Functionalized carbon surfaces for clean electrochemical energy systems

Abstract

The development and implementation of clean energy technologies is the way to overcome the global energy crisis and reduce pollution. Therefore, new energy solutions are rapidly needed. Fuel cells (FCs) may become one such solution. FCs are devices that utilize chemical reactions to directly produce electric energy. While these devices are ideal clean energy sources for the transportation industry, conventional FCs are based on expensive materials that implement platinum catalysts on a carbon support (Pt/C). The high cost and limited availability of platinum hinders the applicability of FCs. Nitrogen and metal-doped carbon supports have been investigated as a non-precious metal replacement for costly precious metal-based materials in various electrochemical energy applications. However, the design of non-precious metal materials (NPMMs) involves high temperature pyrolysis treatments, which leads to an almost random distribution of nitrogen atoms on the surface and therefore can limit efficiency. In this work, a method to graft only the most active nitrogenous groups and/or transition metals on the surface of carbon supports was developed. Specifically, diazonium coupling chemistry to covalently attach molecularly defined moieties bearing a terpyridine (tpy) group onto the surface of carbon supports, followed by the introduction of Fe (or other transition metal) centers into anchored tpy groups. Pyridinic nitrogenous groups, which are the basis of tpy, are believed to be required for high activity in the oxygen reduction reaction (ORR) in FC applications and are thought to increase capacitance in SC applications. Upon metal coordination into the tpy sites, the metal-N3/C catalyst shows promising activity for the ORR and SC applications and opens the door for molecularly controlled, inexpensive, and efficient materials. Importantly, upon an energy intensive heat-treatment, the material’s activity does not improve. Confirming that this system’s properties are dictated by the molecularly defined tpy-Fe units, new efficient NPMMs can be fabricated using energy-saving conditions. This design can be applied and optimized to create a family of NPMMs for various clean energy applications. Modifying carbon-based materials opens the way for new low-cost materials for clean energy systems such as FCs, SC, and water oxidation.