Electrocatalysts are essential components in electrochemical energy conversion systems. For example, hydrogen fuel can be generated by electrochemically splitting water through the hydrogen and oxygen evolution reactions (HER and OER). Electricity can be regenerated in fuel cells where the oxygen reduction reaction (ORR) occurs in the air cathode. Developing noble-metal free electrocatalysts is of great importance for the low-cost and large-scale application of these technologies. Two general guidelines have been adopted to fabricate electrocatalysts. One is to improve the intrinsic activity of active sites, and the other is to increase the number of active sites, both of which require the delicate manipulation of the composition and structure in nano-/micrometer scale. We recently demonstrate several works that enable the controllable synthesis of high-performance electrocatalysts with designable composition and nanostructure.
High-surface-area carbon has been widely used as electrocatalyst support to ensure a large electrochemically active surface. However, the weak interaction between porous carbon support and electroactive components would deteriorate the activity and durability of the catalysts. Additionally, active components formed in conventional one-pot synthesis are usually less controllable. To address these issues, we developed a post-decoration method for the synthesis of efficient Fe-N-C type ORR catalysts (Adv. Energy Mater. 2017, 1701154). The active components in such catalysts, including Fe-Nx and Fe-Ox moieties, are in situ formed by reacting pre-synthesized N-doped porous carbon with iron carbonyl. The pore structure and formation of active sites can be independently modulated and optimized, leading to a remarkable ORR activity comparable to that of Pt/C in alkaline electrolyte.
Alternatively, we have been focused on developing functional materials using metal-organic frameworks (MOFs) for electrochemical energy storage and conversion (Adv. Mater. 2017, DOI: 10.1002/adma.201703614). In virtue of the diverse compositional and structural features of MOFs, they are very unique platforms to synthesize functional materials with desirable nanostructures and composition for various applications. We demonstrate a MOFs-assisted strategy to synthesize mesoporous molybdenum carbide for efficient hydrogen production (Nat. Commun. 2015, 6512). The synthesis relies on the confined and in-situ carburization reaction occurring in a unique MOFs-based compound, which enables the formation of metal carbide nanocrystallites embedded in an amorphous carbon matrix. The porous molybdenum carbide exhibits remarkable electrocatalytic activity for HER in both acidic and basic solutions with good stability. Similar strategy has also been extended to synthesize other high-performance electrocatalysts, including metal-nitrogen-carbon and metal selenide-carbon composite electrocatalysts for various energy conversion applications.