Pt（111）电极上O2与OHad的吸脱附及氧还原反应动力学

研究了Pt（111）电极在0．1mol／LHClO4溶液中O2吸附与OHad脱附及氧还原反应的动力学．研究发现OHad的可逆吸脱附速率很快；在氧还原的动力学或动力学与传质混合控制区，恒电位下氧还原的电流随反应时间缓慢衰减，在转速较大，扫速较慢的情形下正向扫描过程中氧还原的电流总是明显低于逆向扫描的电流；Pt／0．1mol／LHClO4从无O2切换到O2饱和时，其开路电位迅速从0．9V增加到1．0V．结果表明，Pt（111）电极上O2解离生成OHad速率很快，ORR过程中OHad会在表面缓慢积累，氧还原反应的动力学主要由反应 OHad＋H^＋＋e→←H2O的平衡热力学决定．

Kinetics Study on O2 Adsorption and OHad Desorption at Pt(111), Its Implication to Oxygen Reduction Reaction Kinetics (cited: 1)

Kinetics of dissociative O2 adsorption, OHad desorption, and oxygen reduction reaction （ORR） at Pt（111） electrode in 0.1 mol/L HClO4 has been investigated. Reversible OHad adsorption/desorption occurs at potentials from 0.6 V to 1.0 V （vs. RHE） with the exchange current density of ca. 50 mA/cm^2 at 0.8 V, the fast kinetics of OHad desorption indicates that it should not be the rate determining step for ORR. In the kineticor kinetic-mass transport mix controlled potential region, ORR current at constant potential displays slight decrease with reaction time. ORR current in the positive-going potential scan is slightly larger than that in the subsequent negative-going scan with electrode rotation speed （〉800 r/min） and slow potential scan rate （〈100 mV/s）. The open circuit potential of Pt/0.1 mol/L HClO4 interface increases promptly from 0.9 V to 1.0 V after switch from O2 free- to O2-saturated solution. The increase of open circuit potential as well as ORR current decays under potential control due to the accumulation of OHad from dissociative adsorption of O2. It indicates that at Pt（111） the net rate for O2 decomposition to OHad is slightly faster than that for OHad removal, one cannot simply use the assumption of rate determining step to discuss ORR kinetics. Instead, the ORR kinetics is determined by both the kinetics for O2 decomposition to OHad as well as the thermo-equilibrium of OHad＋H^＋＋e→←H2O.