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 (η_HCOO-) 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 mM_HCOO- 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-/η_CO 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

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[5] B. Jiang, X.G. Zhang, K. Jiang, D.Y. Wu, W.B. Cai, to be submitted.