Abstract
AbstractThe properties of porous materials benefit from hierarchical porosity. A less noted element of hierarchy is the occurrence of directionality in functional gradient materials. A sharp boundary is replaced by a transition from one feature to the next. The number of cases known for porous materials with either structural or chemical gradients is small. A method capable of generating combinations of structural and chemical gradients in one material does not exist. Such a method is presented with a focus on silver and nitrogen containing carbon materials because of the potential of this system for electrocatalytic CO2 reduction. A structural gradient results from controlled separation using ultracentrifugation of a binary mixture of template particles in a resorcinol–formaldehyde (RF) sol as carbon precursor. A new level of complexity can be reached, if the surfaces of the template particles are chemically modified. Although the template is removed during carbonization, the modification (Ag, N) becomes integrated into the material. Understanding how modified and unmodified large and small particles sediment in the RF sol enables almost infinite variability of combinations: chemically graded but structurally homogeneous materials and vice versa. Ultimately, a material containing one structural gradient and two chemical gradients with opposing directions is introduced.
Highlights
Introduction achievedMicrofluidic techniques were used to control the distribution of differently sized voids in polystyrene foams
Our approach is based on a paper published in 2016.[29]. A bimodal dispersion of colloidal polystyrene (PS) particles was used as template particles
The generation of carbon materials with a structural gradient overlayed by a functional chemical gradient is straightforward. We show this for small unmodified template particles PS137 and larger Ag-modified Ag@particles was 480 nm (PS480)
Summary
Introduction achievedMicrofluidic techniques were used to control the distribution of differently sized voids in polystyrene foams. Nanostructured carbon holds an outstanding position among dient in porosity resulted in programmable locomotion. Inorganic these materials, especially because of its role and promises in materials with graded porosity have been created by anisotropic future energy-related technologies.[1] It is an important question, sintering, freeze-casting, or gel-casting processes.[11,12,13] Sailor and how properties change or improve by the existence of multiple co-workers showed that electrochemical etching of silicon is suitpore types.
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