在缩的NaOH溶液中氧的电化学:溶解度,扩散系数和超氧化物形成
Cunzhong Zhang1, Fu-Ren F Fan, Allen J Bard
1Center for Electrochemistry, Department of Chemistry and Biochemistry, The University of Texas at Austin, Austin, Texas 78712-0165, USA.
Journal of the American Chemical Society
|December 10, 2008
概括
高度的NaOH会降低氧气扩散和可溶性,影响氧气还原反应机制. 涉及的电子数量从2个变为1个,随着NaOH度的增加.
科学领域:
- 电化学 电化学 电化学
- 物理化学 物理化学
- 材料科学 材料科学 材料科学
背景情况:
- 了解氧降解反应 (ORR) 对能量转换技术至关重要.
- 高离子强度介质对ORR参数的影响尚未完全理解.
- 水性氧化 (NaOH) 溶液由于增加粘度和改变水活性而形成了独特的环境.
研究的目的:
- 调查缩NaOH溶液中氧气减少的扩散系数 (D(O(2)),溶解度 (C(O(2) 和电化学行为.
- 确定NaOH度对ORR的初始步骤中所涉及的电子数 (n) 的影响.
- 用扫描电化学显微镜 (SECM) 描述ORR产品超氧化物 (O(2)(*-) 的电化学行为.
主要方法:
- 在 (Pt) 超微电极上进行循环电压测量和瞬时电压测量.
- 在1-12M的水性NaOH溶液中进行的电化学测量.
- 扫描电化学显微镜 (SECM) 用于产品分析.
主要成果:
- 随着NaOH度的增加,D ((O ((2)) 和C ((O ((2)) 都会减少,与溶液粘度 (eta) 的增加相关.
- 遵守斯托克斯-爱因斯坦关系,表示一个恒定的O(2) 分子半径 (2.8 Å).
- 在第一个ORR步骤中的电子数 (n) 从n=2在1-2M NaOH转移到n=1在>6M NaOH,这与水活动的变化有关.
- 在10M NaOH中进行的SECM分析显示,O(2)/O(2)(*-) 反氧对的表面速度常数为~2.6 x 10(-4) cm/s.
结论:
- 缩的NaOH显著改变了影响ORR动力学和机制的物理性质 (粘度,水活性).
- 该ORR途径取决于NaOH度,从两电子过渡到一个电子过程.
- 在高度电解质中研究ORR产品时,SECM是一个有价值的工具.
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