题目：Carbon Nanomaterials as Metal-free Catalysts for Energy Conversion

报告人：Prof. Liming Dai (Case Western Reserve University, USA)

时间：7月15日（周二）10:30-11:45

地点：李薰楼468会议室

报告摘要：Oxygen reduction reaction (ORR) is an important process in many fields, including energy conversion (fuel cells, metal-air batteries), corrosion, and biosensing. Although Pt nanoparticles have been regarded as the best electrocatalyst for ORR in fuel cells, they are still suffered from multiple problems. For instance, Pt-based cathode electrocatalysts are susceptible to the cross-over effect, long-term instability, and CO poisoning. Furthermore, the high cost of Pt, together with its limited reserve in nature, has been shown to be the “bottleneck” for large-scale commercialization of the fuel cell technology.

Along with the recent intensive research efforts in reducing or replacing Pt-based electrode in fuel cells, we have previously demonstrated that vertically aligned nitrogen-doped carbon nanotubes (VA-NCNTs) produced by pyrolysis of iron (II) phthalocyanine could actively catalyze ORR via a four-electron process free from the crossover and CO poisoning effects with a 3-time higher electrocatalytic activity and better long-term durability than that of commercially available Pt/C electrocatalysts. Similar ORR electrocatalytic activity was also observed for nitrogen-doped graphene (N-graphene). On the basis of these experimental observations and quantum mechanics calculations, we have attributed the observed ORR catalytic activities of the VA-NCNTs and N-graphene to the electron-accepting ability of the chemically-bonded nitrogen atoms, which create a net positive charge (via intramolecular charge-transfer) on adjacent carbon atoms in the nanocarbon structures to readily attract electrons from the anode for facilitating the O2 adsorption and ORR on the cathode. These findings prompted us to develop carbon-based metal-free ORR catalysts by positively charging carbon atoms in the nitrogen-free carbon nanotubes and graphene plane through intermolecular charge-transfer with functionalized/adsorbed moieties. In particular, we have recently used poly(diallyldimethylammonium chloride), PDDA, as an electron acceptor for functionalizing N-free carbon nanotubes and graphene to show remarkable electrocatalytic activity toward ORR. We have also demonstrated that carbon nanotubes and graphene co-doped with N and B showed a synergetic effect toward ORR, and that nitrogen-doped 3D graphene foam (N-GF) could be used as a metal-free electrocatalyst for the reduction of triiodide to replace the Pt cathode in dye-sensitized solar cells (DSSCs). In this talk, we will summarize some of our work on the metal-free ORR catalysts based on carbon nanomaterials, along with an overview on the recent developments in this exciting field.