Interaction of C1 Molecules with a Pt Electrode at Open Circuit Potential: A Combined Infrared and Mass Spectroscopic Study

The interaction of CO, HCOOH, HCHO, and CH3OH molecules with a Pt surface initially covered with a layer of oxide under open circuit potential (OCP) is studied by combined infrared and mass spectroscopy. We found that after switching to the fuel containing solution and concomitantly switching off the electrode potential control at 1.2 V, (i) the OCP decays from 1.2 V down to values of 0.58 V (CO), 0.12 V (HCOOH), 0.08 V(HCHO) and 0.24 V(CH3OH); (ii) CO is the only adsorbate formed at the Pt surface from the fuels; (iii) the rates for the decay of OCP and for the buildup of COad adlayer decrease in the order of CO > HCHO > HCOOH > CH3OH; (iv) the rate of CO2 production and the total amount of CO2 produced decreases in the order of CO > HCOOH > HCHO > CH3OH; and (v) a significant amount of HCOOH is formed for the case with HCHO and the main by product from CH3OH is HCHO. Our results indicate that (i) the change in OCP is determined by the change of net charge at the electrode/electrolyte interface due to the production of electrons from fuel oxidation and the consumption of electrons by O-ad/OHad reduction; and (ii) even without an externally potential control, the reactions occurring at the interface are controlled by the electrochemical potential of the respective reactants and products. The implication from OCP transient to the local potential distribution and local activity in practical fuel cells are discussed.