Different behavior of adsorbed bridge-bonded formate from that of current in the oxidation of formic acid on platinum

Clarification has been made whether or not adsorbed bridge-bonded formate (HCOOB) is the reactive intermediate in the direct path during oxidation of formic acid, using surface-enhanced infrared absorption spectroscopy (SEIRAS) simultaneously with electrochemical measurement. With a decrease in the sweep rate of cyclic voltammetry, the potential of the maximum current in the positive-going sweep decreases from 0.9 to 0.6 V, while that of the maximum HCOOB band intensity in the positive-going sweep is almost constant at approximately 0.9 V. When the potential is held at 0.7 V after a potential increase or decrease, the current monotonically decreases, while the HCOOB band intensity keeps constant. In the absence of adsorbed CO, the current presents a maximum at approximately 0.5 V, while the HCOOB band intensity does at approximately 0.9 V. All these results clearly show that HCOOB is not the reactive intermediate. The second order kinetics for the decomposition of HCOOB has also been discussed.