For the past years, there have been extensive research reporting porous graphene in the energy storage and conversion applications, attributing to its pronounced electronic properties and large surface areas.1 Structurally analogous to graphene, hexagonal boron nitride (h-BN) is of wide-spread interest as well. Owing to the chemical inertness and thermal stability, porous BN nanosheets have been proposed for effective water cleaning.2 Remarkably, affinity but different from either graphene or h-BN, ternary boron carbon nitride (BCN) nanosheets could exhibit striking performances by integrating the advantages of both graphene and h-BN. Since the band gap (0-5.5 eV) is adjustable for the novel semi-conductive material.3,4 Moreover, the heteroatoms of B,N co-doping provides the hetero-polarity, thereby stimulating the electrochemical activity.5 That makes it reasonable for BCN nanosheets as potential electrochemical catalysts. To further improve the catalytic performance, it is necessary to elaborately tailor the porosity. In the previous work, soft template surfactant-poly (ethylene oxide-co-propylene oxide) (P123) is introduced to create pores and regulating the nanosheets structure.5 The as-prepared BCN nanosheets display high surface area of 817 m2 g-1 with both meso and micro pores. Interestingly, as electrochemical catalyst, the hierarchically porous BCN show impressive oxygen reduction reaction (ORR) catalytic performances in both alkaline and acid environment. It is worth noting that, for single N-doped carbon materials, the increased proton concentration in low pH solution would deteriorate the ORR reaction kinetics with protonation of negatively charged N atom. Nevertheless, for BCN nanosheets, the positively charged B atoms likely alleviates the protonation process, which narrows the gap of ORR catalytic performance between alkaline and acid conditions. Furthermore, the micropores and mesopores are able to support a shorter ion-transport pathway, facilitating the exchange of molecules and ions in the electrolytes. However, it should be noted that too large surface areas would conversely decrease the conductivity, thus lessening the catalytic activity. Therefore, there should be a balance between porosity and conductivity when considering rational design of porous BCN nanosheets for ORR.
1 D. Liu, W. Lei, D. Portehault, S. Qin, Y. Chen, J. Mater. Chem. A 2015, 3, 1682.
2 W. Lei, D. Portehault, D. Liu, S. Qin, Y. Chen, Nat. Commun. 2013, 4, 1777.
3 J. Wang, J. Hao, D. Liu, S. Qin, C. Chen, C. Yang, Y. Liu, T. Yang, Y. Fan, Y. Chen, W. Lei
Nanoscale 2017, 9, 9787.
4 J. Wang, C. Chen, C. Yang, Y. Fan, D. Liu, W. Lei, Curr.Graph.Sci. 2017, 1, 1
5 J. Wang, J. Hao, D. Liu, S. Qin, D. Portehault, Y. Lin, Y. Chen, W. Lei, ACS Energy Lett. 2017, 2, 306.