In situ spectroscopic investigation of CO accumulation and poisoning on Pd black surfaces in concentrated HCOOH

摘要

Attenuated total reflection-infrared (ATR-1R) spectroscopy is extended to investigate the surface poisoning species in the processes of (electro)chemical decomposition of formic acid (FA) on a state-of-the-art commercial Pd black catalyst in 5 M FA solution. During the FA decomposition under different potential settings including the open circuit potential (OCP, ca. 0.06V vs. RHE), the constant potential 0.4V (vs. RHE) and the scanned potentials between 0.1 and 0.5 V (vs. RHE), CO is clearly confirmed as a surface poisoning species with its vibrational frequencies located over ～1845 to 2016cm~(-1), featuring different CO bonding configurations (including the triple-, bridge- and linear-bonded CO species) on Pd black surfaces. CO_(ad) coverage increases with increasing operation time and decreasing operation potential. Once formed, CO_(ad) can only be removed at a much higher oxidation potential, corresponding to the reactivation of the Pd black surfaces. The present results provide a molecular level insight into an important aspect of the deactivation issue for a real Pd nanocatalyst in a practical FA concentration relevant to the anode operations of direct formic acid fuel cells (DFAFCs).