Efficient Metal-Free Electrocatalysts for Oxygen Reduction: Polyaniline-Derived N- and O-Doped Mesoporous Carbons

Abstract

The oxygen reduction reaction (ORR)-one of the two half-reactions in fuel cells-is one of the bottlenecks that has prevented fuel cells from finding a wide range of applications today. This is because ORR is inherently a sluggish reaction; it is also because inexpensive and sustainable ORR electrocatalysts that are not only efficient but also are based on earth-abundant elements are hard to come by. Herein we report the synthesis of novel carbon-based materials that can contribute to solving these challenges associated with ORR. Mesoporous oxygen- and nitrogen-doped carbons were synthesized from in situ polymerized mesoporous silica-supported polyaniline (PANI) by carbonization of the latter, followed by etching away the mesoporous silica template from it. The synthetic method also allowed the immobilization of different metals such as Fe and Co easily into the system. While all the resulting materials showed outstanding electrocatalytic activity toward ORR, the metal-free, PANI-derived mesoporous carbon (dubbed PDMC), in particular, exhibited the highest activity, challenging conventional paradigms. This unprecedented activity by the metal-free PDMC toward ORR was attributed to the synergetic activities of nitrogen and oxygen (or hydroxyl) species that were implanted in it by PANI/mesoporous silica during pyrolysis.

Mesoporous Metal–Nitrogen-Doped Carbon Electrocatalysts for Highly Efficient Oxygen Reduction Reaction

“…12 Besides nitrogen and cobalt, the templated catalysts had a significant amount of oxygen species ( Figure S7 and S9), which is due to the oxygen implantation by the inorganic templates. 13 It has been widely reported that the metal-oxygen site exert limited contribution to the total catalytic activity of ORR in acidic media, 12 although metal oxides and Me-Ox sites have exhibited considerable activity in alkaline media. 14 The possible contribution of a small amount of phosphorus element to the ORR activity was also excluded ( Figure S9).…”

Cobalt sulfide/N,S codoped porous carbon core–shell nanocomposites as superior bifunctional electrocatalysts for oxygen reduction and evolution reactions

“…27 In particular, heteroatom (e.g., N, S, B, or P) doped carbon based materials have emerged and attracted great attention because heteroatom can tune the electronic and geometric properties of carbon, offering more active sites and enhancing the interaction between carbon structure and active sites. [27][28][29][30] Remarkably, the combination of transitionmetal metal oxide/sulfide with heteroatom-doped carbon can achieve high catalytic activity and improve durability because of the synergetic effect. …”

Metal–Organic‐Framework‐Derived Dual Metal‐ and Nitrogen‐Doped Carbon as Efficient and Robust Oxygen Reduction Reaction Catalysts for Microbial Fuel Cells

“…Thus, replacing the noble metal based cathode catalyst with the low‐cost catalyst is a favorable approach to reduce the cost of MFCs. Up to now, significant research efforts have been devoted to the exploration of alternative ORR catalysts, and some inexpensive ORR catalysts, such as metal oxide5, 6, 7, 8 and nonmetal heteroatom doped carbon,9, 10, 11, 12, 13, 14, 15, 16 have been developed for the replacing of Pt‐based catalysts. However, it is still challenging to achieve satisfying ORR performance with these inexpensive catalysts due to the sluggish kinetics of ORR.…”