UC Riverside

Development of non-precious metal catalysts (NPMCs) has become a well-known strategy to replace the platinum-based catalysts for the oxygen reduction reactions at the cathode of fuel cells, metal–air batteries and air-breathing cathodes in industrial electrocatalytic processes. There are two crucial factors governing the performance of carbon based catalysts. One is the intrinsic nature of the active sites which are determined by the selection of the doping elements. Another important factor is the large specific area and porous structure feature which can introduce more active sites and promote the electrons and oxygen species transportation. Among numerous carbon-based electrode materials, hollow carbonaceous spheres have attracted attention due to the high surface-to-volume ratios and more accessible active sites on the shell. Here, hierarchical porous carbon-nanoshells with about 40 nm cavities are synthesized by using CdS@mSiO2 core-shell structured materials as hard templates and 4, 4’-bipyridine, FeCl3 as nitrogen, carbon and iron sources. This method demonstrates outstanding stability and electrocatalytic activity for ORR.

Moreover, Metal–organic frameworks (MOFs) as new classes of crystalline porous materials with high surface area, large pore volume and uniform pore distribution can be suitable candidates as precursors and/or templates for the formation of high quality porous carbons for ORR application. The diversity in types of metal ions and organic ligands in MOFs with cavities and pore spaces make them versatile precursors and/or templates for the synthesis of carbon/metal oxide composites and doped carbon-metal materials.

Apart from the above-mentioned advantages, there are some open coordination sites on the metals species or functional groups in the ligands of the developed MOFs. Those open coordination sites can function as the specific interaction sites and be further utilized for the post-synthesis to introduce different heteroatoms with different coordination environments and different functionalities. Targeted species, like metals, heterometals and heteroatoms can be integrated into the targeted materials via different interactions to further maximize the electrocatalytic activities of the synthesized materials.