Boosting Formate Production in Electrocatalytic CO2 Reduction over Wide Potential Window on Pd Surfaces

• Published in: Journal of the American Chemical Society Vol. 140; no. 8; pp. 2880 - 2889
• Main Authors: Jiang, Bei, Zhang, Xia-Guang, Jiang, Kun, Wu, De-Yin, Cai, Wen-Bin
• Format: Journal Article
• Language: English
• Published: American Chemical Society 28.02.2018
• Subjects: carbon; carbon dioxide; carbon monoxide; catalysts; dehydrogenation; density functional theory; electrochemistry; electrolysis; electrolytes; energy; formates; formic acid; palladium; potassium bicarbonate
• ISSN: 0002-7863; 1520-5126; 1520-5126
• DOI: 10.1021/jacs.7b12506

Facile interconversion between CO2 and formate/formic acid (FA) is of broad interest in energy storage and conversion and neutral carbon emission. Historically, electrochemical CO2 reduction reaction to formate on Pd surfaces was limited to a narrow potential range positive of −0.25 V (vs RHE). Herein, a boron-doped Pd catalyst (Pd–B/C), with a high CO tolerance to facilitate dehydrogenation of FA/formate to CO2, is initially explored for electrochemical CO2 reduction over the potential range of −0.2 V to −1.0 V (vs RHE), with reference to Pd/C. The experimental results demonstrate that the faradaic efficiency for formate (ηHCOO– ) reaches ca. 70% over 2 h of electrolysis in CO2-saturated 0.1 M KHCO3 at −0.5 V (vs RHE) on Pd–B/C, that is ca. 12 times as high as that on homemade or commercial Pd/C, leading to a formate concentration of ca. 234 mM mg–1 Pd, or ca. 18 times as high as that on Pd/C, without optimization of the catalyst layer and the electrolyte. Furthermore, the competitive selectivity ηHCOO–/ηCO on Pd–B/C is always significantly higher than that on Pd/C despite a decreases of ηHCOO– and an increases of the CO faradaic efficiency (ηCO) at potentials negative of −0.5 V. The density functional theory (DFT) calculations on energetic aspects of CO2 reduction reaction on modeled Pd(111) surfaces with and without H-adsorbate reveal that the B-doping in the Pd subsurface favors the formation of the adsorbed HCOO*, an intermediate for the FA pathway, more than that of *COOH, an intermediate for the CO pathway. The present study confers Pd–B/C a unique dual functional catalyst for the HCOOH ↔ CO2 interconversion.