Recent progress in nitrogen-doped carbon and its composites as electrocatalysts for fuel cell applications

• Published in: International journal of hydrogen energy Vol. 38; no. 22; pp. 9370 - 9386
• Main Authors: Wong, W.Y., Daud, W.R.W., Mohamad, A.B., Kadhum, A.A.H., Loh, K.S., Majlan, E.H.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Kidlington Elsevier Ltd 26-07-2013; Elsevier
• Subjects: Alternative fuels. Production and utilization; Applied sciences; Carbon; Catalysis; Catalysts; Energy; Exact sciences and technology; Fuel cell; Fuel cells; Fuels; Hydrogen; Nanostructure; Nitrogen-doped carbon; Noble metal free catalyst; Oxygen reduction reaction; Platinum; Reduction; Stability; Nitrogen-doped carbon; Oxygen reduction reaction; Noble metal free catalyst; Fuel cell; Electrocatalysis; Hydrogen; Noble metal; Catalyst
• ISSN: 0360-3199; 1879-3487
• DOI: 10.1016/j.ijhydene.2012.12.095

The emergence of fuel cell technology has created a new tool for the generation of clean, high efficiency alternative energy for humans. The research and development of new catalysts to replace the expensive and rare platinum (Pt) to reduce the overall cost of fuel cells is ongoing in this area. Nitrogen-doped carbon and its composites possess great potential for fuel cell catalyst applications especially at the oxygen reduction cathode. It is proposed that the reaction mechanisms of nitrogen-doped carbon catalysts for oxygen reduction involve adsorption of oxygen at the partially polarised carbon atoms adjacent to the nitrogen dopants, different from the mechanism at platinum catalysts, which utilise d-bands filling at oxygen adsorption sites. Nitrogen doping in both carbon nanostructures and its composites with active metals or ceramics are reviewed. Nitrogen-doped carbon without composite metals, displays high catalytic activity in alkaline fuel cells and exhibits significant activity in proton exchange membrane fuel cells and direct methanol fuel cells. Pt-based catalysts with nitrogen-doped carbon supports show enhanced catalytic activity towards oxygen reduction, attributed to the enhanced anchoring of Pt to the support that results in better dispersion and stability of the electrodes. For nitrogen-doped carbon composites with non-noble metals (Fe, Co, etc), enhanced activity is seen in both proton exchange and alkaline fuel cells. There are many ongoing debates about the nature of nitrogen-carbon bond in catalysis. Pyrrole- and pyridinic-type nitrogen generally considered to be responsible for the catalytic sites in acidic and alkaline media, respectively. In recent years, significant efforts have been made towards increasing the stability of nitrogen-doped carbon catalysts in acidic media through the formation of composites with ceramic or metal oxide materials. This article reviews the progress in the area of this new class of catalysts and their composites for greater enhancement of oxygen reduction activity and stability in various fuel cell applications.
► Progress in N/C composites for the ORR in fuel cell applications. ► ORR mechanisms with nitrogen-doped carbon in acidic and alkaline media. ► Nanostructure effects on nitrogen-doped carbon and its composites in the ORR. ► Improvement in ORR activity and stability through use of metal oxides and N/C composites.