(Invited) B-Doped Pd Catalyst to Boost Formate Production in Electrochemical CO2 Reduction

Abstract

Facile interconversion between CO2 and formate/formic acid is important for energy storage and conversion and for neutral carbon emission. Boron-doped Pd catalyst (Pd-B/C), which was previously found in our group with a high CO tolerance to facilitate dehydrogenation of formic acid/formate to CO2[1-4], is now explored for electrochemical hydrogenation of CO2 with reference to Pd/C over a wide potential window [5]. Faradaic efficiency of formate (ηHCOO-) in the CO2 reduction reaction (CO2RR) reaches above 70% after 2 h of electrolysis in CO2-saturated 0.1 M KHCO3 at -0.5 V (vs RHE) on Pd-B/C, twelve times higher than that on homemade or commerical Pd/C, leading to a partial formate current of nearly 60 mA mg-1 Pd (ca. 300 mMHCOO- mg-1 Pd) without optimization of the catalyst layer and the substrate. Although the η HCOO- decreases and the CO faradaic efficiency (η CO) increases as potential goes more negatively, the competitive selectivity η HCOO-/ηCO is always higher on Pd-B/C than on Pd/C at all the potentials examined. The density functional theory (DFT) calculation on energetic aspects of CO2RR on modelled Pd(111) surfaces with and without H-adsorbate confirms that B-doping in the Pd subsurface favors more the adsorption of HCOO*, an intermediate for the formic acid pathway than that of *COOH, an intermediate for the CO pathway. Our results reveal that Pd-B/C is a unique bifunctional catalyst for promoting the HCOOH « CO2 cycle [5]. Acknowledgements ：Financial support from the NSFC (grant No. 21733004 and 21473039）and the 973 Program (No. 2015CB932303) of MOST is highly appreciated References ： [1] J.Y. Wang, Y.Y. Kang, H. Yang, and W.B. Cai, J. Phys. Chem. C , 113, 8366 (2009). [2] K. Jiang, K. Xu, S.Z. Zou, and W.B. Cai, J. Am. Chem. Soc., 136, 4861 (2014). [3] K. Jiang, J.F. Chang, H. Wang, S. Brimaud, W. Xing, R. J. Behm, and W.B. Cai , ACS Appl. Mater. Interfaces, 8, 7133(2016) [4] J. S.Yoo, Z.-J. Zhao, J. K. Nørskov, and F. Studt, ACS Catal., 5, 6579 (2015). [5] M.Z Wang, X.P. Qin, K. Jiang, Y. Dong, M.H. Shao, and W.B. Cai, J. Phys. Chem. C 121 , 3416(2017). [5] B. Jiang, X.G. Zhang, K. Jiang, D.Y. Wu, W.B. Cai, to be submitted.