parameters and are likely to influence mechanical stability while preserving or enhancing catalytic activity. The curvature of the ligaments can be increased by stirring the electrolyte during dealloying and the width of the ligament diameter size distribution can be adjusted by controlling the coarsening rate. In situ mechanical tests show that grain boundaries can influence crack propagation and that ligaments removed from the crack tip experience both elastic and plastic stress.