(Invited) Combination of Insulating Boron Nitride and Inert Gold Substrate As an Efficient Electrocatalysts for Oxygen Reduction Reaction and Hydrogen Evolution Reaction - Theoretical and Experimental Investigations

Abstract

Large overpotential for oxygen reduction reaction (ORR) is one of the most serious problems in the development of fuel cells. Although Pt group metals are the most efficient electrocatalysts, world-wide efforts have been made to find alternative catalysts because of their high cost, less abundance, poor stability, and still sluggish kinetics. Recently we proposed theoretically that hexagonal boron nitride (h-BN) monolayer, which has similar geometric structure to the graphene but is an insulator with a wide band gap (5.8eV), can be used as an ORR catalyst [1-3]. DFT calculations for BN/Au(111) predicted the possible ORR activity of BN/Au(111) [3] and electrocatalytic activities of various types of BN were experimentally examined [3, 4]. The overpotential for ORR at Au electrode was reduced by ca. 100, ca. 270, and ca.150 mV by spin coating of the dispersion of BN nanotube (BNNT) and BN nanosheet (BNNS), and sputter deposition of BN, respectively, although oxygen is reduced to H2O2 by 2-electron reduction in all the cases, as theoretically predicted. The reason why the BNNS modification resulted in the highest activity is attributed to the presence of B-and/or N-edge structures based on theoretical investigation. While the BN modification was effective to improve ORR activity at Au electrode, it has no and negative effects at GC and Pt electrodes, respectively, suggesting the important role of BN-substrate interaction. One would expect higher ORR activity if we can increase the BN-Au interaction. The interaction was increased by depositing gold nanoclusters (Au-NCs) on BNNS, which was then placed on a Au electrode (Au-BNNS/Au). The decoration of BNNS with gold clusters lead to not only the reduction of overpotential for ORR further by ca. 50 mV, but also opening of a 4-electron reduction route to water, confirming the important role of Au-BN interaction for ORR [5,6]. The increase of the BN-Au interaction can be also achieved by using smaller sized BNNS. Indeed the smaller the BNNS size, the lower the ORR overpotential and the higher the fraction of 4-electron reduction [7]. The combination of BNNS-Au is proved to be a very active electrocatalyst for hydrogen evolution [8]. [1] A. Lyalin, K. Nakayama, K. Uosaki, and T. Taketsugu, J. Phys. Chem. C, 117 (2013) 21359. [2] A. Lyalin, A. Nakayama, K. Uosaki, and T. Taketsugu, Phys. Chem. Chem. Phys., 15 (2013) 2809. [3] K. Uosaki, G. Elumalai, H. Noguchi, T. Masuda, A. Lyalin, A. Nakayama, and T. Taketsugu, J. Am.Chem. Soc. 136 (2014) 6542. [4] G. Elumalai, H. Noguchi, and K. Uosaki, Phys. Chem. Chem. Phys., 16 (2014) 13755. [5] G. Elumalai, H. Noguchi, A. Lyalin, T. Taketsugu, and K. Uosaki, Electrochem. Commun. 66 (2016)53. [6] G. Elumalai, H. Noguchi, H. C. Dinh, and K. Uosaki, J. Electroanal. Chem., in press, DOI:10.1016/j.jelechem.2017.09.033 (2018). [7] H. C. Dinh, H. Noguchi, G. Elumalai, and K. Uosaki, unpublished results. [8] K. Uosaki, G. Elumalai, H. C. Dinh, A. Lyalin, T. Taketsugu, and H. Noguchi, Sci. Rep., 6 (2016)32217.