碱性介质中葡萄糖在铂电极上的阳极氧化

为了进一步探明葡萄糖在铂电极上的氧化机理 ,用循环伏安法 (CV)在 - 0 .9～ 0 .4V(相对于饱和甘汞参比电极 )内研究了葡萄糖在铂电极上催化氧化行为 ,首次详细报道了葡萄糖在电化学氧化过程中的电位振荡现象 ,并用电流扫描法表征了葡萄糖的电位振荡情况 .电流扫描结果表明 ,在较慢的电流扫描速度下 ,电极过程出现了明显的电位振荡 .说明电极上产生了毒化中间物 ,电位振荡是由于毒化中间物在电极上的吸附和在高电位下氧化除去引起的 .

Anodic Oxidation of Glucose on Platinum in Alkaline Media

Glucose as one of the small organic molecules is considered to be used as a fuel in the fuel cells since it can be directly oxidized at the lowtemperature. Aimed at learning the anodic oxidation behavior of glucose on platinum in alkaline media, cyclic voltammetry in the region of -0.9~0.4 Vvs SCE (saturated calomel electrode) was used to characterize the anodic oxidation process. The potential oscillation phenomena of glucose oxidation under constant current polarizationwere firstly presented. Adetailed studywas further performed byusingthe linearthe potential sweep technique. The appearance of three oxidation peaks in the cyclic voltametric curve means that glucose could be oxidized on the surface of platinum. The reaction products or intermediates could accumulate on the surface of platinumelectrodes, resulting in the increase of the overpotential. However, these adsorbed species can be furtheroxidized and removed at high enough potentials. The oscillation potential ranging form -0.9~0.0 V shows the potentials at which the adsorbed species inhibit the electrode activity, formation and oxidation. Glucose can be oxidized in steadystate at lower current densities and the oxidation potential is at -0.4 V. Since the formation and diffusion away of the products are in a equilibriumstate in that case, at higher current densities, the rate of the formation of inhibitive species increases and causes higher overpotentials to reach the critical potential value of about 0.0 V. The oscillation frequency is also related to the current density for glucose oxidation. The higher the current density, the faster the oscillation frequency is. The results reveal that the platinum electrodes could be easily poisoned by the intermediates produced during the process of glucose oxidation in an alkaline solution. The formation of the poisoning species is proportional to the current density used. The electrochemical oxidation of glucose involves the dissociate adsorption of glucose followed by the oxidation of hydrogen atom bound to the carbon C1atom in the glucose molecule. The further process involves the formation of gluconolactone that can be readily hydrolyzed togluconic acid. The gluconic acid exists as a salt in an alkaline solutions and the formation potential shifts to a more negative value than that in acidic solution due to the pHeffect. It is believed that the poisoning species could be the small fragments. For example, COwas formed by the breakdown and dehydrogenation of glucose during the electrochemical oxidation. In view of practical applications, the anodic potential must be low enongh to provide a reasonably large output voltage for awhole fuel cell. On the other hand, if an electrode cannot prevent the poisoning of any species in the solution, its lifetime is definitely short. The potential oscillation behavior is a precursor for a catalyst that cannot afford the long-term polarization owing to the poisoning. Once the oscillation starts, the electrode will eventually lose its activites.